E versus Z diazeniumdiolation of acetoacetate-derived carbanions

Article abstract of DOI:10.1021/jo301025k

Nitric oxide adds to methyl acetoacetate in the presence of KOH in methanol at room temperature to form potassium acetylsydnonate N-oxide (K1) with an (E)-diazeniumdiolation and potassium acetate diazenium diolate (K₂2) from a (Z)-diazeniumdiolation. A study of the reaction with LiOH, NaOH, and NMe₄OH and with ethyl acetate substrate reveals that the temperature of the reaction greatly influences the nitric oxide reactivity. At 23 °C, nitric oxide adds to give both E and Z products, whereas at -5 °C the gas reacts almost exclusively to give Z addition. The (Z)-diazeniumdiolation products, namely, the alkali metal and NMe₄⁺ salts of methyl and ethylbutenoate-2-diazeniumdiolate-3-hydroxylate (3^2- and 4^2-), are isolated in good yields. The alkali metal salts are not amenable for recrystallization because of their ready decomposition in aqueous solutions. However, [NMe₄]₂[MeC(O)C(N₂O ₂)CO₂Me] is readily recrystallized from a methanol/acetonitrile solvent mixture. The crystals are unambiguously characterized by X-ray crystallography. NMR spectra for all of the 3 ^2- and 4^2- salts reveal the presence of two isomers in aq solutions. But the structure of the NMe₄⁺ salt contains only one of the isomers. Our attempts to cyclize the isolated and purified butenoatediazeniumdiolates from the (Z)-diazeniumdiolation to the E-containing sydnonate products were unsuccessful. TGA/DSC data for all of the products demonstrate the thermal instability of the salts at high temperatures. The salts decompose exothermally possibly with the release of N₂O among other gases.

Full text of DOI:10.1021/jo301025k

Article
pubs.acs.org/joc
E versus Z Diazeniumdiolation of Acetoacetate-Derived Carbanions
Navamoney Arulsamy,*,† D. Scott Bohle,*,‡ Carla L. Holman,† and Inna Perepichka‡
†Department of Chemistry, Department 3838, University of Wyoming, 1000 East University Avenue, Laramie, Wyoming 82072-2000,
United States
‡Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal PQ H3A 2EK6, Canada
S
* Supporting Information
ABSTRACT: Nitric oxide adds to methyl acetoacetate in the presence of
KOH in methanol at room temperature to form potassium acetylsydnonate N-
oxide (K1) with an (E)-diazeniumdiolation and potassium acetate diazenium
diolate (K22) from a (Z)-diazeniumdiolation. A study of the reaction with
LiOH, NaOH, and NMe4OH and with ethyl acetate substrate reveals that the
temperature of the reaction greatly influences the nitric oxide reactivity. At 23
°C, nitric oxide adds to give both E and Z products, whereas at −5 °C the gas
reacts almost exclusively to give Z addition. The (Z)-diazeniumdiolation
+
products, namely, the alkali metal and NMe4 salts of methyl and
ethylbutenoate-2-diazeniumdiolate-3-hydroxylate (32− and 42−), are isolated
in good yields. The alkali metal salts are not amenable for recrystallization
because of their ready decomposition in aqueous solutions. However,
[NMe4]2[MeC(O)C(N2O2)CO2Me] is readily recrystallized from a meth-
anol/acetonitrile solvent mixture. The crystals are unambiguously characterized by X-ray crystallography. NMR spectra for all of
the 32− and 42− salts reveal the presence of two isomers in aq solutions. But the structure of the NMe4+ salt contains only one of
the isomers. Our attempts to cyclize the isolated and purified butenoatediazeniumdiolates from the (Z)-diazeniumdiolation to
the E-containing sydnonate products were unsuccessful. TGA/DSC data for all of the products demonstrate the thermal
instability of the salts at high temperatures. The salts decompose exothermally possibly with the release of N2O among other
gases.
However, we have previously reported synthetic observations
that point to either the direct addition of trans-(NO)2 to form
an E or anti-N2O2− intermediate or the addition of cis-(NO)2 to
INTRODUCTION
■
Nitric oxide (NO) is a stable free radical that readily dimerizes
to give a kinetically important ON−NO-bound dimer.1 It is
stubbornly unreactive with substrates such as olefins except
when any one of the gases O2, NO2, or N2O3 is present in at
least catalytic amounts.2−6 However, NO readily reacts with a
variety of dialkylamines7 and enolates,8 forming (NO)2-
addition products. Significantly, the reactions with dialkyl-
amines rarely yield nitrosoamines,9 and the kinetics of NO
addition to diisopropylamine and pyrrolidine imply bimolecular
addition of NO at high concentrations of the gas.10 In addition,
a thorough IR and UV−vis spectroscopic investigation of the
heterogeneous reaction between NO gas and a series of
manganese(II) porphyrinate complexes at 90 K also indicates
the presence of dimeric NO, cis-(NO)2.11 Yet another facet of
the NO reactivity with organic substrates and alkaline sulfites is
that the products formed contain cis (Z) geometry for the
−
form a Z or cis-N2O2 intermediate. The latter is proposed to
subsequently tautomerize into the E anti-N2O2− intermediate in
the eventual formation of sydnonate N-oxide products. In both
−
cases, the final (E) anti-N2O2 intermediate cyclize into
forming the sydnone N-oxide product (Scheme 1).18,19
The reactions of nitric oxide with carbanions derived from
dimethyl malonate,18,19 terminal alkynes,20 and benzyl
Scheme 1
−N2O2 groups.7,8,12−14 This observation lends credence to a
−
theoretical claim that NO exists predominantly as the dimeric
singlet cis-(NO)2 (1A1).15 These calculations also predict three
other shallow NO dimers of slightly higher energy, namely, a
triplet cis-(NO)2 (3B2) and two trans-(NO)2 species (1Ag and
3Au). IR and Raman spectroscopic data measured for NO at low
temperatures prove the existence of the singlet cis-(NO)2, but
there is a scarcity of experimental data for the trans isomers.16,17
Received: May 23, 2012
Published: August 1, 2012
© 2012 American Chemical Society
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cyanide18,21 are the only substrates that have been studied for
such reactions until date. A closely related family of 3-
hydroxysydnoneimines has been known in the literature for
over 40 years.22 These compounds are synthesized from the
nitrosylation of N-(nitriloalkyl)hydroxylamines, RCH(CN)-
NHOH. The intermediate nitrosohydroxylamine, RCH(CN)-
N2O2H, is similarly suggested to undergo intramolecular
condensation to form the hydroxysydnoneimines.22 In the
context of the various physiological roles played by nitric oxide,
it is desirable to establish its reactivity. Therefore, we were
interested in determining the mode of addition of nitric oxide
to carbanions. Specifically, we sought to determine if it is
possible to distinguish between cis- or trans-(NO)2 addition to
give Z or E diazeniumdiolation products, respectively. Toward
this goal, we have now studied the reactions of nitric oxide with
methyl and ethyl acetoacetates under a variety of conditions.
The acetoacetates are particularly suitable as they contain a
highly acidic methylene group but only one α-carboxylate
group. We hoped that the proposed cyclization step in the
formation of the sydnonate N-oxide may be less favored than in
the malonate reaction and that hence it may be possible to
isolate intermediary species. As we discuss below, although we
water, 0.1 N aq KOH, or 0.5 N aq KOH as it undergoes slow
decomposition in solution. In neutral aqueous media, the
product decomposes to form potassium acetate and potassium
oxalate. In basic aqueous solutions K23 is hydrolyzed, and over
a period of 5 d, K22 and potassium acetate are formed. Nearly
quantitative conversion into the two salts is achieved from aq.
KOH solutions containing at least 1 equiv of KOH (eq 3) as
described in the Experimental Section. Recrystallization was
also attempted by the slow evaporation of water under a steady
flow of N2 gas over several days with both the neutral and basic
aq solutions of K23, and similar decompositions were observed.
Unlike K23, salts K1 and K22·H2O are quite stable in
aqueous solution at neutral and basic pH’s. UV−vis, IR, and
NMR spectroscopic data and single-crystal X-ray diffraction
characterize the salts unambiguously. The UV−vis spectrum
measured for K1 exhibits three intense peaks at 206, 239, and
290 nm arising from π → π* transitions.19 K22 exhibits a single
absorption at 249 nm consistent with the presence of the
diazeniumdiolate functional group.12 Crystallographic structural
data establish anti and cis geometry for the N2O2 fragment in
K1 and K22, respectively. Views of the anions are shown in
Figure 1. Although the compounds are unusual and novel, the
−
were able to isolate the corresponding cis-N2O2 -substituted
product and a mixture of both cis- and trans-(NO)2 addition
products, there is no evidence for the conversion of the (Z)-
diazeniumdiolated acetoacetate into the corresponding E
sydnonate-N-oxide. We have also studied the thermal proper-
ties of the new compounds as both diazeniumdiolate and
sydnonate-N-oxide products are known to exhibit exothermic
decomposition properties.8,12,19
RESULTS AND DISCUSSION
■
The reaction of nitric oxide with methyl acetoacetate and 1
equiv of KOH in methanol solvent at room temperature (23
°C) for 24 h yields a mixture of products, eq 1. Slow
Figure 1. Views of 1− (a) and 22− (b). In this and the following
figures, the hydrogen atoms are represented as unlabeled open circles.
The rest of the atoms are drawn as thermal ellipsoids of 50%
probability. Selected bond distances (Å) in 1−: C2−N1, 1.3930(13);
N1−O1, 1.2579(11), N1−N2, 1.3193(13); N2−O2, 1.3861(14), C1−
O2, 1.3720(14), C2−C3, 1.4439(14); C3−O4, 1.2300(13). Selected
bond angles (deg) in 1‑: C1−C2−N1, 125.48(9); O1−N1−N2,
118.72(9); O1−N1−C2, 129.65(9); C2−N1−N2, 111.63(9); N1−
N2−O2, 106.90(8); O2−C1−C2, 107.59(9); C1−C2−C3, 129.62(9).
structures themselves are comparable to previously reported
structures of sydnonate N-oxides and diazeniumdio-
lates.12,18,19,23,24 On the other hand, the characterization of
K23 relies on more indirect spectroscopic data and elemental
analysis data. The IR spectrum measured for K23 exhibits a
strong absorption at 1342 cm−1 attributable to the (ONNO)sym
vibration.25 Solutions of the salt in 0.1 N aq KOH exhibit an
intense absorption at 263 nm in its UV−vis spectrum, although
the elemental analysis data indicate one diazeniumdiolate
substituent. The relatively low energy of the chromophore
compared to other monodiazeniumdiolates, 248 nm, suggests
that as with other polydiazeniumdiolates with 258 and 264 nm
for bis- and tris(diazeniumdiolates), respectively,12,26 the vicinal
carboxylate in K23 also results in a red-shifted Stark effect. The
1H NMR spectrum for K23 in 0.1 N KOD (D2O) exhibits two
pairs of singlets at 3.61 and 3.60, and 2.28 and 1.77 ppm. The
recrystallization of the crude product from 0.1 N aq KOH
readily forms potassium 4-acetylsydnone N-oxide (K1) as the
first crop. On further standing, a mixture of potassium
acetatediazeniumdiolate, CH2(N2O2K)CO2K (K22), and po-
tassium oxalate is formed. Several recrystallizations were
necessary to separate the diazeniumdiolate from the latter
salt. On the other hand, the above reaction carried out at −5 °C
for 4 h yields potassium methyl 2-butenoate-3-hydroxylate-2-
diazeniumdiolate, MeC(OK)C(N2O2K)CO2Me (K23), as the
major product (eq 2) with less than 2% of sodium acetate and
the sydnonate N-oxide impurities. The impurities are readily
removed when the dried precipitate is washed with methanol.
However, we are unable to recrystallize K23 from methanol,
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ratio of the two pairs is identical at 1:1.63. Similarly, the proton-
decoupled 13C spectrum exhibits two sets of five peaks
indicating the presence of two isomers in solution. The
proton-coupled 13C spectrum reveals that the two pairs of the
peaks at 53.4, 53.2, 27.5, and 26.2 ppm are methyl groups.
Therefore, the spectra are assigned to arise from two isomers of
structure CH3C(OK)C(N2O2K)CO2CH3. However, the spec-
tra are insufficient for the assignment of the geometry of the
diazeniumdiolate substituent or for determining the nature of
the two species in solution. Therefore, we extended the study
to ethyl acetoacetate and to reactions in the presence of
sodium, lithium and tetramethylammonium hydroxides. The
reactions of methyl acetoacetate with the bases at −5 °C give
similar results forming the respective 32− salts. The reactions of
ethyl acetoacetate with nitric oxide in the presence of KOH and
NaOH at −5 °C form the respective monodiazeniumdiolates.
Both of them exhibit similar UV−vis, IR and NMR spectra as
K23. Fortunately, the tetramethylammonium salt of 32−
crystallizes from methanol/acetonitrile solvent mixtures allow-
ing for its complete structural characterization.
Table 1. Selected Bond Distances (Å) and Angles (deg) for
the Anions in K22·H2O and [NMe4]23·3H2O·MeOH
K22·H2O
[NMe4]23·3H2O·MeOH
C3−N1
N1−N2
N1−O2
N2−O3
C3−C2
C2−O1
C3−C4
N1−C3−C4
N2−N1−O2
N1−N2−O3
N2−N1−C3
O2−N1−C3
C2−C3−C4
C1−N1
N1−N2
N1−O1
N2−O2
C1−C2
1.4577(8)
1.2906(8)
1.3068(7)
1.2925(7)
1.5321(9)
1.4382(11)
1.2878(11)
1.2934(10)
1.2934(10)
1.3955(13)
1.2617(12)
1.4324(13)
117.29(8)
122.51(7)
114.44(8)
117.53(8)
119.96(7)
125.57(8)
N1−C1−C2
N2−N1−O1
N1−N2−O2
N2−N1−C1
O1−N1−C1
112.13(5)
123.98(5)
114.31(5)
116.25(5)
119.38(5)
conditions in aqueous media. K23 undergoes oxidative
hydrolysis in aqueous solutions under atmospheric conditions
over several days to form acetic acid, potassium oxalate and
methanol while also releasing nitrous oxide gas (eq 4). The
The room-temperature reactions of nitric oxide with the
acetoacetates and the various bases were also studied. The
reactions proceed similarly as the reaction with KOH, but the
fractional crystallization of the sydnonate N-oxide and
acetatediazeniumdiolate salts is more difficult. The products
are contaminated with each other, as well as the alkali acetate
and oxalate salts.
Single-crystal diffraction data for [(NMe4)]23 reveal that it is
−
a monodiazeniumdiolate and that the −N2O2 group is of Z
hydrolysis is completed in 1 h if the solution is heated to 80 °C.
Nitrous oxide was identified by the IR spectrum, which exhibits
strong absorptions at 2236, 2203, 1297, and 1272 cm−1 as
described in the Experimental Section. Significantly, the
spectrum does not contain any peaks attributable to NO or
NO2 gases. The formation of the rest of the products is verified
by the 1H and 13C NMR spectra measured for a solution of K23
in D2O (heated at 80 °C for 1 h).
geometry (Figure 2) as in other known diazeniumdio-
Concentrated solutions of salts of 32− are sufficiently stable
for at least 1 h in D2O, whereas those of the sodium and
potassium salts of 42− are quite unstable. Therefore, the NMR
spectra for the salts of 4 were measured in 0.1 N NaOD/D2O
and 0.1 N KOD/D2O, respectively. As a representative case, the
spectra for salts of K23 were also measured in 0.1 N KOD/
D2O. The spectra are identical to those measured in D2O. The
NMR spectra are valuable in estimating the percentage of the
two isomers. We were particularly interested to see if the NN
bond is responsible for the observed tautomerism as it would
help explain the formation of sydnonate N-oxides. The second
possibility is tautomerism due to the CC bond. The relatively
well-localized NN double bond in 32− and the longer and
delocalized CC bonds suggest that the latter bond may be
Figure 2. View of 32− in [NMe4]23·3H2O·MeOH.
lates.10,12,13,26 The metrical parameters (Table 1) associated
with the diazeniumdiolate substituent do not reveal substantial
differences from those of 22−. However, bonds C2−O1, C2
C3, and C3−C4 of the 2-butenoate-3-hydroxylate backbone
exhibit significant anomalies. Whereas the C−O bond is
significantly shorter than a typical C−O single bond, C2C3
is ca. 0.2 Å longer than a CC double bond, and C3−C4 ca.
0.1 Å shorter than a C−C single bond. In addition the four
atoms are also coplanar. Together, these data suggest
delocalization of the enolate and diazeniumdiolate negative
charges, and the CO and CC double bonds over the 32−
dianion. As could be expected, the mean plane passing through
1
more readily rotated than the NN bond. H NMR spectra
measured for K23 in 0.1 N KOD (D2O) at temperatures 6, 20,
and 50 °C reveal that neither the ratio of the isomers nor their
chemical shifts change significantly at those temperatures. We
interpret this observation as evidence for the absence of any
exchange of tautomers in solution. In agreement with that
conclusion, we are unable to cyclize both 32− and 42− under a
variety of conditions to salts of acetylsydnonate N-oxide.
Therefore, we conclude that the two sets of proton and carbon
peaks observed in the H and 13C NMR spectra for both 32−
−
1
atoms C1, C2, O1 and C3 atoms and that of the −N2O2
substituent dissect at an angle (91.6°) close to 90°. The
observed delocalization of charges and bonds renders the CC
bond prone to hydrolysis under both acidic and neutral
and 42− must be due to tautomerism involving the CC
double bond. The two tautomers can be represented by
structures A and B. The crystallographic structural data reveals
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that there is only one of the tautomers (A) present in the solid
state structure of [NMe4]23. On the basis of the overall
similarity of the IR spectra, we propose that all of the various
salts of 32− and 42− contain only one of the tautomers,
specifically, tautomer A. The ratio of the tautomers in aq or aq
KOH solutions of the salts of 32− are 1:1.63 for the sodium and
potassium salts, 1:2 for the lithium salt, and 1:1.73 for the
Table 2. Thermal Decomposition Data
DSC TOnset
°C
,
ΔH,
TGA
compd
Tmax, °C
J/g
Δm, %
a
K1
270
273
2101
1550
1086
2018
1277
−54.0
−35.8
−64.3
−33.7
a
K22·H2O
K23
308
312
a
269
271
b
c
Na23
226, 250
198
231, 262
203
+
NMe4 salt. The unique ratio for the lithium salt can be
a
Li23·0.67MeOH·0
.33H2O
−59.1
ascribed to strong metal−ligand coordination between the Li+
cations and the enolate and diazeniumdiolate oxygen atoms of
32−. Such interactions are less pronounced or negligible in the
c
[NMe4]23·H2O
K34
159
280
237
170
282
990
1578
1882
−86.3
−37.2
−37.5
+
K+, Na+, and NMe4 salts. In comparison, the ratio of 1:1.26
Na34
264
observed for the K+ and Na+ salts of 42− is significantly
different, and the difference may be due to the presence of the
sterically bulkier ethyl group.
a
b
c
Sample exploded. Two overlapping peaks. Broad weight loss at ca.
100 − 300 °C.
+
that the NMe4 salt is the least exothermic and that the
sydnonate N-oxide is the most exothermic. The sydnonate-N-
oxide salt is also stable up to ca. 250 °C and decomposes at
sharply at 270 °C. Similarly, the alkali salts of 32− and 42− also
exhibit sharp exothermic decomposition at high temperatures.
The formation of salts of 32− and 42− from the reactions of
methyl and ethyl acetoacetates and the bases with nitric oxide
at −5 °C implies that nitric oxide adds exclusively as the cis-
(NO)2 isomer. The formation of salts of 1‑ at higher
temperatures (23 °C) as a coproduct along with those of 32−
reveals that both formal cis- and trans-(NO)2 additions take
place at higher temperatures. The temperature difference may
reflect competition of mechanisms with either carbanion
addition of (NO)2 with stepwise addition of two NO’s to the
carbanion.
Diazeniumdiolates of secondary amines and others have
useful reactivity as nitric oxide or nitroxylate donors.27
Therefore, we also tested the new diazeniumdiolates for such
behavior following literature methods.28,29 The salts release
neither NO nor NO− in aqueous solutions as judged by the
reductive nitrosylation of manganese(III)porphyrins. Nitroxyl
has been proposed to be a rapid and efficient reductive
nitrosylating agent for these porphyrins and their absence here
suggests either that the N−N bond in the diazeniumdiolate is
retained in the product or that the diazeniumdiolate is unable
to reduce the Mn(III). The salts of 32− and 42− appear to lose
the diazeniumdiolate moiety on protonation as N2O gas as
discussed above.
We also examined the thermochemical properties of the new
products by thermogravimetric and differential scanning
calorimetric analysis. As is common for sydnonate N-oxides
and diazeniumdiolates, the new products also exhibit explosive
decomposition properties.8,12,14,18,19,23 The TGA and DSC data
(Table 2) for the products were measured under a steady flow
of N2 gas in partially sealed aluminum cups. Except for
[NMe4]23·H2O, all of them explode if the sample size was
greater than 2 mg, popping the covers of the sample cups.
Therefore, smaller amounts (ca. 0.5−1 mg) were taken for the
studies. The DSC data reveal that the compounds are stable on
heating up to more than 150 °C and with ΔH in the range of
990−2101 J g−1. The decomposition is accompanied by the
mass loss in the range of 33.7 to 86.7%. We speculate that
nitrous oxide is lost in each of the decompositions although it is
not possible to satisfactorily explain the mass loss for all of the
products. It is likely that the sample may be insufficiently
decomposed due to the nonavailability of oxygen and also due
to the observed explosiveness. However, the data clearly show
CONCLUSIONS
■
On the basis of the products formed, it is clear that nitric oxide
formally adds as cis-(NO)2 to carbanions formed from methyl
and ethyl acetoacetates at low temperatures (−5 °C) and as
both cis- and trans-(NO)2 at room temperature. It also appears
that once formed the diazeniumdiolate substituent prefers the
cis geometry, and it does not undergo NN rotation to form
the anti-isomer. In contrast, the CC double bond involving
the enolate and diazeniumdiolate-substituted carbons exhibit
rotation resulting in two tautomers in solution. The products
are explosive due to the presence of the N2O2 grouping.
EXPERIMENTAL SECTION
■
Caution! Although we did not experience any explosions in the course
of this research, we recommend great caution. All products may be
explosive and must be manipulated behind splash shields. TGA/DSC
measurements must be carried out with less than 2 mg samples to
avoid damage to the instrument.
Reagents were purchased from commercial vendors and used as
received. The reactions with nitric oxide were carried out using a nitric
oxide reactor described previously.12 The removal of solvents is
achieved using a rotary evaporator. All products from reactions with
nitric oxide were isolated as solids and dried in a vacuum oven at room
temperature overnight. The UV−vis spectra were measured in water
or 0.1 N aq KOH or aq LiOH or aq NaOH or aq NMe4OH solutions.
The NMR spectra were measured in either D2O or 0.1 N KOD/D2O
or 0.1 N NaOD/D2O on a 600 MHz NMR spectrometer. The D2O
solutions contained DSS-d6 (0.1% w/v) as internal calibration
standards. Carbon chemical shift assignments, where possible, were
made by measuring their proton coupled spectra, direct 13C, which are
included in the Supporting Information. The IR spectra were
measured as powder on an FTIR instrument equipped with an
ATR. Only strong IR bands are listed here. Decomposition of some of
the products in aqueous media was followed by measuring the IR
spectra for the gases released using a gas cell.
Thermogravimetric and differential calorimetric data were measured
on a TGA/DSC instrument in the 25−500 °C temperature region.
These data, which include their melting/decomposition temperatures,
are included in Table 2. A steady flow of nitrogen gas was maintained
as reaction gas. Approximately, 1 mg of the sample was placed in
partially sealed aluminum cups. Melting point data are given in Table
2.
Potassium Acetylsydnonate N-Oxide (K1). A solution of KOH
(85% w/w, 6.6 g, 0.100 mol) in methanol (100 mL) taken in a glass
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pressure bottle was cooled in an ice−salt bath for 30 min and treated
with methyl acetoacetate (5.805 g, 0.05 mol). The colorless cloudy
mixture was degassed by applying reduced pressure (−20 psi) and
filling with N2 gas six times with stirring. Then the ice−salt bath was
removed, and the reaction mixture was allowed to warm to room
temperature (23 °C). The clear pale yellow solution was pressurized
with nitric oxide to 38 psi (2.7 atm). The solution turned yellow as the
reaction progressed. The solution was repeatedly pressurized with
nitric oxide. Rapid absorption occurred in the first 2 h, but the reaction
mixture was stirred overnight while maintaining a nitric oxide pressure
of at least 30 psi. The reaction mixture was cooled and degassed as
described above, and the precipitated pale yellow powder was filtered
and washed with cold methanol (10 mL).
and dried. The dried product was washed with methanol (30 mL),
filtered and dried. The product is characterized as
Li23·2/3MeOH·1/3H2O on the basis of elemental analysis and NMR
data. Yield: 8.120 g (75%). IR (cm−1): 1643 s (νCO, CO2Me), 1461 s,
1
1331 m, 1254 (νC−O, CO2Me). H NMR (600 MHz, D2O): 3.62 (s,
1.98H) 3.60 (s, 1.02H), 3.34 (s, 2H), 2.29 (s, 1.02H), 1.79 (s, 1.98H).
13C NMR (151 MHz, D2O): δ 188.3, 188.2, 171.4, 169.9, 113.0, 112.8,
1
1
1
53.5 (q, J = 147.2 Hz), 51.6 (q, J = 142.4 Hz), 27.5 (q, J = 127.7
Hz), 25.9 (1J = 127.7 Hz). λmax (ε) in 0.1 N aq LiOH: 263 nm (22539
M−1 cm−1). Anal. Calcd for C5.67H9.33N2O6Li2: C, 31.60; H, 4.37; N,
13.01. Found: C, 31.46; H, 4.44; N, 12.88.
Tetramethylammonium Methyl 2-Butenoate-2-diazenium-
diolate-3-hydroxylate ([NMe4]23). The product was synthesized
from NMe4OH·5H2O (7.25 g, 0.040 mol) and methyl acetoacetate
(2.320 g, 0.02 mol) in methanol (100 mL) and nitric oxide as
described above for K23. The product did not precipitate as the alkali
metal salts. The reaction mixture was rotary evaporated to ca. 30 mL
and treated with acetonitrile (100 mL). The cloudy solution was
allowed to stand in refrigerator (5 °C) overnight when colorless
crystals of the product formed. The crystals were separated by
filtration. On standing further, a second crop was obtained. Single
crystal X-ray diffraction data reveal that the salt is a trihydrate
methanolate, whereas elemental analysis data for dried crystals is
consistent as the monohydrate. Yield: 5.170 (74%). IR (cm−1): 1646 s
The combined filtrate was rotary evaporated to a small volume (ca.
20 mL) and cooled in an ice bath for 1 h. The microcrystalline solid
formed was filtered and washed with cold methanol (10 mL). The
solids were combined and dried under reduced pressure at room
temperature overnight. The dried solid (6.75 g) was recrystallized
from 0.1 N aq KOH (50 mL) by slow evaporation. The first crop of
crystals formed after 3 d was filtered, washed with methanol/water
(50:50) solvent mixture (10 mL) and methanol successively, and
dried. Yield: 1.650 g (18%). IR (cm−1): 1723 s (νCO, CH3CO), 1631
1
s (νCO, CO2), 1448 s, 1376 s, 1355 s, 1202 (νC−O, CO2). H NMR
(600 MHz, D2O): δ 2.42 (s). 13C NMR (151 MHz, D2O): δ 191.7 (q,
1
2J = −6.1 Hz), 171.0, 106.9, 29.7 (q, J = 128.8 Hz). Anal. Calcd for
(νCO, CO2Me), 1524 s, 1304 m, 1213 (νC−O, CO2Me). H NMR
(600 MHz, D2O): δ 3.61 (s, 1.90H), 3.59 (s, 1.10H), 3.17 (s, 24H),
2.28 (s, 1.10H), 1.79 (s, 1.90H). 13C NMR (151 MHz, D2O): δ 187.9,
187.3, 171.5, 169.5, 113.6, 113.4, 57.9 (q, 1J = 145.1 Hz), 53.3 (q, 1J =
146.7 Hz), 53.1 (q, 1J = 146.7 Hz), 27.5 (q, 1J = 127.3 Hz), 26.1 (q, 1J
= 127.3 Hz). λmax (ε) in 0.1 N aq NMe4OH: 265 nm (22379
C4H3N2O4K: C, 26.37; H, 1.66; N, 15.38. Found: C, 26.28; H, 1.68;
N, 15.14. λmax (ε) in water: 206 nm (9066 M−1 cm−1), 239 nm (10844
M−1 cm−1), 290 nm (10,931 M−1cm−1). From the filtrate on further
standing, a mixture of crystals of K22·H2O, K23 and potassium oxalate
formed. K22·H2O is more readily synthesized from K23 (see the
following discussion).
M
−1 cm−1). Anal. Calcd for C13H32N4O6, %: C, 45.87; H, 9.47; N,
16.46. Found: C, 45.40; H, 9.48; N, 16.18.
Potassium Methyl 2-Butenoate-2-diazeniumdiolate-3-hy-
droxylate (K23). Product K23 was isolated when the above reaction
was carried out with KOH (85% w/w, 6.6 g, 0.100 mol) and methyl
acetoacetate (5.805 g, 0.05 mol) in methanol (100 mL) as described
above for K1 but at −5 °C in an ice−salt bath. The reaction was
stopped after 4 h as there was no significant absorption of nitric oxide
after 4 h, and the precipitate formed was filtered, washed with ice-cold
methanol (10 mL), and dried. The dried product was further washed
with methanol (30 mL) by stirring at room temperature for 30 min.
The undissolved solid was filtered and dried. Yield: 7.210 g (57%). IR
(cm−1): 1645 s (νCO, CO2Me), 1500 s, 1342 s (νNN), 1310 s, 1242
Potassium Ethyl 2-Butenoate-2-diazeniumdiolate-3-hydrox-
ylate (K24). Product K24 was isolated when the reaction was carried
out with KOH (85% w/w, 6.6 g, 0.100 mol) and ethylacetoacetate (6.5
g, 0.05 mol) in ethanol (100 mL) as described above for K23. The
precipitate formed was filtered, washed with ice-cold methanol (10
mL) and dried. The dried product was further washed with methanol
(30 mL) by stirring at room temperature for 30 min. The undissolved
solid was filtered and dried. Yield: 8.240 g (62%). IR (cm−1): 1649 s
1
(νCO, CO2Me), 1501 s, 1325 s, 1310 s, 1241 (νC−O, CO2Et). H
NMR (600 MHz, 0.1 N KOD/D2O): δ 4.08 (m, 2H), 2.28 (s, 1.33H),
1.77 (s, 1.67H), 1.21 and 1.19 (t, 1J = 7.1, 7.0 Hz, 3H). 13C NMR (151
MHz, 0.1 N KOD/D2O): δ 188.8, 187.3, 171.2, 169.3, 114.0, 113.6,
1
(νC−O, CO2Me). H NMR (600 MHz, D2O): δ 3.61 (s, 1.86H), 3.60
(s, 1.14H), 2.28 (s, 1.14H), 1.77 (s, 1.86H). 13C NMR (151 MHz,
1
1
1
1
62.4 (t, J = 143.4 Hz), 62.2 (t, J = 146.4 Hz), 27.5 (q, J = 127.2),
26.2 (q, 1J = 127.9), 16.6 (t, 1J = 126.5 Hz). λmax (ε) in 0.1 N aq KOH:
264 nm (24545 M−1 cm−1). Anal. Calcd for C6H8N2O5K2: C, 27.06;
H, 3.03; N, 10.52. Found: C, 26.88; H, 2.92; N, 10.27.
D2O): δ 188.0, 189.5, 171.5, 169.6, 113.6, 113.3, 53.4 (q, J = 147.1
1
1
1
Hz), 53.2 (q, J = 147.1 Hz), 27.5 (q, J = 127.6 Hz), 26.2 (q, J =
127.6 Hz). UV−vis in 0.1 N aq KOH, λmax (ε): 263 nm (21669
M
−1 cm−1). Anal. Calcd for C5H6N2O5K2: C, 23.80; H, 2.40; N, 11.10.
Sodium Ethyl 2-Butenoate-2-diazeniumdiolate-3-hydroxy-
late (Na24). Product Na24 was isolated when the reaction was carried
out with NaOH (97% w/w, 4.124 g, 0.100 mol) and ethyl acetoacetate
(6.5 g, 0.05 mol) in methanol (100 mL) as described above for K23.
The precipitate formed was filtered, washed with ice-cold methanol
(10 mL), and dried. The dried product was further washed with
methanol (30 mL) by stirring at room temperature for 30 min. The
undissolved solid was filtered and dried. Yield: 9.330 g (80%). IR
(cm−1): 1639 s (νCO, CO2Me), 1493 s (νC−N), 1325 s (νNN), 1255
(νC−O, CO2Et). 1H NMR (600 MHz, 0.1 N NaOD/D2O: δ 4.10−4.06
(m, 2H), 2.28 (s, 1.33H), 1.77 (s, 1.67H), 1.21 and 1.19 (t, J = 7.1, 7.1
Hz, 3H). 13C NMR (151 MHz, 0.1 N NaOD/D2O): δ 188.9, 187.4,
171.2, 169.3, 114.0, 113.6, 62.5 (t, J = 146.3 Hz), 62.3 (t, J = 148.3
Hz), 27.5 (q, 1J = 127.7 Hz), δ 26.2 (q, 1J = 127.4 Hz), δ 16.64 (q, 1J =
127.1 Hz). λmax (ε) in 0.1 N aq NaOH: 263 nm (23341 M−1 cm−1).
Anal. Calcd for C6H8N2O5Na2, %: C, 30.78; H, 3.44; N, 11.97. Found:
C, 30.86; H, 3.56; N, 11.73.
Found: C, 23.76; H, 2.42; N, 10.88.
Sodium Methyl 2-Butenoate-2-diazeniumdiolate-3-hydrox-
ylate (Na23). The product was synthesized from NaOH (97% w/w,
4.124 g, 0.100 mol) and methyl acetoacetate (5.805 g, 0.05 mol) in
methanol (100 mL) and nitric oxide as described above for K23. Yield:
7.560 g (69%). IR (cm−1): 1642 s (νCO, CO2Me), 1497 s, 1355 m,
1
1331 s, 1223 (νC−O, CO2Me). H NMR (600 MHz, D2O): δ 3.61 (s,
1.86H), 3.60 (s, 1.14H), 2.28 (s, 1.16H), 1.77 (s, 1.84H). 13C NMR
(151 MHz, D2O): δ 188.0, 187.6, 171.5, 169.6, 113.6, 113.3, 53.4 (q, 1J
= 146.1) δ 53.2 (q,1J = 146.1 Hz), 27.5 (q, 1J = 127.7 Hz), 26.1 (q, 1J =
127.7 Hz). λmax (ε) in 0.1 N aq NaOH: 265 nm (22129 M−1 cm−1).
Anal. Calcd for C5H6N2O5Na2: C, 27.29; H, 2.75; N, 12.73. Found: C,
26.65; H, 2.67; N, 12.58.
1
1
Lithium Methyl 2-Butenoate-2-diazeniumdiolate-3-hydrox-
ylate (Li23·2/3MeOH·1/3H2O). LiOH·H2O (4.2 g, 0.100 mol) was
dissolved in boiling methanol (100 mL). The solution was cooled to
room temperature and treated with methyl acetoacetate (5.805 g, 0.05
mol). Subsequent steps were carried out as described above for K23
except for the following modification. After the filtration of the
precipitated white powder, the filtrate was rotary evaporated to ca. 30
mL and the cloudy solution cooled in an ice bath for 1 h. The
microcrystalline product formed was filtered, mixed with the first crop,
Potassium Acetatediazeniumdiolate (K22). Salt K23 (2.532 g,
0.010 mol) was dissolved in 0.5 N aq KOH (50 mL) and the solution
was allowed to evaporate slowly in a fume hood over 5 d. Colorless
needles of K1 formed after 2 d (0.250 g) were filtered off, and the
filtrate allowed to stand further when large colorless crystals formed.
7317
dx.doi.org/10.1021/jo301025k | J. Org. Chem. 2012, 77, 7313−7318

The Journal of Organic Chemistry
Article
The crystals were filtered and washed with methanol/water (50:50)
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Chem. 2008, 73, 8077.
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solvent mixture (10 mL) and methanol, and dried. Yield: 1.630 g
−
(76%). IR (cm−1): 1605 s (νCO, CO2 ), 1379 s, 1306 s, 1253 (νC−O
,
−
CO2 ). 1H NMR (600 MHz, D2O): δ 4.59 (s). 13C NMR (151 MHz,
2
1
D2O): δ 175.9 (t, J = 5.0 Hz), 65.1 (t, J = 142.2 Hz). λmax (ε) in
water,: 249 nm (2207 M−1 cm−1). Anal. Calcd for C2H4N2O5K2: C,
11.21; H, 1.88; N, 13.07. Found: C, 11.16; H, 1.86; N, 12.94.
Decomposition of K23. About 0.1 g of K23 taken in a 25 mL
round-bottom flask was dissolved in 10 mL of water. The flask was
secured with a septum and cooled in an ice bath. The flask and an IR
gas cell were connected using a cannula, and the gas cell was vented
through a mineral gas bubbler. The solution and the gas cell were
thoroughly degassed by passing N2 gas over a period of 30 min as the
solution was cooled. Subsequently, the solution was slowly heated to
ca. 80 °C and the bubbling of N2 stopped. At 60 °C gas bubbles began
to form. After the released gas was allowed to pass through the gas cell
for 2 min, the cell was disconnected and an IR spectrum was
measured. The spectrum consisted of intense absorptions at 2236,
2203, 1297, and 1272 cm−1 indicating that the gas is nitrous oxide.
X-ray Crystallography. The X-ray diffraction data were measured
at 150 K on a Bruker SMART APEX II CCD area detector system
equipped with a graphite monochromator and a Mo Kα fine-focus
sealed tube operated at 1.5 kW power (50 kV, 30 mA). Crystals were
attached to a glass fiber using Paratone N oil. The detector was placed
at a distance of 5.13 cm from the crystal during the data collection.
The structures have been deposited with the Cambridge Crystallo-
graphic Data Center under the deposition nos. 882051, 882052, and
882053 for 1, 2, and 3.
A series of narrow frames of data were collected with a scan width of
0.5° in ω or φ and an exposure time of 10 s per frame. The frames
were integrated with the Bruker SAINT software package using a
narrow-frame integration algorithm.21 The data were corrected for
absorption effects by the multiscan method (SADABS). Crystallo-
graphic data collection parameters and refinement data are deposited
as Supporting Information. The structures were solved by direct
methods using the Bruker SHELXTL (V. 6.14) software package.30 All
non-hydrogen atoms were located in successive Fourier maps and
refined anisotropically. The hydrogen atoms were also located on the
difference Fourier maps and refined isotropically.
(29) Salmon, D. J.; Torres de Holding, C. L.; Thomas, L.; Peterson,
K. V.; Goodman, G. P.; Saavedra, J. E.; Srinivasan, A.; Davies, K. M.;
Keefer, L. K.; Miranda, K. M. Inorg. Chem. 2011, 50, 3262.
(30) Apex2 Software Suite V.2.1-0, Bruker; Bruker AXS: Madison,
WI, 2011.
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic data (CIF) for K1, K22·H2O, and [N-
1
(Me)3]23·3H2O·MeOH. IR spectra (Figures S1−S8), H and
13C NMR spectra (Figures S9−S32), and TGA/DSC profiles
(Figures S33−S40) for all products. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: arulsamy@uwyo.edu; scott.bohle@mcgill.ca.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
N.A. gratefully acknowledges support from the NASA-funded
Wyoming Space Grant Consortium (NNG05G165H), and
D.S.B. and I.P. acknowledge support from NSERC and the
CRC.
REFERENCES
■
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(3) Gyor, M.; Rockenbauer, A.; Tudos, F. Tetrahedraon Lett. 1986,
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dx.doi.org/10.1021/jo301025k | J. Org. Chem. 2012, 77, 7313−7318