Activation parameters of the reactions of 4-nitrophenyl benzoates and S-phenyl benzothioate with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate

Article abstract of DOI:10.1134/S1070428009040095

The kinetics of transesterification of 4-nitrophenyl benzoates and S-phenyl benzothioate with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate were studied. Variation of the substrate reactivity and activation parameters of the process is discussed with respect to the substituent in the benzoic acid fragment.

Full text of DOI:10.1134/S1070428009040095

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 4, pp. 523–527. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © I.A. Os’kina, V.M. Vlasov, 2009, published in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 4, pp. 538–542.
Activation Parameters of the Reactions of 4-Nitrophenyl
Benzoates and S-Phenyl Benzothioate with 4-Chlorophenol
in Dimethylformamide in the Presence of Potassium Carbonate
I. A. Os’kina and V. M. Vlasov
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
e-mail: oi@nioch.nsc.ru
Received June 2, 2008
Abstract—The kinetics of transesterification of 4-nitrophenyl benzoates and S-phenyl benzothioate with
4
-chlorophenol in dimethylformamide in the presence of potassium carbonate were studied. Variation of the
substrate reactivity and activation parameters of the process is discussed with respect to the substituent in the
benzoic acid fragment.
DOI: 10.1134/S1070428009040095
The reactivity of aryl benzoates in transesterifica-
tion processes is determined by several factors, in-
cluding electrophilicity of the carbonyl carbon atom,
nucleophile nature, and solvation [1–5]. The electro-
philicity of the carbonyl carbon atom depends in turn
on the nature of substituents in fragments attached
thereto. We previously studied [4, 5] the effect of
substituents in the benzoyl group on the reactivity of
substituted 4-nitrophenyl benzoates toward 4-chloro-
phenol and benzenethiol in the presence of potassium
carbonate in dimethylformamide. We found that donor
substituents in the benzoyl fragment, as might be
expected [6], reduce the reactivity and that electron-
withdrawing groups enhance it. Presumably, the reac-
tion involves several steps, and the reaction rate is not
determined by removal of departing group [4, 5].
Although dissociation of the bond with departing
group occurs at the stage that is not rate-determining,
the nature of departing group may be expected to
affect the rate and activation parameters of transester-
ification [7].
transesterification processes. The reaction of 4-nitro-
phenyl acetate with 4-chlorophenoxide ion in aqueous
medium was reported to be characterized by the fol-
≠
lowing activation parameters: ∆H = 51.4 kJ/mol,
≠
–1
–1
≠
∆S = –75.7 J mol K , ∆G = 74.0 kJ/mol [11]. In
going to 90% aqueous DMSO, the activation param-
eters of the same reaction insignificantly decreased:
≠
≠
–1
–1
≠
∆H = 38.1 kJ/mol, ∆S = –69.9 J mol K , ∆G =
59.0 kJ/mol [12]. Variations of the enthalpy of activa-
≠
≠
tion ∆H , entropy of activation ∆S , and Gibbs energy
≠
of activation ∆G are very important for elucidating
specific features of transesterification reactions in rela-
tion to the reactant structure.
The goal of the present work was to examine the
effect of the leaving group nature on the reactivity of
4
-nitrophenyl benzoate and S-phenyl benzothioate in
transesterification with 4-chlorophenol (K CO , DMF)
2
3
and analyze the ratio of the enthalpy and entropy con-
tributions to the energy barrier of this reaction. The
difference in the basicities of the leaving groups in
4
-nitrophenyl benzoate (III) and S-phenyl benzothi-
oate (VI) amounts to 1.64 pK units (pK = 12.34 and
0.7 for 4-nitrophenol and benzenethiol, respectively,
It is known that the enthalpy and entropy of activa-
tion can change to a much stronger extent than the
energy of activation [8]. In reactions of carbonyl com-
1
in DMF [13]); presumably, this difference is sufficient
to affect the reaction rate and its activation parameters
pounds with nucleophiles, characterized by similar
≠
(
cf. [14, 15]).
∆
G values, either enthalpy or entropy contribution
may predominate [9, 10]. Despite numerous published
data on the activation parameters of reactions of car-
bonyl compounds with nucleophiles [11], only a few
publications are available on activation parameters of
Aryl benzoates I–VI reacted with 4-chlorophenol
(VII) in DMF in the presence of K CO in the temper-
2
3
ature range from 1.5 to 36°C to give the corresponding
4-chlorophenyl benzoates VIII–XII (Scheme 1). The
5
23

5
24
OS’KINA, VLASOV
Scheme 1.
O
O
K CO , DMF
1.5 to 36°C
Ar
OH
2
3
C H Cl-4
6 4
X
O
+
ArX K+
–
+
R
Cl
R
I–VI
VII
VIII–XII
I–V, Ar = 4-O
2
NC
6
H
4
, X = O; I, VIII, R = MeO; II, IX, R = Me; III, X, R = H; IV, XI, R = Br; V, XII, R = F
3
C;
VI, Ar = Ph, X = S.
products are stable under these conditions [4, 5]. The
apparent rate constants for the reactions of esters III
and VI with nucleophile VII at different temperatures
are given in Table 1. In the examined temperature
range, the transesterification of 4-nitrophenyl benzoate
was faster than the reaction with S-phenyl benzothi-
oate. Both the rate constants and the difference be-
tween them increase as the temperature rises. The
apparent rate constants at 1.5 and 36°C differ by more
than an order of magnitude. In going from 4-nitrophen-
yl benzoate to S-phenyl benzothioate the apparent rate
constants decrease by a factor of 3.6 to 4.7 (Table 1).
The effect of leaving group in transesterification is
determined by such factors as its basicity and polariz-
ability of the atom therein attached to the carbonyl
carbon atom, as well as by solvation of the leaving and
entering groups [14, 15]. Taking into account pK
values of 4-nitrophenol and benzenethiol in DMF
[14] approaches the corresponding value found in
10% aqueous DMSO (k /k = 6.6) [15]. However, in
S
O
the reaction with hydroxide ion as nucleophile in 10%
DMSO the rate constant ratio for S-(4-nitrophenyl)
benzothioate and 4-nitrophenyl benzoate changed to
the opposite (k /k = 1.4) [15]. This relation (k > k )
O
S
O
S
corresponds to the apparent rate constant ratio found
for 4-nitrophenyl benzoate and S-phenyl benzothioate
toward hydroxide ion (k /k = 18.9) in [7] and in the
O
S
present work (Table 1). Obviously, the basicity of the
leaving group is not the main factor responsible for the
substrate reactivity in the transesterification process
under study. The above data are quite consistent with
the assumption [4] that elimination of leaving group is
not the rate-determining stage.
The polarizability of the sulfur atom in phenylsul-
fanyl group is higher than that of the oxygen atom in
4-nitrophenoxy group. Therefore, dissociation of the
C(O)–SAr bond in S-phenyl benzothioate (VI) should
be more facile than dissociation of the C(O)–OAr bond
in 4-nitrophenyl benzoate (III), and the latter should
be less reactive than the former toward 4-chlorophenol.
On the other hand, increased difference in the polariz-
abilities of nucleophile and substrate could lead to
reduced efficiency of their mutual interaction [14].
Presumably, this factor is responsible for the observed
ratio in the reactivities of S-phenyl benzothioate (VI)
and 4-nitrophenyl benzoate (III) toward 4-chloro-
(
12.34 and 10.7, respectively [13]), phenylsulfanyl
group should be expected to favor transesterification
process to a stronger extent, as compared to 4-nitro-
phenoxy group, for benzenethiol is stronger acid than
4
-nitrophenol. However, the observed reactivity ratio
of aryl benzoates III and VI does not fit the relation
between the basicities of the leaving groups.
It is known that the reactivity ratio of esters derived
from phenols and benzenethiols in transesterification
depends on the nature of oxygen-centered nucleophile
phenol (VII) in DMF in the presence of K CO .
[14–18]. For example, the ratio of the rate constants
2
3
for transesterification of S-(4-nitrophenyl) benzothi-
oate and 4-nitrophenyl benzoate with 4-chlorophen-
oxide ion in anhydrous ethanol at 25°C (k /k = 6.1)
The log(k/T) and 1/T values for each aryl benzoate
give rise to a linear relation (see figure). These rela-
tions were used to calculate (according to the Eyring
S
O
Table 1. Apparent rate constants for the reactions of 4-nitrophenyl benzoate (III) and S-phenyl benzothioate (VI) with
4
-chlorophenol in the presence of K
2 3
CO (DMF, 1.5–36°C)
2
a
–1 –1
k
ap ×10 , l mol s
Compound no.
1
.5°C
2.2±0.2
0.61±0.04
15°C
24°C
36°C
III
VI
8.2±0.5
2.1±0.2
15±2
35±3
03.9±0.3
07.4±0.2
a
Average values from the results of at least three parallel runs.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009

ACTIVATION PARAMETERS OF THE REACTIONS OF 4-NITROPHENYL BENZOATES
525
≠
≠
log(kap/T)
equation [19]) the activation parameters ∆H , ∆S , and
∆
≠
G which reflect variation in the reactivity in energy
–2.8
units (Table 2). Compounds III and VI fit isoselective
relationship with an isoselective temperature Tiso of
–
–
–
3.2
3.6
4.0
1
78 K. The latter was determined as the crossing point
of the straight lines shown in figure [20]. The tempera-
ture range examined in the present work is consider-
ably higher than Tiso.
The data in Table 2 show that in going from 4-ni-
1
2
trophenyl benzoate (III) to S-phenyl benzothioate (VI)
≠
the enthalpy of activation ∆H decreases by 5.1 kJ/mol
–4.4
≠
and the entropy of activation ∆S decreases by 29 J×
–
1
–1
mol K ; simultaneously, the Gibbs energy of activa-
–
4.8
≠
tion ∆G increases by 3.3 kJ/mol (Table 2). The change
–1
0
.0032
0.0034
0.0036 1/T, K
of the latter parameter is determined mainly by varia-
tion of the enthalpy of activation. The enthalpies, en-
tropies, and Gibbs energies of activation, found in the
present work, fall into the ranges typical of transester-
ification processes (cf. [12]).
Plots of log(kap/T) versus reciprocal temperature (1/T) for the
reactions of (1) 4-nitrophenyl benzoate (III) and (2) S-phen-
yl benzothioate (VI) with 4-chlorophenol in the presence of
K
2
CO
s = 0.4, n = 4; (2) log(kap/T) = –2596(1/T) + 5; r = 0.995, s =
.5, n = 4.
3
in DMF: (1) log(kap/T) = –2862(1/T) + 6; r = 0.998,
0
It is known that substituent-related change in the
entropy depends on the solvation factor [21, 22].
Considering the leaving group as substituent in 4-nitro-
phenyl benzoate (III) and S-phenyl benzothioate (VI),
we presumed that the lower entropy of activation in the
reaction with S-phenyl benzothioate (VI) than in the
reaction with 4-nitrophenyl benzoate (III) is the result
of stronger difference in nonspecific solvation of the
initial and transition states in the reaction with VI.
Decrease in the enthalpy and entropy of activation in
going from benzoate III to benzothioate VI leads to
increase in the Gibbs energy of activation and is
responsible for the observed reactivity series of aryl
benzoates with respect to the leaving group nature.
trolled. In going to 4-nitrophenyl benzoates with elec-
tron-withdrawing substituents, the enthalpy contribu-
tion appreciably decreases due to increase in the elec-
trophilicity of the carbonyl carbon atom [3, 23–25].
Simultaneously, the entropy of activation decreases as
a result of substituent-related change of solvation, and
the entropy contribution to the energy barrier in-
creases, which suggests enhanced ordering of the
transition state. The observed variation in the ratio of
the enthalpy (∆H ) and entropy contributions (T∆S ) to
the energy barrier, depending on the substituent nature,
is not typical of reactions of carbonyl compounds with
nucleophiles (cf. [9, 10]).
≠
≠
Table 3 contains the enthalpies, entropies, and
Gibbs energies of activation for the reactions of 4-ni-
trophenyl benzoates with 4-chlorophenol in the pres-
ence of potassium carbonate in dimethylformamide.
Thus the revealed relations in the variation of rate
constants (k > k ) allowed us to presume that the
O
S
basicity of the leaving group is not the main factor
responsible for the reactivity of aryl benzoates toward
≠
≠
The parameters ∆H and ∆S change over fairly broad
≠
4
-chlorophenol in the transesterification process. Anal-
ranges, whereas the range of variation of ∆G is typical
ysis of the activation parameters showed that the ratio
of reactions of carbonyl compounds with nucleophiles
[11, 12]. The enthalpy and entropy of activation are
highly sensitive to the substituent in the benzoyl frag-
ment. Increase in the electron-acceptor power of the
substituents is accompanied by appreciable reduction
of both enthalpy and entropy contributions to the over-
all energy barrier.
Table 2. Activation parameters of the reactions of 4-nitro-
phenyl benzoate (III) and S-phenyl benzothioate (VI) with
4
-chlorophenol in the presence of K
2
CO
3
in DMF
≠
≠
≠ a
≠ a
Comp.
∆H ,
–∆S ,
–T∆S ,
∆G ,
–1
–1
no.
III
VI
kJ/mol
J mol K
kJ/mol
kJ/mol
In the transesterification of 4-nitrophenyl benzoates
having electron-donating substituents the contribution
of the enthalpy component to the energy of activation
predominates, so that their reactivity is enthalpy-con-
54.8±2.2 076.1±0.6
49.7±3.5 105.1±0.8
22.6
31.0
77.4
80.7
a
At 24°C.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009

5
26
OS’KINA, VLASOV
a
Table 3. Activation parameters of the reactions of 4-nitrophenyl benzoates (I–V) with 4-chlorophenol in the presence of
K
2 3
CO in DMF
≠
≠
–1
–1
≠ b
≠ b
Compound no.
∆H , kJ/mol
–∆S , J mol K
–T∆S , kJ/mol
∆G , kJ/mol
I
61.2±2.7
55.6±3.5
54.8±2.2
25.6±7.5
04.9±0.8
71.4±3.1
80.5±3.2
21.2
23.9
22.6
47.0
63.2
82.4
79.5
77.4
72.6
68.1
II
III
IV
V
76.1±0.6
158.2±30.3
212.9±30.4
a
≠
≠
≠
The activation parameters ∆H , ∆S , and ∆G were estimated from the corresponding values found for 4-nitrophenyl benzoate (III) and
≠
≠
≠
≠
≠
≠
≠
≠
≠
differences ∆∆H = ∆H (R) – ∆H (H), ∆∆S = ∆S (R) – ∆S (H), and ∆∆G = ∆G (R) – ∆G (H) for compounds I, II, IV, and V [4].
b
At 24°C.
of the enthalpy and entropy contributions to the overall
energy barrier changes to the opposite one with varia-
tion of the substituent nature.
and analyzed by GLC. According to the GLC data, the
mixture contained compound X (recovery 97%) and
4-nitrophenol (recovery 68%) or compound X (recov-
ery 96%) and benzenethiol ( recovery 93%).
EXPERIMENTAL
Kinetic study of the reactions of 4-nitrophenyl
benzoate (III) and S-phenyl benzothioate (VI) with
The reaction mixtures were analyzed by gas–liquid
chromatography on an LKhM-72 instrument equipped
with a thermal conductivity detector; linear oven tem-
perature programming from 50 to 270°C at a rate of
4
-chlorophenol (VII) in the presence of potassium
carbonate in dimethylformamide. Insofar as potas-
sium carbonate is almost insoluble in DMF [26], the
use of the direct kinetic method was complicated due
to heterogeneity of the reaction system. The state of
nucleophile generated from 4-chlorophenol and potas-
sium carbonate in the two-phase system (K CO –
1
0 deg/min; SKTFT-803 column, stationary phase 15%
of VS-1 on Chromaton W; carrier gas helium, flow
rate 60 ml/min. The components were quantitated
using internal normalization technique with hexameth-
ylbenzene as reference and were identified by com-
parison with authentic samples. Commercial dimethyl-
formamide was distilled under reduced pressure first
over calcium hydride and then over molecular sieves
and was stored over molecular sieves under argon.
Commercial potassium carbonate was ground, bolted
through a 0.5-mm sieve, calcined in a muffle furnace,
and again ground and bolted through a 0.5-mm sieve.
Commercial 4-chlorophenol was purified according to
standard procedures. Aryl benzoates were synthesized
as described in [4, 5]; their physical constants were
consistent with published data.
2
3
DMF) was studied in [27, 28]. According to the proce-
dure described in [29] we estimated parameters en-
suring that the reaction rate depended neither on the
K CO surface area accessible to contact with the reac-
2
3
tant nor on the rate of transition of nucleophilic com-
plex to solution: K CO –4-chlorophenol ratio ≥1.4:1,
2
3
K CO grain size ≤ 0.5 mm, speed of stirring
2
3
≥
750 rpm, and time for generation of nucleophilic
complex ≥30 min. These settings were applied while
determining the apparent rate constants for the reac-
tions of esters III and VI with 4-chlorophenol in the
presence of K CO in dimethylformamide.
2
3
A flask was purged with argon and charged with
The stability of compound X under the trans-
esterification conditions was checked as follows.
A flask was purged with argon and charged with
K CO (grain size ≤0.5 mm) and a solution of
4-chlorophenol in 2 ml of DMF was added to attain
2
3
a K CO –4-chlorophenol ratio of ≥1.4:1. The mixture
2
3
0
.40 or 0.47 mmol of potassium carbonate and a solu-
tion of 0.14 mmol of compound X and 0.14 mmol of
-nitrophenol or 0.16 mmol of X and 0.16 mmol of
was stirred using a magnetic stirrer (≥750 rpm) for
30 min at a required temperature. The initial reactant
–
2
4
concentrations were (2–6)×10 M. A solution of the
corresponding aryl benzoate in 2 ml of DMF, adjusted
to the same temperature, was added, and the mixture
was stirred. Samples were withdrawn at definite time
intervals and poured into a mixture of chloroform with
10% hydrochloric acid. The organic phase was sepa-
benzenethiol in 2 ml of DMF. The mixture was main-
tained for 1 h at 36°C, a mixture of 2 ml of chloroform
and 2 ml of 10% hydrochloric acid was added to
terminate the reaction, and the organic phase was sepa-
rated, washed with 2 ml of water, dried over CaCl2,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009

ACTIVATION PARAMETERS OF THE REACTIONS OF 4-NITROPHENYL BENZOATES
527
rated, dried, and analyzed by GLC using artificial mix-
tures for quantitation (internal standard hexamethyl-
benzene). The rate constants were calculated by the
second-order equation:
14. Kwon, D.-S., Park, J.-Y., and Um, I.-H., Bull. Korean
Chem. Soc., 1994, vol. 15, p. 860.
1
1
1
5. Um, I.-H., Kim, G.-R., and Kwon, D.-S., Bull. Korean
Chem. Soc., 1994, vol. 15, p. 585.
6. Hupe, D.J. and Jencks, W.P., J. Am. Chem. Soc., 1977,
vol. 99, p. 451.
k = {2.303/[τ(a – b)]}log{[b(a – x)]/[a(b – x)]},
7. Kwon, D.-S., Choi, K.-E., and Um, I.-H., Bull. Korean
Chem. Soc., 1989, vol. 10, p. 610; Kwon, D.-S.,
Choi, K.-E., and Um, I.-H., Bull. Korean Chem. Soc.,
where a and b are the initial reactant concentrations
(
M), x is the concentration of the product (M), and τ is
1
990, vol. 11, p. 362.
the reaction time (s).
1
1
8. Guthrie, J.P., J. Am. Chem. Soc., 1978, vol. 100,
p. 5892.
REFERENCES
. Um, I.-H., Lee, J.-Y., Fujio, M., and Tsuno, Y., Org.
Biomol. Chem., 2006, vol. 4, p. 2979.
. Um, I.-H., Hong, Y.-Z., and Kwon, D.-S., Tetrahedron,
9. Gordon, A.J. and Ford, R.A., The Chemist’s Com-
panion, New York: Wiley, 1972. Translated under the
title Sputnik khimika, Moscow: Mir, 1976, p. 158.
1
2
3
4
5
6
2
2
0. Liu, L. and Guo, Q.X., Chem. Rev., 2001, vol. 101,
p. 673.
1
997, vol. 53, p. 5073.
1. Parker, A.J., Chem. Rev., 1969, vol. 69, p. 1; Cramp-
ton, M.R. and Stevens, J.A., J. Chem. Soc., Perkin
Trans. 2, 1990, p. 1097; Crampton, M.R. and
Stevens, J.A., J. Chem. Soc., Perkin Trans. 2, 1989,
p. 925.
. Um, I.H., Han, H.J., Ahn, J.A., Kang, S., and
Buncel, E., J. Org. Chem., 2002, vol. 67, p. 8475.
. Os’kina, I.A. and Vlasov, V.M., Russ. J. Org. Chem.,
2
006, vol. 42, p. 865.
. Os’kina, I.A. and Vlasov, V.M., Russ. J. Org. Chem.,
007, vol. 44, p. 561.
2
2
2
2
2
2. Ruff, F., Internet Electr. J. Mol. Des., 2004, vol. 3,
2
p. 474.
. Connors, K.A., Structure Reactivity Relationships: The
Study of Reaction Rates in Solution, New York: VCH,
3. Um, I.-H., Lee, J.-Y., Kim, H.-T., and Bae, S.-K.,
J. Org. Chem., 2004, vol. 69, p. 2436.
4. Neuvonen, H., Neuvonen, K., Koch, A., Kleinpeter, E.,
and Pasanen, P., J. Org. Chem., 2002, vol. 67, p. 6995.
5. Neuvonen, H., Neuvonen, K., Koch, A., and Pasanen, P.,
1
990, p. 311.
7
8
9
. Um, I.-H., Chun, S.-E., and Kwon, D.-S., Bull. Korean
Chem. Soc., 1991, vol. 12, p. 510.
. Leffler, J.F. and Grunwald, E., Rates and Equilibria of
Organic Reactions, New York: Wiley, 1963.
. El Seoud, O.A., Ferreira, M., Rodrigues, W.A., and
Ruasse, M.F., J. Phys. Org. Chem., 2005, vol. 18,
p. 173.
J. Org. Chem., 2004, vol. 69, p. 3794.
6. Kaninskii, P.S., Abramov, I.G., Yasinskii, O.A., Miro-
nov, G.S., and Plakhtinskii, V.V., Zh. Org. Khim., 1992,
vol. 28, p. 1232.
2
7. Landini, D. and Penso, M., J. Org. Chem., 1991,
vol. 56, p. 420; Albanese, D., Landini, D., Maia, A., and
Penso, M., J. Mol. Catal. A: Chem., 1990, vol. 150,
p. 113.
1
0. Koh, H.J., Han, K.L., Lee, H.W., and Lee, I., J. Org.
Chem., 1998, vol. 63, p. 9834.
11. Vlasov, V.M., Usp. Khim., 2006, vol. 75, p. 851.
1
2. Um, I.H. and Buncel, E., J. Org. Chem., 2000, vol. 65,
28. Khalfina, I.A., Beregovaya, I.V., and Vlasov, V.M.,
p. 577.
Russ. J. Org. Chem., 2003, vol. 39, p. 1104.
1
3. Maran, F., Seladon, D., Severin, M.G., and Vianello, E.,
29. Mil’to, V.I., Orlov, V.Yu., Mironov, G.S., and Kopei-
J. Am. Chem. Soc., 1991, vol. 113, p. 9320.
kin, V.V., Kinet. Katal., 2001, vol. 42, p. 523.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009