Mechanism of nitration of nitrogen-containing heterocyclic N-acetonyl derivatives. General approach to the synthesis of N-dinitromethylazoles

Russian Chemical Bulletin, International Edition, Vol. 58, No. 10, pp. 2077—2096, October, 2009

2077

Mechanism of nitration of nitrogenꢀcontaining heterocyclic Nꢀacetonyl

derivatives. General approach to the synthesis of Nꢀdinitromethylazoles

V. V. Semenov, S. A. Shevelev, A. B. Bruskin, M. I. Kanishchev, and A. T. Baryshnikov

N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,

4

7 Leninsky prosp., 119991 Moscow, Russian Federation.

Fax: +7 (499) 137 2966. Eꢀmail: vs@zelinsky.ru

A general synthetic procedure for the synthesis of Nꢀdinitromethyl derivatives of nitrogenꢀ

containing heterocycles has been developed. The procedure includes the destructive nitration

of heterocyclic Nꢀacetonyl derivatives of tetrazoles, 1,2,4ꢀ and 1,2,3ꢀtriazoles, pyrazoles, imidꢀ

azoles and their bicyclic analogs, as well as imides of carboxylic and sulfonic acids and substitutꢀ

ed hydrazines with mixtures of sulfuric and nitric acids. The kinetic study of the reaction

mechanism was performed using UV and NMR spectroscopy. It was found that the NO groups

2

were sequentially introduced into the methylene fragment by the addition of the nitronium ion

to multiple bonds of intermediate enols followed by hydrolysis of the acetyl moiety. The rate

and direction of the enolization (due to the CH and CH groups) of the Nꢀacetonyl comꢀ

2

3

pounds in sulfuric acid solutions were determined by the study of the deuterium exchange

kinetics. The synthesis of the Nꢀdinitromethyl compounds is complicated by side reactions,

such as the decomposition of intermediate αꢀnitroketone, the nitration of the methyl group in

the acetonyl moiety, and the nitration of the dinitromethyl products to trinitromethyl derivatives.

Key words: nitration, kinetics, enolization, nitronium ion, Nꢀacetonylazoles, Nꢀdinitroꢀ

methylazoles, Nꢀtrinitromethylazoles, tetrazoles, triazoles, pyrazoles, imidazoles.

Nitration with acidic nitrating mixtures of the active

of this reaction using easily accessible Nꢀacetonylazoles¹⁰

methylene moiety of carbonyl structures (1) to form diniꢀ

tromethyl compounds (destructive nitration) was studied.

as an example.

1

It can be assumed that the process proceeds through the

formation of dinitromethylene derivatives of carbonyl

compounds (1´), whose hydrolysis affords dinitromethyl

compounds (2) (Scheme 1).

Results and Discussion

We have earlier¹¹studied by ¹³С NMR spectroscopy

the state of Nꢀacetonylazoles in an H SO solution for the

2

4

lowestꢀbasicity tetrazole derivatives. It turned out that on

going from solutions in neutral solvents to solutions in

concentrated H SO the direct spinꢀspin coupling (SSC)

Scheme 1

2

4

1

constants ( J ) for the N—CH group and СH cycle

C,H

2

increase by 4—5 and 16—18 Hz for 1ꢀ and 2ꢀacetonyltetꢀ

razoles and 5ꢀmethyltetrazole analogs, respectively. The

1

same increase in J

in neutral media is characteristic of

C,H

Nꢀacetonyltetrazolium salts 4 compared to nonꢀquaterꢀ

nized Nꢀacetonyltetrazoles 3: these constants for the carbon

atoms in the N—CH , N—Me, and C—Me fragments inꢀ

2

crease by 4—5 Hz, whereas for the С cycle they increase

5

1

by 15—20 Hz. It follows from this that the Nꢀacetonyl

derivatives of tetrazole and 5ꢀmethyltetrazole in concenꢀ

trated H SO are protonated to the nitrogen atom of the

cycle. Even in the case of lowꢀbasicity nitrotetrazole

(pK_B_H= –9.26), the corresponding ketone is protonated,

In these works, the nitration conditions were selected

empirically without revealing regularities of the reaction

and its mechanism, which impedes the optimization of

synthesis of dinitromethyl compounds.

2

4

1

2

13

+

13

In the present work, in order to detail processes of

most likely, to a considerable extent: the С NMR specꢀ

trum exhibits a noticeable increase in the direct SSC conꢀ

2

—9

destructive nitration of active methylene compounds,

we studied the mechanism, kinetics, and conditions

stants in the СН (by 1.5 Hz) and Me (by 1.8 Hz) groups.

2

Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2014—2033, October, 2009.

1

2078

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

Therefore, the nitrating mixtures (conc. HNO + conc.

Table 1. Parameters in the equations of the linear anamorphoses

3

(

lnC /С = Кt + A) of the disappearance of Nꢀdinitromethylimidꢀ

0

H SO ) should nitrate Nꢀacetonylazole cations 3´

2

4

–

1

–1

azoles (0.02 mol L ) in Н SO —KNO solutions (1.15 mol L

)

(

Scheme 2, route b), as they nitrate salts 4, from which

imidazolium, triazolium, tetrazolium, pyridinium, and

2

4

3

and correlation coefficients (R)

pyridazinium Nꢀdinitromethylides 5 have been obtained

previously (Scheme 2, route a).

5

–1

4

NꢀDinitroꢀ

methylꢀ

azole

Volume

ratio

К•10 /s

А

R

In the present study, we used analogous conditions for

the synthesis of Nꢀdinitromethyl structures with the

uncharged cycle. In all cases, the nitration of various

Nꢀacetonylazoles in sulfuric—nitric acid mixtures containꢀ

ing a noticeable amount of water gave Nꢀdinitromethylꢀ

azoles, viz., derivatives of pyrazoles, imidazoles, 1,2,4ꢀtriꢀ

azoles, 1,2,3ꢀtriazoles, and tetrazoles (see Scheme 2, strucꢀ

tures 6a—t).*

H SO : Н О

2

4

2

6a

5% oleum

0.60±0.1

1.73±0.4

1.35±0.04 0.007±0.011 0.998

9.00±0.1

2.40±0.5

0.36±0.06 0.060±0.021 0.933

0.029±0.011 0.918

0.019±0.013 0.998

1

2 : 0

2 : 1

6

d

c

h

12 : 1

0.001±0.019 0.999

0.018±0.051 0.951

In the most cases, the yields of Nꢀdinitromethyl comꢀ

pounds pass a maximum in time and then decrease. Thereꢀ

fore, to develop the preparative method for synthesis of

Nꢀdinitromethyl derivatives, regularities of their accumuꢀ

lation and disappearance in sulfuric—nitric acid mixtures

should be studied.

The results on nitration of 2ꢀdinitromethylꢀ5ꢀnitrotetꢀ

razole 6a in media of various acidity (Fig. 1) indicate the

formation of Nꢀtrinitromethylazoles via the mechanism

of direct proton substitution for nitronium ions, as in the

16—18

case of trinitromethane and dinitroacetonitrile.

In

Interaction of Nꢀdinitromethylazoles with sulfuric—nitric

acid mixtures. All Nꢀdinitromethylazoles in conc. H SO

concentrated H SO (mixture 12 : 0) the apparent rate

2

4

2

4

constant for the disappearance of 6a is fivefold higher than

at room temperature do not decompose for at least 24 h,

but have different stability in sulfuric—nitric acid mixꢀ

tures. For instance, it is known that 1,2,4ꢀtriazole derivaꢀ

that in 5% oleum, as for the nitration of trinitromethane

16—18

and dinitroacetonitrile.

As the acid is diluted, К_a_p_pdecreases as the concentraꢀ

tion of nitronium ions decreases (mixture 12 : 1 v/v, 87.5%

H SO ), whereas in 76% H SO (mixture 12 : 5) comꢀ

7

,8

tives are nitrated to stable trinitromethyl derivatives 7h,

whose presence was monitored by TLC and the amount

was determined by UV spectroscopy (by an increase in the

absorption maximum of the dinitrocarbanionic fragment

upon the addition of KI and Na S O ). According to our

2

4

2

4

pound 6a does not undergo nitration.

Thus, when optimizing the synthesis of Nꢀdinitromeꢀ

thylazoles, one can find such conditions under which the

formation of Nꢀtrinitromethyl derivatives would be reduced

to minimum.

2

3

data,¹Nꢀtrinitromethyltetrazoles 7a—g are unstable and

decompose even at 0 °C to form Nꢀtrinitromethylnitrile

imines and N₂.

5

The kinetics of disappearance of Nꢀdinitromethylazoles

–

1

in 89.2% H SO containing KNO (1.15 mol L ) was

C (%)

2

4

3

0

(12 : 5)

studied by UV spectroscopy at 20 °C. The concentration

100

–

1

of Nꢀdinitromethylazoles (0.02—0.03 mol L ) was conꢀ

siderably lower, which made it possible to use a firstꢀorder

equation for the calculation of the kinetics of their deꢀ

composition. The logarithmic anamorphoses of the kinetꢀ

ic curves of disappearance of Nꢀdinitromethyltetrazoles

0.36 (5% oleum)

8

6

4

2

0

(

6a,c,d) and ꢀ1,2,4ꢀtriazoles (6h,j) represent straight lines

the equations are given in Table 1), indicating the disapꢀ

1

.35±0.04 (12 : 1)

pearance of Nꢀdinitromethylazoles in the reaction of the

pseudoꢀfirst order. The apparent rate constants for the

disappearance of other Nꢀdinitromethylazoles were calꢀ

culated similarly (Table 2).

As follows from Table 2, the compounds with low

CHꢀacidity, viz., Nꢀdinitromethyl derivatives of imidaꢀ

zole 6s and pyrazoles 6p,q, are stable in this medium for

day. Tetrazole derivatives 6a,c,d react with nitronium

ions more rapidly than triazole analogs 6h,m, which is due

to the higher acidity of the dinitromethyl group in 6a,c,d.

1.73±0.04 (12 : 0)

4

8

12

16

20

t/h

Fig. 1. Kinetic curves of the conversion of 2ꢀdinitromethylꢀ5ꢀ

nitrotetrazole 6a in H SO solutions by the action of nitronium

ions. The initial concentrations of 6a and КNO are 0.02 and

1

2

4

3

–

1

.15 mol L , respectively. The numbers on the curves are

5

–1

K_a_p_p•10 (s ); the volume ratios H SO : Н О in the nitrating

2

4

2

*

For the preliminary publication, see Ref. 14.

mixtures are given in parentheses, and C is the conversion.

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2079

Scheme 2

X = N, CH

Note. The azolyl fragments

are shown, the pK values are given in parentheses.

a

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

Table 2. Apparent rate constants for the disappearance of Nꢀdinitromethylazoles in an H SO —Н О

2

4

2

–

1

(

12 : 1, vol.)—KNO (1.15 mol L ) mixture, 20 °C

3

6

–1

Compound

К_a_p_p•10 /s

2

1

2

ꢀDinitromethyltetrazole (6d)

ꢀDinitromethyltetrazole (6c)

ꢀDinitromethylꢀ5ꢀnitrotetrazole (6a)

90.0±1

24.0±5

13.5±0.4

11.0±1

Bis(1ꢀdinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀyl) (6j)

1

2

1

ꢀDinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazole (6h)

ꢀDinitromethylꢀ4ꢀnitroꢀ1,2,3ꢀtriazole (6m)

ꢀDinitromethylꢀ4ꢀnitropyrazole (6p)

ꢀDinitromethylꢀ3,4ꢀdinitropyrazole (6q)

ꢀDinitromethylꢀ4ꢀnitroimidazole (6s)

3.6±0.6

0.6±0.01

No nitration for 3—4 days

Pyridinium dinitromethylide

Isolation of intermediate nitration products. The study

of the nitration of Nꢀacetonyl derivatives 3a,b (Scheme 3)

change the accumulation rate and the yield of Nꢀdiniꢀ

tromethyl compounds.

showed that in a mixture of sulfuric and nitric acids the

In the case of nitration of 3a,b, nitro groups are introꢀ

duced sequentially (route b), which is favored by the isolaꢀ

tion in a series of nitrating mixtures of intermediate monoꢀ

nitro products (8b and 10a,b) in high yields.

nitration of the СH moiety does not proceed through the

2

preliminary nitrosation to form compound A (route a), as

it is accepted for the formation of α,α´ꢀnitroketones

1

c,d,g

(

5—7% yields) in the aliphatic series.

we found for the nitration of Nꢀacetonylpyridinium and

ꢀacetonylꢀ5ꢀnitrotetrazole 3а in sulfuric—nitric acid mixꢀ

For example,

Hydrolysis with the removal of the acetyl group occurs

only after the second nitro group was introduced, because

the mononitromethyl derivatives (10a,b), which are the

hydrolysis products in the first step, are incapable of transꢀ

forming into Nꢀdinitromethyl compounds under the

nitration conditions. In other examples of nitration

of Nꢀacetonylazoles (in aliquots of reaction mixtures

100—1000ꢀfold diluted with water) the formation of monoꢀ

nitroketones can be detected in the first steps by UV specꢀ

troscopy. For example, in the case of 1ꢀacetonylꢀ4ꢀnitroꢀ

imidazole and 1ꢀacetonylꢀ4ꢀnitropyrazole, the correꢀ

2

tures that the absence of nitrosating agents in the reaction

mixture exerts no effect on the course and result of nitraꢀ

tion, which was shown for the reaction with freshly puriꢀ

fied KNO instead of HNO and in the presence of an

3

excess removing nitrogen oxides (urea, hydrazine, or sulꢀ

faminic acid).

At the same time, the introduction of nitrosating agents

(

nitrogen oxides or NaNO ) into the reaction does not

2

Scheme 3

R = NO₂(3a, 6a, 8a, 9a, 10a), C(NO₂)₃(3b, 6b, 8b, 9b, 10b)

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2081

sponding mononitroketones have lower electronꢀwithꢀ

drawing ability of the cycles and, hence, undergo hydrolyꢀ

sis more slowly than the tetrazole analogs. The UV spectra

of these mononitroketone anions exhibit characteristic inꢀ

tense maxima at 310—320 nm, whose intensity decreases

during the detection of the UV spectra due to the transforꢀ

mation of these nitroketones into the mononitromethyl

derivatives (analogs 10a,b) and, possibly, as a result of

other side processes related to the destruction of the nitro

group.¹

Enolization of Nꢀacetonylazoles. Since the enolization

rate and the relative content of enols in various ketones

can substantially affect the formation rate of the Nꢀdiniꢀ

tromethyl derivatives, we had to study the enolization abilꢀ

ity of these ketones in media, whose acidity coincides with

2

that in nitrating mixtures. It is known that for aliphatic

ketones the enolization rate increases with an increase in

the acidity of the medium according to the equation

+

V = [K ][Ket][H ], where K is the enolization rate conꢀ

en

9—21

+

stant; [Ket] and [H ] are the concentrations of ketone and

H , respectively. However, in highly concentrated acids

+

The kinetic data obtained by UV spectroscopy, nameꢀ

ly, the rate of absorbance increase in the absorption maxiꢀ

ma of Nꢀdinitromethylazole anions (330—350 nm upon

the dilution of reaction solutions with water), indicate

that the accumulation of the Nꢀdinitromethyl compounds

occurs very rapidly, which confirms the assumption about

the involvement of highly reactive enol forms of Nꢀacetoꢀ

nyl derivatives and intermediate αꢀnitroketones in the proꢀ

cess. It is clear from this why poorly enolized structures,

such as analogous derivatives of acetic acid N—CH СО R,

(beginning from ~85% H SO ) the enolization rate deꢀ

2

4

creases again (10—30ꢀfold decrease in the 85—90% range)

2

3

and is described by another equation.

According to the general kinetic equation, the formaꢀ

tion of the Nꢀdinitromethyl compounds (Scheme 4) is

affected by the enolization rate and also by the keto—enol

tautomeric equilibrium constant К = К /K_k_e_t. However,

t

en

1

no enol form is observed in the H NMR spectra of all

Nꢀacetonylazoles synthesized. Therefore, with allowance

2

cannot be transformed into Nꢀdinitromethyl compounds.

for the accuracy of the method K does not exceed 0.01.

t

Scheme 4

V = K [Ket]

V = (K /K )[Ket][NO ⁺

]

2 en ket 2

1

en

K_e_n<< K_N_O₂[NO₂⁺]

I)

K_e_n>> K_N_O₂[NO₂⁺]

(

(II)

V /V = 10—15

1

2

2082

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

Therefore, the enol form in these ketones is determined by

indirect methods.²⁴At the same time, the qualitative

change in the enol content as a function of the change in

the withdrawing properties of the cycle can be estimated

by the easily measurable enolization rate.

For other objects (3r,s), which differ strongly in the

electronꢀwithdrawing ability of the cycle and in the transꢀ

formation rate into Nꢀdinitromethylazoles, analogous linear

dependences were obtained (Scheme 5, Tables 3 and 4). It was

found that these ketones are enolized not only due to the CH₂

moiety but also (with rather high rates) due to the Me group.

In 89.2% H SO Meꢀenolization is almost the same

Indeed, the К constant changes according to a change

t

in the ratio of rates of the rateꢀdetermining steps of enoꢀ

lization and ketonization.²²

2

4

for all ketones, whereas CH ꢀenolization is accelerated

2

In the whole series of Nꢀacetonylazoles, steric condiꢀ

tions for proton elimination in the rateꢀdetermining step

with the enhancement of the withdrawing properties of

the nitrous substituent, which results in an increase in the

relative fraction of CH ꢀenol (K ). Unlike the azole deꢀ

(

approach of a base to the protonated form of ketone)

2

D

remain almost unchanged. However, with an enhanceꢀ

ment of the withdrawing properties of the cycle the proton

elimination rate should inrease and the rate of the inverse

rivatives, acetonyltrimethylammonium is enolized preꢀ

dominantly due to the Me group, which is associated,

most likely, with unsuccessful attempts to nitrate acetoꢀ

nyltrimethylammonium to the Nꢀdinitromethyl comꢀ

pound with a sulfuric—nitric acid mixture.

step should decrease, and as a result, К increases.

t

We studied the enolization of the Nꢀacetonyl comꢀ

1

pounds in D SO solutions by H NMR spectroscopy from

On going to 76.7% D SO , the enolization rates due to

2

4

2

4

2

5,26

the rate of proton deuteriosubstitution,

which is deꢀ

the Me and СH groups decrease nonproportionally and,

2

termined by the enolization rate. The kinetic equations for

butanꢀ2ꢀone deuteration in acidic media²⁶were used for

the calculation of the enolization rate constant by the

H/Dꢀsubstitution constant value. The enolization rate

constants are related to the rate constants of H/Dꢀsubstiꢀ

as a result, the fraction of CH ꢀenols increases sharply. In

2

the more concentrated (93.6%) acid the enolization rate

and the relative content of enols remain unchanged comꢀ

pared to those in 89.2% D SO .

2

4

As shown above, the determined enolization rates are

in essence the enolization rates of the corresponding

1

tution K_o_b_sobserved in the H NMR spectra by the followꢀ

ing equations:

K (СН ) = –2K (СН ),

K (Me) = –3K_o_b_s(Me).

Scheme 5

en

2

obs

2

en

Our experimental data on the decrease in the signals of

the methyl and methylene groups in time correspond

to the H/Dꢀsubstitution rate according to the pseuꢀ

doꢀfirstꢀorder equation. The logarithmic anamorphoses

ln[H ]/[H] = kt according to the results of deuteriosubstiꢀ

0

tution in 2ꢀacetonylꢀ5ꢀnitrotetrazole 3а are shown in Fig. 2.

log[H ]/[H]

0

2.5

2.0

1.5

1.0

0.5

0

Table 3. Rate constants for enolization of the Nꢀacetonyl derivaꢀ

tives in D SO₄

2

1

2

[

D SO ] K_M_e•10⁴K_C_H₂•10⁴

K_D=

2

4

(%)

= K_C_H₂/K_M_e

8

7

9.2

6.7

10.80

2.49

28.6

13.4

2.7

5.4

3

4

8

7

9.2

6.7

8.70

0.48

22.2

2.68

2.5

6.0

1

0

20

30

t/min

8

9.2

10.80

9.60

21.0

7.2

1.9

0.8

Fig. 2. Logarithmic anamorphoses of the kinetics of deuterioꢀ

substitution of methylene (1, 2) and methyl groups (3, 4) in 2ꢀaceꢀ

tonylꢀ5ꢀnitrotetrazole 3а (initial concentration 0.35 mol L^–) in

D SO solutions. Volume ratios of D SO to D O: 12 : 1 (1, 3)

1

2

4

2

4

2

and 12 : 5 (2, 4).

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2083

Table 4. Parameters of equations of the logarithmic anamosphoses (ln(H /H) = Kt + A) of deuterioexchange in the Nꢀacetonyl

0

derivatives (0.35 mol L^–¹) and correlation coefficients (R)

NꢀAcetonyl

Me Group

СН Group

2

derivative

4

–1

4

–1

D SO : D O (vol.)

К•10 /s

А

R

К•10 /s

A

R

2

4

2

5

4

ꢀNitrotetrazole (3а)

ꢀNitroimidazole (3s)

12 : 5

0.83±0.07 –0.006±0.070

0.970

0.993

0.971

0.829

0.991

0.999

06.70±0.2

14.30±0.9

14.90±0.8

1.34±0.04

11.10±0.4

10.50±0.5

03.60±0.3

0.019±0.026

0.140±0.093

0.086±0.033

0.020±0.015

0.017±0.031

–0.003±0.045

–0.028±0.028

0.994

0.993

0.996

0.998

0.995

0.986

1

2 : 1

2 : 0

3.60±0.2

3.60±0.4

0.16±0.04

2.90±0.2

3.60±0.07

3.20±0.07

0.007±0.024

0.038±0.017

0.029±0.012

0.011±0.017

0.007±0.001

0.007±0.006

12 : 5

2 : 1

1

Imidazole (3r)

Trimethylammonium

12 : 1

Nꢀacetonylcycloimmonium salts. It should be mentioned

intensity of the absorption maximum of this anion

(λ = 311.5 nm) decreases gradually (by ~30% within

30 min) because of hydrolysis to 2ꢀnitromethylꢀ5ꢀnitroꢀ

tetrazole 10а. The position of the absorption maximum of

compound 8а remains unchanged upon the acidification

of the medium to pH = 1; however, its intensity decreases

in time much more rapidly than at pH = 4, indicating that

8а decomposes via another direction, because the rate of

hydrolysis to nitromethyltetrazole 10а in an acidic mediꢀ

um should be retarded. In addition, if an aliquot of the

reaction mixture is poured at once into a solution of

Na CO , anion 10а is formed in larger amounts than in

the case when the aliquot is poured first into water and

then the medium is alkalized (to pH = 10). Therefore, in

an acidic medium before alkalization a portion of nitroꢀ

ketone 10а has time to decompose, but not due to hydrolꢀ

ysis. The decomposition of 8а in the reaction medium is

also indicated by the decrease in the yield of 2ꢀdinitromeꢀ

thylꢀ5ꢀnitrotetrazole 6а with the retardation of the rate of

transformation of nitroketone 8а into 6а, i.e., when KNO₃

is added not at once but in portions during several hours.

For the kinetic curves of accumulation of 8а (Fig. 3,

curves 1—3), the logarithmic anamorphoses at the equiꢀ

that in a neutral medium (D O and CD OD) the deuterioꢀ

2

3

exchange of the methylene moiety in Nꢀacetonyltetrazoles

is substantially slower than that in the corresponding

Nꢀacetonyltetrazolium salts.¹¹This also indicates the highꢀ

er enolization rates of ketones with protonated cycles.

The study of the kinetics of destructive nitration of the

Nꢀacetonyl functional group by UV spectroscopy and

1

H NMR spectroscopy showed (see below) that this proꢀ

cess consisted of two consecutive irreversible reactions:

the introduction of the first and second nitro groups, each

of which consists, in turn, of two steps, namely, the reꢀ

versible enolization of ketone and the irreversible addition

of the nitronium ion to the double bond of enol. The rate

of this reaction, which occurs in the quasiꢀstationary reꢀ

gime, is described in the general form by the equaꢀ

tion presented in Scheme 4. At the low enolization rate

2

3

(compared to the nitration rate) this equation is reduced

to Eq. (I), whereas at the high rate is reduced to Eq. (II).

Kinetics of nitration of 2ꢀacetonylꢀ5ꢀnitrotetrazole. The

detailed study of the nitration kinetics was carried out for

2

ꢀacetonylꢀ5ꢀnitrotetrazole 3а, because easily identified

products are formed in this case and the reaction is rather

selective. The kinetics of accumulation of mononitrokeꢀ

tone 8а in 89.2% H SO was studied at room temperature

molar (1´) and double (2´) amount of KNO represent

3

straight lines only in the initial regions, i.e., the concenꢀ

2

4

by UV spectroscopy according to the change in the conꢀ

tration of KNO remains yet almost unchanged. Then

3

centration of 2ꢀnitromethylꢀ5ꢀnitrotetrazole anion 10а

their slope decreases, indicating the dependence of the

(

λ =312 nm, ε = 8500), which is the product of hydrolysis

reaction rate on the KNO concentration, i.e., the overall

3

of nitroketone 8а (see Scheme 3).

reaction order exceeds 1. The apparent rate constant calꢀ

culated in the initial region increases twofold with a twoꢀ

At low KNO concentrations only one hydrogen atom

3

in the methylene unit is substituted for the NO group

fold increase in the KNO concentration, indicating the

2

3

even under the conditions of the twofold molar amount of

first order with respect to potassium nitrate. For the fourꢀ

KNO . At the maximum yield of nitroketone 8а (76% in

fold increase in the amount of KNO the logarithmic anꢀ

3

4

3

5 min) the yield of 2ꢀdinitromethylꢀ5ꢀnitrotetrazole 6а is

—4%. After 17 h the yield of dinitromethyl derivative 6а

amorphosis (curve 3´) is a straight line in the whole reꢀ

gion, which is usually observed in the case of bimolecular

reactions carried out under the pseudoꢀfirstꢀorder condiꢀ

tions. It is important that in this case K_a_p_pincreases only

threefold instead of the fourfold increase, i.e., the order

with respect to the nitronium ion decreases.

achieves only 6%, whereas the yield of nitroketone 8а

decreases to 25—30% because of side decomposition reꢀ

actions.¹

In acidic media nitroketone 8а is not quite stable. For

example, in a weakly acidic medium (pH = 4) nitroketone

9—21

The maximum yield (82%) of mononitroketone 10а

from this mixture (see Fig. 3, curve 3) is achieved 20 min

8

a dissociates to form the corresponding anion. The

2084

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

Y (%)

even in the case of a higher KNO concentration. At the

3

8

6

4

2

0

same time, this value is comparable with the rate of enoꢀ

2

–

3 –1

lization of 3а in this medium (2.8•10

s ).

The high rate constant for the nitration of the methylꢀ

ene moiety in 3а indicates that another, more reactive

form (enol form) is nitrated. Since the apparent rate conꢀ

stant for the accumulation of nitroketone 8а depends on

the concentration of nitronium ions, the reaction rate is

determined by the overall kinetic equation (see Scheme 4),

i.e., the nitration of the enol form is the rateꢀdetermining

step. At a low concentration of nitronium ions, the rate

of addition of [NO₂⁺] is lower than the enolization

0

1

0

20

30

40

t/min

rate and the whole process depends on the concentration

ln[100/(100 – Y)]

+

of nitronium ions. At the high concentration [NO

]

2

3

´

–

1

(

>0.3–0.4 mol L ), the addition rate of nitronium ions is

1

0

.6

.2

.8

.4

0

equal to the enolization rate and is independent of the

concentration [NO₂⁺], i.e., it is described by Eq. (I).

The apparent rate constant for the disappearance of

ketone 3а in 89.2% H SO at the high KNO concentraꢀ

1

.49±0.05

2´

0

.99±0.12

2

4

3

–1

1

´

tion (1.15 mol L ) was estimated by Н NMR spectrosꢀ

copy from a decrease in the intensity of signals of protons

0

.50±0.03

of the СН moiety. The values of this constant range from

2

–

3

–3 –1

1

.7•10 to 2.7•10

enolization rate constant (2.8•10

s , i.e., almost coincide with the

–

3 –1

s

) in this medium.

Thus, at the stage of introduction of the first nitro

group into the methylene moiety, the enolization rate and

1

0

20

30

40

t/min

Fig. 3. Kinetic curves of accumulation (1—3) of 2ꢀacetonylꢀ(1´ꢀ

nitro)ꢀ5ꢀnitrotetrazole 8а and the corresponding logarithmic anꢀ

amorphoses of disappearance (1´—3´) of 2ꢀacetonylꢀ5ꢀnitrotetrꢀ

azole 3а in 89.2% H SO (H SO : H O = 12 : 1, vol.) at different

the rate of addition of the nitronium ion to the double

+

bond have close values: at the high concentration [NO

]

2

–1

(

>0.36 mol L ) the enolization is the rateꢀdetermining

2

4

2

4

2

–1

step, whereas at the low concentration (<0.14 mol L

)

initial concentrations of KNO : 0.058 (1, 1´), 0.116 (2, 2´),

3

the rate is determined by the addition of the nitronium ion.

–

1

and 0.232 mol L (3, 3´). The initial concentration of 3а is

.058 mol L . Figures on the anamorphoses are the values of

K_a_p_p•10 (s ); Y is the yield of the product.

–

1

Kinetics of accumulation of 2ꢀdinitromethylꢀ5ꢀnitroꢀ

0

3

–1

tetrazole (6а) was studied at 24 °C in 89.2% H SO conꢀ

2 4

–

1

taining KNO in a high concentration (1.15 mol L ) usꢀ

3

ing UV spectroscopy. The change in the absorbance of the

reaction mixture samples diluted with water was studied at

the absorption wavelength of anion 6а (336 nm, ε = 17500).

after the beginning of the reaction, and the yield of dinitro

derivative 6а is 4—5% at this moment. After 7—8 h the

largest amount of 6а is formed: 37%.

–1

The concentration of the starting ketone 3a (0.058 mol L )

should be 20ꢀfold lower than the concentration of KNO₃

for the reaction to be pseudoꢀmonomolecular with respect

to the starting ketone 3a. The kinetics of accumulation of

6а (Fig. 4) is described by the Sꢀlike curve with the inflecꢀ

tion point in the initial region, which is characteristic of

consecutive reactions. An analysis of the kinetic equations

of these reactions shows that if the rate of one step is

considerably lower than the rates of other steps, then after

some time interval the kinetic curve of this process is well

The values of the rate constants for the formation of

mononitroketone 8а indicate that the replacement of the

proton of the methylene moiety in 3а by the nitro group

does not proceed via the mechanism of concerted attack

of [NO₂⁺] to the carbon atom with the simultaneous atꢀ

1

7,18

tack of a base (Н О or HSO ) to the hydrogen atom.

2

4

Indeed, the mobility of the СН proton in 3а (рК > 7) is

2

а

significantly lower than that of the СН(NO ) proton in

2

6

а (рК = –1.7). Hence, according to this mechanism,

а

2

7

the nitration of the СН moiety should occur much more

described by an equation of the first order.

2

slowly than nitration at the dinitromethyl group or should

At the high KNO concentration, the rate of formaꢀ

3

not occur at all (as, e.g., in the case of gemꢀdinitroethane,

tion of intermediate product 8а will be equal to the enoꢀ

–

3 –1

рК = +5.30).

lization rate (K_a_p_p= 2.8•10

s ). It can easily be calcuꢀ

a

However, the experimental K_a_p_pvalue of the rate of

nitro group introduction into the methylene moiety of 3а

lated that already 11 min after nitroketone 8а is formed in

84% yield. At the same time, according to the experimenꢀ

tal data, at this moment (the second experimental point in

curve 2) the final product 6а is formed in 8% yield, i.e., the

1.49•10^–

3

s

–1

) is two orders of magnitude higher than

(

K_a_p_pfor the nitration of 6а to the trinitromethyl derivative

Synthesis of Nꢀdinitromethylazoles

Y (%)

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2085

Thus, the rate constant for the introduction of the first

nitro group is considerably higher (10—15ꢀfold) than that

for the second nitro group, while the latter is an order of

magnitude higher than the rate constant of nitration of 6а

to the trinitromethyl derivative, which excludes the nitraꢀ

tion of mononitroketone 8а according to the mechanism

of direct electrophilic substitution (see above). In addiꢀ

tion, the absence of the kinetic isotope effect during nitraꢀ

1

2

6

5

4

3

2

1

0

ln[76/(84 – Y)]

3

0.8

0

.6

.4

.2

tion of 3а in D SO indicates that the proton transfer is

2 4

not a rateꢀdetermining step of the reaction, as it takes

place in the case of nitration of the dinitromethyl comꢀ

pounds according to the concerted mechanism.

1

7,18

As follows from the data on the rate of accumulation of

6

а (Fig. 5), the nitration is accelerated with an increase in

the H SO concentration (in the 76—91.6% range), whereꢀ

2

4

as in the range of 91.6—5% oleum the rate remains almost

1

2

t/h

unchanged (see Fig. 5). Although via the mechanism of

Fig. 4. Kinetic curves of accumulation of compound 6а for the

nitration of ketone 3а: 1, D SO + D O (12 : 1, vol.); 2, H SO +

17,18

concerted substitution

the nitration rate should deꢀ

2

4

2

4

crease with an increase in the H SO concentration, while

2

4

+

H O (12 : 1, vol.); 3, logarithmic anamorphosis of curve 2

2

in 100% H SO no nitration occurs. When the influence

2

4

(

i.e., disappearance of nitroketone 8а after an autoacceleration

of the concentration of nitronium ions on the rate of final

product formation was studied, in essence this was the study

of the kinetics of nitration of intermediate nitroketone,

because this step is substantially slower than the first step.

period of 11 min). The initial concentrations of KNO and 6a

3

_a_r_e₁_.₁₅_a_n_d₀_.₀₅₈_m_o_l_L_–1, respectively.

+

true amount of 8а is 84 – 8 = 76% due to its further

transformation into 6а (the amount of 8а at later moꢀ

ments is calculated similarly). Beginning from this moꢀ

ment, the kinetic curve of accumulation of 6а corresponds

to the transformation of nitroketone 8а into 6а and should

obey an equation of the first order. In fact, the logarithmic

anamorphosis (3) for the disappearance of nitroketone 8а

plotted after the induction period (11 min) represents

a straight line with the correlation coefficient 0.99 until

The concentration [NO ] was changed both at the constant

2

H SO concentration and by the variation of the acidity of

2

4

the medium at the constant amount of KNO . The reacꢀ

3

tion rates were determined after the induction periods

(5—10 min) and were compared only for the curves with

high yields of 6а (∼ 60%). According to Ref. 28, the conꢀ

centration [NO₂⁺] increases sharply (from 0 to 98%) in the

range of H SO concentrations 81—93%. The rate of forꢀ

2

4

mation of 6а increases strongly in the same interval (Fig. 6).

+

2

ꢀdinitromethylꢀ5ꢀnitrotetrazole is formed in 35% yield.

Since the rate of transformation of HNO to NO in

3

2

3 –1 28

Then the slope of the anamorphosis decreases gradually

because of the increasing error of the calculation of unreꢀ

acted nitroketone 8а due to its side decomposition and an

increase in the decomposition rate of accumulated 2ꢀdiꢀ

this media (К_N_O₂= 10 —10 s

)

is six—seven orders of

magnitude higher than the rate of introduction of both the

first and second nitro groups, the apparent concentration

+

[NO₂] can be accepted constant during the reaction,

–

5 –1

nitromethylꢀ5ꢀnitrotetrazole 6а (K_a_p_p= 1.35•10

s

in

because the KNO concentration is 10—20ꢀfold higher

3

the same mixture). The apparent rate constant for the

than the concentration of ketone 3а.

disappearance of nitroketone 8а (i.e., the introduction of

In 89.2% H SO at a twofold increase in the KNO

2

4

3

–

4 –1

the second group, K_a_p_p= 1.9•10

s

) is 15ꢀfold lower

concentration, the effective concentration of nitronium

ions increases only 1.24ꢀfold due to some decrease in the

acidity of the medium. The same increase, namely,

1.27ꢀfold, is characteristic of the apparent rate constant

for the formation of 6а (see Fig. 5, curves 3 and 4).

than the rate constant of its accumulation, which is equal

to the enolization rate of the starting Nꢀacetonyltetrazole

3

а in this mixture (see above). Analogous K_a_p_pvalues at

–

1

other initial concentrations of 3а (0.02 and 0.08 mol L

)

confirm the first order of the reaction with respect to the

starting ketone.

If the concentration of nitronium ions increases due to

the threefold increase in the acidity of the medium withꢀ

The kinetic curve of accumulation 6а in D SO in the

out changing the amount of KNO (see Fig. 5, curves 1

2

4

3

region of formation coincides up to 30% with the curve in the

and 3), then K_a_p_pof formation of 6а increases considerꢀ

ably (2.6ꢀfold), although the rate of enolization of 3а in

these mixtures is the same. The K_a_p_p/[NO₂⁺] ratio reꢀ

mains constant, i.e., the rate of introduction of the second

nitro group depends linearly on the concentration of niꢀ

tronium ions.

nonꢀdeuterated acid, and then K_a_p_pin D SO decreases

2

4

somewhat more slowly than in Н SO . It is most likely that

2

4

the nitration of 6а to the trinitromethyl derivative in D SO

2

4

occurs more slowly, which is consistent with the known

1

6—18

mechanism of nitration of the dinitromethyl group.

2086

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

Thus, at the stage of introduction of the second nitro

within the experimental error. The rate of this reaction

group, the reaction has approximately the first order with

respect to the nitronium ion and the overall second order

depends on the keto—enol equilibrium constant К and

t

the concentration of nitronium ions [NO₂⁺] rather than

Y (%)

1

6

4

2

0

4

3

1

2

3

4

t/h

Fig. 5. Kinetic curves of accumulation of compound 6а for the nitration of ketone 3а (0.058 mol L^–¹) in H SO —KNO mixtures at

2

4

3

different effective concentrations of nitronium ions. The apparent rate constants (K_a_p_p) for the introduction of the second nitro group

after 10ꢀmin induction periods:

[KNO₃]₀[NO₂⁺]_e_f_f

K_a_p_p•10⁴

/s^–¹

К = K_a_p_p•10 /[NO₂⁺]

4

Curve

Volume ratio

H SO : Н О

[H SO ]

(%)

2

4

/mol L^–¹

s

–1

2

4

2

_m_o_l_L–1

1

3

4

12 : 0

12 : 1

93.64

89.23

1.15

0.575

1.08

0.36

0.29

4.9±0.1

1.9±0.2

1.5±0.1

4.5

5.3

5.2

Y (%)

40

5

4

3

2

1

0

7

6

(

12 : 0)

(

12 : 5)

2

8

(

12 : 1)

30

20

10

0

(

12 : 2)

(

5% oleum)

8

16

24

32

40

48

56 t/h

20 40

60

80

100 120 140 t/h

Fig. 6. Kinetic curves of accumulation of compound 6а for the nitration of ketone 3а (0.058 mol L^–¹) in H SO —KNO mixtures at

2

4

3

different effective concentrations of nitronium ions. The apparent rate constants (K_a_p_p) for the introduction of the second nitro group

after induction periods: after 12 min (5) and 1 h (7) by the first five points; after 5 min by the first four points (8):

Curve

Volume ratio

H SO : Н О

[H SO ]

(%)

[KNO₃]₀[NO₂⁺]_e_f_f

K_a_p_p•10⁴

2

4

2

4

2

_m_o_l_L–1

_/_s–1

2

5

6

7

8

12 : 0

12 : 1

12 : 2

12 : 5

93.64

89.23

76.77

—

0.575

2.3

1.15

0.575

1.15

0.56

0.31

0.10

0.00

1.15

—

1.1+0.2

—

0.05+0.1

1.8+0.2

5% oleum

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2087

on the enolization rate. The addition of nitronium ions is

much slower than the formation of the enol form of interꢀ

mediate nitroketone, and the reaction rate is described by

Eq. (II). In the general case, the rate of introduction of the

second nitro group is 1—1.5 times of magnitude lower

than the rate of introduction of the first group.

solution (mixture 3, see caption to Fig. 5) at 24 °C (the

azolyl fragments are shown) are given below.

The absence of the kinetic isotope effect also confirms

that the enolization rate does not determine the nitration

rate in the second step. Note that the introduction of the

nitro group into the СН moiety of Nꢀacetonylazoles

2

should increase the keto—enol equilibrium constant К_t,

as, e.g., in the case of acetoacetic and nitroacetoacetic

esters.²Therefore, the significant difference in the rates

of introduction of the first and second groups is due only

to the slower addition of the nitronium ion to nitroenol

than to the starting enol.

9

Compound 6а is formed rather rapidly in 5% oleum as

–

4 –1

well (K_a_p_p= 1.8•10

s ). However, side processes relatꢀ

ed to the decomposition of intermediate nitroketone 8а

and cycle destruction occur rapidly in the medium conꢀ

sidered, which is indicated by appreciable gas release. The

yield of 6а does not exceed 25%, although this substance is

relatively stable in the medium considered.

In the general case, the yield of 6а increases under the

conditions when the nitration rate of nitroketone 8а exꢀ

ceeds the decomposition rate. As a rule, with an increase

in the KNO concentration, the yield of 6а increases but

The rates of introduction of the first nitro group into

the methylene moiety are close in all examples, because

they are determined by the enolization rates, which differ

3

to a certain limit. For instance, at the very high concenꢀ

–

1

tration of KNO (2.3 mol L ) the effective concentration

3

slightly for various heterocycles (К_e_n= (2—2.9)•10^–

s ).

3

–1

of nitronium ions decreases due to a decrease in the acidiꢀ

ty of the medium, resulting in a decrease in the nitration

rate and in the yield of 6а (see Figs 5, 6; curves 3 and 5). At

Therefore, the difference in the accumulation rates of the

Nꢀdinitromethyl derivatives depends on the rate of introꢀ

duction of the second nitro group. This rate is one to three

orders of magnitude and depends on the amount of nitroꢀ

the same time, an increase in the effective concentration

+

[

(

NO₂] due to an increase in the acidity of the medium

89.2—93.6% H SO ) increases the fraction of Meꢀenol

К_D= 2.7, see Table 3), favoring the side nitration of the

enol in the mixture, i.e., on К . For Nꢀacetonylazoles. the

2

4

t

enolization rate К_e_nand the percent content of enol К_t

Me group (see below).

increase with the enhancement of the withdrawing propꢀ

Rather high yield (42%) of compound 6а in dilute

H SO (76.77%, see Fig. 6, curve 7) should be noted, in

spite of the low nitration rate and concentration [NO₂].

The final product 6а and, most likely, intermediate niꢀ

troketone 8а are most stable just in this medium. In addiꢀ

erties of the cycle. It is most likely that К for monoꢀ

t

nitroacetonylazoles will change in the same order and,

hence, for the more enolized objects the Nꢀdinitromethyl

derivatives are formed more rapidly. For instance, 2ꢀacꢀ

etonylꢀ5ꢀnitrotetrazole 3a is more rapidly transformed into

the Nꢀdinitromethyl derivative than 1ꢀacetonylimidazole

3r and 1ꢀacetonylꢀ4ꢀnitroimidazole 3s, because its enoꢀ

lization is higher (see Table 3) and, therefore, the percent

content of enol for the corresponding nitroketone is also

higher. At the same time, acetonyltrimethylammonium

nitrate is not transformed into the Nꢀdinitromethyl derivꢀ

ative, because it is enolized much more slowly than acetoꢀ

nylazoles, and its enolization proceeds predominantly due

to the Me group.

2

4

+

tion, at this acidity the favorable ratio of СН ꢀ and

2

Meꢀenols equal to 5.4 is observed (see Table 3). As can be

seen from Fig. 6, the yield of 6а in dilute H SO (12 : 5) is

2

4

higher than that in the more concentrated acid (12 : 2),

although in the latter mixture the effective concentration

of nitronium ions and the rate of formation of compound

6

а are substantially higher.

Kinetics of accumulation of Nꢀdinitromethylazoles 6 was

studied similarly. The induction periods were 10—60 min,

depending on the rate of formation of the final products.

In the general case, the apparent rate constants for the

accumulation of the Nꢀdinitromethyl structures increase

with an increase in the number of nitro groups and nitroꢀ

gen atoms in the cycle.

6

–1

The K_a_p_p•10 (s ) values of the accumulation of

Nꢀdinitromethylazoles 6 for the nitration of Nꢀacetonylꢀ

azoles 3 obtained by UV spectroscopy in an H SO —KNO

2

4

3

2088

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

The studies performed made it possible to reduce side

processes to minimum and to direct the reaction in the

required direction.

time, the maximum 100% conversion of HNO to the

NO₂ion and the highest enolization rate are observed in

3

+

93—94% H SO and further do not increase. Therefore, it

2

4

On the one hand, according to the kinetics of formaꢀ

tion of the Nꢀdinitromethyl group, one should attain high

concentrations of nitronium ions and increase the amount

is unreasonable to use more concentrated media. In addiꢀ

tion, intermediate αꢀnitroketone decomposes more rapidꢀ

ly in these media. The yields of Nꢀdinitromethylazoles

presented in Scheme 2 were optimized not in all cases,

and there are opportunities to increasing them.

of HNO . At the same time, it is undesirable to take

3

a high amount of HNO over H SO during the work in

3

2

4

concentrated nitrating mixtures, because this decreases

the acidity of the medium and, hence, the effective conꢀ

centration of nitronium ions. The optimal volume ratio

H SO : HNO ranges from 10 : 1 to 10 : 4.

The methods for synthesis of some structures have been

developed in more detail. For example, in the "standard"

mixture 2ꢀdinitromethylꢀ5ꢀnitrotetrazole 6a was obtained

in 70—78% yield at 30—35 °C for 8 h, whereas at 20 °C

this yield was achieved for 2—3 days. The nitration of

2ꢀacetonylꢀ5ꢀ(trinitromethyl)tetrazole 3b in the "standard"

mixture ceases at the step of formation of mononitrokeꢀ

tone 8b (76% yield), which precipitates from the reaction

mixture.

However, in more concentrated mixtures compound

8b is nitrated further to Nꢀdinitromethyltetrazole 6b, which

can also be obtained, under these conditions, in one step

from the corresponding Nꢀacetonyltetrazole 3b.

2

4

3

On the other hand, as solutions of H SO are diluted,

2

4

the fraction of СН ꢀenol increases compared to that of

2

Meꢀenol in the Nꢀacetonyl derivatives. Therefore, the

nitration with sulfuric—nitric acid mixture occurs better

in the presence of a large amount of water, although the

effective concentration of nitronium ions decreases. This

is especially important for the lowly nitrated cycles and

those containing a small number of nitrogen atoms, nameꢀ

ly, pyridine, imidazole, pyrazole, and their mononitro deꢀ

rivatives. In concentrated media their K_Dvalue, i.e., the

The most complicated case is the nitration of bis(2ꢀaceꢀ

tonylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀyl) 3j, which is insoluble in

the "standard" mixture. In anhydrous mixtures in which 3j

is soluble, the bis(2ꢀdinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ

5ꢀyl) 6j that formed is easily nitrated to the trinitromethyl

derivative. Nevertheless, in an H SO solution containing

ratio СН ꢀenol/Meꢀenol, is lower than in Nꢀacetonylꢀ

2

azoles with electronꢀwithdrawing cycles of the 5ꢀnitroꢀ

tetrazole type.

Nitrating mixtures diluted with water should also be

used in the case of formation of Nꢀdinitromethyl comꢀ

pounds that are readily nitrated further to undesirable triꢀ

nitromethyl derivatives (for example, tetrazoles and nitroꢀ

triazoles). The decrease in the general acidity of the mediꢀ

um upon the addition of water also favors the enhanceꢀ

ment of stability of intermediate nitroketones. However,

the rate of their transformation into dinitroketones deꢀ

creases because of a decrease in the effective concentraꢀ

tion of nitronium ions.

As a whole, for the reasons indicated, the optimal deꢀ

gree of dilution can differ for different types of compounds.

In several cases, the poor solubility of Nꢀacetonylazoles

and intermediate acetonylazoles in nitrating mixtures

should be taken into account. For instance, in the presꢀ

ence of a large amount of water in the nitration of the

acetonyl derivatives of 5ꢀtrinitromethyltetrazole 3b and

bis(3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀyl) 3j, the reaction ceases at

the step of formation of mononitroketones precipitating

from the reaction mixtures. When selecting the nitration

conditions, it is important to take into account the ability

to enolization determining the rate of the whole process.

The latter can be qualitatively evaluated by the chemical

2

4

small amounts of HNO and water in a ratio of 12 : 1 : 1,

3

the starting ketone 3j is rather soluble and the undesirable

formation of the trinitromethyl derivative is not too fast.

Therefore, the target product 6j can be obtained in 50%

yield accompanied by rigid spectrophotometric monitorꢀ

ing almost without admixture of trinitromethyl compound.

Bis(2ꢀdinitromethylꢀ4ꢀnitroꢀ1,2,3ꢀtriazolꢀ5ꢀyl) 6o was

obtained in 50% yield in a mixture of concentrated

H SO —HNO (1 : 1), because this compound is much

2

4

3

difficultly nitrated to the trinitromethyl derivative and the

use of concentrated acids accelerates the process and inꢀ

creases the solubility of the starting acetonylazole.

The characteristic property of the strongly nitrated

azoles is the capability of easy nucleophilic substituting of

the NO group, which manifests itself in the nitration of

2

Nꢀacetonylꢀ3,5ꢀdinitroꢀ1,2,4ꢀtriazole 3i and results in the

substitution of the NO group for OH to form triazolone

2

6i (Scheme 6).

Attempts to nitrate the Nꢀacetonyl derivatives of 2,4,5ꢀtriꢀ

nitroimidazole and bis(4,5ꢀimidazolꢀ2ꢀyl) and 1,2ꢀisomers

of bis(acetonylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀyl) failed for the

same reason.

shift (δ) of the СН protons: the weaker the field δ, the

2

faster the nitration.

NꢀDinitromethylimides of carboxylic and sulfonic acids

11a—c. To prevent destruction processes, milder nitrating

mixtures CF COOH—HNO (3 : 2 v/v) with lower acidiꢀ

Optimal methods for synthesis of the Nꢀdinitromethyl

compounds. The maximally diluted nitrating mixture

H SO —HNO —Н О (12 : 5 : 5 v/v) was chosen experiꢀ

3

ty and hydrolytic activity were used (Scheme 7).

2

4

3

2

mentally. This is the "standard nitrating mixture" in which

the reaction of destructive nitration can occur. At the same

The principal possibility for the destructive nitration of

βꢀdicarbonyl compounds was shown using the synthesis

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2089

Scheme 6

Scheme 8

R = Me (13 (48%), 14a), OEt (13 (26%), 14b)

Scheme 9

Scheme 7

Structure of Nꢀdinitromethyl compounds. The structure

of Nꢀdinitromethyl compounds was proved by a complex

of spectral methods.

In the H and ¹³С NMR spectra, the total set of signals

and SSC constants in the heterocycle remain almost unꢀ

changed when the Nꢀacetonyl group is replaced by the

Nꢀdinitromethyl one (Table 5).

1

of substituted Nꢀdinitromethylhydrazine 13 as an examꢀ

ple (Scheme 8). According to our data, the starting

The presented parameters of the Nꢀdinitromethyl and

Nꢀdinitrocarbanionic moieties correspond to their posiꢀ

tion at the electronegative group, in this case, at the nitroꢀ

gen atom of the heterocycle. The tendency of shifting ν_a_s

to the highꢀfrequency region on going to more electronꢀ

withdrawing cycles is observed. The UV spectra of aqueꢀ

ous solutions of all Nꢀdinitrocarbanionic structures conꢀ

tain an intense absorption maximum at 330—350 nm, beꢀ

ing shorterꢀwavelength than that of the dinitromethane

2

ꢀhydrazinylꢀsubstituted βꢀdiketones 14a,b (see Ref. 30)

exist in the enol form by 66% for R = Me and by 100% for

R = CO Et in a CDCl solution, whereas in sulfuric acid

2

3

solutions the content of enols is higher. Therefore, they

are rapidly transformed into substituted Nꢀdinitromethylꢀ

hydrazine 13, probably, through the consecutive steps of

nitration, removal of the acetyl group, and introduction of

the second nitro group.

3

4

The synthesis of Nꢀdinitromethylhydrazines under the

conditions of destructive nitration with sulfuric—nitric acid

mixtures was shown for the oxobutyl derivative 15 (see

Ref. 31). In this case, the reaction proceeds, most likeꢀ

ly, according to the mechanism of successive eliminaꢀ

anion (362.5 nm), which corresponds to its binding with

3

4

the electronꢀwithdrawing group.

In the general case, an increase in the electronꢀwithꢀ

drawing ability of the cycle results in the hypsochromic

shift of the absorption maximum. The high molar absorpꢀ

tion coefficients indicate the planar (at ε = 17 000) or

7

,8,32,33

tion—addition

(Scheme 9).

2090

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

Table 5. Main spectral parameters of the dinitromethyl and dinitrocarbanionic fragments at the nitrogen atom of the heterocycle

Fragment

IR, ν/cm^–¹

ν_a_s

UV

NMR, δ (J/Hz)

ν_s

λ_m_a_x/nm

ε

¹H

¹³C

¹⁵N (relative to MeNO₂)

N—CH(NO₂)₂1300—1500 1580—1620

—

8.2—8.8

102—110

–(28—29)

= 13—14)

N,C

1

(

J_С_,_Н

=

( J

=

188—190)

N—C(NO₂)₂^–

1230—1280 1460—1505 330—350 15000—19000

—

125—137

–(27—30)

J_N_,_C= 28—30)

(¹

close to planar structure of the dinitrocarbanionic moiety.

It was also concluded on the basis of the regular change in

and the hydrolysis with the acetyl moiety removal occurs

only after the introduction of two nitro groups.

2. The reaction occurs by the addition of nitronium

ions to the double bond of the enol forms of Nꢀacetonylꢀ

azoles and intermediate nitroketones.

3. The introduction of nitrosating agents exerts no efꢀ

fect on the yields of Nꢀdinitromethylazoles.

4. The introduction of the first nitro group proceeds

with the rate close to the enolization rate of Nꢀacetonylꢀ

azole. At the low concentration [NO₂⁺], the rate of adꢀ

dition of nitronium ions is lower than the enolization

13

the chemical shift of these groups in the С NMR spectra

and the SSC constants (J_C_,_N) that the carbon atom changes

its tetrahedral configuration to the trigonal (planar) one.

According to the Xꢀray diffraction analysis data for

potassium salt 6а (Fig. 7), the aromatic nitro group

in position 5 is almost coplanar to the tetrazole cycle

plane and, hence, is conjugated with it. The dinitroꢀ

carbanionic moiety is planar and unfolded relative to the

ring by 80.6°, due to which no conjugation between them

is observed.

rate and the whole process depends on the concentꢀ

ration [NO₂⁺]. At the higher concentration [NO

+

]

The acidity of the Nꢀdinitromethyl groups was deterꢀ

mined in H SO —H O solutions by the spectrophotometꢀ

2

–

1

(>0.3—0.4 mol L ), the rate of addition of nitronium

ions is equal to the enolization rate and the process is

independent of the concentration [NO₂⁺].

2

4

2

3

5

ric method using the Boyd acidity functions H_ similarꢀ

ly to the procedure described. The obtained pK values

3

6

a

(

see Scheme 2) show that Nꢀdinitromethylazoles are strong

5. The rate of addition of the second nitro group is

1—1.5 orders of magnitude lower than that of the first

group; it depends on the amount of the enol form and

concentration [NO₂⁺] but is independent of the enolizaꢀ

tion rate. In this case, the addition of nitronium ions is

much slower than the formation of the enol form of interꢀ

mediate nitroketone.

3

7

CHꢀacids exceeding trinitromethane (pK = 0.06).

a

The structures bearing a substituent in the orthoꢀposiꢀ

tion to the dinitromethyl group have anomalously high

CHꢀacidity, i.e., they manifest the orthoꢀeffect, indicating

a considerable turn of the planar С(NO ) moiety relative

2

3

8

to the heterocycle plane.

General regularities. The following conclusions can be

drawn on the basis of the obtained results.

6. The role of the heterocycle in the destructive nitraꢀ

tion is related to its influence on the enolization step. In

1

. During the nitration of Nꢀacetonylazoles, the nitro

the series of structurally related ketone, the CH ꢀenolizaꢀ

2

groups are introduced directly into the methylene moiety,

tion rate increases with an increase in the withdrawing

properties of the cycle. According to the known mechaꢀ

nism of the enolization—ketonization process, the keto—

O(122)

N(2)

O(121)

enol equilibrium constant increases (К = К /K =

t

en

ket

O(111)

N(11)

=

[En]/[Ket] (%)). The K value in mononitroacetonylaꢀ

t

zoles should increase similarly. Therefore, the formation

of the Nꢀdinitromethyl derivatives is faster in the case of

substances with high enolization rates.

N(12)

C(2)

N(22)

O(222)

N(1)

C(5)

7

. For the nitration of various Nꢀacetonyl derivatives,

O(112)

the first nitro group is rapidly introduced into almost all

CH moieties and the difference in the rates of formation

2

N(4)

N(3)

of the Nꢀdinitromethyl compounds is mainly related to

the step of introduction of the second nitro group.

O(221)

8

. For the nitration of Nꢀacetonylazoles, the protonaꢀ

tion of the nitrogen atom of the heterocycle favors the

acceleration of enolization and increases the content of

Fig. 7. Projection of the anion of 2ꢀdinitromethylꢀ5ꢀnitrotetrꢀ

azole potassium salt Kꢀ6а on the plane passing through the N(2),

C(2), N(12), and N(22).

enol in the mixture (increasing К ). That is why, probably,

t

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2091

+

–

the protonated forms, i.e., cycloimmonium salts, are niꢀ

trated. In the case of the most withdrawing cycles, the

yields of Nꢀdinitromethylazoles are higher, as a rule, beꢀ

and H2SO4 solutions were detected with Me4N ClO4 as the

internal standard, whose chemical shift in these solvents has a

3

9

constant value of 3.10 ppm relative to Me Si. This standard is

not deuterated in D SO for at least several hours. IR spectra

4

2

4

cause the content of СН ꢀenol in them is higher comꢀ

2

were obtained on a URꢀ20 instrument (KBr pellts), and UV

spectra were measured on a Specord UV—Vis spectrometer. Mass

spectra were recorded on a Kratos МSꢀ30 instrument (70 eV)

with direct sample injection into the source at the temperature of

the ionization chamber 250 °C.

pared to that of Meꢀenol.

9

. The formation of Nꢀdinitromethylazoles is deterioꢀ

rated by the following side processes (Scheme 10). A. The

decomposition of intermediate nitroketones was confirmed

kinetically and chemically; this process is accelerated with

an increase in the acidity of the medium and is due, most

The starting Nꢀacetonylazoles were obtained according to

1

0

known procedures.

Synthesis of Nꢀdinitromethylazoles 6 (general procedure). Niꢀ

tric acid (d = 1.5 g cm^–³) (1—5 mL) was added dropwise to

likely, to the elimination of an acetic acid molecule to

_f_o_r_m_n_i_t_r_i_l_e_o_x_i_d_e_.1

9—21

B. Since the enolization of the

a solution of Nꢀacetonylazole 3 (2 g) in H SO₄(10—12 mL)

2

acetonyl compounds occurs due to the Me group, the nitraꢀ

tion also occurs at this group to form polynitro derivatives

of methane and Nꢀheterylacetic acids, which cannot transꢀ

form into Nꢀdinitromethyl compounds under the nitraꢀ

tion conditions. In an experiment on the nitration of aceꢀ

tone, we pioneered to isolate dinitromethane in 5% yield,

which was also detected spectrophotometrically upon the

nitration of 2ꢀacetonylꢀ5ꢀnitrotetrazole 3а. C. In several

cases, derivatives of electronꢀwithdrawing cycles are charꢀ

acterized by the nitration of Nꢀdinitromethylazoles to trinꢀ

itromethyl compounds. The kinetic studies showed that

this process occurs one—two orders of magnitude more

slowly than the accumulation of Nꢀdinitromethylazoles,

while in the presence of significant amounts of water at

the volume ratio H SO : H O = 12 : 5 the process does

(

76.8—93.6%) with ice cooling (5—10 °C) The ratio H O : H SO

2 2 4

d = 1.83 g cm^–³) for the preparation of sulfuric acid solutions of

indicated concentrations and the temperature and duration of

storage of the reaction mixtures are given below in examples.

NꢀDinitromethylazoles insoluble in sulfuric—nitric acid mixtures

were isolated by filtration. In other cases, the reaction mixture

was poured into 50 g of finely divided ice with vigorous stirring,

urea was added to remove nitrogen oxides, and the mixture was

extracted with ether, ethyl acetate, or dichloromethane

(

3×10 mL). To obtain aqueous solutions of Nꢀdinitromethylꢀ

azoles, water was added to ethereal solutions, and the ether was

evaporated on a rotary evaporator. A saturated solution of potasꢀ

sium acetate in methanol or water was added to a solution of

Nꢀdinitromethylazole 6 in an organic solvent or water until

the precipitate of poorly soluble Nꢀdinitromethylazole potasꢀ

sium salt stopped to form. Analytically pure potassium salts of

Nꢀdinitromethylazoles were obtained after recrystallization from

water. The analytically pure compounds with high CHꢀacidity

2

4

2

not occur.

(

pK < 0) can be obtained using a KI solution in water. The

a

Experimental

yields and рК values are indicated in Scheme 2.

а

2

ꢀDinitromethylꢀ5ꢀnitrotetrazole (6а). Water (10 mL) was

¹H, ¹³C, and ¹⁵N NMR spectra were recorded on a Bruker

added dropwise with ice cooling to a solution of 2ꢀacetonylꢀ5ꢀ

nitrotetrazole 3а (5 g) in H SO (d = 1.83 g cm ) (24 mL), then

HNO (d = 1.5 g cm ) (10 mL) was added, and the reaction

1

–3

AMꢀ300 instrument with the working frequencies 300.13 ( H),

2

4

13

15

–3

7

5.47 ( C), and 21.68 MHz ( N). The chemical shift values are

3

given in ppm, and the SSC constant values are expressed in Hz.

mixture was stored for 3 days (or heated for 5 h at 40 °C). The

precipitate that formed was filtered off, washed with trifluoroꢀ

acetic acid, and dried in a vacuum desiccator over Р О . Techꢀ

19

The standards were Me Si (internal) and CF COOH ( F) and

4

3

15

MeNO ( N) (external). The NMR spectra in D O, D SO ,

2

4

2

5

Scheme 10

Destruction

2092

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

nical 6а (5 g) was obtained, which contains (according to the UV

analysis data) 4.6 g (72%) of the major substance. Compound 6а

can be used without purification for further syntheses. Found

187.31 (C=O). IR, ν/cm^–¹: 1365, 1610, 1590 (C(NO ) ; 1280,

2

3

1590 (NO at CH); 1760 (С=О).

2

2ꢀNitromethylꢀ5ꢀtrinitromethyltetrazole (10b). A solution of

nitroketone 8b (1 g) in methanol (8 mL) was heated to 60 °C,

water (8 mL) was added, and the mixture was stored for 14 h at

20 °C. The precipitate that formed was filtered off, washed with

water, and dried in air. Compound 10b was obtained in a yield of

(

%): C, 10.97; H, 0.38; N, 45.04. C HN O . Calculated (%):

2 7 6

1

C, 10.96; H, 0.46; N, 44.76. H NMR (CF COOH), δ: 8.47

(

3

–

1

s, CH). IR, ν/cm : 1320, 1596, 1620 (CH(NO ) ); 1373, 1570

2 2

NO arom.). pK (H O—H SO ) –1.7.

2

a

2

4

Potassium salt Kꢀ6а. A saturated aqueous solution of potasꢀ

sium acetate (1 mL) was added to a solution of compound 6а

1 g). The precipitate that formed was filtered off, washed with

methanol and ether, and dried in air. The analytically pure salt

0.83 g (96%) as colorless crystals, m.p. 83 °C (from СHCl ).

3

Found (%): C, 13.01; H, 0.87; N, 40.38. C H N O . Calculated

3

2

8

(

(%): C, 12.95; H, 0.72; N, 40.29. UV (H O), λ/nm (ε): 313

2

(6600). IR, ν/cm^–: 1360, 1605, 1620 (C(NO ) ); 1280, 1585

1

2

3

13

1

was obtained in a yield of 1 g (85%). C NMR (DMSOꢀd ), δ:

(NO at CH); 1760 (С=О). H NMR (CD CN), δ: 7.6 (s, СН ).

6

2

3

2

–

13

1

31.5 (С(NO₂)₂, J_C_,_N= 30.0 Hz), 166.2 (C(5)). UV (H O),

C NMR (СD СN), δ: 81.49 (СН , J

= 169 Hz); 120.5

2

3

2

C,H

–1

–

–1

λ/nm (ε): 336 (18000). IR, ν/cm : 1260, 1300, 1493 (C(NO₂)₂);

350, 1587 (NO₂arom.). According to the UV spectroscopic

(C(NO ) ); 153.52 (C(5)). IR, ν/cm : 1360, 1605, 1620 (C(NO ) );

2 3 2 3

1

1280, 1585 (NO at CH ).

2

data, the mother liquor contains 0.22 g (18%) of 2ꢀdinitromethꢀ

ylꢀ5ꢀnitrotetrazole 6а.

Bis(1ꢀdinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀyl) (6j). A soluꢀ

–

3

tion prepared from HNO (d = 1.5 g cm ) (10 mL) and water

3

2

ꢀNitromethylꢀ5ꢀnitrotetrazole (10а). Ketone 3a (1 g) was

(10 mL) was added dropwise with stirring to a solution of dikeꢀ

–

3

dissolved in an HNO —H SO —H O (5 : 12 : 5, vol.) nitrating

tone 3j (10 g) in H SO (d = 1.83 g cm ) (120 mL) at 10 °C. The

3

2

4

2

4

mixture (11 mL), and the reaction mixture was stored for 2 h at

0 °C and poured into 50 g of ice. The precipitate that formed

was filtered off, washed with water, and dried in air. Compound

0a was obtained in a yield of 0.14 g (14%), m.p. 138—139 °C

MeОН—Н О). Found (%): C, 13.71; H, 0.95; N, 47.93.

reaction mixture was stored for 1 h at 40 °C and for 1 h more at

20 °C. The precipitate that formed was filtered off and washed

2—3 times with a small amount of water. According to the UV

spectroscopic data, the wet product contains 25% of the major

substance 6j. The yield based on the pure product was 48—55%.

Bis(1ꢀdinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀyl) dipotassium

salt (2Кꢀ6j). Sodium bicarbonate was carefully added with stirꢀ

ring to a suspension of nonꢀpurified compound 6j (3 g) in water

(30 mL) to pH of the medium 6—7. A hot solution of KCl (1 g) in

water (5 mL) was added at 80 °C to the obtained solution of

disodium salt 6j filtered from undissolved admixtures. Analytiꢀ

cally pure dipotassium salt 2Кꢀ6j crystallized during slow coolꢀ

ing. The yield was 2.8 g (80%). The decomposition temperature

2

1

(

2

C H N O . Calculated (%): C, 13.80; H, 1.16; N, 48.28.

2

6

4

1

H NMR (CD CN), δ: 7.64 (s, CH ). UV (H O, рН = 8), λ/nm (ε):

12 (8600). IR, ν/cm : 1305, 1560, 1590 (NO group).

3

2

–

1

3

2

ꢀDinitromethylꢀ5ꢀtrinitromethyltetrazole (6b). Nitration

conditions: HNO —H SO —H O (12 : 12 : 1, vol.), 20 °C, 3 h.

3

2

4

2

M.p. 58—59 °C (CHCl —hexane). UV (H O), λ/nm (ε): 336

3

2

(

16500). Found (%): C, 11.22; H, 0.38; N, 39.12. C HN O .

3 9 10

Calculated (%): C, 11.15; H, 0.31; N, 39.02.

Potassium salt Kꢀ6b crystallizes from water. M.p. 148 °C

was 254 °C (decomp. onset 221 °C). UV (H O), λ/nm (ε): 338

2

13

–1

–

(

with decomp.). UV (H O), λ/nm (ε): 336 (16 800). C NMR

(33 600). IR, ν/cm : 1240, 1287, 1488 (C(NO₂)₂); 1351, 1361,

2

–

13

–

DMSOꢀd ), δ: 120.8 (C(NO ) ); 131.0 (C(NO ) ); 152.6

1581 (NO arom.). C NMR (DMSOꢀd ), δ: 130.7 (С(NO ) ),

6

2 3

2 2

2

6

2 2

C(5)).

,5ꢀBis(dinitromethyltetrazole) dipotassium salt. A solution

144.7 (С(5)), 162.3 (С(3)).

2

Analytically pure bis(1ꢀdinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazolꢀ5ꢀ

of KOH (0.48 g, 7.6 mmol) in methanol (8 mL) was added

dropwise with stirring at 0—5 °C to a solution of hydroxylamine

hydrochloride (0.11 g, 1.5 mmol). Compound 6b (0.32 g, 1 mmol)

in methanol (5 mL) was added to the resulting solution. The

reaction mixture was stored for 1 h at 10 °C, and the precipitate

that formed was filtered off, washed with water and methanol,

and dried in air. Salt 2Кꢀ6b was obtained in a yield of 0.34 g

yl) (6j). Salt 2Кꢀ6j (3 g) was added with stirring to H SO

2

4

(d = 1.83 g cm^–) (15 mL), and the mixture was stored for 30 min

at ~20 °C, during which the yellowish salt transformed into a colꢀ

orless precipitate. The precipitate was filtered off, washed with

1

СF COOH, and dried in air. Compound 6j was obtained in

3

a yield of 2 g (78%). Found (%): C, 16.69; H, 0.56; N, 38.90.

C H N O . Calculated (%): C, 16.60; H, 0.46; N, 38.71. M.p.

6

2

12 12

(

91%). The decomposition temperature was 146 °C (H O).

164—165 °C (decomp., СF COOH). UV (H O), λ/nm (ε): 338

3 2

2

(33 400). IR, ν/cm^–: 1315, 1590, 1615 (CН(NO ) ); 1357, 1570

1

Found (%): C, 10.27; K, 22.02; N, 31.83. C K N O . Calculatꢀ

3

2

8

2 2

ed (%): C, 10.17; K, 22.07; N, 31.63. UV (H O), λ/nm (ε): 343

(NO arom.).

2

13

–

(

28 800). C NMR (DMSOꢀd ), δ: 123.76 (СC(NO ) ); 131.04

NC(NO₂)₂); 158.85 (C(5)). IR, ν/cm : 1280, 1500, 1550

C(NO₂)₂^–).

Bis(2ꢀdinitromethylꢀ4ꢀnitroꢀ1,2,3ꢀtriazolꢀ5ꢀyl) (6o). Dikeꢀ

6

2 2

–

–1

tone 3o (2.38 g) was dissolved in a mixture of 12 mL of HNO

3

–1

(d = 1.5 g cm ) and 12 mL of H SO (d = 1.83 g cm ), and the

2

4

2

ꢀ(1´ꢀNitro)acetonylꢀ5ꢀtrinitromethyltetrazole (8b). Ketone

mixture was stored for 1 h with stirring for 20 °C, preventing the

temperature increase. Then the reaction mixture was poured

into 250 mL of a mixture of ice with water, washed 2—3 times

(10 mL at once) of cool water, and dried for 10 min on the filter.

According to the UV analysis data, the wet product contains

25—35% of the major substance 6o. The yield based on the pure

product was 55—75%. Pure 6o (51%) was isolated through the

dipotassium salt.

3

(

b (1 g) was added with mixing to an HNO —H SO —H O

5 : 12 : 5, vol.) nitrating mixture (11 mL), and the mixture was

stored at 20 °C for 20 h. The precipitate that formed was filtered

off, washed with СF COOН, and dried in a vacuum desiccator

over P O . Compound 8b was obtained in a yield of 0.88 g (76%)

as white crystals, m.p. 86 °C (from СF COOН). Found (%):

C, 18.63; H 1.12; N, 34.91. C H N O . Calculated (%): C, 18.76;

H, 1.76; N, 35.00. H NMR (CD CN), δ: 2.48 (s, Me); 8.22

3

2

4

2

3

2

5

3

5

4

8

9

1

Analytically pure compound 6o was obtained similarly to comꢀ

pound 6j through the corresponding dipotassium salt. Found (%):

C, 16.71; H, 0.49; N, 38.84. C H N O . Calculated (%):

3

13

(

9

s, CH). C NMR (СD СN), δ: 27.12 (Me, J_C_,_H= 131 Hz);

5.26 (CH, J_C_,_H= 169 Hz); 120.4 (C(NO ) ); 153.9 (C(5));

2 3

3

6

2

12 12

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2093

1

3

C, 16.60; H, 0.46; N, 38.71. UV (H O), λ/nm (ε): 339 (34 000).

(NO arom.). C NMR (DMSOꢀd ), δ: 130.4 (С(NO ) ^–), 151.6

2

6

2 2

–

1

IR, ν/cm : 1315, 1600, 1620 (СH(NO ) ); 1355, 1567 (NO

2

(С(5)); 162.7 (C(3)).

2

13

arom.). C NMR (CD CN), δ: 107.2 (СH(NO ) ), 134.3 (С(5)),

2ꢀDinitromethylꢀ5ꢀnitroꢀ2,4ꢀdihydroꢀ3Нꢀ1,2,4ꢀtriazolꢀ3ꢀone

(6i). An HNO —H SO —H O (5 : 12 : 5) mixture, 20 °C, 72 h.

3

2 2

1

54.2 (С(4)).

Bis(2ꢀdinitromethylꢀ4ꢀnitroꢀ1,2,3ꢀtriazolꢀ5ꢀyl) dipotassium

3

2

4

2

M.p. 135 °C (СHCl ). Found (%): C, 15.50; H, 0.93; N, 35.97.

3

salt (2Кꢀ6o) was obtained similarly to compound 2Кꢀ6j. The

decomposition temperature was 172 °C (decomp. onset 152 °C).

C H N O . Calculated (%): C, 15.39; H, 0.86; N, 35.90. UV

3

2

6

7

–

1

(H O), λ/nm (ε): 350 (19 700). IR, ν/cm : 1320, 1350, 1390,

2

–

1

13

UV (H O), λ/nm (ε): 339 (34 000). IR, ν/cm : 1258, 1485,

1597 (CH(NO ) ); 1568 (NO arom.). C NMR (СН NO ), δ:

2

2 2

2

3

2

–

13

1

508 (С(NO₂)₂; 1370, 1565 (NO arom.). C NMR (DMSOꢀd ),

δ: 134.4 (С(NO₂)₂), 132.0 (С(5)), 151.5 (С(4)).

ꢀDinitromethyltetrazole (6c). Nitration conditions: HNO —

103.5 (СH(NO ) ), 151.7 (C=О), 149.1 (C(3)).

2

6

2 2

–

Dipotassium salt 2Кꢀ6i. The decomposition temperature was

1

338 °C (decomp. onset 225 °C). UV (H O), λ/nm (ε): 350

3

2

–

1

–

—

H SO —H O (1 : 12 : 1), 20 °C, 4 h. Found (%): C, 13.75;

(19 900). IR, ν/cm : 1342, 1495 (С(NO₂)₂); 1318, 1522

(NO₂arom.). C NMR (DMSOꢀd ), δ: 132.0 (С(NO ) ),

2

4

2

13

–

H, 1.05; N, 48.36. C H N O . Calculated (%): C, 13.80; H, 1.16;

2

6

4

6

2 2

N, 48.28.

J_C_,_N= 28.4); 160.9 (C=O); 163.0 (C(5)).

Potassium salt Кꢀ6с. The decomposition temperature was

Bis(5ꢀazidoꢀ1ꢀdinitromethylꢀ1,2,4ꢀtriazolꢀ3ꢀyl) (6k). Nitraꢀ

tion conditions: HNO —H SO —H O (5 : 12 : 5), 20 °C, 24 h.

Found (%): C, 16.84; H, 0.52; N, 52.65. C H N O . Calculatꢀ

6 2 16 8

1

51 °C (decomp. onset 127 °C). UV (H O), λ/nm (ε): 344

2

3

2

4

2

–

1

(

17 200). IR, ν/cm^–¹: 1259, 1277, 1485, (C(NO ) ). H NMR

2

13

DMSOꢀd ), δ: 9.72 (s, 1 Н). C NMR (DMSOꢀd ), δ: 127.6

С(NO₂)₂), 147.3 (С(5), J_C_,_H= 222 Hz).

ꢀDinitromethyltetrazole (6d). Nitration conditions: HNO —

ed (%): C, 16.91; H, 0.47; N, 52.58. UV (H O), λ/nm (ε): 342

6

–

6

2

–1

(32800). IR, ν/cm : 1314, 1591, 1610 (CН(NO ) ), 2164 (N(3)).

2 2

2

Dipotassium salt 2Кꢀ6k. The decomposition temperature was

3

—

H SO —H O (5 : 12 : 5), 40 °C, 1 h. Found (%): C, 13.72;

120—121 °C (decomp.). UV (H O), λ/nm (ε): 342 (32 800).

2

4

2

IR, ν/cm^–: 1240, 1260, 1487 (С(NO₂)₂); 2125 (N(3)).

1ꢀDinitromethylꢀ4ꢀnitroꢀ1,2,3ꢀtriazole (6l). Nitration conꢀ

ditions: HNO —H SO —H O (10 : 10 : 0), 20 °C, 40 min. UV

1

–

H, 1.08; N, 48.21. C H N O . Calculated (%): C, 13.80; H, 1.16;

N, 48.28.

2

6

4

Potassium salt Кꢀ6d. The decomposition temperature was

3

2

4

2

–

1

84 °C (decomp. onset 160 °C). UV (H O), λ/nm (ε): 341

(H O), λ/nm (ε): 345 (19 200). IR, ν/cm : 1320, 1610, 1625

(СH(NO ) ); 1350, 1565 (NO arom.). H NMR (CD СN), δ:

8.75 (s, СH(NO ) ); 9.33 (s, 1 Н, С(5)Н). C NMR (CD СN),

2

17 700). IR, ν/cm^–¹: 1265, 1290, 1502 (C(NO ) ). H NMR

–

1

(

2

2 2

2

3

13

DMSOꢀd ), δ: 9.22, (s, 1 Н). C NMR (DMSOꢀd ), δ: 130.6

6

–

6

2 2

3

С(NO₂)₂), 153.5 (С(5), J_C_,_H= 216 Hz).

ꢀDinitromethylꢀ5ꢀmethyltetrazole (6е). Nitration condiꢀ

tions: HNO —H SO —H O (5 : 12 : 5), 55 °C, 40 min. Found (%):

δ: 105.3 (СH(NO ) ), J

= 187.7 Hz); 126.6 (C(5), J_C_,_H=

2 2

C,H

1

= 214.5 Hz); 154.0 (С(4)).

Potassium salt Кꢀ6l. The decomposition temperature was

178 °C (decomp. onset 165 °C). Found (%): C, 14.20; H, 0.36;

K, 15.237; N, 32.92. C HKN O . Calculated (%): C, 14.07;

3

2

4

2

C, 19.22; H, 2.22, N, 44,76. C H N O . Calculated (%):

C, 19.16; H, 2.14; N, 44.68.

3

4

6

4

3

6

Potassium salt Кꢀ6e. The decomposition temperature was

H, 0.39; K, 15.26; N, 32.81. UV (H O), λ/nm (ε): 345 (19 300).

2

IR, ν/cm : 1225, 1465 (С(NO₂)₂^–); 1318, 1385, 1570 (NO arom.).

–

1

(

1

62 °C (decomp. onset 136 °C). UV (H O), λ/nm (ε): 345.5

2

17 000). IR, ν/cm^–¹: 1220, 1240, 1462, 1505 (C(NO ) ).

–

1

H NMR (DMSOꢀd ), δ: 9.82 (s, 1 Н, С(5)Н). C NMR

13

2

6

13

–

H NMR (DMSOꢀd ), δ: 2.37 (s, 3 Н). C NMR (DMSOꢀd ),

δ: 8.1 (Me), 127.0 (С(NO₂)₂^–), 156.0 (С(5)).

ꢀDinitromethylꢀ5ꢀmethyltetrazole (6f). Nitrating agent

(DMSOꢀd ), δ: 130.7 (С(NO ) ), 129.7 (С(5), J

= 210.8

6

2 2

C,H

15

Hz); 152.8 (С(4), J_C_,_H= 7.4 Hz). N NMR (DMSOꢀd ), δ:

6

2

135.2 (N(1), J_N₍₁₎_,_H₍₅₎= 4.2 Hz); 7.2 (N(2)); 32.2 (N(3)); 25.6

–

3

HNO (d = 1.5 g cm ), 20 °C, 3.5 h. Found (%): C, 19.28;

(NO arom.); 29.0 (NO aliphat.).

3

2

H, 2.03, N, 44.55. C H N O . Calculated (%): C, 19.16; H, 2.14;

N, 44.68.

2ꢀDinitromethylꢀ4ꢀnitroꢀ1,2,3ꢀtriazole (6m). Nitration conꢀ

ditions: HNO —H SO —H O (1 : 12 : 1), 20 °C, 2 h. UV (H O),

3

4

6

4

3

2

4

2

–

1

Potassium salt Кꢀ6f. The decomposition temperature was

λ/nm (ε): 342 (18 800). IR, ν/cm : 1318, 1595, 1615

1

74 °C (decomp. onset 154 °C). UV (H O), λ/nm (ε): 341

(СH(NO ) ); 1358, 1565 (NO arom.). H NMR (CD СN), δ:

2

2 2

2

3

17 300). IR, ν/cm^–¹: 1225, 1268, 1495 (C(NO ) ). H NMR

–

1

8.76 (s, СH(NO ) ); 8.73 (s, 1 Н, С(5)Н). C NMR (H SO ),

13

(

2

2 2

2

4

DMSOꢀd ), δ: 2.75 (s, 3 Н). ¹³C NMR (DMSOꢀd ), δ: 10.4

Me), 130.6 (С(NO₂)₂^–), 162.5 (С(5)).

δ: 105.6 (СH(NO ) ), J

= 187.7 Hz); 134.0 (C(5), J_C_,_H=

6

2 2

C,H

= 212.7 Hz); 154.4 (C(4), J_C_,_H= 9.2 Hz).

Bis(2ꢀdinitromethyltetrazolꢀ5ꢀyl) (6g). Nitration conditions:

HNO —H SO —H O (10 : 12 : 0), 35 °C, 2 h. UV (H O), λ/nm

Potassium salt Кꢀ6m. The decomposition temperature was

229 °C (decomp. onset 222 °C). Found (%): C, 14.17; H, 0.45;

K, 15.35; N, 32.74. C HKN O . Calculated (%): C, 14.07;

3

2

4

2

(

ε): 338 (33 200). Found (%): C, 13.93; H, 0.54; N, 48.63.

3

6

C H N O . Calculated (%): C, 13.88; H, 0.58; N, 48.56.

H, 0.39; K, 15.26; N, 32.81. UV (H O), λ/nm (ε): 342 (19 000).

4

2

12

8

2

IR, ν/cm^–: 1255, 1292, 1490, 1510 (С(NO ) ); 1355, 1550

1

–

Dipotassium salt 2Кꢀ6g. The decomposition temperature was

2 2

1

2

3

10 °C (decomp. onset 140 °C). UV (H O), λ/nm (ε):

(NO arom.). H NMR (DMSOꢀd ), δ: 9.67 (s, 1 Н, С(5)Н).

2 6

2

38 (33 400). IR, ν/cm^–¹: 1260, 1505 (C(NO ) ^–). ¹³C NMR

13

C NMR (DMSOꢀd ), δ: 134.6 (С(NO ) ); 132.8 (С(5),

–

2

6

2 2

–

15

(

DMSOꢀd ), δ: 131.0 (С(NO ) ), 155.6 (С(5)).

J_C_,_H= 207.2 Hz); 154.2 (C(4), J_C_,_H= 8.3 Hz). N NMR

(DMSOꢀd ), δ: 29.5 (N(1), J = 11.9 Hz); 136.8 (N(2));

6

2 2

7

1

ꢀDinitromethylꢀ3ꢀnitroꢀ1,2,4ꢀtriazole (6h). Nitration condiꢀ

6

N(1),H(5)

tions: HNO —H SO —H O (5 : 12 : 5), 40 °C, 1.5 ч. Found (%):

44.5 (N(3)); 26.8 (NO arom.); 28.1 (NO aliphat.).

3

2

4

2

C, 16.59; H, 0.88; N, 38.41. C H N O . Calculated (%):

2ꢀDinitromethylꢀ4,5ꢀdinitroꢀ1,2,3ꢀtriazole (6n). Nitration

conditions: HNO —H SO —H O (10 : 10 : 0), 10 °C, 4 h. UV

3

2

6

C, 16.52; H, 0.92; N, 38.54. UV (H O), λ/nm (ε): 344 (17 600).

2

3

2

4

2

Potassium salt Кꢀ6h. The decomposition temperature was

(H O), λ/nm (ε): 337 (17 400).

2

(

06 °C (decomp. onset 193 °C). UV (H O), λ/nm (ε): 344

Potassium salt Кꢀ6n. The decomposition temperature was

2

17 700). IR, ν/cm^–¹: 1235, 1495 (C(NO₂)₂); 1308, 1370, 1578

–

191 °C (decomp. onset 177 °C). UV (H O), λ/nm (ε): 337

2

2094

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

Semenov et al.

(

17 500). Found (%): C, 11.88; K, 12.86; N, 32.73. C KN O .

0.25 mol) in methanol (200 mL), and the mixture was stirred for

10 min and cooled to 20 °C, and bromoacetone (25 mL, 0.3 mol)

was added for 30 min, maintaining the temperature at 20—25 °C.

The reaction mixture was stored at this temperature for 30 min

more, and KBr that precipitated was filtered off. The solution

was evaporated in vacuo, acetone (200 mL) was added, and preꢀ

cipitated KBr was filtered off. The solvent was evaporated, ether

(100 mL) was added to the semicrystalline mixture that formed,

and the precipitate was filtered off, washed with ether, and reꢀ

3

–

7

8

1

Calculated (%): C, 11.96; K, 12.98; N, 32.56. IR, ν/cm : 1260,

1

290, 1485, 1516 (С(NO₂)₂^–); 1360, 1558, 1577 (NO arom.).

2

–

H NMR (DMSOꢀd ), δ: 134.4 (С(NO₂)₂); 144.8 (С(4), C(5)).

6

1

ꢀDinitromethylꢀ4ꢀnitropyrazole (6р). Nitration conditions:

HNO —H SO —H O (5 : 12 : 5), 20 °C, 20 h. UV (H O), λ/nm

(

J_C_,_H= 189.6 Hz); 137.3 (d, C(4), J_C_,_H= 212.5 Hz); 137.2 (С(5));

1

3

2

4

2

13

ε): 347 (17 550). C NMR (H SO ), δ: 103.9 (d, (СH(NO ) ),

2 4 2 2

38.9 (C(3)).

Potassium salt Кꢀ6р. The decomposition temperature was

65 °C (decomp. onset 192 °C). Found (%): C, 18.92; H, 0.87;

crystallized from МеОН—CCl (1 : 3). Compound 12a was obꢀ

tained in a yield of 22 g (56%), m.p. 72—73 °C. Found (%):

4

1

K, 15.48; N, 27.55. C H KN O . Calculated (%): C, 18.83;

C, 54.30; H, 5.94; N, 9.12. C H NO . Calculated (%): (C);

4

2

5

6

7

9

3

1

H, 0.79; K, 15.32; N, 27.44. UV (H O), λ/nm (ε): 347 (17 700).

54.19; H, 5.85; N, 9.03. H NMR (CDCl ), δ: 2.2 (s, 3 H); 2.78

2

3

IR, ν/cm : 1252, 1462, (C(NO₂)₂^–); 1329, 1520 (NO arom.).

–

1

(s, 4 Н); 4.3 (s, 2 Н).

2

1

H NMR (DMSOꢀd ), δ: 8.75 (s, 1 Н, С(3)Н); 9.28 (s, 1 Н,

Nꢀ(Acetonyl)phthalimide (12b). Bromoacetone (21 mL,

0.25 mol) was added to potassium phthalimide (37 g, 0.2 mol) in

DMF (200 mL), maintaining the temperature at 20—25 °C. The

reaction mixture was stored at this temperature for 1 h and poured

into water. The precipitate that formed was filtered off and reꢀ

6

13

–

С(5)Н). C NMR (DMSOꢀd ), δ: 133.8 (С(NO ) ); 135.9

6

2 2

(

1

C(5), J_C_,_H= 201.6); 136.1 (dd, C(4), J_C_,_H= 5.5 Hz, J_C_,_H= 6.5 Hz);

37.1 (dd, С(3), J_C_,_H= 197.9 Hz, J_C_,_H= 6.5 Hz).

ꢀDinitromethylꢀ3,4ꢀdinitropyrazole (6q). Nitration condiꢀ

tions: HNO —H SO —H O (5 : 12 : 5), 20 °C, 20 h. UV (H O),

1

crystallized from МеОН—СCl (1 : 3). Compound 12b was obꢀ

3

2

4

2

1

2

4

λ/nm (ε): 343 (17 800). H NMR (СDCl ), δ: 8.75 (s, 1 Н,

(

tained in a yield of 0.31 g (76%), m.p. 120 °C (cf. Ref. 40: m.p.

118 °C).

3

13

СH(NO ) ); 9.2 (s, 1 Н, С(5)Н)). C NMR (H SO ), δ: 106.4

2 2 2 4

(

1

d, СH(NO ) , J = 187.7 Hz); 129.4 (d, C(4), J_C_,_H= 3.7 Hz);

C,H

36.6 (d, C(5), J_C_,_H= 210.8 Hz); 149.5 (С(3)).

Potassium salt Кꢀ6q. The decomposition temperature was

00 °C (decomp. onset 170 °C). Found (%): C, 16.07; H, 0.42;

oꢀSulfobenzoic acid Nꢀ(acetonyl)imide (12с). Bromoacetone

(10 mL, 0.12 mol) was added to a suspension of saccharine sodiꢀ

um salt (20.5 g, 0.1 mol) in MeOH (400 mL), and the mixture

was heated to 60 °C and stirred to a homogeneous solution. The

reaction mixture was cooled and evaporated, acetone (400 mL)

was added, and precipitated NaBr was filtered off. Acetone was

removed in vacuo, and the residue was recrystallized from

2

K, 13.22; N, 27.90. C HKN O . Calculated (%): C, 16.00;

H, 0.34; K, 13.02; N, 28.00. UV (H O), λ/nm (ε): 343 (17 900).

IR, ν/cm : 1215, 1500, (C(NO ) ); 1338, 1380, 1543, 1560,

1

4

6

8

2

–

1

–

2

520 (NO arom.). ¹H NMR (DMSOꢀd ), δ: 9.82 (s, 1 Н,

СHCl —MeOH (10 : 1). Compound 12c was obtained in a yield

2

3

6

3

1

–

С(5)Н). C NMR (DMSOꢀd ), δ: 133.0 (С(NO ) ); 126.8

of 18 g (75%) m.p. 142 °C (cf. Ref. 41: m.p. 143 °C).

6

2 2

(

d, C(4), J_C_,_H= 4.6 Hz); 139.1 (d, C(5), J_C_,_H= 207.1 Hz); 148.3

d, C(3), J_C_,_H= 7.4 5 Hz).

Synthesis of Nꢀdinitromethylimides of acids 11a—c (general

procedure). NꢀAcetonyl derivative 12a—c (1 g) was dissolved in

–

1

ꢀDinitromethylimidazole (6r). Nitration conditions:

a mixture of CF COOH (6 mL) and HNO (d = 1.51 g cm ,

3

HNO —H SO —H O (5 : 12 : 5, vol.), 60—70 °C, 1.5 h. The

decomposition temperature was 133 °C (decomp. onset 90 °C).

4 mL). The reaction mixture was stored for 24—90 h at ~20 °C

and poured into ice. The precipitate formed was filtered off,

washed with water, and dried over P O . NꢀDinitromethylimide

3

2

4

2

Found (%): C, 27.82; H, 2.45; N, 32.46. C H N O . Calculatꢀ

4

2

5

ed (%): C, 27.92; H, 2.34; N, 32.55. UV (H O), λ/nm (ε): 347

potassium salts were obtained by the treatment of solutions of

Nꢀdinitromethylimides in nitromethane or acetonitrile with

potassium acetate in methanol. The yields were 80—90%.

NꢀDinitromethylsuccinimide (11а). Synthesis conditions:

20—25 °C, 70 h. M.p. 154—155 °C (МеОН). Found (%): C, 29.48;

H, 2.41; N, 20,38. C H KN O S. Calculated (%): C, 29.57;

2

–

1

–

(

13 700). IR, ν/cm : 1220, 1260, 1495 (C(NO₂)₂).

Potassium salt Кꢀ6r. Found (%): C, 27.82; H, 2.45; N, 32.46.

C H N O . Calculated (%): C, 27.92; H, 2.34; N, 32.55. UV

4

–

1

(

H O), λ/nm (ε): 358 (13 700). IR, ν/cm : 1210, 1240, 1470

C(NO₂)₂).

2

–

8

4

3

7

–

1

ꢀDinitromethylꢀ4ꢀnitroimidazole (6s). Nitration conditions:

H, 2.48; N, 20.69. UV (H O), λ/nm (ε): 353 (15 700). IR, ν/cm

:

2

1

HNO —H SO —H O (5 : 12 : 5), 50 °C, 2 h. Found (%):

1329, 1370, 1587, 1612 (CH(NO ) ); 1742 (С=О). H NMR

3

2

4

2

2 2

13

C, 22.15; H, 1.29; N, 32.23. C H N O . Calculated (%):

(DMSOꢀd ), δ: 3.05 (s, 4 Н); 8.08 (s, 1 H). C NMR (DMSOꢀd ),

4

3

5

6

C, 22.13; H, 1.39; N, 32.26. UV (H O), λ/nm (ε): 351 (16 700).

δ: 29.6 (CH ); 104.9 (CH(NO ) ); 175.5 (C=O).

2

2 2

Potassium salt Кꢀ6s. The decomposition temperature was

Potassium salt Кꢀ11a. UV (H O), λ/nm (ε): 353 (15 700).

2

IR, ν/cm^–: 1235, 1500 (C(NO₂)₂); 1728 (С=О). C NMR

1

–

13

1

(

93 °C (decomp. onset 169 °C). UV (H O), λ/nm (ε): 351

2

–

1

–

(DMSOꢀd ), δ: 29.2 (CH ); 126.1 (C(NO₂)₂^–); 177.0 (C=O).

16800). IR, ν/cm : 1210, 1477 (C(NO₂)₂); 1355, 1566

NO arom.). H NMR (DMSOꢀd ), δ: 8.12 (s, 1 Н); 8.70 (s, 1 Н).

6

2

1

NꢀDinitromethylphthalimide (11b). Synthesis conditions:

20—25 °C, 90 h. M.p. 135—137 °C (МеОН). Found (%):

C, 43.15; H, 2.13; N, 16.66. C H N O . Calculated (%): C, 43.04;

2

6

1

ꢀDinitromethylꢀ4,5ꢀdinitroimidazole (6t). Nitration condiꢀ

tions: HNO —H SO —H O (5 : 12 : 5), 50 °C, 2 h. Found (%):

3

2

4

2

9

5

3

6

–1

C, 16.04; H, 0.42; K, 12.93; N, 27.91. C HKN O . Calculatꢀ

H, 2.01; N, 16.73. UV (H O), λ/nm (ε): 352 (15 200). IR, ν/cm

1309, 1320, 1580, 1602 (CH(NO ) ); 1742 (С=О). H NMR

(DMSOꢀd ), δ: 7.88 (s, 4 Н); 8.02 (m, 4 H). C NMR (DMSOꢀd₆),

:

4

6

8

2

1

ed (%): C, 16.00; H, 0.34; K, 13.02; N, 28.00. UV (H O), λ/nm

2

2 2

13

(

ε): 347 (15 500).

6

Potassium salt Кꢀ6t. The decomposition temperature was

δ: 109.5 (CH(NO ) ); 124.9, 130.7, 136.4, 164.7 (C=O).

2

1

38 °C (decomp. onset 103 °C). UV (H O), λ/nm (ε): 347 (15700).

Potassium salt Кꢀ11b. UV (H O), λ/nm (ε): 352 (15 200).

2

IR, ν/cm : 1249, 1479 (C(NO₂)₂^–); 1350, 1550 (NO arom.).

–

1

IR, ν/cm^–¹: 1215, 1482 (C(NO₂)₂); 1721 (С=О). C NMR

–

13

2

–

Nꢀ(Acetonyl)succinimide (12a). A solution of KOH (14 g) in

(DMSOꢀd ), δ: 124.5 (C(NO ) ); 124.0, 131.1, 135.5,

6

2 2

MeOH (100 mL) was added to a solution of succinimide (25 g,

166.1 (C=O).

Synthesis of Nꢀdinitromethylazoles

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009

2095

–

4

oꢀSulfobenzoic acid Nꢀ(dinitromethyl)imide (11c). Synthesis

conditions: 20—25 °C, 24 h. M.p. 120—122 °C (МеОН).

The concentrations of measured solutions ranged from 10 to

10 mol L . The Lambert—Beer law was fulfilled.

–

5

–1

–

1

UV (H O), λ/nm (ε): 349 (15 000). IR, ν/cm : 1580, 1607

Kinetic studies. For kinetic studies Nꢀacetonylazoles were

purified by successive crystallization from methanol and dichloꢀ

roethane, and Nꢀdinitromethylazole potassium salts were crysꢀ

tallized from water. Then all samples were dried in vacuo over

P O . Potassium nitrate was prepared according to a procedure

2

1

(

8

1

CH(NO ) ); 1760 (С=О). H NMR (DMSOꢀd ), δ: 8.04 (s, 1 Н);

.16 (m, 4 H). C NMR (DMSOꢀd ), δ: 102.7 (CH(NO ) );

6 2 2

56.8 (C=O).

Potassium salt Кꢀ11c. Found (%): C, 29.65; H, 1.32; K, 12.13;

N, 12.84; S, 9.95. C H KN O S. Calculated (%): C, 29.54;

2

6

13

2

5

4

described earlier, providing the purification from KNO . In all

8

4

3

7

2

H, 1.24; K, 12.02; N, 12.92; S, 9.86. UV (H O), λ/nm (ε): 349

(

experiments on the deuterioexchange and nitration kinetics, the

temperature was maintained at 24±0.5 °C with a thermostat.

The results obtained are given in Table 1.

2

15 000). IR, ν/cm^–¹: 1221, 1480 (C(NO₂)₂^–); 1726, 1750 (С=О).

ꢀDinitromethylꢀ1,2ꢀdicarboethoxyhydrazine potassium salt

Кꢀ13). А. Diketone 14a (see Ref. 30) (1 g) was added with

1

(

Dynamics of signal changing in the H NMR spectrum in the

stirring for 5 min at 0—5 °C to a mixture of 6 mL of CF COOH

nitration of 2ꢀacetonylꢀ5ꢀnitrotetrazole (3а) in 89.2% H SO

3

2

4

–

3

–1

and 4 mL of HNO (d = 1.5 g cm ). Thirty minutes after the

with potassium nitrate (1.15 mol L ): the signals of the MeCO

(δ 2.6) and CH₂(δ 6.03) groups disappear, while the signals

of AcOH (see Ref. 45) (δ 2.2 for the nonꢀprotonated form

(∼ 5—10%) and 2.66 for the protonated form (90—95%)) and the

signal of the СH(NO ) group (δ 8.9) appear.

3

dissolution of the all amount of the substance, the cooling bath

was removed and the reaction mixture was stored for 17 h at

~

20 °C. An aliquot of the reaction mixture (0.5 mL) was diluted

with water to 250 mL, potassium acetate (0.5—1 g) was added,

and the amount of compound 13 was determined spectrophotoꢀ

metrically. The yield was 48%. The reaction mixture was poured

into 50 g of iceꢀcold water, and the mixture was extracted with

ether (2×20 mL). Water (2 mL) was added to the extract, ether

was evaporated, and the extract was neutralized with potash to

pH = 8. After cooling, crystals of salt Кꢀ13 precipitated from the

obtained solution were filtered off, washed with iceꢀcold water,

and recrystallized from water. Found (%): C, 26.52; H, 3.57;

K, 12.40; N, 17.51. C H KN O . Calculated (%): C, 26.42;

2

In addition, 20 min after the beginning of the reaction, the

total signal intensity of the protons of the Me groups in ketone 3а

and AcОН decreases by 20% due to the nitration at the Ne group

to form dinitromethane. Since the latter is unstable in this mixꢀ

ture, its presence can indirectly be judged from the change in the

absorbance of an aliquot of the reaction mixture upon the nitraꢀ

tion of ketone 3a: the difference in the absorbance at pH = 0—1,

when compound 6а is completely dissociated and dinitromethane

is suppressed, and at pH = 6—7, when both substances are dissoꢀ

ciated, is 10—15%.

7

11

4

8

H, 3.48; K, 12.28; N, 17.60. UV (H O), λ/nm (ε): 359 (14 800).

2

–

1

–

IR, ν/cm : 1190, 1220, 1250, 1485 (C(NO₂)₂); 1700 and 1743

Deuterioexchange of methyl and methylene groups in Nꢀaceꢀ

tonylazoles occurred by 93% due to the accumulation in a mediꢀ

(

C=O); 3290 (NH); the IR spectrum is identical to that of the

4

2

+

authentic sample obtained by an earlier described procedure.

um of H and retarded at the end. For this reason, the deuterioꢀ

B. Under analogous conditions, the nitration of ketoester

4b (see Ref. 30) affords, according to the UV analysis results,

substitution rate constants were calculated at the deuteriosubstiꢀ

tution "depth" not more than 75%. The concentrations of keꢀ

1

–

1

compound 13 (26%). Salt Кꢀ13 was isolated similalrly.

Maleic acid Nꢀdinitromethylhydrazide (16). Nitric acid (d =

tones in D SO were 0.35 mol L . The equations of logarithmic

2 4

anamorphoses of the experimental curves on the kinetics of proꢀ

ton deuterioexchange obtained by the leastꢀsquares processing

are given in Table 4.

–

3

=

1.5 g cm ) (8 mL) was added dropwise with cooling (0—5 °C)

and stirring to a solution of 2ꢀ(3ꢀoxobutyl)ꢀ6ꢀhydroxyꢀ3(2Н)ꢀ

–

3

pyridazinone 15 (2 g) (see Ref. 43) in H SO (d = 1.84 g cm

)

For studying the nitration kinetics of Nꢀacetonylazoles, the

reaction solutions were prepared prior to the reaction. To create

a homogeneous medium, prior to the reaction the overall amount

of H SO was divided into two portions: KNO was dissolved in

2

4

(

11 mL). The reaction mixture was stored for 4 days at ~20 °C,

then poured into 50 g of iceꢀcold water, extracted with ether

5×20 mL), and evaporated. The residue was dissolved in a satuꢀ

(

2

4

3

rated aqueous solution of potassium acetate (2 mL). After coolꢀ

ing, the precipitated crystals of potassium salt Кꢀ16 were filtered

off and recrystallized from water. The yield of salt Кꢀ16 was

one portion, the nitrated object was dissolved in another porꢀ

tion, and then both solutions were poured together.

To observe the 2ꢀnitromethylꢀ5ꢀnitrotetrazole anion 10a in

the nitration of 3а, aliquots of the reaction mixture were poured

into 200 mL of a 10% solution of Na CO . The amount of anions

0

.27 g (10%). The decomposition temperature was 185 °C (deꢀ

comp. onset 137 °C). Found (%): C, 23.70; H, 1.26; K, 15.43;

2

3

N, 22.21. C H KN O . Calculated (%): C, 23.63; H, 1.19;

of 1ꢀdinitromethylꢀ4ꢀnitroimidazole 6s and 1ꢀdinitromethylꢀ4ꢀ

nitropyrazole 6p was determined spectrophotometrically upon

pouring the reaction solution (0.5 mL) into 100 mL of water

containing potassium acetate (2 g, рН = 3). The amount of

anions of other Nꢀdinitromethylazoles with higher acidity was

determined upon pouring into water.

5

3

4

6

K, 15.38; N, 22.04. IR, ν/cm : 1247, 1290, 1470 (C(NO₂)₂^–);

–

1

673 (C=O); 3515, 3635 (ОН); 2550—3000 (NH amide). UV

(

H O), λ/nm (ε): 354.5 (18 000).

2

Procedure of determination of the acidity of Nꢀdinitromethyl

compounds. The equations for monoꢀ and dibasic acids were

used for the calculation.³An aliquot part of an aqueous solution

of Nꢀdinitromethylazole salt was 100ꢀfold diluted with water,

and the absorbance was measured spectrophotometrically. An

analogous aliquot part was 100ꢀfold diluted with H SO soluꢀ

6

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2

4

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i sintez [Chemistry of

Received February 25, 2009;

in revised form July 1, 2009

(

Article Doi

Mechanism of nitration of nitrogen-containing heterocyclic N-acetonyl derivatives. General approach to the synthesis of N-dinitromethylazoles

DOI: 10.1007/s11172-009-0285-y

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Full text of DOI:10.1007/s11172-009-0285-y

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