Kinetic effects of electrolytes in oxidation of sodium, potassium, and tetrabutylammonium 1-acetonyl-2,4-dinitrocyclohexa-2,5-dienides with 1,4-benzoquinone

Article abstract of DOI:10.1023/A:1012343520743

The kinetics of oxidation of sodium, potassium, and tetrabutylammonium 1-acetonyl-2,4-dinitrocyclohexa-2,5-dienides with 1,4-benzoquinone in acetonitrile and tetrahydrofuran was studied spectrophotometrically. The reaction is of the first order with respe

Full text of DOI:10.1023/A:1012343520743

Russian Journal of General Chemistry, Vol. 71, No. 4, 2001, pp. 599 604. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 4, 2001,
pp. 644 649.
Original Russian Text Copyright
2001 by Kurenkova, Alifanova, Atroshchenko, Akhromushkina, Gitis, Kaminskii.
Kinetic Effects of Electrolytes in Oxidation
of Sodium, Potassium, and Tetrabutylammonium
1-Acetonyl-2,4-dinitrocyclohexa-2,5-dienides
with 1,4-Benzoquinone
Yu. V. Kurenkova, E. N. Alifanova, Yu. M. Atroshchenko,
I. M. Akhromushkina, S. S. Gitis, and A. Ya. Kaminskii
Tolstoi State Pedagogical University, Tula, Russia
Received December 21, 1999
Abstract The kinetics of oxidation of sodium, potassium, and tetrabutylammonium 1-acetonyl-2,4-dinitro-
cyclohexa-2,5-dienides with 1,4-benzoquinone in acetonitrile and tetrahydrofuran was studied spectrophoto-
metrically. The reaction is of the first order with respect to the substrate and quinone and of the total second
order. In the course of the process, a charge-transfer complex with an absorption maximum at about 716 nm
is formed, accelerating the reaction. The rates of its accumulation and consumption increase with increasing
concentrations of reactants and decrease on addition of sodium or tetrabutylammonium perchlorate. The
factors facilitating association of adducts in solution (increase of the concentration in THF, addition of
NaClO4 or [N(C4H9)4]ClO4), decelerate oxidation owing to decrease of the negative charge in the cyclohexa-
dienide ring of the contact ion pair of the
adduct as compared to the free ion.
Oxidation of anionic adducts of nitroarenes with
quinones, on the one hand, is of interest as a route to
substituted -phenyl ketones, because this process
occurs under relatively mild conditions and with a
fairly high yield [1]. On the ohter hand, quinones and
their one-electron reduced species play a key role in
studies of electron transfer and conversion of biologi-
cal energy [2 5]. For example, in photosynthetic proc-
esses they act as electron acceptors [6]; also, they are
constituents of oxyreductases [7]. Much attention is
also given to the mechanism of hydrogen transfer in
reactions involving quinones. Various types of hy-
dride transfer are discussed in the literature, and in
some cases the intermediate stage is formation of a
charge-transfer complex detected by a characteristic
absorption band in the electronic spectra [8]. Since
adducts are organic -electron donors and quinones
are acceptors, oxidation of adducts can be inter-
preted in terms of donor acceptor interaction between
the reactants.
on the oxidation rate constant is exerted by the elec-
trophilicity of the medium.
Adducts are ionic compounds occurring in weak-
ly polar media both as free ions and as ion pairs [13,
14]; their reactivity is different. As shown in [14 16],
the shift of the ion-pair equilibrium (including that
induced by addition of salts) affects both the rate and
the regio- and stereoselectivity of the reaction. There-
fore, we suggest that addition of electrolytes should
also affect the rate of reaction of adducts with qui-
nones. Study of the kinetic effects of electrolytes (salt
effects) will give a deeper insight into the reaction
mechanism and allow the choice of the optimal reac-
tion conditions.
Thus, the goal of this work was to study the kinet-
ics of the reaction of sodium, potassium, and tetra-
butylammonium 1-acetonyl-2,4-dinitrocyclohexa-2,5-
dienides (Ia Ic, respectively) with 1,4-benzoquinone
in solvents of different polarity (acetonitrile, THF)
in which these compounds are relatively stable and
sufficiently soluble and to examine the influence of
We have studied previously [9, 10] the kinetic and
thermodynamic features of oxidation of
adducts
sodium and tetrabutylammonium perchlorates on the
reaction rate.
with quinones and suggested a bimolecular reaction
scheme involving formation of a charge-transfer com-
plex, with the ionic mechanism of hydrogen transfer.
We have also studied the effect of solvents on the
To gain insight into the reaction mechanism, we
performed a systematic kinetic analysis [17]. The
reaction rate [11, 12] and found that the major effect semilogarithmic anamorphoses of the kinetic curves
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600
KURENKOVA et al.
of consumption of adduct Ib in acetonitrile at vari-
ous initial concentrations of Ib are parallel straight
On mixing the reactants, a broad absorption band
appeared in the range 714 833 nm, belonging to
charge-transfer complex III of quinone with the
adduct. By normalization and differentiation of the
spectrum, we determined the position of the band
maximum: about 716 nm. Apparently, this complex
has a stack structure stabilized by electrostatic inter-
actions similarly to complexes of quinones with other
organic donors [18]. With increasing concentration
of the adduct the rates of formation and consump-
tion of the intermediate increase (Fig. 2).
3
lines; at the adduct concentration varied from 10
5
to 10 M, the rate constant remains practically un-
3
1
changed [k (3.13 0.09) 10 s ], which suggests
the first order of the reaction with respect to the sub-
strate (n 1.02 0.02). The linear dependence of the
rate constant on the quinone concentartion proves the
first order of the reaction with respect to the oxidant
also (n 1.02 0.04). The kinetic curves of consump-
tion of Ib at its different initial concentrations cannot
be made coincident by shifting along the x axis, and
the plot of the initial reaction rate vs. time of addition
of a fresh portion of the complex is a convex curve
(Fig. 1). Hence, the reaction course is influenced by
intermediate III [scheme (1)] [17]. The increase in
The hydride transfer in the course of transformation
of the charge-transfer complex into the reaction prod-
ucts can occur either in a one two-electron stage or in
steps via formation of radicals and radical anions.
However, addition of radical scavengers (hydroqui-
none, nitrosobenzene) and removal of oxygen from
the reaction mixture did not affect significantly the
3
the rate constant from (0.96 0.02) 10 to (1.25
3
1
0.06) 10
s
on adding 2,4-dinitrophenylacetone
(IV) confirms participation of this compound in the
transition state. Calculations of the rate constants of
the first and second stages of the process showed that
the limiting stage is formation of the intermediate
4
1
reaction rate [k (4.98 0.12) 10
bubbling and (4.89 0.01) 10
s
without argon
with argon bub-
4
1
s
bling], which suggests the predominantly ionic char-
acter of the process under these conditions.
4
4
1
(k1 2.76 10 , k2 5.73 10 s ), which is practi-
17
1
cally irreversible (k 10
s ).
Thus, the reaction can be described by scheme (1):
1
O M+
O
CH2COCH3
NO2
O
CH3COCH
2 H
CH3COCH
2 H
NO2
NO2
k1
k1
k2
(1)
+
+
NO2M+
NO2M+
NO2
O
OH
O
I
II
III
M+ = Na+ (a), K+ (b), [N(C4H9)4]+ (c).
IV
V
monium perchlorate. In acetonitrile, adducts Ia and
Ic mostly exist as free ions and solvent-separated
ion pairs. In less polar THF, sodium and potassium
ions form with the anion contact ion pairs whose vis-
ible absorption spectra differ from those of the free
0.35
0.30
0.25
0.20
ions:
586 nm for free ions, 539 nm for contact
max
ion pairs with the sodium ion, and 551 nm for contact
ion pairs with the potassium ion (Table 1). Despite
the fact that, according to conductometric data, the
adduct with tetrabutylammonium ion Ic is an
2
7
12
, min
4
electrolyte of medium strength (Kdis 3.01 10 in
Fig. 1. Initial reaction rate vs. time of addition of a fresh
portion of adduct Ib.
THF), its spectral characteristics in both solvents are
similar to those of the solvent-separated ion pairs
and free ions. This is due to the fact that the bulky
[N(C4H9)4]+ ion (r 3.5 ) does not affect significantly
To examine the influence of electrolytes on this
process, we have studied the dependence of the spec- the electronic state of the anion owing to the large dis-
tral characteristics of the reactants and of the reaction tance between the positively charged nitrogen center
rate on the concentration of sodium or tetrabutylam- and the negatively charged oxygen atoms of the nitro
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KINETIC EFFECTS OF ELECTROLYTES IN OXIDATION
601
groups. For the same reason, addition of [N(C4H9)4]
D/t,1
ClO4 to solutions of adducts Ib and Ic in acetonitrile
and Ic in THF does not affect their absorption spectra
(Table 1). The absorption maximum in the spectra of
adducts Ia and Ib in THF at a large excess of the
salt shifts toward longer waves owing to a decrease
in the content of contact ion pairs on replacement of
Na+ and K+ in the initial adduct by [N(C4H9)4]+:
cm
0.8
0.6
6
An K+ + [N(C4H9)4]+
An [N(C4H9)4]+ + K+. (2)
0.4
0.2
0
Addition of sodium perchlorate causes a hypso-
chromic shift of the absorption maxima of adducts
Ia and Ic due to formation of stronger contact ion
pairs of the anion with the sodium ion. In THF, the
ion-pair equilibrium is shifted at Csalt/Cad = 0.5, and
in CH3CN this ratio is 3. At higher concentrations of
sodium perchlorate, higher associates consisting of
three, four, etc., ions are formed, as indicated by a
small bathochromic shift of the absorption maxima at
a 100 200-fold excess of the salt.
5
4
3
2
1
10
20
30
40
, min
Variation of the ratio of the ions and ion pairs in
solutions of adducts on adding salts should affect
the rate of their oxidation by the mechanism of simul-
taneously acting primary and secondary kinetic elec-
trolyte effects. The increase in the concentration of
[N(C4H9)4]ClO4 does not noticeably affect the oxida-
tion rate of Ic in both solvents and of Ia and Ic in
CH3CN, since in these solutions no shift of the ion-
pair equilibrium was observed. As was expected from
the equation lnk = lnk0 + 2ZAZBAI1/2 [where k is the
rate constant at a given ionic strength I, k0 is the rate
constant at I = 0, ZA and ZB are the charges of the
reacting species, and A is the constant of the Debye
Huckel theory (for solution in THF, A 17.62)], for the
reaction between the adduct anion and the quinone
molecule the logarithm of the second-order rate con-
stant is practically independent of the square root of
the solution ionic strength (Fig. 3).
Fig. 2. Kinetic curves of accumulation and consumption
of the intermediate at various concentrations of adduct
5
5
Ib (C ) in MeCN. C , M: (1) 1 10 , (2) 1.8 10
,
.
ad
ad
4
4
4
3
(3) 1 10 , (4) 2 10 , (5) 4 10 , and (6) 1 10
0.8
ln k2
0.6
0.4
I1/2
0.01
0.06
0.11
Fig. 3. Logarithm of the rate constant of reaction of
adduct Ic with benzoquinone as a function of the square
root of the ionic strength of the solution (addition of
[NBu ]ClO ) in CH CN.
4
4
3
ions. A PM3 calculation of the energy of the highest
occupied molecular orbital in Ib, the major contribu-
tion to which is made by the ring carbon atoms, gave
for the free ion and ion pair the values of 4.83 and
8.56 eV, respectively. Thus, the decrease in the nega-
tive charge in the cyclohexadienide ring and its in-
crease on the nitro group under the influence of the
cation weaken the reductive activity of the adduct.
Owing to decrease in the electron-donor power of the
ring, the accumulation and consumption of the inter-
mediate decelerate (Fig. 4) with increasing concentra-
tion of NaClO4.
Addition of sodium perchlorate affects not only the
ionic strength of solution but also the degree of asso-
ciation of the
adduct. As the concentration of the
like ion on its addition to a solution of adduct Ia in
THF is increased, the content of the contact ion pairs
increases, and the oxidation rate decreases. A similar
trend is observed on adding NaClO4 to solutions of Ib
in CH3CN and THF.
In contrast to acetonitrile solutions in which there
is no association and the rate constant is independent
of the adduct concentration, in THF the observed
rate constant decreases with increasing degree of asso-
The cation exchange between
adduct Ic and
[N(C4H9)4]ClO4 decelerates its oxidation in THF, and
the exchange between Ic and NaClO4 accelerates its
oxidation in CH3CN and THF (Table 2). Hence, the
solution of Ic contains contact ion pairs which are less
ciation 1/ of
adduct Ib (Table 2).
Our experimental data show that the adducts in
the form of ion pairs are less reactive than the free
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 4 2001

602
KURENKOVA et al.
1
Table 1. Positions of absorption maxima ( max, nm) and oxidation rate constants (k, dm3 mol 1 s ) of adducts Ia Ic as
influenced by the ratio of the salt and adduct concentrations Csalt/Cad (298 K)
Comp.
no.
C
salt/Cad
k 101
CH3CN
k 101
k 101
k 101
max1
max2
max1
max2
max1
max2
max1
max2
THF
NaClO4
[N(C4H9)4]ClO4
NaClO4
[N(C4H9)4]ClO4
Ia
0
0.5
1
3
5
350 538 3.32 0.02
350 538 3.34 0.01
350 537 3.27 0.01
349 536 3.02 0.04
349 536 2.75 0.06
349 535 2.73 0.03
348 535 2.53 0.05
348 534 1.92 0.03
348 536 1.49 0.01
10
20
50
100
0
Ib
361 580 2.11 0.09 361 580 2.11 0.09 357 554 3.63 0.09 356 551 3.18 0.09
361 580 1.99 0.07 361 580 2.22 0.05 355 543 2.49 0.15 357 562 2.47 0.12
361 579 1.95 0.03 361 580 2.27 0.05 354 535 2.18 0.18 359 562 2.28 0.08
0.5
1
3
359 579
361 580
354 535 1.97 0.06 361 567 2.11 0.13
5
359 577 1.93 0.03 361 580 2.39 0.05 354 535 1.86 0.12 361 569 1.92 0.11
358 574 1.92 0.03 361 580 2.36 0.04 354 535 1.88 0.08 362 574 1.94 0.09
10
20
50
100
200
0
358 573
361 580
354 535 1.83 0.07 361 577 1.71 0.08
357 569 1.86 0.07 361 580 2.32 0.01 354 535 1.80 0.13 361 579 1.69 0.09
356 567 1.82 0.01 361 580 2.33 0.03 354 535 1.67 0.03 361 580 1.34 0.09
356 567
361 580
354 537
362 580
Ic
360 580 1.81 0.05 360 580 1.81 0.02 363 580 2.54 0.05 362 580 2.54 0.05
360 580 1.85 0.13 360 580 1.82 0.13 361 569 2.59 0.03 362 580 2.43 0.04
360 580 1.79 0.08 360 580 1.76 0.03 357 559 2.71 0.05 362 580 2.44 0.01
0.5
1
3
360 580
360 580
355 536
362 580 2.46 0.02
5
360 580 2.01 0.11 360 580 1.76 0.09 355 527 2.73 0.05 362 580 2.44 0.02
359 579 1.99 0.02 360 580 1.91 0.06 354 526 2.75 0.06 362 580 2.46 0.06
10
20
50
100
200
359 577
360 580
355 533 2.79 0.02 362 580
359 577 2.02 0.01 360 580 1.86 0.05 355 535 2.83 0.01 362 580 2.34 0.04
356 569 1.95 0.11 360 580 1.84 0.05 355 536 2.81 0.01 362 580 2.34 0.06
356 569
360 580
355 536
362 580
Table 2. Rate constant of oxidation of
influenced by its concentration in THF (298 K)
adduct Ib as
Thus, oxidation of the adducts is a bimolecular
reaction with intermediate formation of a charge-
transfer complex. The primary kinetic electrolyte
effect does not noticeably influence the reaction rate,
and the secondary effect consists in shifting the ion-
pair equilibria in solutions of adducts in the pres-
ence of salts. In the reaction under consideration, the
free ions are more reactive than the ion pairs.
1
104, M
kapp 103, s
Cad
1.83
2.42
9.31
4.89 0.02
4.78 0.04
1.34 0.05
1.43 0.04
0.29
0.25
0.13
0.11
12.61
EXPERIMENTAL
reactive than those with the sodium and potassium
ions, owing to steric hindrance produced by the tetra-
butylammonium ion in formation of the charge-trans-
fer complex. For the same reason, adduct Ic in both
solvents is oxidized more slowly than Ia and Ib.
The Yanovskii
adducts and 1,4-benzoquinone
were prepared by procedures described in [19] and
[20], respectively. Their structure was proved by elec-
1
tronic, H NMR, and IR spectroscopy. The solvents
were dehydrated according to [21]; their purity was
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 4 2001

KINETIC EFFECTS OF ELECTROLYTES IN OXIDATION
Acta, 1983, no. 726, pp. 149 185.
603
D 10
0.5
3. Morton, R.A., Biochemistry of Quinones, New York:
Academic, 1965.
1
4. Robinson, H.H. and Crofts, A.R., FEBS Lett., 1983,
0.4
0.3
2
no. 153, pp. 221 226.
3
5. Trumpower, B.L., Function of Quinones in Energy
Conversing Systems, New York: Academic, 1982.
6. Smirnova, J.A., Hagerhall, S., Konstantinov, A.A.,
and Hederstedt, L., FEBS Lett., 1995, no. 359,
pp. 23 26.
0.2
0.1
7. Ferber, D.M., Moy, B., and Maier, R.J., Biochim.
Biophys. Acta, 1995, no. 1229, pp. 334 346.
0
500
1000
1500 t, s
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Fig. 4. Kinetic curves of accumulation and consumption
of the intermediate at various C /C ratios in CH CN.
9. Atroshchenko, Yu.M., Akhromushkina, I.M., Gi-
tis, S.S., Nevodchikov, V.I., Savinova, L.N., Druzh-
kov, I.O., Kaminskii, A.Ya., and Nechet, O.V., Zh.
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salt ad
3
C
/C : (1) 0, (2) 10, and (3) 50.
salt ad
checked refractometrically with an IRF-22 device.
Sodium perchlorate was purified and dried according
to [22].
10. Alifanova, E.N., Atroshchenko, Yu.M., Akhromushki-
na, I.M., Savinova, L.N., Gitis, S.S., and Kamin-
skii, A.Ya., Zh. Obshch. Khim., 1996, vol. 66, no. 7,
pp. 1173 1176.
Tetrabutylammonium perchlorate. A 2-l beaker
was charged with 500 g of a tetrabutylammonium
hydroxide solution ( 10%), 50 ml of H2O was added,
and HClO4 was gradually added with stirring to pH
5.5. The resulting precipitate was filtered off on a
Buchner funnel and washed by stirring with double-
distilled water for 4 h. The washed product was filtered
off and dried at temperature no higher than 60 C.
Yield 90%.
11. Alifanova, E.N., Atroshchenko, Yu.M., Akhromushki-
na, I.M., Savinova, L.N., Gitis, S.S., Kamin-
skii, A.Ya., and Sychev, V.V., Zh. Obshch. Khim.,
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Temnov, V.S., and Kaminskii, A.Ya., Zh. Org. Khim.,
1993, vol. 29, no. 6, pp. 1835 1842.
The reaction kinetics was monitored spectrophoto-
metrically [23]. The spectra were taken on a Specord
M-40 spectrophotometer.
13. Alifanova, E.N., Gitis, S.S., and Kaminskii, A.Ya.,
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1394.
The oxidation rate of adducts was monitored by
the decrease in the optical density in the absorption
maximum of the adduct. The concentration of the
charge-transfer complex was monitored by absorption
at 833 nm, because its absorption maximum (716 nm)
14. Alifanova, E.N., Gitis, S.S., Kaminskii, A.Ya., and
Shakhkel’dyan, I.V., Izv. Vyssh. Uchebn. Zaved., Khim.
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is overlapped by absorption of the
adduct. The
15. Alifanova, E.N., Atroshchenko, Yu.M., Kamin-
skii, A.Ya., Gitis, S.S., Grudtsyn, Yu.D., Naso-
nov, S.N., Alekhina, N.N., and Illarionova, L.V., Zh.
Org. Khim., 1993, vol. 29, no. 7, pp. 1412 1418.
measurements were performed under pseudo-first-
order conditions at a 50 100-fold excess of benzo-
quinone.
The first- and second-order rate constants were
calculated following the recommendations in [24].
16. Golopolosova, T.V., Savinova, L.N., Glaz, A.I., and
Gitis, S.S., Sint., Anal. Strukt. Org. Soedin., 1979,
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