Reactions of aryl benzoates with potassium aryloxides: Solvent effects on reaction pathway and kinetics

Article abstract of DOI:10.1002/kin.20909

Temperature dependences of the relative reactivity of potassium aryloxides XC₆H₄O^-K⁺ toward 2,4-dinitrophenyl benzoate in 50 mol% dimethylformamide (DMF)-50 mol% H₂O mixture have been studied using the competitive reactions technique. Correlation analyses of the relative rate constants k_X/k_H and differences in the activation parameters (ΔΔCyrillic capital letter en^≠ and ΔΔS^≠) of the competitive reactions have revealed the existence of two isokinetic series of the reactions of 2,4-dinitrophenyl benzoate with potassium aryloxides with electron-donating substituent (EDS) and electron-withdrawing substituent (EWS), respectively. We have investigated the effect of the substituent X on the activation parameters for each isokinetic series and concluded that the mechanism of the reactions of 2,4-dinitrophenyl benzoate with potassium aryloxides XC₆H₄O^-K⁺ in 50 mol% DMF-50 mol% H₂O mixture is the same as in DMF. Analysis of the obtained data with using the method of two-dimensional reaction coordinate diagram leads to the conclusion that the variation of the solvent from DMF to 50 mol% DMF-50 mol% H₂O mixture affects the reaction pathway. The rate constant k_X for the reaction of 3-nitrophenyl benzoate with potassium 4-methoxyphenoxide and the relative rate constants k_X/k_H for the reaction of 3-nitrophenyl benzoate with potassium aryloxides XC₆H₄O^-K⁺ with EDS were measured in 50 mol% DMF-50 mol% H₂O mixtures at 25C, and it has been shown that the addition of water to DMF does not change the mechanism but slows down these reactions.

Full text of DOI:10.1002/kin.20909

Reactions of Aryl Benzoates
with Potassium Aryloxides:
Solvent Effects on Reaction
Pathway and Kinetics
IRINA A. KHALFINA1
,2
1N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry of Siberian Branch of Russian Academy of Sciences,
Novosibirsk, 630090, The Russian Federation
2Novosibirsk State University, Novosibirsk, 630090, The Russian Federation
Received 24 October 2014; revised 14 January 2015; accepted 16 February 2015
DOI 10.1002/kin.20909
Published online 18 March 2015 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Temperature dependences of the relative reactivity of potassium aryloxides
−
+
XC6H4O K toward 2,4-dinitrophenyl benzoate in 50 mol% dimethylformamide (DMF)–
0 mol% H2O mixture have been studied using the competitive reactions technique. Correla-
tion analyses of the relative rate constants kX/kH and differences in the activation parameters
5
ࣔ
ࣔ
(
ꢀꢀМ and ꢀꢀS ) of the competitive reactions have revealed the existence of two isokinetic
series of the reactions of 2,4-dinitrophenyl benzoate with potassium aryloxides with electron-
donating substituent (EDS) and electron-withdrawing substituent (EWS), respectively. We have
investigated the effect of the substituent X on the activation parameters for each isokinetic
series and concluded that the mechanism of the reactions of 2,4-dinitrophenyl benzoate with
−
+
potassium aryloxides XC6H4O K in 50 mol% DMF–50 mol% H2O mixture is the same as in
DMF. Analysis of the obtained data with using the method of two-dimensional reaction coor-
dinate diagram leads to the conclusion that the variation of the solvent from DMF to 50 mol%
DMF–50 mol% H2O mixture affects the reaction pathway. The rate constant kX for the reaction
of 3-nitrophenyl benzoate with potassium 4-methoxyphenoxide and the relative rate constants
−
+
kX/kH for the reaction of 3-nitrophenyl benzoate with potassium aryloxides XC6H4O K with
EDS were measured in 50 mol% DMF–50 mol% H2O mixtures at 25°C, and it has been shown
that the addition of water to DMF does not change the mechanism but slows down these
reactions. ꢀC 2015 Wiley Periodicals, Inc. Int J Chem Kinet 47: 302–314, 2015
INTRODUCTION
erable body of data on the kinetics and mechanisms of
those processes [1–28]. Two distinct mechanisms are
mainly discussed for these reactions in water, alcohol,
and aqueous mixtures of organic solvents: concerted
ANDN (the nucleophilic attack at a carbonyl center
occurs concertedly with the leaving group departure)
and stepwise AN+DN (the reaction occurs through a
tetrahedral intermediate) [1,2].
The reactions of carboxylic esters with anionic nucle-
ophiles in solution still remain the subject of extensive
studies although it has already been obtained a consid-
Correspondence to: I. Khalfina; e-mail: khalfina@nioch.nsc.ru.
ꢀ
C
2015 Wiley Periodicals, Inc.

REACTIONS OF ARYL BENZOATES WITH POTASSIUM ARYLOXIDES
303
Scheme 1
− +
6 4
of potassium aryloxides XC H O K in dimethylfor-
In a series of studies by Williams and Jencks, it was
concluded that the reactions of aryl acetates as well as
aryl formates with aryloxides in aqueous solution pro-
ceed through the concerted mechanism ANDN [3–5].
This mechanism has also been proposed for the reac-
tions of methyl aryl carbonates with aryloxides and
substituted benzenethiolates in water [6,7]. The evi-
dence mainly consisted of the absence of a break in
the Brønsted-type plot when the pKa value of the in-
coming aryloxide corresponded to that of the leaving
aryloxide. Moreover, the concerted mechanism ANDN
has been supported by the results of the kinetic isotope
effect studies in the reactions of 4-nitrophenyl acetate
mamide (DMF) [17,18]. This mechanism has been sup-
ported by enthalpy–entropy correlations and involves
four steps: (1) the nucleophilic attack of aryloxide at
the carbonyl carbon generating the tetrahedral inter-
mediate T1, (2) the intramolecular nucleophilic attack
of alkyloxide at the ipso position in the leaving group
leading to the formation of the spiro-σ-complex, (3)
the spiro ring opening with yielding the zwitterionic
intermediate T2, and (4) the departure of the leaving
group (Scheme 1) [17].
In accordance with Scheme 1, the reactions of aryl
benzoates with potassium aryloxides can be discussed
−
−
−
with OH , RO , and PhO in water [8,9] and the
in terms of a nucleophilic aromatic substitution (S Ar)
N
observation of anti-Hammond effect in the reactions
mechanism. The formation of the spiro-σ-complex is
the rate-determining step (RDS).
−
of 4-nitrophenyl substituted benzoates with OH and
−
PhO in 10% v/v MeCN−H2O mixture [10].
To shed more light on the solvent effects on the
kinetics and reaction mechanism, we carried out stud-
ies on the reactions of 3-nitro- and 2,4-dinitrophenyl
benzoates with the series of potassium aryloxides
By contrast, Buncel and Um concluded that the reac-
tions of aryl acetates with aryloxides in DMSO−H2O
mixtures and the reactions of aryl-substituted ben-
−
−
−
+
zoates with OH and CN in 20 mol% DMSO−
XC H O K in 50 mol% DMF−50 mol% H O
6
4
2
8
0 mol% H2O mixture proceed through the stepwise
mixture.
0
mechanism AN+DN because the σ constants for the
leaving group substituent exhibit a better Hammett cor-
−
relation than the σ constants [11,12]. The nonlinear
EXPERIMENTAL
Materials
Hammett plots for the reactions of aryl benzoates with
−
−
−
OH , CN , and N3 as well as the nonlinear Brønsted-
type plots for the reactions of 4-nitrophenyl-substituted
benzoates with aryloxides in 20 mol% DMSO−
2,4-Dinitro- and 3-nitrophenyl benzoates were pre-
pared as described previously [29]. Their purity was
checked by means of their melting points and spectral
8
0 mol% H2O mixture are also the argument for the
stepwise mechanism AN+DN [13,14]. A similar con-
clusion about the reaction mechanism was drawn from
kinetic studies of the reactions of aryl benzoates with
alkoxides, aryloxides, and acetophenone oximates in
absolute ethanol [15,16].
1
data such as IR and H NMR characteristics. Commer-
cial substituted phenols of chemically pure grade were
purified using standard methods. Potassium aryloxides
were prepared from the reactions of substituted phenols
with potassium methoxide in absolute methanol [30].
Water was distilled. Commercial DMF of analytical
A new type of the stepwise mechanism has been pro-
posed for the reactions of aryl benzoates PhCO2C6H4Y
˚
(
Y = H, 4-Cl, 3-NO2, 4-NO2, 2,4-(NO2)2) with a series
grade was dried over 4-A molecular sieves and distilled
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

3
04
KHALFINA
over calcium hydride under reduced pressure. The
adjusted to the same temperature and then added in
one portion. After 5 min, a sample (3–5 mL) was col-
lected in a 10-mL test tube filled with 5 mL of the
cooled mixture of diethyl ether and water (2:3). The
test tube was then shaken to stop the reaction. The or-
ganic phase was withdrawn; the aqueous phase was
extracted with diethyl ether (2×3 mL). The extracts
were combined with the organic phase, the solvent was
distilled off, and the residue was analyzed by GLC. In
each case, we found only the resulting aryl benzoates
(PhCO2C6H4X), which practically did not undergo re-
verse reactions. Because the competition reactions for
each pair of potassium aryloxides were performed at
equimolar concentrations exceeding the concentration
of the substrate by a factor of 5, the concentration ratio
of the products was directly proportional to the ratio of
the second-order rate constants for each reaction.
Potassium phenoxide was used as the reference
compound for reactions of 2,4-dinitrophenyl benzoate
with potassium 4-methoxy-, 4-methyl-, 3-methyl-, and
4-bromophenoxides; the relative rate constants kX/kH
are given in Table I (columns 1–4). We also determined
the relative rate constants k4-Br/k3-NO2 and k3-NO2/k4-CN,
whichwere recalculatedtokX/kH for potassium 3-nitro-
and 4-cyanophenoxides (Table I, columns 1–4).
5
0 Mol% DMF−50 mol% H2O mixture was prepared
by weight.
Experimental Procedures
The direct-measurement kinetic method was used to
determine the rate constants kX for the relative slow
reaction of 3-nitrophenyl benzoate with potassium 4-
methoxyphenoxide (t1/2 > 10 s). In a typical procedure,
the glass reactor was initially charged with 5 mmol
of potassium aryloxide in 50–100 mL of 50 mol%
DMF−50 mol% H2O mixture, placed in a circulating
constant temperature bath and heated to 25 ± 0.2°C.
The magnetic stirrer was turned on. The solution of
0.5 mmol of 3-nitrophenyl benzoate in 1 mL of
5
0 mol% DMF−50 mol% H2O mixture was adjusted
to the same temperature and added in one portion.
From that point, the reaction was timed. Samples were
drawn at prespecified time intervals. Approximately
10 samples were collected during the course of each
reaction. Samples (3–5 mL) were collected in 10-mL
test tubes filled with 5 mL of the cooled mixture of
diethyl ether and water (2:3). The test tubes were then
shaken to stop the reaction. The organic phase was
withdrawn; the aqueous phase was extracted with di-
ethyl ether (2×3 mL). The extractswere combined with
the organic phase, the solvent was distilled off, and the
residue was analyzed by Gas-liquid chromatography
Analogically, the relative rate constants kX/kH for
reactions of 3-nitrophenyl benzoate with potassium
4-methoxy-, 4-methyl-, and 3-methylphenoxides in
50 mol% DMF−50 mol% H2O mixture at 25°C were
measured (Table II, columns 1–3, row 1).
(GLC).
The pseudo–first-order rate constants (kobs) were
obtained from the linear plots of ln(Aꢀ – At) vs. t,
which were linear up to 90% of the reactions. Four
different nucleophile concentrations were used to de-
termine the second-order rate constant (kX) from the
slope of the linear plot of kobs vs. potassium arylox-
ide concentration, which showed near-zero intercepts,
indicating that potassium aryloxide does not exist as
dimers or other aggregates [31] the correlation co-
efficient of the plot was 0.998 (Table II, column 1,
row 1).
Analysis
Samples were analyzed by GLC using an LKhM-72
gas chromatograph equipped with a thermal conduc-
tivity detector (4000×4-mm column packed with 15%
of SKTFT-803 on Chromaton-W, carrier gas—helium,
the linear oven temperature programmed from 70 to
270°C at a rate of 10 deg/min); the components were
quantitated by the absolute calibration technique us-
ing calibration plots and identified by adding authentic
samples.
It was difficult to use this direct kinetic method
for studying fast reactions. The relative rate constants
kX/kH for the fast reactions of 2,4-dinitrophenyl ben-
zoate with potassium aryloxides in 50 mol% DMF−
RESULTS AND DISCUSSION
50 mol% H2O mixture were determined using the com-
Hammett and Brønsted Correlations
petitive reactions technique [17,18]. In a typical run,
the solution of a pair of potassium aryloxides with the
pKa values being larger than that of the leaving ary-
loxide (2.5 mmol + 2.5 mmol) in 50 mL of DMF was
placed in a glass reactor equipped with a magnetic
stirrer and heated to the desired temperature. The so-
lution of 0.5 mmol of 2,4-dinitrophenyl benzoate in
The reactivity–selectivity correlations are permanently
utilized to interpret the mechanisms of acyl-transfer re-
actions [3–7,10–16,19]. Earlier, we reported about the
concave downward Hammett-type plot with a break at
−
σ (Х) ꢁ 0 (ρ electron-donating substituents (EDS) >
0 and ρ electron-withdrawing substituents (EWS) < 0),
1
mL of 50 mol% DMF−50 mol% H2O mixture was
which is the characteristic feature for the reactions of
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

REACTIONS OF ARYL BENZOATES WITH POTASSIUM ARYLOXIDES
305
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

3
06
KHALFINA
Table II Relative Rate Constants kX/kH, Rate Constants kX and Selectivity Parameters (ρ(EDS) and βNuc(EDS)) for
Reactions of 3-Nitrophenyl Benzoate with Potassium Aryloxides with EDS in 50 mol% DMF−50 mol% H2O Mixture and
DMF at 25°C
X
Solvent
4-MeO
1
4-Me
2
3-Me
3
H
4
ρ(EDS)
βNuc(EDS)
5
6
d
ꢁ0.4e
1
2
DMF– H2O
kX/kH
1.35 ± 0.05
1.08 ± 0.04 0.86 ± 0.04
1
−0.98 ± 0.01
−1 −1
−2a
−2b
−2b
−2b
kX (М
s
)
14.0 ± 0.6 × 10
10.5 × 10
8.3 × 10
6.6 × 10
DMF
kX/kHc
1.47
1.84
5.06 × 10
2.32
6.38 × 10
1
0.99
−0.22
c
−1 −1
2
2
2
2
kX (М
s
)
4.04 × 10
2.75 × 10
a
The rate constants k
The rate constants k
Data are taken from [17].
X
X
were calculated by the direct-measurement kinetic method.
were calculated using the relative rate constants k /k
b
c
d
e
X
H
.
r 0.999.
DMF
H2O
H2O
Nuc
DMF
The βNuc(EDS) value at 25°С was estimated as 2/(1/βNuc + 1/βNuc ); β
= 1.33 ± 0.63, r 0.903; βNuc = 0.22 ± 0.01, r 0.998.
Therefore, for the reactions of 2,4-dinitrophenyl
benzoate with potassium aryloxides XC6H4O K in
0
,5
,0
−
+
0
5
0 mol% DMF−50 mol% H2O mixture, the Hammett-
−
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
−
type plot has the break at σ (Х) ꢁ 0, too. Moreover, the
curvature in the Hammett-type plot is concave down-
ward because the negative value of ρ(X) reduces when
the substituent X is changed from EDS to EWS. The
−
−
−
−
−
−
−
−
2
,4-(NO2)
2
−
lg(kX/kH) vs. σ (Х) plots for the corresponding reac-
3
-NO2
tions in 50 mol% DMF−50 mol% H O mixture at 25°С
2
4
-NO2
1,2
are shown in Fig. 2a: ρ(EDS) = −0.83 and ρ(EWS)
−
2.31. As a rule, a concave downward Hammett-type
plot has been interpreted as a change in RDS within
the stepwise mechanism [33]. However, we concluded
that a change in the structure of the transition state for
the RDS (TS) is responsible for the nonlinear Hammett
plot found for these reactions [17].
−
0,4
−0,2
0,0
0,2
0,4
0,6
0,8
1,0
1,4
–
σ
(X )
Figure 1 Hammett-type plots for the reactions of 3-nitro-,
-nitro-, and 2,4-dinitrophenyl benzoates with potassium ary-
loxides XC6H4O K in DMF at 25°C [17,18].
4
−
+
An excellent linear correlation (r = 0.999) has also
−
been obtained in the lg(kX/kH) vs. σ (Х) plot for the
3
-nitro-, 4-nitro-, and 2,4-dinitrophenyl benzoates with
reactions of 3-nitrophenyl benzoate with a series of
−
+
potassium aryloxides XC6H4O K in DMF proceeded
through the four-step mechanism (Fig. 1) [17,18]. To
study the reactions of 2,4-dinitrophenyl benzoate with
potassium aryloxides in 50 mol% DMF−50 mol%
H2O mixture, we used the relative rate constants kX/kH.
Excellent linear correlations (r ࣙ 0.999) have been
potassium aryloxides with EDS in 50 mol% DMF−
50 mol% H O mixture at 25°С (Fig. 2a): ρ(EDS) =
2
−0.98. As shown in Fig. 2a, the point for potassium
phenoxide exhibits deviation from the linearity, i.e.
−
this Hammett-type plot has the break at σ (Х) ꢁ 0,
too.
−
obtained in the lg(kX/kH) vs. σ (Х) plots for the re-
It should be emphasized that the addition of water
to DMF changes a sign of the ρ(EDS) values for the
reaction series of 2,4-dinitro- and 3-nitrophenyl ben-
zoates with potassium aryloxides with EDS; e.g., it
decreases from 0.49 [18] to −0.83 (Table I, column 7,
row 1) and from 0.99 [17] to −0.98 (Table II, column
5, row 1) at 25°С, respectively. Traditionally, it is in-
terpreted as a variation in the reaction mechanism [34].
But, in line with Scheme 1 the key feature of the TS
structure is that the entering group substituent X oppo-
sitely influences the O- and C-reaction centers [17]. As
actions of 2,4-dinitrophenyl benzoate with a series of
potassium aryloxides with EDS (EWS) at four temper-
atures (0, 25, 40, and 50°C). As can be seen from Table
I (column 7, rows 1,2), the ρ(X) values are negative
for both reaction series in the range 0–50°C. Since in-
creasing the temperature decreases the magnitude of
ρ(EDS) but increases it of ρ(EWS), so these parame-
ters in 50 mol% DMF−50 mol% H2O mixture as well
as in DMF are controlled by enthalpic and entropic
factors, respectively [18].
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

REACTIONS OF ARYL BENZOATES WITH POTASSIUM ARYLOXIDES
307
0
,5
,0
a
0,5
b
0
0,0
3
-NO2
−0,5
−1,0
−1,5
−2,0
−
0,5
−1,0
−1,5
−2,0
2
,4-(NO2)2
4
-NO2
2
,4-(NO2)2
−0,4
−0,2
0,0
0,2
0,4
0,6
0,8
1,0
1,2
−0,4
−0,2
0,0
0,2
0,4
0,6
0,8
1,0
1,2
–
σ
–
σ
(X )
(X )
Figure 2 (a) Hammett-type plots for the reactions of 2,4-dinitro- and 3-nitrophenyl benzoates with a series of potassium
aryloxides with EDS and for the reactions of 2,4-dinitrophenyl benzoate with a series of potassium aryloxides with EWS in
5
0 mol% DMF−50 mol% H2O mixture at 25°C (solid lines). (b) Hammett-type plots for the reactions of 2,4-dinitrophenyl
benzoate with potassium aryloxides in 50 mol% DMF−50 mol% H2O mixture at 25°C (solid line). The dashed line is Hammett-
type plot for the reactions of 4-nitrophenyl benzoate with potassium aryloxides in 20 mol% DMSO−80 mol% H2O mixture at
2
5°C (the rate constants k4-MeO, k4-Me, kH, k4-Cl, and k4-CN are estimated from the Brønsted-type plot [14] and recalculated to
kX/kH).
a consequence, the sign of ρ(EDS) can change from
positive to negative if the effect of the substituent X on
the O-reaction center becomes more than that on the C-
reaction center. On the other hand, the addition of water
to DMF decreases the magnitude of the ρ(EWS) value
for the reaction series of 2,4-dinitrophenyl benzoate
with potassium aryloxides with EWS; e.g., it changes
from −2.99 [17] to −2.31 (Table I, column 7, row 2) at
Um et al. also reported that the excellent Brønsted-
type correlation with using the pKa values of phe-
nols in water has been obtained for the reactions of
4-nitrophenyl benzoate with potassium aryloxides in
20 mol% DMSO−80 mol% H2O mixture at 25°С;
H2O
Nuc
β
= 1.04 [14].
The good linear correlation (r = 0.987) has been
obtained in the single lg(kX/kH) vs. pKa(H2O) plot for
2
5°С. If the reactivity–selectivity principle (RSP) held
the reactions of 2,4-dinitrophenyl benzoate with potas-
it would mean that the reactivity of the reactants in-
creases with adding water [35]. However, we reported
that for the reactions of aryl benzoates with potassium
aryloxides with EWS in DMF the RSP fails [17].
Despite the fact that two reaction series have been
found, a good linear correlation (r = 0.988) has been
sium aryloxides in 50 mol% DMF−50 mol% H2O
H2O
Nuc
mixture at 25°С; β
= 0.95 (Table I, column 2).
The worse linear correlations (r ࣙ 0.864) have been
obtained in the lg(kX/kH) vs. pKa(H2O) plots for both
reaction series at 0, 25, 40, and 50°C (Table I, col-
H2O
H2O
umn 8, rows 1,2);βNuc (EDS) = 1.11 and βNuc (EWS)
= 1.26 at 25°С.
−
obtained in the single lg(kX/kH) vs. σ (Х) plot for the
reactions of 2,4-dinitrophenyl benzoate with potassium
On the other hand, if the pK values of phenols in
a
aryloxides in 50 mol% DMF−50 mol% H2O mixture at
DMF are used the better linear correlations will be
obtained in the corresponding plots, but the Brønsted
coefficient values will dramatically decrease (Table I,
2
5°С; ρ(X) = −1.86 (Table I, column 2; Fig. 2b). Sim-
ilarly, Um et al. informed about the good linear Ham-
mett correlation with ρ(X) = −1.96 for the reactions
of 4-nitrophenyl benzoate with potassium aryloxides
in absolute ethanol at 25°С [15]. Moreover, the excel-
lent linear correlation (r = 0.999) in the lg(kX/kH) vs.
DMF
column 8, rows 1,2); e.g., β
(EDS) = 0.18 and
Nuc
DMF
β
(EWS) = 0.51 at 25°С. The good linear corre-
Nuc
lation (r = 0.988) has also been obtained in the single
DMF
lg(k /k ) vs. pK (DMF) plot at 25°С; β
Nuc
X
H
a
= 0.41
−
σ (Х) plot can be obtained, if the rate constants mea-
(Table I, column 2).
sured for the reactions of 4-nitrophenyl benzoate with
potassium aryloxides in 20 mol% DMSO−50 mol%
H2O mixture at 25°С are used [14]; ρ(X) = −1.89
Obviously, to obtain the correct βNuc values, we
should use the pK values of phenols in 50 mol%
a
DMF−50 mol% H O mixture, but those are not known.
2
(
Fig. 2b). The stepwise mechanism AN+DN with a
Nevertheless, Buncel et al. reported that the pK val-
a
formation of the tetrahedral intermediate being RDS
has been proposed for these reactions [14,15].
ues for phenols in DMSO−H O mixtures monoton-
2
ically increase with decreasing the concentration of
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

3
08
KHALFINA
ꢁ=
ꢁ
ꢁ=
H
water and in each case the pKa value in 50 mol%
DMSO−50 mol% H2O mixture is slightly less than
and ꢀꢀS = ꢀS −ꢀS obtained by the Eyring-
X
type equation are summarized in Table I (columns
,6). As can be seen from Table I, the magnitudes
of ꢀꢀH (column 5, rows 1,2) and ꢀꢀS (col-
umn 6, rows 1,2) significantly increase when the sub-
stituent X is changed from EDS to EWS. The vari-
ation of the solvent from DMF to 50 mol% DMF
(
pKa (DMSO) + pKa (H2O))/2 [11]. If it holds for phe-
5
nols in DMF−H2O mixtures, the 1/βNuc value can be
ꢁ
ꢁ=
DMF
Nuc
H2O
)/2. Then, βNuc(EDS)
Nuc
estimated as (1/β
ꢁ
+ 1/β
0.3, βNuc(EWS) ꢁ0.7 (Table I, column 8, rows 1,2),
and βNuc ꢁ0.6 at 25°С (Table I, column 2), and these
values are in accordance with the concerted mecha-
nism [6,37]. Analogically, the βNuc(EDS) value for
the reactions of 3-nitrophenyl benzoate with potassium
aryloxides with EDS in 50 mol% DMF−50 mol% H2O
mixture is ꢁ0.4 (Table II, column 6, row 1).
ࣔ
ࣔ
−
50 mol% H2O mixture affects the ꢀꢀH and ꢀꢀS
ࣔ
ࣔ
values, e.g., the ꢀꢀH (4-CN) and ꢀꢀS (4-CN) val-
ues change from −87.6 [18] to −81.5 (Table I, column
5
(
, row 2) kJ/mol and from −280.4 [18] to −312.8
Table I, column 6, row 1) J/(mol·K), respectively,
Therefore, analysis of the Hammett- and Brønsted-
type correlations for the reactions of 2,4-dinitro- and
ࣔ ࣔ
and the ꢀꢀH (4-MeO) and ꢀꢀS (4-MeO) values
change from 6.6 [18] to −2.99 (Table I, column 5, row
3-nitrophenyl benzoates with potassium aryloxides
1
) kJ/mol and from 23.5 [18] to −5.5 (Table I, col-
in 50 mol% DMF−50 mol% H2O mixture leads
to contradictory conclusions concerning the reaction
mechanism.
umn 6, row 1) J/(mol·K), respectively. Interestingly,
the addition of water to DMF increases the magni-
ࣔ
ࣔ
ࣔ
tudes of ꢀꢀH (4-CN)/ꢀꢀH (4-MeO) and ꢀꢀS (4-
CN)/ꢀꢀS (4-MeO) from 13.3 to 27.2 and from
ࣔ
1
1.9 to 56.9, respectively, although it decreases the
Isokinetic and Compensation Effects
ࣔ
ࣔ
magnitude of (ꢀꢀH (4-CN) − ꢀꢀH (4-MeO)) by
ࣔ
Each reaction series has been tested in terms of the
isokinetic and compensation effects [39–42]. The ex-
istence of the isokinetic relationship (IKR) can serve as
an argument that the reaction series follow a common
mechanism [43–46].
15.7 kJ/mol and increases the magnitude of (ꢀꢀS (4-
ࣔ
CN) − ꢀꢀS (4-MeO)) only by 4.3 J/(mol·K).
The intersections of the linear plots of lg(k /k ) vs.
X
H
1/T near the same point for each reaction series can
be considered as an argument for the existence of the
IKR (Table III, column 1, rows 1,2). The Tiso values
determined from the lg(k /k )−1/T, ρ(X)−1/T [47],
Good linear correlations (r ࣙ 0.989) obtained in
the plots of lg(kX/kH) vs. 1/T for the reactions of
X
H
2,4-dinitrophenyl benzoate with both series of potas-
β
−1/T , and lg(k /k ) −lg(k /k ) [48] plots dif-
Nuc
X
H T2
X
H T1
sium aryloxides in 50 mol% DMF−50 mol% H2O
mixture suggest that all the reactions follow the Ar-
rhenius temperature dependence. The differences in
fer slightly (Table III, columns 1–4, rows 1,2), which
is better evidence for the existence of the IKR [49].
The compensation temperature Тcomp values for
the isokinetic series determined from the slopes of
ꢁ
ꢁ
ꢁ
the activation parameters ꢀꢀH = ꢀH −ꢀH
X
H
Table III Isokinetic Temperatures Tiso Determined from Four Dependences and Compensation Temperatures Тcomp
−
+
for Reactions of 2,4-Dinitrophenyl Benzoate with Potassium Aryloxides XC6H4O K in 50 mol% DMF−50 mol% H2O
Mixture
Tiso (K)
Тcomp (K)
ꢀꢀHࣔ − ꢀꢀSࣔ e
5
X
lg(kX/kH) −1/T а
ρ(X) −1/T
b
βNuc −1/T
c
lg(kX/kH)T2 − lg(kX/kH)T1
d
1
2
3
4
1
2
EDSf
EWS
406
254
406
255
400
255
407
255
404
255
g
a
b
c
d
e
f
T
iso is the temperature of intersection of the plots lg(k
X
/k
H
)−1/T.
T
iso is calculated from the equation ρ (X) = const(1− Tiso /T).
DMF
Nuc
Tiso is calculated from the equation β
= const(1− Tiso /T).
X H X
Tiso is calculated from the equations lg(k
/k
)
T2 = a + b lg(k
/k
H
)
T1 and Tiso = T
2
T
1
(b − 1)/(bT
2 1
– T ).
ꢁ
ꢁ=
Т
comp is calculated from the equation ꢀꢀH = const + ТcompꢀꢀS .
DMF
Nuc
Tiso = 406 K s = 6; ρ(Х) = (2.33 ± 0.09) − (946 ± 28)/Т (r = 0.999, s = 0.012, n = 4); β
= −(0.53 ± 0.02) + (212 ± 7)/Т (r =
= 323 K (r = 0.999, s = 0.010, n = 3);
0
ꢀ
.999, s = 0.003, n = 4); lg(k
Х
/k /k T1 for T
H
)
T2 = (0.046 ± 0.001) + (0.53 ± 0.01)lg(k
Х
H
)
1
= 273 K, T
2
ꢁ=
3
ꢁ=
ꢀH = −(0.76 ± 0.02) + (0.404 ± 0.004) × 10 ꢀꢀS (r = 0.999, s = 0.025, n = 3).
g
DMF
Nuc
Tiso = 254 K s = 2; ρ(X) = −(15.98 ± 0.15) + (4075 ± 45)/Т (r = 0.999, s = 0.019, n = 4); β
= (3.48 ± 0.05) – (886 ± 14)/Т (r =
= 323 K (r = 0.998, s = 0.107, n =
0
3
.999, s = 0.006, n = 4); lg(k
Х
/k
H
)
T2 = −(0.819 ± 0.094) + (3.21 ± 0.19)lg(k
Х
/k
H
)
T1 for T
1
= 273 K, T
2
ꢁ=
3
ꢁ=
); ꢀꢀH = – (1.92 ± 0.26) + (0.255 ± 0.001) ×10 ꢀꢀS (r = 0.999, s = 0.187, n = 3).
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

REACTIONS OF ARYL BENZOATES WITH POTASSIUM ARYLOXIDES
309
ꢁ
=
ꢁ
ࣔ
ࣔ
theꢀꢀH vs. ꢀꢀS plots are also summarized in Ta-
ble III (column 5). A similarity of the Тcomp and Tiso
values for each of the reaction series suggests that the
compensation and isokinetic effects can be synony-
mous [43].
DMF, but the negative δꢀH (EDS) and δꢀS (EDS)
values characterize the reactions of 4-chloro-, 2,4-
dinitro-, and unsubstituted phenyl benzoates with
potassium aryloxides with EDS in DMF [17]. The
ࣔ
same solvent variation decreases the δꢀH (EWS) and
δꢀS (EWS) values from –36.9 to –77.9 kJ/mol and
ࣔ
For all the isokinetic series in the current study, the
Tiso values are positive, but Тexp < Tiso for the isokinetic
series with EDS and Тexp > Tiso for the isokinetic series
with EWS, i.e. the effects of the entering group sub-
stituent X on the reactivity are controlled by enthalpic
and entropic factors, respectively [39–42,50].
The δꢀH and δꢀS reaction constants, which can
be used for the characterization of the electronic and
steric effects of the substituents on the reactivity, are the
from –185.1 to –305.9 J/(mol·K), respectively (Table
IV, columns 1,2, rows 2,4). Analogically, the negative
ࣔ
ࣔ
δꢀH (EWS) and δꢀS (EWS) values obtained for the
reactions of aryl benzoates with potassium aryloxides
with EWS in DMF decrease when the leaving group
substituent is changed from 4-NO2 to 3-NO2 and 2,4-
(NO2)2 [17,18]. It should be emphasized that the addi-
tion of water to DMF increases the Tiso value for each
of the isokinetic series (Table IV, column 3, rows 1,3
and 2,4).
ࣔ
ࣔ
ꢁ
ꢁ
ꢁ
ꢁ=
slopes of the ꢀH and ꢀS (or ꢀꢀH and ꢀꢀS )
vs. σ (Х) plots, respectively [39–41,49].
−
Good linear correlations (r ࣙ 0.993) have been ob-
Earlier, we concluded that the variation of the leav-
ing group substituent does not change the reaction
mechanism but affects the TS structure [17]. The same
conclusion can be drawn about the variation of solvent
from DMF to 50 mol% DMF−50 mol% H2O mixture.
ꢁ
ꢁ
−
tained in the ꢀꢀH and ꢀꢀS vs. σ (Х) plots for
each isokinetic series. The δꢀH and δꢀSࣔ values
determined from the slopes of the corresponding plots
are summarized in Table IV (columns 1,2; rows 1,2).
These reaction constants have also been determined
from the slopes and intersections, respectively, of the
linear plots of ρ(X) vs. 1/T. The results obtained inde-
ࣔ
Hammond and anti-Hammond Effects
ࣔ
pendently are close, and so the validity of the δꢀH
We have employed a two-dimensional reaction coordi-
nate diagram, also known as a More O’Ferrall–Jencks
diagram, to explain the substituent effect on the TS
structure [51,52]. In the present study we used the
More O’Ferrall–Jencks diagram to interpret the sol-
vent effect on the TS structure.
ࣔ
and δꢀS values are confirmed. Table IV ( columns
1
,2; rows 3,4) also contains previously published data
for the reactions of 2,4-dinitrophenyl benzoate with
potassium aryloxides in DMF [18].
As can be seen from Table IV (columns 1,2; rows
ࣔ
ࣔ
1
,3), the δꢀH (EDS) and δꢀS (EDS) values in-
As shown in Fig. 3, in the two-dimensional reaction
coordinate diagram the reactants are depicted in the
0,0 corner, the spiro-σ-complex is in the 1,1 corner,
crease from –21 to 18 kJ/mol and from –61.5 to
4
4.5 J/(mol·K), respectively, when the solvent is
ꢂ
−
+
changed from DMF to 50 mol% DMF−50 mol%
the tetrahedral intermediate Ph(Ar O)C(OAr)−O K
ꢂ
H2O mixture. It should be noted that the positive
(Ar = 2,4-(NO2)2C6H3, Ar = X-C6H4) is in the 1,0
ࣔ
ࣔ
−
+
δꢀH (EDS) and δꢀS (EDS) values have been ob-
tained for the reactions of 4-nitro- and 3-nitrophenyl
benzoates with potassium aryloxides with EDS in
corner, and the zwitterionic intermediate and ArO K
are in the 0,1 corner. The CAr−O bond formation pro-
ceeds along the y-axis, and the C−O bond formation
ꢁ
ꢁ=
Table IV Isokinetic Temperature Tiso and Reaction Constants δꢀH and δꢀS for Reactions of 2,4-Dinitrophenyl
−
+
Benzoate with Potassium Aryloxides XC6H4O K in 50 mol% DMF − 50 mol% H2O Mixture and DMF
ꢁ
ꢁ
δꢀH (kJ/mol)
δꢀS (J/(mol·K))
Tiso (К)
X
Solvent
1
2
3
1
2
EDSa
EWSb
DMF−H2O
18.0 (18.1)
−77.9 (78.0)
44.5 (44.6)
−305.9 (305.7)
405
255
3
4
EDSc
DMF
−21.0
−61.5
345
215
c
EWS
−36.9
−185.1
aδꢀH is the slope of the plot ꢀꢀH vs. σ (X); ꢀꢀH = (1.9 ± 0.1) + (18.0 ± 0.2)σ (X) (r = 0.999, s = 0.024, n = 3). δꢀS is the
ꢁ
=
ꢁ
−
ꢁ
−
ꢁ=
ꢁ
−
ꢁ
−
slope of the plot ꢀꢀS vs. σ (X); ꢀꢀS = (6.5 ± 0.2) + (44.5 ± 0.9)σ (X) (r = 0.999, s = 0.122, n = 3). Data in the brackets are obtained
from the dependence ρ(X) − 1/T (Table III). The average value of Tiso is taken from Table III (columns 1–4, row 1).
b
c
ꢁ=
δꢀH
Data are taken from [18].
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

3
10
KHALFINA
C–O bond order
NO
2
NO
2
K+
NO
O
XC H O
O
−
+
6
4
O
O K
(
0,0)
(0,1)
NO
+
−
2
(1,0)
(1,1)
−
2
Ph
O
Ph
O
O
O
Ph
O N
O N
NO2
2
2
XC H O
O N
+
6 4
2
+
-
+
- +
XC
6
H
4
O K
6 4
XC H O K
Figure 3 More O’Ferrall–Jencks diagram for two steps of mechanism for the reactions of 2,4-dinitrophenyl benzoate with
potassium aryloxides [17]. The positions of TS in DMF and 50 mol% DMF−50 mol% H2O mixture are represented by points
(
·) and (ο), respectively (see text for discussion). The effects of the electronic nature of the entering group substituent X on the
relative energies at the 0,1, 1,0, and 1,1 corners in DMF (EDS and EWS) and 50 mol% DMF−50 mol% H2O mixture (EDS*
and EWS*) are shown.
ࣔ
ࣔ
proceeds along the x-axis. The reaction pathway rep-
resenting a stepwise process traverses near the edges
of the More O’Ferrall–Jencks diagram; TS is located
at a saddle point on the right-hand limb of the path-
way. The TS motion can be discussed in terms of two
vectors, one along the reaction coordinate (a normal
Hammond effect [53]) and one perpendicular to it (an
anti-Hammond effect [54]).
The negative δꢀH and δꢀS values, which char-
acterize early TS, suggest that the substituent sensitiv-
ity of the C-reaction center is higher than that of the
O-reaction center. However, the TS movement along
the reaction coordinate toward the spiro-σ-complex re-
duces the substituent sensitivity of the C-reaction cen-
ter due to an increase in the magnitude of its positive
charge. Obviously, in some point the substituent sen-
sitivity of the O-reaction center becomes higher than
that of the C-reaction center and it reverses the sign of
the δꢀHࣔ and δꢀSࣔ values. It should be noted that
Because the entering group substituent X in the TS
structure oppositely influences the O- and C-reaction
centers, each reaction parameter is determined by the
two opposite contributions. The ratio of these contri-
butions changes with varying the TS structure. Earlier,
we discussed how the TS movements along or perpen-
ࣔ
the Hammond effect on the reaction parameter δꢀH
should be more than that on δꢀS because the isoki-
netic temperature T , which is the δꢀH /δꢀS ratio,
increases with the TS movement along the reaction
ࣔ
ࣔ
ࣔ
iso
ࣔ
dicular to the reaction coordinate affect the Tiso, δꢀH ,
ࣔ
and δꢀS values [17].
coordinate away from the 1,0 corner [17].
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

REACTIONS OF ARYL BENZOATES WITH POTASSIUM ARYLOXIDES
311
ࣔ
ࣔ
Figure 4 Effects of the variations of the TS structure on the δꢀH , δꢀS , and Tiso values [17].
On the other hand, the TS movement perpendicular
to the reaction coordinate away from the 1,0 corner,
which not only increases the magnitude of the charge
on the C-reaction center but and decreases the magni-
tude of the charge on the O-reaction center (Fig. 4),
the variation of the substituent X from EWS to EDS
in the case of 50 mol% DMF−50 mol% H2O mix-
ture moves TS not only along but also perpendicu-
lar to the reaction coordinate away from the 1,0 cor-
ner (see above). Similarly, the variation of the solvent
from DMF to 50 mol% DMF−50 mol% H2O mix-
ࣔ
ࣔ
increases the δꢀH and δꢀS parameters from neg-
ative values to positive, too [17]. However, the anti-
ࣔ
ࣔ
ture increases the δꢀH (EDS) and δꢀS (EDS) values
by 39 kJ/mol and 106 J/(mol·K), respectively, but the
Tiso(EDS) value only by 60 K (Table IV, columns 1–3,
rows 1,3). It follows that adding water to DMF moves
TS(EDS) mainly along and additionally perpendicular
to the reaction coordinate away from the 1,0 corner.
On the other hand, the variation of the solvent from
DMF to 50 mol% DMF−50 mol% H2O mixture in-
ࣔ
Hammond effect on the reaction parameter δꢀH
ࣔ
should be less than that on δꢀS because the isoki-
netic temperature Tiso decreases with the TS movement
perpendicular to the reaction coordinate away from the
1,0 corner [17]. It may be assumed that the TS move-
ments along and perpendicular to the reaction coordi-
nate away from the 1,0 corner oppositely influence the
Tiso value, but both these TS movements increase the
ࣔ
ࣔ
creases the δꢀH (EWS) and δꢀS (EWS) values by
41 kJ/mol and 120.8 J/(mol·K), respectively, but de-
creases the Tiso(EWS) value only by 40 K (Table IV,
columns 1–3, rows 2,4). It can be assumed that adding
water to DMF moves TS(EWS) mainly perpendicu-
lar to and additionally along the reaction coordinate
toward the 1,0 corner.
ࣔ
ࣔ
δꢀH and δꢀS values.
As can be seen from Table IV that the variation of
the substituent X from EWS to EDS in the reactions
of 2,4-dinitrophenyl benzoate with potassium arylox-
ࣔ
ࣔ
ides increases the δꢀH , δꢀS , and Tiso values by
1
5.9 kJ/mol, 123.6 J/(mol·K), and 130 K, respectively,
−
+
ꢂ
−
+
in DMF ( columns 1–3, rows 3,4) and by 95.9 kJ/mol
and 350.4 J/(mol·K), 150 K, respectively, in 50 mol%
DMF−50 mol% H2O mixture ( columns 1–3, rows
Because ArO K and Ph(Ar O)C(OAr)−O K
are depicted in the 0,1 and 1,0 corners, respectively,
we assume that the variation of the substituent X from
EWS to EDS increases but the addition of water to
DMF decreases the relative energies at these corners.
Buncel et al. reported that the pKa values of phenols
in DMSO−H2O mixtures increase monotonically with
an increase in the concentration of the organic solvent,
and a change in the pKa value of phenol with EWS is
less than that in the pKa value of phenol with EDS [11].
If it holds for phenols in DMF−H2O mixtures, the sta-
bilizing effect of the addition of water to DMF on the
1,2). Using the proposed approach, we can conclude
that in each case TS shifts along the reaction coor-
dinate away from the 1,0 corner, and, moreover, the
Hammond effect increases with the addition of water
to DMF.
However, adding water to DMF increases strongly
ࣔ
ࣔ
the values of |δꢀH (EWS) − δꢀH (EDS)| and
ࣔ
ࣔ
|
δꢀS (EWS) − δꢀS (EDS)| but insignificantly the
value of |Tiso(EWS) − Tiso(EDS)|. It can be realized if
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

3
12
KHALFINA
relative energy at the 0,1 corner will increase when the
substituent X is changed from EWS to EDS. More-
These considerations lead to conclusion that the
electronic nature of the substituent X affects the sta-
bility of the spiro-σ-complex more than the stabilities
−
+
over, such a solvent variation stabilizes ArO K with
ꢂ
−
+
−
+
ꢂ
−
+
EWS less than Ph(Ar O)C(OAr)−O K with EWS
due to the delocalization of a negative charge by the
resonance interaction. For the same reason, the solvent
variation from DMF to 50 mol% DMF−50 mol% H2O
mixture should slightly influence the stability of the
zwitterionic intermediate which is also depicted in the
of ArO K and Ph(Ar O)C(OAr)−O K , and this ef-
fect increases with the addition of water to DMF. More-
over, the variation of the solvent from DMF to 50 mol%
−
+
DMF−50 mol% H2O mixture stabilizes ArO K with
EDS much more than the spiro-σ-complex with EDS,
−
+
but ArO K with EWS much less than the spiro-σ-
complex with EWS, and as a result it shifts TS(EDS)
mainly in the Hammond direction but TS(EWS) mainly
in the anti-Hammond direction.
0,1 corner.
In line with the ideas about the Hammond and anti-
Hammond effects for the More O’Ferrall–Jencks dia-
gram, different changes in the relative energies at the
Therefore, using the proposed approach we inter-
preted the solvent effect on the TS structure and stabil-
ities of the intermediates, i.e. on the reaction pathway.
1,0 and 1,1 corners will move TS along the reaction
coordinate toward the corner of increasing relative en-
ergy and different changes in relative energies at the
0
,1 and 1,0 corners will move it perpendicular to the
Solvent Effect on Reactivity
reaction coordinate away from the corner of increasing
relative energy [2].
It has been previously remarked that the reactions of
aryl benzoate with potassium aryloxides in DMF are
faster than those in 20 mol% DMSO−80 mol% H2O
mixture [17]. For example, the rate constants kX for
the reactions of 4-nitrophenyl benzoate with potas-
sium 4-methoxy-, 4-chlorophenoxides, and unsubsti-
tuted phenoxide at 25°С were determined to be 2.07 ×
Then, the variation of the substituent X from EWS
to EDS in the reactions of 2,4-dinitrophenyl benzoate
with potassium aryloxides in DMF increases the rela-
tive energy at the 1,0 corner as well as at the 0,1 corner
but less than at the 1,1 corner, and as a consequence,
TS moves along the reaction coordinate away from the
3
2
3
−1 −1
1,0 corner (Fig. 3).
10 , 5.95 × 10 , and 3.50 × 10 M
s
, respectively,
−
1
−1
On the other hand, the variation of the solvent from
in DMF [17] and ꢁ1.3, 1.7 × 10 and 3.6 × 10
−
1
−1
DMF to 50 mol% DMF−50 mol% H2O mixture for
the isokinetic series with EDS decreases the relative
energy at the 1,0 corner little less than at the 0,1 cor-
ner but much more than at the 1,1 corner causing the
TS(EDS) movements mainly along and additionally
perpendicular to the reaction coordinate away from the
M
s
, respectively, in 20 mol% DMSO−80 mol%
H2O mixture (the data are estimated from the Brønsted-
type plot [14]), i.e. these reactions are slowed down in
ꢁ1560, 3500, and 9700 times, respectively, when the
solvent is changed from DMF to 20 mol% DMSO−
80 mol% H2O mixture.
1
,0 corner (Fig. 3). The same variation for the isoki-
Because the fast reactions of 2,4-dinitrophenyl
−
+
netic series with EWS decreases the energy at the 1,0
corner much more than at the 0,1 corner but little less
than at the 1,1 corner causing the TS(EWS) move-
ments mainly perpendicular to and additionally along
the reaction coordinate toward the 1,0 corner (Fig. 3).
As can be seen from Fig. 3, the variation of the
substituent X from EWS to EDS in the reactions of
benzoate with potassium aryloxides ArO K cannot
be studied by the direct kinetic method, we deter-
mined the rate constant kX for the relative slow re-
action of 3-nitrophenyl benzoate with potassium 4-
methoxyphenoxide in 50 mol% DMF−50 mol% H2O
−
1
−1 −1
M s (Table II,
mixture at 25°С; kX is 1.40 × 10
column 1, row 1). The rate constant kH for the reac-
tion of 3-nitrophenyl benzoate with potassium unsub-
stituted phenoxide in 50 mol% DMF−50 mol% H2O
mixture at 25°С was calculated with using the relative
2,4-dinitrophenyl benzoate with potassium aryloxides
in 50 mol% DMF−50 mol% H2O mixture increases
the relative energy at the 1,0 corner much less than
the relative energy at the 1,1 corner but more than the
relative energy at the 0,1 corner. Such changes in the
energies at the 0,1, 1,0, and 1,1 corners shift TS along
and perpendicular to the reaction coordinate away from
the 0,1 corner (Fig. 3). It should be noted that the mag-
nitudes of the TS movements along and perpendicular
to the reaction coordinate caused by the variation of
the substituent X from EWS to EDS increase when
the solvent is changed from DMF to 50 mol% DMF−
−2
−1 −1
rate constant k4-MeO/kH to be 6.57 × 10
M s
(Table II, column 4, row 1). The rate constants kX for
these reactions in DMF were determined to be 4.04 ×
2
2
−1 −1
s
10 and 2.75 × 10 M
at 25°С [17]. Thus, the
reactions of 3-nitrophenyl benzoate with potassium 4-
methoxyphenoxide and unsubstituted phenoxide are
slowed down in ꢁ 3000 and 4200 times, respectively,
when the solvent is changed from DMF to 50 mol%
DMF−50 mol% H2O mixture. We assume that the re-
actions of 2,4-dinitrophenyl benzoate with potassium
5
0 mol% H2O mixture.
International Journal of Chemical Kinetics DOI 10.1002/kin.20909

REACTIONS OF ARYL BENZOATES WITH POTASSIUM ARYLOXIDES
313
aryloxides are slowed down with the addition of water
to DMF, too.
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8. Hengge, A. J Am Chem Soc 1992, 114, 6575.
Importantly, decreasing the relative energies at the
9. Hengge, A.; Hess, R. A. J Am Chem Soc 1994, 116,
0,0, 0,1, 1,0, and 1,1 corners caused by the variation
1
1256–11257.
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of the solvent from DMF to 50 mol% DMF−50 mol%
H2O mixture can be considered as an argument for
the stabilizing solvent effect on all points of a free
energy surface of the More O’Ferrall–Jencks diagram
including a ground state (GS) and TS (the first sol-
vent effect). On the other hand, the addition of water
to DMF changes the TS position on the diagram, i.e.
affects the TS stability (the second solvent effect). In
our opinion, the second solvent effect is the reason of
the rate retardation in the case of the isokinetic series
with EWS because TS(EWS) is destabilized when it
becomes earlier and tighter. By contrast, TS(EDS) is
stabilized by the second solvent effect. Nonetheless,
the solvent stabilization of TS(EDS) can be less than
that of GS, if the TS(EDS) structure is similar to the
spiro-σ-complex with EDS. In this case, the reactions
of the isokinetic series with EDS are slowed down, too.
1
1
1
2
1
2. Um, I.-H.; Lee, J. Y.; Lee, H. W.; Fujio, M.; Tsuno, Y.
Org Biomol Chem 2006, 4, 2979–2985.
13. Um, I.-H.; Han, H. J.; Ahn, J. A.; Kang, S.; Buncel, E.
J Org Chem 2002, 67, 8475–8480.
4. Um, I.-H.; Min, J.-S.; Jeon, J.-S.; Kwon, D.-S. Bull
Korean Chem Soc 1995, 16, 569–571.
5. Um, I.-H.; Oh, S.-J.; Kwon D.-S. Bull Korean Chem Soc
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1
1
1
1996, 17, 802–807.
6. Kwon, D.-S.; Park, J.-Y.; Um, I.-H. Bull Korean Chem
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18. Khalfina, I. A.; Vlasov, V. M. Russ J Org Chem 2011,
47, 845–854.
1
2
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2
9. Ba-Saif, S.; Colthurst, M.; Waring, M. A.; Williams, A.
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CONCLUSIONS
4
859–4864.
1. Um, I.-H.; Hwang, S. J.; Buncel, E. J Org Chem 2006,
1, 915–920.
2. Khalfina, I. A.; Vlasov, V. M. Russ J Org Chem 2008,
4, 1619–1626.
3. Os’kina, I. A.; Vlasov, V. M. Russ J Org Chem 2009,
5, 523–527.
The present study has allowed us to conclude the fol-
lowing: (1) the solvent variation from DMF to 50 mol%
DMF−50 mol% H2O mixture slows down the reac-
tions of 3-nitro- and 2,4-dinitrophenyl benzoates with
potassium aryloxides but does not change the reaction
mechanism. (2) The nonlinear Hammett-type plots for
these reactions have been attributed to the difference
between the TS(EDS) and TS(EWS) structures. (3)
The addition of water to DMF influences the TS(EDS)
and TS(EWS) structures, and we have discussed it in
terms of the Hammond and anti-Hammond effects.
7
4
4
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6, 1817–1821.
6. Os’kina, I. A. Russ J Org Chem 2012, 48, 1197–
199.
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7. Os’kina, I. A. Trends Org Chem 2012, 16, 85–92.
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The author would like to thank her teacher Prof. V. M. Vlasov
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