Kinetic study of hydrolysis of benzoates. Part XXIV-variation of the ortho substituent effect with solvent in the alkaline hydrolysis of substituted phenyl benzoates

Article abstract of DOI:10.1002/poc.967

The second-order rate constants k₂ (M^-1 s ^-1 ) for the alkaline hydrolysis of meta-, para- and orthosubstituted phenyl benzoates, C₆H₅CO ₂C₆H₄X, in aqueous 0.5 M n-Bu₄NBr were measured spectrophotometrically. The dependence of substituent effects, especially ortho inductive, resonance and steric terms on different solvent parameters, was studied using the following equation: Δ log k _ortho = c₀ + c_1(ortho) σ₁ + c_2(ortho) σ_R⁰ + c _3(ortho)E_s^B + c₄ΔE + c ₅ΔY + c₆ΔP + c_7(ortho) ΔEσ_I + c_8(ortho)ΔYσ_I + c_9(ortho) ΔPσ_I + c_10(ortho) ΔEσ_R⁰ + c_11(ortho) ΔYσ_R⁰ + c_12(ortho) ΔPσ_R⁰ where Δlog k = log k^X - log K^H, σI, σ_R⁰ and E _S^B are the inductive, resonance and steric substituent constants and E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In data treatment ΔE = E _s - E_H2O, ΔY = Y_S -Y_H2O and ΔP = P_S - P_H2O were used. The solvent electrophilicity was found to be the main factor responsible for changes in the ortho, para and meta polar substituent effects with medium. The variation of the ortho inductive term with the solvent electrophilicity E_S was found to be ca threefold smaller than that for para substituents, whereas the ortho resonance term appeared to vary with solvent very similarly to that for para substituents. The steric term of ortho substituents was found to be approximately independent of solvent parameters. The ortho effect caused by the supplementary inductive effect from ortho position was found to disappear in a solvent whose electrophilic solvating power is comparable to that of 60% aqueous ethanol (E ≈ 13.3). Copyright

Full text of DOI:10.1002/poc.967

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2005; 18: 1138–1144
Published online 29 June 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.967
Kinetic study of hydrolysis of benzoates. Part XXIV—
Variation of the ortho substituent effect with solvent in
the alkaline hydrolysis of substituted phenyl benzoates
Vilve Nummert, Mare Piirsalu,* Vahur M a¨ emets and Ilmar Koppel
Institute of Chemical Physics, Tartu University, Jakobi 2, 51014 Tartu, Estonia
Received 20 June 2004; revised 25 March 2005; accepted 28 April 2005
ꢀ
1
ꢀ1
s
substituted phenyl benzoates, C H CO C H X, in aqueous 0.5 M n-Bu NBr were measured spectrophotometrically.
ABSTRACT: The second-order rate constants k (M
) for the alkaline hydrolysis of meta-, para- and ortho-
2
6
5
2
6
4
4
The dependence of substituent effects, especially ortho inductive, resonance and steric terms on different solvent
parameters, was studied using the following equation:
0
R
B
s
Á log kortho ¼ c0 þ c1ðorthoÞꢀI þ c2ðorthoÞꢀ þ c
E þ c4ÁE þ c5ÁY þ c6ÁP þ c
ÁEꢀI
3ðorthoÞ
7ðorthoÞ
0
0
0
þ c8ðorthoÞÁYꢀI þ c9ðorthoÞÁPꢀI þ c10ðorthoÞÁEꢀ þ c
ÁYꢀ þ c
ÁPꢀ
R
R
11ðorthoÞ
R
12ðorthoÞ
X
H
0
R
B
s
where Álog k ¼ log k ꢀ log k , ꢀ , ꢀ and E are the inductive, resonance and steric substituent constants and E, Y
I
and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In data treatment
ÁE ¼ ES ꢀ EH O; ÁY ¼ YS ꢀ YH O and ÁP ¼ PS ꢀ PH O were used. The solvent electrophilicity was found to be
2
2
2
the main factor responsible for changes in the ortho, para and meta polar substituent effects with medium. The
variation of the ortho inductive term with the solvent electrophilicity E was found to be ca threefold smaller than that
S
for para substituents, whereas the ortho resonance term appeared to vary with solvent very similarly to that for para
substituents. The steric term of ortho substituents was found to be approximately independent of solvent parameters.
The ortho effect caused by the supplementary inductive effect from ortho position was found to disappear in a solvent
Jw o hh on s eW ei ll ee cy t r&o p Sh oi lni cs ,s Lo tl dv .a ting power is comparable to that of 60% aqueous ethanol (E ꢁ 13.3). Copyright # 2005
Supplementary electronic material for this paper is available in Wiley Interscience at http://www. interscience.
wiley.com/jpages/0894-3230/suppmat/
KEYWORDS: esters; phenyl benzoates; alkaline hydrolysis; substituent effects; ortho effects; solvent effects; kinetics
INTRODUCTION
Recently, the study of substituents effects in the alkaline
hydrolysis of ortho-, meta- and para-substituted phenyl
5
tosylates was extended to aqueous 0.5 M Bu NBr. In the
The purpose of the present work was to study the
dependence of substituent effects, especially ortho in-
ductive, resonance and steric terms on solvent electro-
philicity, polarity and polarizability parameters, in the
alkaline hydrolysis of substituted phenyl benzoates. In
previous papers, we studied the substituent effects, espe-
cially ortho effect, in the alkaline hydrolysis of ortho-,
meta- and para-substituted phenyl benzoates, C H CO -
4
present work the second-order rate constants for the
alkaline hydrolysis of substituted phenyl benzoates
[X ¼ H, 4-NO , 4-CN, 4-Cl, 4-F, 4-CH , 4-OCH , 4-
2
3
3
NH , 3-NO , 3-Cl, 3-CH , 3-NH , 2-NO , 2-CN, 2-CF ,
2
2
3
2
2
3
2-F, 2-Cl, 2-I, 2-CH , 2-OCH , 2-C(CH ) , 2-N(CH ) ] in
3
3
3 3
3 2
aqueous 0.5 M Bu NBr at various temperatures are re-
4
ported. The electrophilic solvating power of aqueous
0.5 M Bu NBr is reduced compared with pure water and
6
5
2
C H X, and tosylates, 4-CH C H SO OC H X, in water,
6
4
3
6
4
2
6
4
4
aqueous 2.25 M Bu NBr, 80% (v/v) DMSO and 5.3 M
4
5.3 M NaClO . However, it is higher than that of aqueous
4
NaClO (see Refs 1–4 and references cited therein).
4
2.25 M Bu NBr and 80% (v/v) DMSO.
4
Lately, in order to study the significance of different
solvent parameters for the substituent effects, in particu-
lar ortho effects, in the alkaline hydrolysis of ortho-,
meta- and para-substituted phenyl tosylates, the
log k values in various media have been analyzed ac-
6
cording to the modified Fujita and Nishioka equation:
*
Correspondence to: M. Piirsalu, Institute of Chemical Physics, Tartu
University, Jakobi 2, 51014 Tartu, Estonia.
E-mail: mare.piirsalu@ut.ee
Contract/grant sponsor: Estonian Science Foundation; Contract/grant
number: 5226.
5
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144

ORTHO SUBSTITUENT EFFECT IN ALKALINE HYDROLYSIS OF BENZOATES
1139
0
ꢂ
18
4-chlorophenyl benzoate, m.p. 86.5–87.7 C (lit. 88–
89 C), 4-methylphenyl benzoate, m.p. 69.7 C (lit.
Álog km; p;ortho ¼ c0 þ c1ðm; p;orthoÞꢀ þ c2ðorthoÞꢀI þ c3ÁE
ꢂ
ꢂ
18
0
0
þ c ÁY þ c ÁP þ c
ÁEꢀ þ c
ÁYꢀ
4
5
6ðm; p;orthoÞ
7ðm; p;orthoÞ
ꢂ
7
8
0.4–71.2 C), 4-methoxyphenyl benzoate, m.p. 86.6–
0
þ c8ðm; p;orthoÞÁPꢀ þ c9ðorthoÞÁEꢀI þ c10ðorthoÞÁYꢀI
þ c11ðorthoÞÁPꢀI
ꢂ
19
7.8 C (lit. 87–88 C), 2-iodophenyl benzoate, b.p.
ꢂ
ꢂ
162 C/0.9 mmHg, 2-tert-butylphenyl benzoate, m.p.
ꢂ
6
1
1
9.1–70.3 C, 2-trifluoromethylphenyl benzoate, b.p.
ꢂ
ð1Þ
25–126 C/1.5 mmHg, 4-aminophenyl benzoate, m.p.
ꢂ
20
60.5–161.5 C (lit. 153–154 C) tetrabutylammonium
ꢂ
X
H
0
where Álog k ¼ log k ꢀ log k ; ꢀ and ꢀ are the Taft
I
hydroxide (0.0184 M) was used as the reagent. The
purification of Bu NOH and Bu NBr was described
polar and inductive substituent constants, ÁE ¼ E ꢀ
S
4
4
E
H2O
; ÁY ¼ Y ꢀ Y ; ÁP ¼ P ꢀ P
and E, Y and
H2O
S
H2O
S
1–5
previously.
The kinetics were measured spectrophotometrically
P are the solvent electrophilicity, polarity and polariz-
7
ability parameters of the Koppel–Palm equation.
,8
1
–5,10,11
5
as described.
The second-order rate constants, k
1 ꢀ1
s ), for the alkaline hydrolysis of substituted phe-
In an earlier paper, it was shown, that in the alkaline
hydrolysis of substituted phenyl tosylates the solvent
electrophilicity was the main factor responsible for
changes in the ortho, para and meta polar substituent
effects due to medium [c6(m,p,ortho) ¼ ꢀ0.0856]. The
ortho inductive term appeared to vary with the solvent
electrophilicity, E, nearly half as much as that for para
substituents [c9(ortho) ¼ 0.0480] whereas the ortho reso-
nance term was found to change with solvent at nearly the
ꢀ
(M
nyl benzoates in aqueous 0.5 M Bu NBr at 15, 20, 25, 30
4
ꢂ
35, 40 50 and 55 C and the wavelength ꢁ used in
spectrophotometric kinetic measurements are given in
ꢀ1 ꢀ1
Table S2. The second-order rate constants, k (M s ),
for 2-cyano- and 4-cyanophenyl and non-substituted
ꢂ
phenyl benzoates in water at 25 C are given in Table S3.
5
same rate as that for para substituents.
DATA PROCESSING
On the basis of our earlier kinetic data for various
media (Refs 1–4, 9 and references cited therein) and
kinetic data reported in this work, it was interesting to
check on the significance of different solvent parameters
for the substituent effects, especially ortho inductive,
resonance and steric terms, in the alkaline hydrolysis of
substituted phenyl benzoates, C H CO C H X, using a
multilinear relationship similar to Eqn (1), including an
additional steric term for ortho derivatives.
In the present paper, the substituent effects in alkaline
hydrolysis of substituted phenyl benzoates for aqueous
For the study of substituent effects at a single tempera-
ture, the log k values for the alkaline hydrolysis of
substituted phenyl benzoates, C H CO C H X, in aqu-
2 6 4
eous 0.5 M Bu NBr were treated according to the Taft
4
equation, Eqn (2), and the modified Charton equations,
Eqns (3) and (4):
6
5
2
1
2
2
6
5
2 6 4
0
0
log km; p ¼ log k0 þ ðꢂ Þm; pꢀ
ð2Þ
ð3Þ
ð4Þ
0
.5 M Bu NBr are also analyzed.
4
0
0
log km; p;ortho ¼ log k0 þ ðꢂ Þ ꢀ þ ðꢂIÞorthoꢀI
m; p
0
R
B
s
þ ðꢂRÞorthoꢀ þ ꢃE
0
R
B
s
EXPERIMENTAL
log kortho ¼ log k0 þ ðꢂIÞorthoꢀI þ ðꢂRÞorthoꢀ þ ꢃE
The preparation procedure and characteristics of most
substituted phenyl benzoates are described in Refs 1–5,
In order to study the dependence of the substituent
effects on different solvent parameters, the Álog k ¼
X
H
1
0–12 and references cited therein. In this work, nine
log k ꢀ log k values for ortho-, meta- and para-substi-
ꢂ
new phenyl benzoates were synthesized. To synthesize
the substituted phenyl benzoates, C H CO C H X, three
tuted phenyl benzoates at 50 C in various media were
correlated with Eqn (5):
6
5
2
6
4
methods were used: the reaction of benzoyl chloride with
the corresponding substituted phenol in 10% aqueous
0
0
Álog km; p;ortho ¼ a0 þ a
ꢀ þ a2ðorthoÞꢀI þ a3ðorthoÞ
ꢀ
R
1
ðm; pÞ
13
NaOH solution (X ¼ 4-CN, 2-CN, 4-Cl, 4-CH , 4-
3
B
0
14
þ a4ðorthoÞE þ a5ÁE þ a6ÁY þ a7ÁP þ a8ðm; pÞÁEꢀ
s
OCH , 2-I), the Einhorn method (in pyridine) [X ¼ 2-
3
0
0
þ a9ðm; pÞÁYꢀ þ a
ÁPꢀ þ a
ÁPꢀ þ a
ÁPꢀ
ÁEꢀI
C(CH ) , 2-CF ] and reduction of 4-nitrophenyl benzoate
3
10ðm; pÞ
11ðorthoÞ
3
3
15
(
ethanol, dried in a desiccator over P O or purified by
X ¼ 4-NH ). Esters were recrystallized from aqueous
0
2
þ a12ðorthoÞÁYꢀ þ a
þ a15ðorthoÞÁYꢀ þ a
ÁEꢀ
R
I
13ðorthoÞ
I
14ðorthoÞ
2
5
0
R
0
16ðorthoÞ
R
vacuum- distillation. The esters were identified by NMR
chemical shifts [Table S1 (Tables S1–S6 are available in
Wiley Interscience)] and by melting or boiling points:
ð5Þ
ꢂ
16
ꢂ
4
2
-cyanophenyl benzoate, m.p. 91 C (lit. 91–92 C),
The inductive effect from the ortho position, different
from that from the meta and para positions, was
ꢂ
17
-cyanophenyl benzoate, m.p. 105.5 C (lit. 105 C),
ꢂ
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144

1
140
V. NUMMERT ET AL.
6,22–24
assumed.
Similarly, in the case of ortho substitu-
The standard medium, where ÁE, ÁY and ÁP are equal
to zero, is pure water and the standard substituent is
X ¼ H. The electrophilicity E values of Koppel and
ents, the variation of the inductive term with solvent
parameters, different from that for meta and para deri-
vatives, was assumed. The steric term of ortho substitu-
ents in the alkaline hydrolysis of phenyl benzoates was
considered to be independent of the solvent and the
corresponding cross-terms with the solvent parameters
30–33
Palm,
polarity Y calculated as a function of dielectric
constant " in the form ð" ꢀ 1Þ=ð" þ 2Þ and the polariz-
2,4
ability P as a function of refractive index n in the form
D
2
2
ðn ꢀ 1Þ=ðn þ 2Þ were used (see Table S5). The data
(ÁE, ÁY, ÁP) were omitted. In the data processing
processing was carried out using a multiple parameter
34
including only ortho-substituted derivatives the log k
value for unsubstituted derivative (X ¼ H) as standard
was included besides the ortho-substituted derivatives.
linear least-squares (LLSQ) procedure. Significantly
deviating points were excluded using a Student criterion.
The exclusion of the significantly deviating points was
performed on different confidence levels of the t-test.
Results of the data treatment in the present work are given
mainly at the 0.99 confidence level.
0
25,26
27
The Taft’s polar ꢀ
0
, inductive ꢀI, the resonance
0
0
28
ꢀ
processing. E constants
[ꢀ ¼ (ꢀ )
ꢀ ꢀ ] scales were used in the data
R
R
para
B
I
2,4
B
X
H
(E ¼ log k
þ
ꢀ log k
þ
;
are the rate constants for the acidic
s
s
H
H
X
H
where kH
hydrolysis of ortho-substituted and unsubstitued phenyl
þ
and kH
þ
The results of the data treatment with Eqns (2)–(5) are
presented in Tables 1 and 2. The values of substituent
ꢂ
29
benzoates in water at 50 C ) were used as the steric
0
0
B
constants ꢀ , ꢀ , ꢀ and E used in the correlations and
I
R s
ꢀ
1
the values of log A and activation energies, E (kJ mol ),
constants for ortho substituents (Table S4). The previous
statistical data treatment confirmed that there was no
resonance in the case of 2-N(CH ) substituent and in the
common data processing the correction ꢂ ꢀ was added.
In the data processing according to Eqn (5), the log k
values for the alkaline hydrolysis of ortho-, meta- and
2,4
for the alkaline hydrolysis of substituted phenyl benzo-
ates in aqueous 0.5 M Bu NBr, calculated with the Ar-
3
2
4
0
0
rhenius equation (log k ¼ log A ꢀ E=2:3RT), are listed in
Table S4. The values of solvent characteristics used in
data treatment with Eqn (5) are collected in Table S5.
R
ꢂ
para-substituted phenyl benzoates at 50 C in pure water,
aqueous 0.5 M Bu NBr (present work, Table S2), aqueous
4
1
NaClO and 4.8 M NaCl (Refs 1–4, 9 and references cited
M Bu NBr, 2.25 M Bu NBr, 80% (v/v) DMSO, 5.3 M
DISCUSSION
4
4
4
therein) were included. In Eqn (5) the values of ÁE, ÁY
and ÁP are the differences in electrophilicities, polarities
and polarizabilities on going from pure water to the
Substituent effects in aqueous 0.5 M Bu NBr
4
For most substituted phenyl benzoates the transition from
pure water to aqueous 0.5 M Bu NBr solution results in a
decrease in the rate constants of the alkaline hydrolysis.
corresponding aqueous binary solution, ÁE ¼ E ꢀ
s
4
E
H2O
; ÁY ¼ Y ꢀ Y ; ÁP ¼ P ꢀ P , respectively.
S
H2O
S
H2O
Table 1. Results of the correlation with Eqns (2)–(4) for alkaline hydrolysis of substituted phenyl benzoates, C H CO C H X, in
6
5
2 6 4
a
aqueous 0.5 M Bu NBr and in pure water
4
ꢂ
0
m; p
Temperature ( C) Eqn No.
log k0
ꢂ
ðꢂIÞortho
ðꢂ Þ
ꢃortho
R
s
n
R
ortho
0
.5 M Bu NBr
4
5
0
0
5
0
5
2
3
4
2
3
4
2
3
4
2
3
4
2
3
4
ꢀ0.084 ꢃ 0.016 1.31 ꢃ 0.05
ꢀ0.074 ꢃ 0.059 1.30 ꢃ 0.06
—
—
—
0.995 0.049 11
1.46 ꢃ 0.06 1.22 ꢃ 0.08
1.30 ꢃ 0.08 0.997 0.061 21
ꢀ0.026 ꢃ 0.061
—
ꢀ0.324 ꢃ 0.020 1.37 ꢃ 0.06
1.41 ꢃ 0.09 1.24 ꢃ 0.10
1.38 ꢃ 0.13 0.994 0.070 11
4
2
2
1
—
—
—
0.994 0.061 12
ꢀ0.316 ꢃ 0.036 1.36 ꢃ 0.05
1.50 ꢃ 0.07 1.25 ꢃ 0.09
1.33 ꢃ 0.09 0.994 0.066 22
ꢀ0.299 ꢃ 0.065
—
ꢀ0.754 ꢃ 0.019 1.45 ꢃ 0.05
1.49 ꢃ 0.10 1.25 ꢃ 0.11
1.36 ꢃ 0.14 0.993 0.074 11
—
—
—
0.994 0.059 11
ꢀ0.748 ꢃ 0.037 1.45 ꢃ 0.06
1.63 ꢃ 0.07 1.37 ꢃ 0.09
1.34 ꢃ 0.09 0.995 0.067 21
ꢀ0.727 ꢃ 0.066
—
ꢀ0.923 ꢃ 0.027 1.54 ꢃ 0.06
1.61 ꢃ 0.10 1.37 ꢃ 0.11
1. 38 ꢃ 0.14 0.994 0.076 11
—
—
—
0.995 0.056
8
ꢀ0.903 ꢃ 0.055 1.51 ꢃ 0.07
1.72 ꢃ 0.09 1.23 ꢃ 0.12
1.53 ꢃ 0.17 0.995 0.070 15
ꢀ0.853 ꢃ 0.085
—
ꢀ1.044 ꢃ 0.041 1.49 ꢃ 0.07
ꢀ1.032 ꢃ 0.045 1.47 ꢃ 0.07
1.66 ꢃ 0.12 1.25 ꢃ 0.14
1.62 ꢃ 0.22 0.994 0.080
0.992 0.077
8
b
—
—
—
9c
1.64 ꢃ 0.08 1.26 ꢃ 0.12
1.31 ꢃ 0.10 0.994 0.071 18
c
ꢀ1.004 ꢃ 0.061
—
1.61 ꢃ 0.14 1.28 ꢃ 0.16
1.36 ꢃ 0.26 0.994 0.069 10
Water
5
2
2
3
4
ꢀ0.377 ꢃ 0.025 1.11 ꢃ 0.05
ꢀ0.375 ꢃ 0.034 1.11 ꢃ 0.04
—
—
—
0.988 0.067 12
1.52 ꢃ 0.06 0.92 ꢃ 0.08
1.05 ꢃ 0.11 0.994 0.055 22
ꢀ0.377 ꢃ 0.040
—
1.54 ꢃ 0.05 0.95 ꢃ 0.07
1.09 ꢃ 0.11 0.997 0.047 13
a
b
c
2
The log k values reported previously and measured in the present work were included.
The log k value for the unsubstitued derivative, calculated with the Arrhenius equation, was included.
3 3
The log k value for 2-CH - and 2-OCH -subsituted and unsubstituted derivative, calculated with the Arrhenius equation, were included.
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144

ORTHO SUBSTITUENT EFFECT IN ALKALINE HYDROLYSIS OF BENZOATES
1141
Table 2. Results of the correlation with Eqn (5) for kinetic data for alkaline hydrolysis of substituted phenyl benzoates,
ꢂ
a
C H CO C H X, in various media at 50 C
6
5
2 6 4
Reaction
constant
meta and
para derivatives
ortho, meta and
para derivatives
Weight
ortho derivatives
Weight
Weight
b
Solvent electrophilicity parameter, ÁE, was included
a0
ꢀ0.004 ꢃ 0.017
0.014 ꢃ 0.046
—
1.428 ꢃ 0.059
0.838 ꢃ 0.075
1.228 ꢃ 0.090
—
ꢀ0.0212 ꢃ 0.0059
ꢀ0.0685 ꢃ 0.0089
41/46
0.001 ꢃ 0.033
1.069 ꢃ 0.040
1.437 ꢃ 0.052
0.829 ꢃ 0.068
1.199 ꢃ 0.070
ꢀ0.0645 ꢃ 0.0046
ꢀ0.0211 ꢃ 0.0054
ꢀ0.0685 ꢃ 0.082
76/84
a1(m,p)
a2(ortho)
a3(ortho)
a4(ortho)
a8(m,p)
a11(ortho)
a14(ortho)
n/n0
1.075 ꢃ 0.033
0.700
0.300
0.357
0.145
0.145
0.121
0.146
0.013
0.073
—
—
0.538
0.226
0.067
—
ꢀ0.0646 ꢃ 0.0038
—
—
0.047
0.122
42/45
0.992
0.061
0.126
0.97
R
s
s0
t
0.988
0.081
0.991
0.074
0.153
0.95
0.136
0.97
c
Solvent electrophilicity, ÁE, and polarity, ÁY, parameters were included
a0
ꢀ0.004 ꢃ 0.017
0.014 ꢃ 0.046
ꢀ0.044 ꢃ 0.039
0.993 ꢃ 0.060
1.444 ꢃ 0.051
0.822 ꢃ 0.068
1.198 ꢃ 0.063
ꢀ0.0722 ꢃ 0.0052
–4.08 ꢃ 1.87
ꢀ0.0212 ꢃ 0.0055
ꢀ0.0689 ꢃ 0.0083
77/84
a1(m,p)
a2(ortho)
a3(ortho)
a4(ortho)
a8(m,p)
a9(m,p)
a11(ortho)
a14(ortho)
n/n0
1.075 ꢃ 0.033
0.700
—
0.329
0.128
0.133
0.145
0.166
0.021
0.012
0.067
—
—
1.428 ꢃ 0.059
0.838 ꢃ 0.075
1.228 ꢃ 0.090
—
0.538
0.226
0.069
—
ꢀ0.0646 ꢃ 0.0038
0.300
—
—
—
ꢀ0.0212 ꢃ 0.0059
ꢀ0.0685 ꢃ 0.0089
41/46
0.047
0.122
—
42/45
0.992
0.061
0.126
0.97
R
s
0.988
0.081
0.992
0.075
0.130
0.99
s0
t
0.153
0.95
a
ꢂ
A table containing the results of the correlations with Eqs (5) for kinetic data for alkaline hydrolysis of substituted phenyl benzoates in various media at 50 C
when three solvent parameters, the solvent electrophilicity, ÁE, the solvent polarity, ÁY, and the solvent polarizability, ÁP, were included, is available as
supplementary material (Table S6). If the scale is not shown in the table, the corresponding argument scale is excluded as insignificant during the data
processing (a ¼ 0).
b
In most cases exclusion of significantly deviating points performed before excluding insignificant argument scales and cross terms are formed from non-
5,34
centered basic argument scales.
0
0
0
0
In Eqn (5) the terms a
processing.
6
ÁY, a
7
I I R
R
ÁP, a9(m,p)ÁYꢀ , a10(m,p)ÁPꢀ , a12(ortho)ÁYꢀ , a13(ortho)ÁPꢀ , a15(ortho) ÁYꢀ and a16(ortho)ÁPꢀ were omitted before data
c
0
0
R
In Eqn (5) the terms a
7
ÁP, a10(m,p)ÁPꢀ , a13(ortho)ÁPꢀ
I
, and a16(ortho)ÁPꢀ were omitted before data processing.
The retardation is larger for esters with electron-donating
substituents than that for esters with electron-withdraw-
ing substituents (Table S2).
1.30–1.54 and 1.46–1.72, respectively. Earlier the
0
(ꢂ ) and (ꢂI)ortho values for pure water were found to
m,p
2
be in the ranges 0.90–1.15 and 1.26–1.72 respectively.
On going from pure water to aqueous 0.5 M Bu NBr the
polar effect of meta and para substituents increases by ca
In the alkaline hydrolysis of of meta- and para-
substituted phenyl benzoates in aqueous 0.5 M Bu NBr,
4
4
0
0.4 units of (ꢂ )m,p. The change in the susceptibility to the
the dependence of the reaction rates on the substituent
0
effects is nicely described with ꢀ values [Eqn (2)].
ortho inductive effect, (ꢂ )
0.10 units of (ꢂI)ortho. Earlier it was found that the ꢂ
m,p
, is essentially lower by ca
I ortho
5 0
1
–4
As found earlier
aqueous 5.3 M NaClO and aqueous 80% DMSO, the
for water, aqueous 2.25 M Bu NBr,
4
values in the alkaline hydrolysis of substituted phenyl
tosylates on going from pure water to aqueous 0.5 M
4
0
B
inductive, ꢀ , resonance, ꢀ , and steric, E , constants
I
R
s
0
m;p
were used in the case of ortho substituents (Table 1).
The values of reaction constants (ꢂI)ortho, (ꢂ ) and ꢃ
Bu NBr changed by nearly the same extent (ꢂ by ca
4
0
m;p
0.5–0.6 units and (ꢂI)ortho by 0.15–0.20 units) as the ꢂ
R ortho
calculated from Eqn (4) separately for ortho-substituted
derivatives are approximately the same as those calcu-
lated simultaneouly with ortho-, meta- and para-substi-
tuted derivatives using Eqn (3) (see Table 1).
and (ꢂI)ortho values in the alkaline hydrolysis of phenyl
benzoates.
The analysis of the data for the alkaline hydrolysis of
phenyl benzoates in aqueous 0.5 M Bu NBr demonstrates
4
In the alkaline hydrolysis of substituted phenyl benzo-
0
ates, the (ꢂ )
once again that the ortho inductive term varies with
solvent less than the para inductive term. In water, the
inductive influence from the ortho position was found to
and (ꢂI)ortho values for aqueous 0.5 M
Bu NBr for various temperatures are in the ranges
m,p
4
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144

1
142
V. NUMMERT ET AL.
ꢂ
be 1.5 times stronger than that from the para and meta
positions. Whereas the variation of the susceptibility of
the para inductive term with solvent is nearly double the
variation of the ortho inductive term, in aqueous 0.5 M
tuted phenyl benzoates, the Álog k values at 50 C for
various media were subjected to the multilinear regres-
sion analysis according to Eqn (5) in three different ways:
(i) only the solvent electrophilicity, ÁE, was included,
(ii) both the solvent electrophilicity, ÁE, and the solvent
polarity, ÁY, were included or (iii) all three solvent
parameters, the solvent electrophilicity, ÁE, the solvent
polarity, ÁY, and the solvent polarizability, ÁP, were
included. For comparison, the data treatment is shown
separately for meta- and para-substitued derivatives,
ortho-substituted derivatives and simultaneously for
ortho-, meta- and para-substituted derivatives [Eqn (5),
Tables 2 and S6]. If the scale is not shown in the table, the
corresponding argument scale is excluded during the data
processing as insignificant.
Bu NBr solution the para inductive effect reaches nearly
4
the level of the ortho inductive effect [in aqueous 0.5 M
Bu NBr (ꢂ )
0
surpasses the (ꢂ )
value only by
m,p
4
I ortho
0
.1 units of ꢂ].
In the alkaline hydrolysis of substituted benzoates in
aqueous 0.5 M Bu NBr solution, the susceptibility to the
4
steric effect was (ꢃ ꢁ 1.35, Tables 1 and 2) nearly the
2
–4
same as we have found earlier
2
for water, aqueous
.25 M Bu NBr, aqueous 5.3 M NaClO and aqueous
4 4
8
0% DMSO (the ꢃ values range from 1.0 to 1.4).
From the dependence of ꢂ on temperature, ꢂ ¼ c þ
T
0
35
c (1/T), where ꢄ ¼ ꢀc /c , the isokinetic temperatures
The reaction constants a , a1(m,p), a2(ortho), a3(ortho) and
0
1
1
0
ꢄ for the ortho inductive term and meta and para polar
effect in the alkaline hydrolysis of substituted phenyl
a4(ortho) in pure water appeared to be fairly constant
values that do not depend significantly on the method
used for the data treatment: the data included are either
only for meta- and para-substitued derivatives or for
ortho-substitued derivatives, or the data set can embrace
the data simultaneously for ortho-, meta- and para-sub-
stituted derivatives. The reaction constant a1(m,p) shows
the susceptibility to the polar effect of meta and para
benzoates in aqueous 0.5 M Bu NBr were calculated. For
4
aqueous 0.5 M Bu NBr ꢄ
¼ 872 K [(ꢂ
¼
4
3
I(ortho)
I(ortho)
(
(
[
ꢀ0.837) þ 0.730(10 /T)] and ꢄ ¼ 1355 K [(ꢂ
¼
m,p
m,p
3
ꢀ0.411) þ 0.557(10 /T)]. For water ꢄ
¼ 832 K
I(ortho)
3
(ꢂ
I(ortho)
¼ (ꢀ0.89) þ 0.741(10 /T)] and ꢄ ¼ 1 K. For
m,p
aqueous 2.25 M Bu NBr ꢄ
¼ 702 K [(ꢂ
¼
4
I(ortho)
I(ortho)
3
36
ꢂ
(
ꢀ1.51) þ 1.06(10 /T)] and ꢄ ¼ 628 K (ꢄ ¼ 628 K )
substituents in standard solution, in water at 50 C
(Tables 2 and S6). The values of a1(m,p) found in different
ways appeared to vary in a narrow range, from 0.99 to
m,p
m,p
3
[
(ꢂ ¼ (ꢀ2.14) þ 1.34(10 /T)]. The values of ꢄ for the
m,p
alkaline hydrolysis of substituted phenyl benzoates in
various media demonstrate that the isokinetic tempera-
ture ꢄI(ortho) for the ortho inductive effect varies with
solvent considerably less than the isokinetic temperature
0
1.10. Earlier the (ꢂ ) value for the alkaline hydrolysis
m,p
ꢂ
of substituted benzoates in water at 50 C was found to be
2
in the range 0.96–1.01. The calculated values of a2(ortho),
for polar effect of meta and para substituents, ꢄm,p
.
a3(ortho) and a4(ortho) as the susceptibilities to the ortho
inductive, resonance and steric effects in pure water, were
in ranges 1.41–1.45, 0.83–0.86 and 1.15–1.20, respec-
In the alkaline hydrolysis of ortho-, meta- and para-
substituted phenyl benzoates, the dependence of the
activation energies E on the substituent effects in aqueous
tively. Earlier, the corresponding values of (ꢂ )
,
I ortho
(ꢂ )ortho, and (ꢃ)ortho for pure water at 50 C were found
0
R
ꢂ
0
.5 M Bu NBr is entirely caused by polar effects of
4
substituents (Table S4), whereas electron-withdrawing
substituents decrease and electron-donating substituents
increase it. The activation energy for ortho-substituted
derivatives with electronegative substituents was found to
be lower than those for para-substitued derivatives owing
to the additional inductive influence from ortho position.
The influence of the ortho, meta and para substituent
polar effects on the activation energy is greater in aqu-
to be in the ranges 1.50–1.52, 0.94–1.01 and 0.97–1.20,
2
respectively.
The solvent electrophilicity parameter, ÁE, was the
main factor responsible for the dependence of the sub-
stituent effects on medium as the contribution of cross
0
0
R
terms [a8
ÁEꢀ ; a
ÁEꢀ ; a
I
ÁEꢀ ] con-
ðm; pÞ
11ðorthoÞ
14ðorthoÞ
taining the solvent electrophilicity parameter ÁE was
significant when the Álog k values were processed
according to Eqn (5) (Tables 2 and S6). Consequently,
in the alkaline hydrolysis of substituted phenyl benzoates
the variation of the meta, para polar effect, the ortho
inductive and ortho resonance effects with solvent occurs
mainly due to the change in electrophilicity of the
medium considered.
eous 0.5 M Bu NBr than in the pure water. However, in
4
X
para
X
ortho
0
.5 M Bu NBr a decrease in the difference E
4
ꢀ E
compared with that in pure water could be observed.
The steric factor of ortho substituents appeared to be
independent of temperature and therefore influences the
log A value. The log A values for ortho-substituted deri-
vatives in aqueous 0.5 M Bu NBr were smaller than that
4
for para derivatives (Table S4) owing to the steric
influence from ortho position.
The cross term containing the solvent polarity
0
a9(m,p)ÁYꢀ was different from zero for the simultaneous
data treatment with Eqn (5) for ortho, meta and para
derivatives. However, the contribution of solvent polarity
on the polar effect of substituents could be considered as
almost insignificant owing to its very low relative weight.
Further, in the separate data treatment for meta and
Influence of solvent on substituent effects
To study the influence of the solvent parameters on the
substituent effects in the alkaline hydrolysis of substi-
0
para derivatives the term a9(m,p)ÁYꢀ was excluded as
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144

ORTHO SUBSTITUENT EFFECT IN ALKALINE HYDROLYSIS OF BENZOATES
1143
insignificant. The terms a12(ortho)ÁYꢀ and a13(ortho)ÁPꢀI,
were significant when the data for ortho derivatives were
processed with Eqn (5). Owing to very low weight, the
An excellent fit between the experimental log k values
ꢂ
I
at 50 C (Tables S2 and S3, Refs 1–5 and references cited
therein) and predicted log k values calculated with Eqns
(6) and (7), was found:
term a12(ortho)ÁYꢀ was excluded during the data proces-
I
sing when data for aqueous 80% DMSO were excluded
before data treatment. Similarly, the term a13(ortho)ÁPꢀI
was excluded as insignificant when Eqn (5) included only
the solvent electrophilicity, ÁE, and the solvent polariz-
ability, ÁP, and the corresponding cross terms.
ðÁlog kobsÞm; pðorthoÞ ¼ ð0:057 ꢃ 0:008Þ þ ð0:997 ꢃ 0:015Þ
ꢄ ðÁlog k Þ
cal m; pðorthoÞ
ð8Þ
ð9Þ
The variation of the meta and para polar effects with
the solvent electrophilicity is three times higher than that
for the ortho inductive effect. The corresponding value
for reaction constants a8(m,p) are in the range from ꢀ0.065
to ꢀ0.072. In the case of ortho substituents, the suscept-
ibility of the inductive effect to variation of the solvent
electrophilicity ranges from 0 to ꢀ0.023. Earlier, nearly
R ¼ 0:992; s ¼ 0:069; s0 ¼ 0:126; n=n0 ¼ 76=84
ðÁlog k
Þ
¼ ꢀð0:002 ꢃ 0:012Þ
þ ð0:993 ꢃ 0:023ÞðÁlog kcalÞortho
obs ortho
the same values for reaction constants a8
(m,p)
¼ ꢀ0.0856
R ¼ 0:990; s ¼ 0:076; s ¼ 0:144; n=n ¼ 41=46
0
0
and a11(ortho) ¼ ꢀ0.0376 were found for the alkaline
5
hydrolysis of substituted phenyl tosylates. The ortho
In the alkaline hydrolysis of substituted phenyl benzo-
ates, the induction factor from the ortho position, 1.5-fold
higher than from the para position in water, varies nearly
three times less than the polar effect from the para
position with change in solvent. From Eqn (6) could be
calculated the value of solvent electrophilicity at which
the ortho effect caused by the additional inductive effect
from ortho position, becomes zero:
resonance effect appears to vary with the solvent electro-
philicity to nearly the same extent as the polar effect of
para substituents, a8(m,p) ꢁ a14(ortho).
The results of data treatment in Tables 2 and S6
confirm that the steric effect of ortho substituents could
be really considered independently of solvent parameters
as assumed in Eqn (5).
Therefore, in the alkaline hydrolysis of substituted
phenyl benzoates, the polar effect of meta and para
substituents, the ortho inductive and resonance effect
vary with the solvent electrophilicity to the same extent
ð1:069ꢀIÞ ꢀ ð0:0645ÁEꢀIÞ ¼ ð1:437ꢀIÞ
p
p
ortho
ð10Þ
ꢀ
ð0:0211ÁEꢀIÞortho
5
as found earlier for the alkaline hydrolysis of substituted
phenyl tosylates, although the ratio of the susceptibilities
to polar effect of substituents in water differs twofold, i.e.
In the alkaline hydrolysis of substituted phenyl benzo-
ates, the polar effects of ortho and para substituents
become equals in a solvent with an electrophilic solvating
power nearly the same as that of 60% aqueous ethanol and
0
m; p Tos
0
m; p Benz
2
ðꢂ
Þ
=ðꢂ
Þ
¼ ðꢂ
Þ
=ðꢂ
Þ
ꢁ 2.
IðorthoÞ Tos
IðorthoÞ Benz
It follows from Table 2 that in medium considered the
total substituent effect in the alkaline hydrolysis of
substituted phenyl benzoates could be expressed by
Eqns (6) and (7):
1 M Bu
60% aqueous ethanol and aqueous 1 M Bu
effect, caused by the supplementary inductive effect from
the ortho position, will disappear and the ortho effect is
caused only by steric effect of ortho substituents.
4
NBr ½ÁEðꢂIÞ ¼ðꢂIÞ ¼ ꢀ8:48ꢅ. Consequently, in
ortho
para
NBr the ortho
4
X
H
0
The present work shows that in the alkaline hydrolysis
of substituted phenyl benzoates, similarly to the alkaline
hydrolysis of phenyl tosylates, the polar effects of ortho,
meta and para substituents increase on going from water
Álog k
¼ log k ꢀ log k ¼ 0:001 þ ð1:069ꢀ Þ
m; pðorthoÞ
m; p
0
B
þ ð1:437ꢀIÞortho þ ð0:829ꢀ Þ
ð0:0645ÁEꢀ Þ ꢀ ð0:0211ÁEꢀIÞortho
þ ð1:199E Þ
R ortho
s
ortho
0
ꢀ
ꢀ
m; p
0
to aqueous solutions of organic salts (0.5 M Bu NBr, 1.0 M
4
ð0:0685ÁEꢀ Þ
ð6Þ
R ortho
Bu NBr, 2.25 M Bu NBr and 80% DMSO) the electro-
4
4
philic solvating power of which is reduced compared
with water. On the other hand, the polar effects of
ortho, meta and para substituents decreased on going
from water to inorganic salt solutions (5.3 M NaClO4,
4.8 M NaCl) whose electrophilic solvating power is higher
than that of water. In the alkaline hydrolysis of substi-
tuted phenyl benzoates, the variation of ortho, para
and meta polar effects with solvent electrophilicity prop-
erties, ÁE, occurs to nearly the same extent as found
earlier for the alkaline hydrolysis of substituted phenyl
R ¼ 0:991; s ¼ 0:074; s0 ¼ 0:136; n=n0 ¼ 76=84
X
H
Álog k
¼ log k ꢀ log k
ðorthoÞ
0
R
B
s
¼
0:014 þ 1:428ꢀI þ 0:838ꢀ þ 1:228E
0:0212ÁEꢀI ꢀ 0:0685ÁEꢀR
0
ꢀ
ð7Þ
5
R ¼ 0:988; s ¼ 0:081; s ¼ 0:153; n=n ¼ 41=46
0
0
tosylates.
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144

1
144
V. NUMMERT ET AL.
. Nummert V, Piirsalu M. Org. React. 1997; 31: 101–109.
3
Supplementary material
4
. Nummert V, Piirsalu M. Collect. Czech. Chem. Commun. 2003;
7: 1833–1857.
6
The following tables are available as supplementary
material in Wiley Interscience:
5. Nummert V, Piirsalu M, Lepp M, M a¨ emets V, Koppel I. Collect.
Czech. Chem. Commun. 2005; 70: 198–222.
6
. Fujita T, Nishioka T. Prog. Phys. Org. Chem. 1976; 12: 49–89.
. Koppel IA, Palm VA. In Advances in Linear Free Energy
Relationships, Chapman NB, Shorter J (eds). Plenum Press:
London, 1972; Chapt. 5, 203.
1
Table S1, NMR spectra of substituted phenyl benzoates,
7
C H COOC H X; Table S2, second-order rate constants
6
5
6 4
k for the alkaline hydrolysis of substituted phenyl benzo-
ates, C H CO C H X, in aqueous 0.5 M Bu NBr at var-
ious temperatures; Table S3, pseudo-first-order rate
8. Koppel IA, Palm VA. Org. React. 1971; 8: 291–301.
. Nummert V, Piirsalu M. Org. React. 1977; 14: 263–279.
0. P u¨ ssa TO, Nummert (Marem a¨ e) VM, Palm VA. Org. React. 1972;
: 697–728.
11. Nummert V, Eek M, Piirsalu M. Org. React. 1981; 18: 363–
74.
2. Nummert VM, Piirsalu MV. Org. React. 1975; 11: 899–910.
9
6
5
2
6
4
4
1
9
ꢀ
1
constants k (s ) and the second-order rate constants k
1
ꢀ
1 ꢀ1
3
(M
s ) for the alkaline hydrolysis of substituted phenyl
ꢂ
1
benzoates, C H CO C H X, in water at 25 C; Table S4,
4
6
5
2
6
13. Bauerova I, Ludvig M. Collect. Czech. Chem. Commun. 2000; 65:
1777–1790.
substituent constants used in the correlations and values
ꢀ
1
1
1
1
4. Pirinccioglu N, Williams A. J. Chem. Soc. Perkin Trans. 2 1998;
3
5. Uhlmann F, Meyer GM, Loewenthal O, Gilli E. Liebigs Ann.
Chem. 1904; 332: 38–81.
6. Correia VR, Cuccovia IM, Chaimovich H. J. Phys. Org. Chem.
of log A and activation energy, E (kJ mol ), for the
alkaline hydrolysis of substituted phenyl benzoates,
C H CO C H X, in aqueous 0.5 M Bu NBr; Table S5,
7–40.
6
5
2
6
4
4
values of electrophilicity, E, dielectric permittivity, ",
2
1
17. Auwers K, Walker AJ. Chem. Ber. 1899; 31: 3037–3046.
991; 4: 13–18.
refractive index, n , polarizability, P ¼ ðn ꢀ 1Þ=
D
2
ꢂ
ðn þ 2Þ, and polarity, Y ¼ ð" ꢀ 1Þ=ð" þ 2Þ, at 25 C
for various aqueous solutions; Table S6, results of the
correlation with Eqn (5) for kinetics of alkaline hydro-
lysis of substituted phenyl benzoates, C H CO C H X,
in various media at 50 C (solvent electrophilicity, ÁE,
polarity, ÁYand polarizability, ÁP, parameters included).
18. Kirch JF, Clewell W, Simon A. J. Org. Chem. 1968; 33: 127–132.
1
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2
21. Taft RW Jr. In Steric Effects in Organic Chemistry, Newman MS
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6
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2 6 4
ꢂ
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2
2
2
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Acknowledgement
2
2
2
This work was supported by the grant No. 5226 of the
Estonian Science Foundation.
1
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Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 1138–1144