Kinetic study of hydrolysis of benzoates. Part XXV. Ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in water

Article abstract of DOI:10.1135/cccc20060107

The second-order rate constants k₂ for alkaline hydrolysis of phenyl esters of meta-, para-and ortho-substituted benzoic acids, X-C ₆H₄CO₂C₆H₅ (X = H, 3-Cl, 3-NO₂, 3-CH₃, 4-NO₂, 4-Cl, 4-F, 4-CH ₃, 4-OCH₃, 4-NH₂, 2-NO₂, 2-CN, 2-F, 2-Cl, 2-Br, 2-I, 2-CH₃, 2-OCH₃, 2-CF₃, 2-NH₂), and of substituted phenyl esters of benzoic acid, C ₆H₅CO₂C₆H₄-X (X = 2-I, 2-CF₃, 2-C(CH₃)₃, 4-Cl, 4-CH₃, 4-OCH₃, 4-NH₂), have been measured spectrophotometrically in water at 25 °C. The substituent effect in alkaline hydrolysis of phenyl esters of para-substituted benzoic acids, similar to that for ethyl esters of para-substituted benzoic acids, was found to be precisely described by the Hammett relationship (p = 1.7 in water). The log k value for alkaline hydrolysis of phenyl and ethyl esters of meta-, para- and ortho-substituted benzoic acids, X-C₆H₄CO₂R, was nicely correlated with log k_m,p,ortho = log k_o + (ρ)_m,pσ + (ρ_I)_orthoσ_I + (ρ° _R)_orthoσ°_R + δ _orthoΕ_s^B where σ, σ_I, σ°_R are the Hammett polar, Taft inductive and Taft resonance (σ°_R = σ° - σ_I) substituent constants, respectively. Ε _S^B is the steric scale for ortho substituents calculated on the basis of the log k values for the acid hydrolysis of ortho-substituted phenyl benzoates in water owing to the ortho substituent in the phenyl of phenyl benzoates. In water, the main factors responsible for changes in the ortho substituent effect in alkaline hydrolysis of phenyl and ethyl esters of ortho-substituted benzoic acids, X-C₆H₄CO₂R, were found to be the inductive and steric factors while the role of the resonance term was negligible ((ρ°_R)_ortho ca. 0.3). In alkaline hydrolysis of substituted benzoates in neat water, the ortho inductive effect appeared to be 1.5 times and steric influence 2.7 times higher than the corresponding influences from the ortho position in the phenyl of phenyl benzoates. The contributions of the steric effects in alkaline hydrolysis of esters of ortho-substituted benzoic acids was found to be approximately the same as in acid hydrolysis of esters of ortho-substituted benzoic and acid esterification of ortho-substituted benzoic acids.

Full text of DOI:10.1135/cccc20060107

Kinetic Study of Hydrolysis of Benzoates
107
KINETIC STUDY OF HYDROLYSIS OF BENZOATES. PART XXV.
Ortho SUBSTITUENT EFFECT IN ALKALINE HYDROLYSIS OF
PHENYL ESTERS OF SUBSTITUTED BENZOIC ACIDS IN WATER
1,
2
3
Vilve NUMMERT, Mare PIIRSALU *, Vahur MÄEMETS and Ilmar KOPPEL
Institute of Chemical Physics, Tartu University, Jakobi 2, 51014 Tartu, Estonia;
1
2
3
e-mail: mare.piirsalu@ut.ee, vahur.maemets@ut.ee, ilmar.koppel@ut.ee
Received July 26, 2005
Accepted Decem ber 12, 2005
Th e secon d-order rate con stan ts k2 for alkalin e h ydrolysis of ph en yl esters of meta-, para-
an d ortho-substituted ben zoic acids, X-C6H4CO2C6H5 (X = H, 3-Cl, 3-NO2, 3-CH3, 4-NO2,
4-Cl, 4-F, 4-CH3, 4-OCH3, 4-NH2, 2-NO2, 2-CN, 2-F, 2-Cl, 2-Br, 2-I, 2-CH3, 2-OCH3, 2-CF3,
2-NH2), an d of substituted ph en yl esters of ben zoic acid, C6H5CO2C6H4-X (X = 2-I, 2-CF3,
2-C(CH3)3, 4-Cl, 4-CH3, 4-OCH3, 4-NH2), h ave been m easured spectroph otom etrically in wa-
ter at 25 °C. Th e substituen t effect in alkalin e h ydrolysis of ph en yl esters of para-substituted
ben zoic acids, sim ilar to th at for eth yl esters of para-substituted ben zoic acids, was foun d to
be precisely described by th e Ham m ett relation sh ip (ρ = 1.7 in water). Th e log k value for
alkalin e h ydrolysis of ph en yl an d eth yl esters of meta-, para- an d ortho-substituted ben zoic
acids, X-C6H4CO2R, was n icely correlated with log km ,p,orth o = log ko + (ρ)m ,pσ + (ρI)orth oσI
+
(ρ°R)orth oσ°R + δorth oEsB wh ere σ, σI, σ°R are th e Ham m ett polar, Taft in ductive an d Taft reso-
n an ce (σ°R = σ° – σI) substituen t con stan ts, respectively. EsB is th e steric scale for ortho sub-
stituen ts calculated on th e basis of th e log k values for th e acid h ydrolysis of ortho-
substituted ph en yl ben zoates in water owin g to th e ortho substituen t in th e ph en yl of ph en -
yl ben zoates. In water, th e m ain factors respon sible for ch an ges in th e ortho substituen t
effect in alkalin e h ydrolysis of ph en yl an d eth yl esters of ortho-substituted ben zoic acids,
X-C6H4CO2R, were foun d to be th e in ductive an d steric factors wh ile th e role of th e reso-
n an ce term was n egligible ((ρ°R)orth o ca. 0.3). In alkalin e h ydrolysis of substituted ben zoates
in n eat water, th e ortho in ductive effect appeared to be 1.5 tim es an d steric in fluen ce 2.7
tim es h igh er th an th e correspon din g in fluen ces from th e ortho position in th e ph en yl of
ph en yl ben zoates. Th e con tribution s of th e steric effects in alkalin e h ydrolysis of esters of
ortho-substituted ben zoic acids was foun d to be approxim ately th e sam e as in acid h ydrolysis
of esters of ortho-substituted ben zoic an d acid esterification of ortho-substituted ben zoic ac-
ids.
Keyw ord s: Esters; Ph en yl ben zoates; Alkalin e h ydrolysis; Ortho effect; Substituen t effects;
Ham m ett equation .
In our previous papers th e in fluen ce of th e substituen t effects, in particular
ortho substituen ts, on th e kin etics of alkalin e h ydrolysis of meta-, para- an d
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128
© 2006 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20060107

108
Nummert, Piirsalu, Mäemets, Koppel:
ortho-substituted ph en yl esters of ben zoic acid, C6H5CO2C6H4X, in water,
aqueous 80% DMSO, 2.25 M Bu4NBr, 1.0 M Bu4NBr, 0.5 M Bu4NBr, 5.3 M
NaClO4 an d 4.8 M NaCl (see lit.1–5 an d referen ces th erein ) h as been studied.
In th e presen t paper we exten ded th e study of th e ortho substituen t effects
to th e acyl part of substituted ph en yl ben zoates. With th at aim in th e pres-
en t work th e secon d-order rate con stan ts for alkalin e h ydrolysis of ph en yl
esters of substituted ben zoic acid, X-C6H4CO2C6H5 (X = H, 3-Cl, 3-NO2,
3-CH3, 4-NO2, 4-Cl, 4-F, 4-CH3, 4-OCH3, 4-NH2, 2-NO2, 2-CN, 2-F, 2-Cl,
2-Br, 2-I, 2-CH3, 2-OCH3, 2-CF3, 2-NH2), in n eat water at 25 °C were deter-
m in ed an d an alyzed. Recen tly, Bauerová an d Ludwig6,7 studied th e sub-
stituen t effects in th e base-catalyzed h ydrolysis of ph en yl esters of para- an d
ortho-substituted ben zoic acid, X-C6H4CO2C6H5, in 50% (v/v) aqueous
dim eth yl sulfoxide at 25 °C. To our kn owledge, n o system atic kin etic data
on alkalin e h ydrolysis in water of ph en yl esters of substituted ben zoic acids
con tain in g ortho-substituted derivatives togeth er with meta- an d para-sub-
stituted derivatives are in literature.
Th e m ain purpose of th e presen t work was to ch eck wh ich structure fac-
tors, in ductive, reson an ce, or steric, are respon sible for th e ortho substituen t
effect in alkalin e h ydrolysis of ph en yl esters of substituted ben zoic acids in
water an d to com pare th e susceptibilities to th e correspon din g structure
factors in acyl an d in aryl part of ph en yl ben zoates. To separate th e in duc-
tive, reson an ce an d steric com pon en ts, th e kin etic data for alkalin e h ydro-
lysis of ph en yl esters of substituted ben zoic acids were subjected to
correlation an alysis usin g th e Ch arton an d th e com bin ed Ham m ett–
Ch arton equation s.
Com pared to alkalin e h ydrolysis of ph en yl esters of substituted ben zoic
acids, m uch m ore kin etic data are available in literature for alkalin e h ydro-
lysis of eth yl esters of substituted ben zoic acids, X-C6H4CO2C2H5, in various
m edia8–13 in cludin g th e data for ortho-, meta- an d para-substituted deriva-
tives in th e sam e reaction series. To com pare th e substituen t effects, in par-
ticular th e ortho effects in alkalin e h ydrolysis of ph en yl esters of substituted
ben zoic acids with th e substituen t effects in alkalin e h ydrolysis of eth yl
esters of substituted ben zoic acids, th e kin etic data for substituted eth yl
ben zoates in 5% aqueous eth an ol, 56% (w/w) aqueous aceton e, 85% (w/w)
aqueous eth an ol an d 65% aqueous DMSO were treated usin g th e Ham m ett,
Ch arton an d th e com bin ed Ham m ett–Ch arton equation s.
It was in terestin g to com pare th e con tribution of th e steric effects of ortho
substituen ts in alkalin e h ydrolysis of ph en yl an d eth yl esters of ortho-substi-
tuted ben zoic acids with th ose in acid h ydrolysis of esters used to calculate
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
109
th e polar substituen t con stan ts σ*o (ref.14) for ortho substituen ts from th e
In gold–Taft equation . Th erefore th e rate data for acid-catalyzed esterific-
ation of both ortho-substituted an d meta- or para-substituted ben zoic acids
with m eth an ol an d cycloh exan ol an d acid h ydrolysis of ortho-substituted
m eth yl ben zoates taken from literature8,15, were subjected to statistical
an alysis usin g th e in ductive σI, reson an ce σ°R an d steric EsB scales.
Earlier (see lit.1–5 an d referen ces th erein ) th e log k values for alkalin e h y-
drolysis of substituted ph en yl ben zoates, C6H5CO2C6H4-X, in th e case of
meta an d para substituen ts were foun d to correlate with σ° con stan ts. In th e
case of ortho substituen ts, th e log k values for alkalin e h ydrolysis of substi-
tuted ph en yl ben zoates gave exellen t correlation accordin g th e Ch arton
equation usin g th e in ductive σI, th e reson an ce σ°R an d steric EsB scales
(EsB = log kHX+ − log kHH+ , wh ere kHX+ an d kHH+ are th e rate con stan ts for acid
h ydrolysis of ortho-substituted an d un substituted ph en yl ben zoates in water
at 50 °C 2,5). In water in alkalin e h ydrolysis of substituted ph en yl ben zoates,
th e in ductive in fluen ce from ortho position was foun d to be 1.5 tim es stron -
ger th an th at from meta an d para position . In alkalin e h ydrolysis of substi-
tuted ph en yl ben zoates, th e in fluen ce of th e reson an ce term from ortho
position appeared to be n early th e sam e as from para position . Th e varia-
tion of th e in ductive effect of ortho substituen ts with solven t was foun d to
be ca. th ree tim es sm aller th an th at for para substituen ts, wh ile th e ortho
reson an ce term ch an ged with solven t n early sim ilarly to th at for para sub-
stituen ts. In alkalin e h ydrolysis of substituted ph en yl ben zoates, th e sus-
ceptibility to th e steric effect of ortho substituen ts δ ran ged between 0.9 an d
1.4 an d th e values of δ appeared approxim ately in depen den t of th e solven t
ch aracter.
EXPERIMENTAL
Ph en yl esters of substituted ben zoic acids, X-C6H4COOC6H5 (X = 4-NO2, 3-NO2, 3-Cl, 4-Cl,
4-F, 4-OCH3, 4-CH3, 3-CH3, 2-CF3), were syn th esized by th e Sch otten –Baum an n m eth od
from th e correspon din g substituted ben zoyl ch lorides by th e reaction with ph en ol in 10%
aqueous NaOH solution an d th en recrystallized from aqueous eth an ol. Purity of esters was
determ in ed by com parin g th eir m eltin g poin ts with th ose reported in th e literature. Ph en yl
4-n itroben zoate: yield 65%, m .p. 126 °C (ref.6 119–121 °C, ref.16 128–129 °C, ref.17 126 °C).
Ph en yl 3-n itroben zoate: yield 54%, m .p. 95.4–96.0 °C (ref.17 98 °C, ref.18 90–92 °C). Ph en yl
3-ch loroben zoate: yield 46%, m .p. 55.5–55.9 °C (ref.17 53 °C, ref.18 57–58 °C). Ph en yl
4-ch loroben zoate: yield 72%, m .p. 101.7–102.2 °C (ref.16 103.5–104.5 °C, ref.17 100 °C, ref.19
100.5–101.5 °C). Ph en yl 4-fluoroben zoate: yield 61%, m .p. 61.8 °C (ref.6 51–53 °C, ref.20
63.5–64.5 °C). Ph en yl 4-m eth ylben zoate: yield 78%, m .p. 72.8–73.7 °C (ref.17 73 °C, ref.19
70.5–72.5 °C). Ph en yl 4-m eth oxyben zoate: yield 72%, m .p. 71.1–71.8 °C (ref.19 67.5–69 °C).
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

110
Nummert, Piirsalu, Mäemets, Koppel:
Ph en yl 3-m eth ylben zoate: yield 30%, b.p. 129–130 °C/186 Pa (m .p. ref.17 59 °C). Ph en yl
2-(trifluorom eth yl)ben zoate: 41%, b.p. 125–126 °C /106 Pa (ref.7 106–108 °C/133 Pa).
Ph en yl 4-am in oben zoate was syn th esized from 4-n itroben zoate in an h ydrous eth an ol by
reduction with Sn Cl2·2H2O in con cen trated HCl solution : yield 12%, m .p. 167.5–168.3 °C
(ref.21 173 °C).
Ph en yl esters of substituted ben zoic acids, X-C6H4CO2C6H5 (X = 2-F, 2-Cl, 2-OCH3,
2-CH3), were syn th esized from th e correspon din g substituted ben zoyl ch lorides an d ph en ol
in pyridin e solution (th e Ein h orn m eth od22). Ph en yl 2-fluoroben zoate: yield 89%, m .p.
69.0–70.0 °C (ref.23 70–71 °C). Ph en yl 2-ch loroben zoate: yield 59%, b.p. 144–145 °C/133 Pa
(ref.24 138 °C/80 Pa). Phenyl 2-m ethoxybenzoate: yield 77%, m .p. 56.2–57.2 °C (ref.25 57–58 °C).
Ph en yl 2-m eth ylben zoate: yield 47%, b.p. 125–127 °C/93 Pa.
Ph en yl ben zoates, X-C6H4COOC6H5 (X = 2-NO2, 2-Br, 2-OCH3, 2-I), were syn th esized by
addition of on e equivalen t of SOCl2 to an equim olar m ixture of th e correspon din g substi-
tuted ben zoic acid an d ph en ol in pyridin e8. Ph en yl 2-n itroben zoate: yield 69%, m .p.
50.5–52.4 °C (ref.18 50–52 °C, ref.23 52–53 °C). Ph en yl 2-brom oben zoate: yield 17%, b.p.
142–143 °C/80 Pa (ref.7 137–139 °C/133 Pa). Ph en yl 2-iodoben zoate: yield 16%, b.p.
165–167 °C/93 Pa (ref.7,26 146–148 °C/133 Pa).
Ph en yl 2-cyan oben zoate was syn th esized sim ilarly to eth yl 2-cyan oben zoate27 from
ph th alic m on oam ide an d ph en ol in pyridin e solution in th e presen ce of p-toluen esulfon yl
ch loride: yield 68%, m .p. 70–71 °C (ref.28 73 °C).
Ph en yl 2-am in oben zoate was obtain ed from isatoic acid an h ydride an d ph en ol in
1,4-dioxan e solution in th e presen ce of NaOH pellets29: yield 87%, m .p. 69.4–70.1 °C (ref.30
70 °C).
Purity of substituted ph en yl ben zoates, X-C6H4COOC6H5 (X = 2-Cl, 2-Br, 2-I, 2-CH3,
2-CF3), was con firm ed by 1H an d 13C NMR spectroscopy. Th e 1H an d 13C NMR spectra were
m easured in deuterated ch loroform . Th e 1H an d 13C NMR ch em ical sh ifts δ (in ppm ) were
m easured at 25 °C with th e Bruker AC-200 spectrom eter operatin g at 200.13 MHz for 1H an d
at 50.32 MHz for 13C. Th e ch em ical sh ifts are referen ced to an in tern al TMS. Couplin g con -
stan ts (J) are given in Hz.
6
5
3
9
10
12
O
1
8
4
11
C
7
O
2
13
X
Ph en yl 2-ch loroben zoate (X = Cl): 1H NMR: 7.20–7.55 m , 8 H (H-3,4,5,9,10,11,12,13);
8.03 m , 1 H (H-6), 3J = 7.7. 13C NMR: 129.60 (C-1); 134.36 (C-2); 131.31 (C-3); 133.08 (C-4);
126.73 (C-5); 131.82 (C-6); 164.05 (C-7); 150.83 (C-8); 121.61 (C-9,13); 129.52 (C-10,12);
126.08 (C-11).
Ph en yl 2-brom oben zoate (X = Br): 1H NMR: 7.72 m , 1 H (H-3); 7.20–7.50 m , 7 H
(H-4,5,9,10,11,12,13); 8.00 m , 1 H (H-6). 13C NMR: 131.71 (C-1); 122.22 (C-2); 133.04 (C-3);
134.61 (C-4); 127.30 (C-5); 131.74 (C-6); 164.54 (C-7); 150.84 (C-8); 121.58 (C-9,13); 129.52
(C-10,12); 126.10 (C-11).
Ph en yl 2-iodoben zoate (X = I): 1H NMR: 8.01 dd, 1 H (H-3), 3J = 7.9, 4J = 0.4; 7.15–7.24 m ,
4 H (H-4,9,11,13); 7.35–7.45 m , 3 H (H-5,10,12); 8.00 dd, 1 H (H-6), 3J = 7.8, 4J = 0.4. 13C NMR:
134.39 (C-1); 94.43 (C-2); 141.51 (C-3); 133.05 (C-4); 128.00 (C-5); 131.34 (C-6); 164.74
(C-7); 150.72 (C-8); 121.50 (C-9,13); 129.43 (C-10,12); 126.09 (C-11).
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
111
Ph en yl 2-m eth ylben zoate (X = CH3): 1H NMR: 7.13–7.50 m , 8 H (H-3,4,5,9,10,11,12,13);
8.15 dd, 1 H (H-6), 3J = 8.6, 4J = 2.0; 2.66 s, 3 H (H-14). 13C NMR: 128.79 (C-1); 141.17
(C-2); 131.12 (C-3); 132.62 (C-4); 125.90 (C-5); 131.93 (C-6); 165.76 (C-7); 151.07 (C-7);
121.82 (C-8,13); 129.44 (C-9,12); 125.75 (C-10); 21.82 (C-14).
6
5
9
10
12
O
1
8
4
11
C
7
O
2
3
13
CH3
14
Ph en yl 2-(trifluorom eth yl)ben zoate: 1H NMR: 7.75 m , 1 H (H-3); 7.50–7.65 m , 2 H (4,5);
7.92 m , 1 H (H-6); 7.15–7.30 m , 3 H (H-9,11,13); 7.30–7.45 m , 2 H (H-10,12). 13C NMR:
2
3
4
129.04 q (C-2), JC-F = 32.6; 126.93 q (C-3), JC-F =5.4; 132.02 q (C-4), JC-F = 1.2; 131.77
(C-5); 130.61 (C-6); 165.23 (C-7); 150.89 (C-8); 121.44 (C-9,13); 129.66 (C-10,12); 126.32
1
(C-11); 123.69 q (C-14), JC-F = 273.6.
6
5
9
10
12
O
1
8
4
11
C
7
O
2
3
13
CF3
14
Th e preparation procedure an d ch aracteristics of substituted ph en yl ben zoates,
C6H5CO2C6H4-X (X = 4-Cl, 4-CH3, 4-OCH3, 4-NH2, 2-CF3, 2-I, 2-C(CH3)3), were described in
lit.5
Th e kin etics was m easured spectroph otom etrically as described earlier1–4. Th e kin etic m ea-
surem en ts were carried out un der pseudo-m on om olecular con dition s. Th e pseudo-first-order
rate con stan ts, k1 (s–1), were determ in ed usin g a least-squares com puter program . Rate con -
stan ts for each ph en yl esters of substituted ben zoic acids were m easured at various NaOH
con cen tration s. Th e m easurem en t at each h ydroxide con cen tration s was repeated an d th e
arith m etic m ean s of th e correspon din g pseudo-first-order rate con stan ts, k1 (s–1), were calcu-
lated. Th e secon d-order rate con stan ts k (dm 3 m ol–1 s–1) were calculated as slopes of th e
pseudo-first-order rate con stan ts vs NaOH con cen tration depen den ces accordin g to th e fol-
lowin g equation
k1 = kcOH – + con st .
(1)
Th e secon d-order rate con stan ts k for alkalin e h ydrolysis of ph en yl esters of substituted ben -
zoic acids, X-C6H4CO2C6H5, in water at 25 °C an d th e wavelen gth λ used in spectroph oto-
m etric kin etic m easurem en ts are given in Table I.
Th e secon d-order rate con stan ts k for alkalin e h ydrolysis of substituted ph en yl esters of
ben zoic acids, C6H5CO2C6H4-X (X = 4-Cl, 4-CH3, 4-OCH3, 4-NH2, 2-CF3, 2-I, 2-C(CH3)3), in
water at 25 °C an d th e wavelen gth λ used in spectroph otom etric kin etic m easurem en ts are
given in Table II.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

112
Nummert, Piirsalu, Mäemets, Koppel:
TABLE I
Th e secon d-order rate con stan ts k (in dm 3 m ol–1 s–1) for alkalin e h ydrolysis of ph en yl esters
of substituted ben zoic acids, X-C6H4CO2C6H5, in water at 25 °C
k
k
c
c
λ, n m a
X
λ, n m a
n/n1
n/n1
X
dm 3 m ol–1 s–1b
dm 3 m ol–1 s–1b
H
244, 292
225, 292
225, 292
250
0.363±0.008 8/34
2-NO2 235, 292
1.25±0.04
8.47±0.44
4/414
4/14
4/17
4/22
4/25
4/12
3-Cl
1.50±0.03
5.59±0.17
8/39
5/24
2-CN
2-F
235
3-NO2
3-CH3
4-NO2
4-Cl
230, 292
250, 292
250, 292
250
1.42±0.02
0.296±0.009 3/8
2-Cl
2-Br
2-I
0.962±0.039
0.657±0.031
0.530±0.035
235
7.90±0.54
5/20
282
0.837±0.028 5/22
0.470±0.006 3/14
0.203±0.011 3/17
0.109±0.002 3/12
0.0245±0.0015 3/9
4-F
245
2-CF3
230
0.0780±0.0034 4/14
4-CH3
235, 292
2-NH2 235, 292 0.0416±0.0010 3/15
2-OCH3 235 0.188±0.004 3/12
2-CH3 250, 292 0.0812±0.0027 3/15
4-OCH3 235
4-NH2 235
a
b
λ is th e wavelen gth used in kin etic m easurem en ts. To calculate th e secon d-order rate
c
con stan ts, k, Eq. (1), k1 = kcOH − + con st, was used. n equals to th e n um ber of NaOH con cen -
tration s used to determ in e th e k value accordin g to Eq. (1), n1 equals to th e total n um ber of
m easurem en ts used in determ in ation of th e k value.
TABLE II
Th e secon d-order rate con stan ts k (in dm 3 m ol–1 s–1) for alkalin e h ydrolysis of substituted
ph en yl esters of ben zoic acids, C6H5CO2C6H4-X, in water at 25 °C
k
k
X
λ, n m a
nc
X
λ, n m a
nc
dm 3 m ol–1 s–1b
dm 3 m ol–1 s–1b
4-Cl
302
296
307
240
0.958±0.031
0.235±0.006
0.315±0.012
0.192±0.007
3
4
5
3
2-CF3
2-I
301
301
0.703±0.026
0.536±0.031
4
4
3
4-CH3
4-OCH3
4-NH2
2-C(CH3)3 240
0.0745±0.0167
a
b
λ is th e wavelen gth used in kin etic m easurem en ts. Th e secon d-order rate con stan ts, k,
were calculated by dividin g th e pseudo-first-order rate con stan ts, k1, by alkali con cen tration .
c
0.0192 M NaOH was used. n equals to th e n um ber of m easurem en ts used to determ in e th e
value of k.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
113
DATA PROCESSING
For study of th e substituen t effects in alkalin e h ydrolysis of ph en yl esters of
substituted ben zoic acids, th e log k values, m easured in th e presen t work
(Table I) were treated usin g th e Ham m ett31 equation (2), th e com bin ed
Ham m ett–Ch arton equation (3), an d th e Ch arton 32 equation (4)
log km ,p = log ko + (ρ)m ,p
log km ,p,orth o = log ko + (ρ)m ,p σ + (ρI)orth o σI + (ρ°R)orth o σ°R + δorth o EsB (3)
log korth o = log ko + (ρI)orth o σI + (ρ°R)orth o σ°R + δorth o EsB
σ
(2)
.
(4)
To correlate th e log k values for meta- an d para-substituted derivatives th e
Ham m ett equation (2) was used. Th e log k values for ortho-substituted de-
rivatives togeth er with meta- an d para-substituted derivatives were treated
usin g th e Ham m ett–Ch arton com bin ed equation (3). For com parison , th e
data on ly for ortho-substituted derivatives were correlatated with th e
Ch arton equation (4).
In th e data processin g, usin g th e Eq. (4) th e log k value for un substituted
derivative (X = H) as stan dard was in cluded besides th e ortho-substituted de-
rivatives. Th e values of th e Ham m ett polar substituen t con stan ts, σ, re-
34
viewed by Han sch , Leo an d Taft33, th e Taft in ductive σI an d reson an ce
σ°R con stan ts35 (σ°R = σ° – σI) were used in th e data processin g. As th e steric
con stan ts for ortho substituen ts we em ployed th e values of EsB determ in ed
on th e basis of th e acid h ydrolysis of ortho-substituted ph en yl ben zoates,
B
C6H5CO2C6H4-X, with ortho substituen ts in th e ph en yl part2,5 (Es
=
log kHX+ − log kHH+ , wh ere kHX+ an d kHH+ are th e rate con stan ts for th e acid h y-
drolysis of ortho-substituted an d un substituted ph en yl ben zoates in water at
50 °C 36). Th e values of σI, σ°R an d EsB are listed in Table VII. In th e data
processin g usin g Eqs (2)–(4), th e secon d-order rate con stan ts k of alkalin e
h ydrolysis of ph en yl esters of ortho-, meta- an d para-substituted ben zoic ac-
ids at 25 °C, listed in Table I, were used. For com parison , th e log k for alka-
lin e h ydrolysis of ph en yl esters of ortho- an d para-substituted ben zoic acids
in 50% aqueous DMSO reported by Bauerova an d Ludwig6,7 an d eth yl esters
of ortho-, meta- an d para-substituted ben zoic acids for 5% aqueous eth an ol,
56% (w/w) aqueous aceton e, 85% (w/w) aqueous eth an ol an d 65% aqueous
DMSO at 25 °C, taken from literature8, were processed usin g Eqs (2)–(4) as
well (Tables III an d IV). To com pare steric con tribution s of ortho substitu-
en ts in alkalin e h ydrolysis an d in acid h ydrolysis of esters, th e log k values
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

114
Nummert, Piirsalu, Mäemets, Koppel:
TABLE III
Correlation of th e log k values for alkalin e h ydrolysis of ph en yl esters of substituted ben zoic
6,7
acids, X-C6H4CO2C6H5, at 25 °C with Eqs (2)–(4) in water an d 50% aqueous DMSO
Meta an d
para
substituen ts
Eq. (2)
Ortho, meta
an d para
substituen ts
Eq. (3)
Ortho
substituen ts
Eq. (4)
Reaction
con stan t
Weigh t
Weigh t
Weigh t
Watera
log ko
–0.451±0.011
1.720±0.025
–0.433±0.045
–0.439±0.042b
–0.438±0.065c
1.710±0.055
1.713±0.046b
1.713±0.080c
2.244±0.084
2.193±0.075b
2.230±0.124c
0.236±0.102
0.398±0.105b
0.380±0.147c
2.536±0.117
2.263±0.142b
–1.168±0.081c
20/20
–0.333±0.078
–0.363±0.084b
–0.356±0.102c
ρm ,p
1.00
0.538
0.570
0.544
0.223
0.271
0.224
0.015
0.034
0.025
0.223
0.125
0.207
(ρI)orth o
2.128±0.122
2.117±0.119b
2.123±0.163c
0.312±0.134
0.433±0.140b
0.442±0.171c
2.669±0.160
2.398±0.214b
–1.262±0.102c
11/11
0.538
0.636
0.538
0.039
0.082
0.056
0.423
0.280
0.406
(ρ°R)orth o
δorth o
n/n0
10/10
0.999
0.033
0.044
0.990
17/17b
20/20c
8/8b
10/11c
R
s
0.995
0.997b
0.989c
0.992
0.994b
0.987c
0.072
0.060b
0.106c
0.085
0.079b
0.113c
s0
0.101
0.080b
0.148c
0.126
0.105b
0.160c
t
0.990
0.990
0.990b
0.990b
0.999c
0.990c
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
115
TABLE III
(Continued)
Meta an d
para
substituen ts
Eq. (2)
Ortho, meta
an d para
substituen ts
Eq. (3)
Ortho
substituen ts
Eq. (4)
Reaction
con stan t
Weigh t
Weigh t
Weigh t
50% aqueous DMSOd
log ko
–0.018±0.028
2.322±0.062
–0.015±0.065
–0.017±0.061e
2.321±0.061
2.322±0.061e
2.357±0.157
2.308±0.163e
0.726±0.160
0.842±0.194e
2.593±0.197
2.395±0.271e
26/26
0.047±0.104
0.021±0.122e
ρm ,p
1.00
0.836
0.848
0.062
0.079
0.021
0.027
0.081
0.045
(ρI)orth o
2.310±0.157
2.284±0.164e
0.777±0.167
0.862±0.189e
2.693±0.232
2.477±0.323e
10/10
0.62
0.69
(ρ°R)orth o
0.102
0.152
0.276
0.158
δorth o
n/n0
17/17
0.994
0.114
0.105
0.990
25/25e
9/9e
R
s
0.993
0.987
0.993e
0.986e
0.113
0.106
0.113e
0.106e
s0
0.119
0.167
0.117e
0.164e
t
0.990
0.990
0.990e
0.990e
a
Th e log k values for ortho-substituted esters, X-C6H4CO2C6H5, wh ere X = H, 2-NO2, 2-F, 2-I,
b
2-Br, 2-Cl, 2-NH2, 2-CN, 2-OCH3, 2-CF3, 2-CH3, were in cluded. Th e log k values for 2-CF3,
2-I, 2-Br derivatives were excluded before data treatm en t. In th e case of ortho-substituted
esters th e steric scale of υ was used (Table VII). Th e log k values for ortho-substituted esters
wh ere X = H, 2-NO2, 2-F, 2-I, 2-Br, 2-Cl, 2-NH2, 2-OCH3, 2-CF3, 2-CH3, were in cluded. Th e
c
d
e
log k value for 2-CF3 derivative was excluded before data treatm en t.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

116
Nummert, Piirsalu, Mäemets, Koppel:
TABLE IV
Correlation of th e log k values for alkalin e h ydrolysis of eth yl esters of substituted ben zoic
acids, X-C6H4CO2C2H5, with Eqs (2)–(4) at 25 °C for water, 56% aqueous aceton e, 85%
8
aqueous eth an ol an d 65% aqueous DMSO
Meta an d
para
substituen ts
Eq. (2)
Ortho, meta
an d para
substituen ts
Eq. (3)
Ortho
substituen ts
Eq. (4)
Reaction
con stan t
Weigh t
Weigh t
Weigh t
5% aqueous eth an ola
log ko
–1.483±0.031
1.437±0.075
–1.465±0.104
–1.477±0.074b
1.413±0.140
1.425±0.072b
1.947±0.249
1.537±0.169b
–
–1.444±0.241
–1.519±0.032b
ρm ,p
1.00
0.503
(ρI)orth o
–0.043
1.942±0.359
1.532±0.429b
–
0.546
0.862
(ρ°R)orth o
0.334±0.231b
3.466±0.339
2.733±0.286b
14/14
0.293±0.061b
3.526±0.689
2.595±0.094b
7/7
0.028
0.454
0.110
δorth o
0.540
n/n0
8/8
12/12b
5/5b
R
s
0.991
0.079
0.136
0.990
0.975
0.991b
0.930
0.998b
0.148
0.077b
0.212
0.019b
s0
t
0.221
0.138b
0.368
0.054b
0.990
0.990
0.999b
0.990b
56% (w/w) aqueous aceton ec
log ko
ρm ,p
–2.471±0.035
2.332±0.079
–2.472±0.096
–2.472±0.084d
–2.514±0.232
–2.521±0.202d
1.00
2.333±0.093
2.333±0.084d
2.357±0.157
2.457±0.188d
0.751±0.288
0.743±0.256d
2.891±0.378
2.770±0.352d
28/28
0.766
0.764
0.046
0.074
0.043
0.041
0.144
0.120
(ρI)orth o
(ρ°R)orth o
δorth o
2.394±0.325
2.508±0.283d
0.731±0.395
0.720±0.340d
2.815±0.597
2.683±0.514d
10/10
n/n0
19/19
26/26d
8/8d
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
117
TABLE IV
(Continued)
Meta an d
para
substituen ts
Eq. (2)
Ortho, meta
an d para
substituen ts
Eq. (3)
Ortho
substituen ts
Eq. (4)
Reaction
con stan t
Weigh t
Weigh t
Weigh t
R
s
0.990
0.141
0.142
0.990
0.985
0.988d
0.167
0.152d
0.175
0.154d
0.990
0.999d
0.960
0.978d
0.225
0.190d
0.278
0.209d
0.999
0.999d
s0
t
85% (w/w) aqueous eth an ole
–3.167±0.075
log ko
–3.168±0.044
2.546±0.097
–3.207±0.062
ρm ,p
1.00
2.544±0.089
2.607±0.142
1.228±0.182
2.637±0.272
10/10
0.772
(ρI)orth o
0.062
0.046
0.119
2.608±0.080
1.178±0.112
2.507±0.191
5/5
(ρ°R)orth o
0.991
δorth o
n/n0
6/6
R
s
0.996
0.081
0.085
0.990
0.997
0.998
0.074
0.042
s0
t
0.083
0.060
0.990
0.990
65% (w/w) aqueous DMSOf
–1.401±0.072
log ko
–1.397±0.027
2.376±0.069
–1.476±0.101
ρm ,p
1.00
2.379±0.077
2.257±0.150
1.247±0.152
2.161±0.243
9/9
0.690
(ρI)orth o
0.151
0.103
0.056
2.249±0.146
1.216±0.149
1.921±0.292
5/5
(ρ°R)orth o
δorth o
n/n0
5/5
R
s
0.998
0.058
0.058
0.990
0.997
0.996
0.064
0.062
s0
t
0.074
0.093
0.990
0.990
a
Th e log k values for ortho-substituted esters, X-C6H4CO2C2H5, wh ere X = H, 2-NO2, 2-Br,
b
2-Cl, 2-NH2, 2-OCH3, 2-CH3, were in cluded. Th e log k values for 2-OCH3 an d 2-NH2 deriv-
atives were excluded before data treatm en t. Th e log k values for ortho-substituted esters,
wh en X = H, 2-NO2, 2-CN, 2-F, 2-Br, 2-Cl, 2-I, 2-NH2, 2-OCH3, 2-CH3, were in cluded. Th e
log k values for 2-CF3, 2-I, 2-Br derivatives were excluded before data treatm en t. Th e log k
c
d
e
f
values for ortho-substituted esters, wh en X = H, 2-NO2, 2-F, 2-Cl, 2-CH3, were in cluded. Th e
log k values for ortho-substituted esters, wh en X = H, 2-NO2, 2-Cl, 2-OCH3, 2-CH3, were in -
cluded.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

118
Nummert, Piirsalu, Mäemets, Koppel:
for acid esterification of substituted ben zoic acids in m eth an ol at 25 °C 15
,
acid h ydrolysis of substituted m eth yl esters in 80% (v/v) aqueous m eth an ol
at 100.8 °C 8 an d acid esterification of substituted ben zoic acids in cyclo-
h exan ol at 55 °C 15 were correlated with Eq. (3) as well (Table V).
Th e results of th e data treatm en t with Eqs (2)–(4) for alkalin e h ydrolysis
of substituted ph en yl ben zoates in water at 25 °C in cludin g th e rate con -
stan ts m easured in th e presen t work an d th ose reported earlier1 are sh own
in Table VI.
For com parison , we correlated th e log k values for alkalin e h ydrolysis of
ph en yl esters of ortho-, meta- an d para-substituted ben zoic acids at 25 °C,
substituted ph en yl ben zoates in water at 25 °C an d for acid esterification of
TABLE V
Th e results of correlation of th e Taft steric E°s values14 with Eq. (4) an d th e log k values for
15
acid esterification of substituted ben zoic acids in m eth an ol at 25 °C
(set A), acid h ydroly-
8
sis of substituted m eth yl esters in 80% (v/v) aqueous m eth an ol at 100.8 °C (set B) an d acid
esterification of substituted ben zoic acids in cycloh exan ol at 55 °C15 (set C) with Eq. (3)
Reaction
con stan t
Taft steric E°sa
Eq. (4)
Set Ab
Eq. (3)
Set Bc
Eq. (3)
Set Cd
Eq. (3)
log ko
ρm ,p
(ρI)orth o
(ρ°R)orth o
δorth o
n/n0
R
0.518±0.176
–3.696±0.052
–3.713±0.067e
–0.525±0.063
–0.497±0.085e
–0.365±0.101
–0.491±0.101
–1.793±0.128
–1.885±0.167e
2.657±0.182
–1.087±0.102e
14/14
–3.787±0.084
–0.119±0.087
–0.556±0.163
–1.641±0.328
3.076±0.201
9/9
–4.741±0.057
0.320±0.090
0.122±0.113
–1.021±0.124
1.852±0.196
15/15
–0.135±0.119
–1.262±0.284
2.520±0.466
7/7
14/14e
0.993
0.992
0.985e
0.986
0.981
s
0.062
0.053
0.071e
0.054
0.060
s0
0.112
0.126
0.170e
0.168
0.193
a
Th e Taft steric E°s values for 2-NO2, 2-Cl, 2-F, 2-Br, 2-I, 2-CH3, 2-OCH3 were in cluded.
2-NO2, 2-Cl, 2-F, 2-Br, 2-I, 2-CH3 derivatives were in cluded. Th e log k value for 2-OCH3 de-
b
c
d
rivative was excluded. 2-Cl, 2-F, 2-Br, 2-I, 2-CH3 derivatives in cluded. 2-NO2, 2-Cl, 2-F,
2-Br, 2-I, 2-CH3, 2-OCH3 derivatives in cluded. In th e case of ortho substituted esters th e
e
steric scale of υ was used (Table VII).
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
119
TABLE VI
Th e results of th e correlation of th e log k values for alkalin e h ydrolysis of substituted ph en yl
esters of ben zoic acids, C6H5CO2C6H4-X, with Eqs (2)–(4) at 25 °C in water
Meta an d
para
substituen ts
Eq. (2)
Ortho, meta
an d para
substituen ts
Eq. (3)
Ortho
substituen ts
Eq. (4)
Reaction
con stan t
Weigh t
Weigh t
Weigh t
Watera
log ko
–0.396±0.035
1.145±0.046
–0.396±0.045
–0.399±0.033b
–0.397±0.034c
1.142±0.051
1.145±0.041b
1.143±0.050c
1.549±0.067
1.566±0.041b
1.541±0.066c
1.077±0.085
1.097±0.159b
1.166±0.085b
0.952±0.080
–0.427±0.034b
–0.449±0.038c
22/22
–0.406±0.078
–0.430±0.027b
–0.410±0.061c
ρm ,p
1.00
0.404
0.705
0.405
0.261
0.136
0.260
0.190
0.013
0.202
0.144
0.146
0.133
(ρI)orth o
1.560±0.097
1.573±0.041b
1.556±0.041c
1.070±0.104
1.033±0.083b
1.155±0.104c
0.937±0.122
–0.400±0.023b
–0.440±0.056c
11/11
0.590
0.941
(ρ°R)orth o
0.267
–0.092
δorth o
0.142
0.152
n/n0
12/12
0.991
0.059
0.131
0.990
18/18b
22/22c
7/7b
11/11c
R
s
0.992
0.993b
0.993c
0.992
0.998b
0.993c
0.065
0.052b
0.064c
0.075
0.024b
0.073c
s0
0.123
0.117b
0.121c
0.126
0.060b
0.123c
t
0.990
0.990
0.990b
0.990c
0.990b
0.993c
a
Th e Taft substituen t con stan ts σ° used in Eqs (2) an d (3). Th e log k values for ortho-substi-
tuted esters, C6H4CO2C6H4-X, wh ere X = H, 2-NO2, 2-CN, 2-F, 2-I, 2-Cl, 2-N(CH3)2, 2-OCH3,
b
2-CF3, 2-CH3 2-C(CH3)3, were in cluded. In th e case of ortho-substituted esters th e steric
scale of υ was used (Table VII). X = H, 2-F, 2-I, 2-Cl, 2-CF3, 2-CH3, 2-C(CH3)3 derivatives
c
were in cluded.
Th e steric scale of υ was used. X = H, 2-NO2, 2-CN, 2-F, 2-I, 2-Cl,
2-N(CH3)2, 2-OCH3, 2-CF3, 2-CH3, 2-C(CH3)3 derivatives were in cluded.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

120
Nummert, Piirsalu, Mäemets, Koppel:
substituted ben zoic acids in m eth an ol at 25 °C 15 with Eqs (3) an d (4) usin g
two steric scales for ortho substituen ts: th e EsB con stan ts an d th e Ch arton
scale of υ 37 (Tables III, V an d VI).
In th e case of substituen ts X = H, F, Br, Cl, I, CH3, t-Bu, CF3, th e steric
con stan ts EsB appeared to be n early lin ear fun ction of th e υ values, based on
a con sideration of van der Waals radii rv. Th e values of rv proposed in lit-
TABLE VII
Substituen t param eters for correlation s usin g Eqs (3) an d (4)
34
37,d
X
σI
σR° 34
EsB 2,5,36
υ
H
0
0
0
0
2-NO2
2-CN
2-F
0.63
0.58
0.52
0.47
0.45
0.39
0.10
0.10
–0.05
0.41
0.25
–0.07
0.19
–0.374
–0.030
–0.155
–0.243
–0.270a
–0.300b
–0.425
–0.425
–0.264
–0.593c
–0.308
–0.604
0.76e
0f
0.11
–0.35
–0.20
–0.19
–0.12
–0.48
–0.54
–0.10
0.10
0.2737
0.5537
0.6537
0.7837
0.76e
0.76e
0.5637
1.24g
0.56h
1.2437
2-Cl
2-Br
2-I
2-NH2
2-N(CH3)2
2-CH3
2-CF3
2-OCH3
2-C(CH3)3
–0.41
–0.08
Average value, calculated from log k = 0.477 + (1.145)o,m ,pσ° + (0.454)oσI + 0.884EsB (R =
0.990, s = 0.06), wh ere k are th e rate con stan ts for alkalin e h ydrolysis of substituted ph en yl
acetates in 3% eth an ol at 25 °C; from log k = –4.364 + (1.108)o,m ,pσ° +1.660EsB (R = 0.987, s
= 0.07), wh ere k are th e rate con stan ts for alkalin e h ydrolysis of substituted ph en yl
N,N-dim eth yl carbam ates (Nish ioka T, Fujita T., Kim utara K., Nakajim a M.: J. Org. Chem.
1975, 40, 2520); an d from kin etic data for alkalin e h ydrolysis of substituted eth yl ben zoates
a
in 5% aqueous eth an ol9 (Table IV in th e presen t work). Average value, calculated from log
k = 0.477 + (1.145)o,m ,pσ° + (0.454)oσI + 0.884EsB (R = 0.990, s = 0.06), wh ere k are th e rate
b
con stan ts for alkalin e h ydrolysis of substituted ph en yl acetates in 3% eth an ol at 25 °C an d
5
kin etic data for alkalin e h ydrolysis of substituted ph en yl ben zoates in water at 25 °C (Table
c
VI in th e presen t work). Average value, calculated from kin etic data for alkalin e h ydrolysis
of ph en yl esters of substituted ben zoic acids in 50% aqueous DMSO (Table III in th e presen t
work) an d kin etic data for alkalin e h ydrolysis of substituted ph en yl esters of ben zoic acid in
d
e
f
water (Table VI in th e presen t work). ν = rνX –rνH
value of υ for H
.
Th e value of υ for iPr 37 was used. Th e
37
g
37
h
37
was used. Th e value of υ for t-Bu
was used. Th e value of υ for Et
was used.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
121
erature for th e polyatom ic substituen ts NO2 (υ = 0.35 37, 1.39 37, 0.98 38
,
0.59 39), NH2 (υ = 0.35 37,40), N(CH3)2 (υ = 0.43 40), OCH3 (υ = 0.36 40) an d
CN (υ = 0.40 37,40) deviate from th is lin earity. Th erefore, we used in correla-
tion s for polyatom ic substituen ts th e value of υ for th e followin g isosterical
substituen ts41: for NO2, NH2, N(CH3)2 th e value of υ for CH(CH3)2 (υ =
0.76 37) an d for OCH3 th e value of υ for CH2CH3 (υ = 0.56 37) (Table VII).
Th e data processin g was carried out usin g a m ultiple param eter lin ear
least-squares (LLSQ) procedure42. Sign ifican tly deviatin g poin ts were ex-
cluded usin g th e Studen t criterion . Results of th e data treatm en t in th e
presen t work are given m ain ly on th e con fiden ce level t = 0.99.
DISCUSSION
Effect of Place of Substitution
Previously6, th e variation of th e reaction rates due to th e polar effect of sub-
stituen ts in alkalin e h ydrolysis of ph en yl esters of para-substituted ben zoic
acids in 50% aqueous DMSO at 25 °C an d in alkalin e h ydrolysis of eth yl
esters of para-substituted ben zoic acids in various m edia h as been described
by th e Ham m ett σ con stan ts9,10,31. Sim ilarly, th e log k values for alkalin e
h ydrolysis of ph en yl esters of meta- an d para-substituted ben zoic acids in
water at 25 °C, determ in ed in th e presen t work, gave excellen t correlation
with th e Ham m ett σ con stan ts (Table III). Th e susceptibility to th e polar ef-
fect of meta an d para substituen ts in alkalin e h ydrolysis of ph en yl esters of
meta- an d para-substituted ben zoic acids in water at 25 °C (ρm ,p = 1.72) is
com parable with th e polar substituen t effect in alkalin e h ydrolysis of eth yl
esters of meta- an d para-substituted ben zoic acids in 5% aqueous eth an ol at
25 °C (ρm ,p = 1.44) (Table IV). Th e susceptibility to th e polar effect of meta
an d para substituen ts in alkalin e h ydrolysis of ph en yl esters of meta- an d
para-substituted ben zoic acids in water at 25 °C is 1.6 tim es h igh er th an th e
polar effect in alkalin e h ydrolysis of meta- an d para-substituted ph en yl es-
ters of ben zoic acid in n eat water at 25 °C (ρ°m ,p = 1.14) (Table VI). Con se-
quen tly, in alkalin e h ydrolysis of substituted ph en yl ben zoates in water at
25 °C, th e polar effect of meta an d para substituen ts from acyl com pon en t
appeared to be ca. 1.6 tim es h igh er th an th e polar in fluen ce of meta an d
para substituen ts from th e ph en yl com pon en t.
Previously1–5, in alkalin e h ydrolysis of substituted ph en yl ben zoates,
C6H5CO2C6H4-X, th e in fluen ce of ortho substituen ts from th e ph en yl com -
pon en t of ester in various m edia an d at various tem peratures was precisely
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

122
Nummert, Piirsalu, Mäemets, Koppel:
described by th e in ductive, σI, reson an ce, σ°R, an d steric, EsB, con stan ts
(Table VII). Th erefore, in th e presen t paper we used th e sam e substituen t
con stan ts for ortho substituen ts (σI, σ°R, EsB) to correlate th e log k values
for alkalin e h ydrolysis of ph en yl an d eth yl esters of ortho-substituted ben -
zoic acids (X-C6H4CO2C6H5, X-C6H4CO2C2H5), in cludin g ortho substituen ts
in th e acyl com pon en t of ester. Th e values of reaction con stan ts (ρI)orth o
,
(ρ°R)orth o an d δorth o calculated from Eq. (4) separately for ortho-substituted
derivatives are approxim ately th e sam e as th ose calculated togeth er with
ortho-, meta- an d para-substituted derivatives usin g Eq. (3) (see Tables III
an d IV).
Th e in fluen ce of th e ortho substituen ts in alkalin e h ydrolysis of ph en yl
an d eth yl esters of substituted ben zoic acids is n icely described with th e σI,
(ρ°R)orth o an d EsB con stan ts (Tables III an d IV). In alkalin e h ydrolysis of
ph en yl esters of substituted ben zoic acids in water, th e m ain factors respon -
sible for th e ortho substituen t effect were foun d to be in ductive ((ρI)orth o
=
2.12) an d steric (δorth o = 2.67) factors wh ile th e reson an ce factor appeared to
be n egligible ((ρ°R)orth o = 0.3). Figure 1 illustrates th e depen den ce of th e in -
1.2
2-NO
2
1.0
0.8
0.6
0.4
0.2
2-CN
2-Cl
2-I
2-F
2-Br
2-CF
3
2-OCH
3
0.0
2-NH
2
–0.2
2-CH
3
–0.4
H
–0.6
–0.4 –0.2 0.0
0.2
0.4
0.6
0.8
1.0
σ
I
FIG. 1
Th e depen den ce of th e in ductive term (log k – 0.3σ°R – 2.67EsB) on σI values for alkalin e h ydro-
lysis of ph en yl esters of ortho-substituted ben zoic acids, X-C6H4CO2C6H5, in water at 25 °C
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
123
B
ductive term , represen ted as (log k – 0.3σ°R – 2.67ES ) on th e σI values for al-
kalin e h ydrolysis of ph en yl esters of ortho-substituted ben zoic acids in wa-
ter. In th e case of ortho substituen ts, th e susceptibility to th e in ductive
in fluen ce in ph en yl an d eth yl esters of substituted ben zoic acids in water
an d 5% aqueous eth an ol, respectively, was foun d to be ca. 1.3 tim es stron -
ger th an th e in ductive in fluen ce for meta an d para substituen ts. In water,
th e ortho in ductive effect from th e acyl com pon en t of esters appeared to be
1.5 tim es h igh er th an th at from th e ph en yl com pon en t of esters.
In alkalin e h ydrolysis of ph en yl esters of ortho-substituted ben zoic acids
th e con tribution of th e steric effects in water (δorth o = 2.67) was foun d to be
th e sam e as in 50% aqueous DMSO (δorth o = 2.69, Table III). In alkalin e h y-
drolysis of eth yl esters of ortho-substituted ben zoic acids th e values of δorth o
appeared in th e ran ge from 1.9 to 3.1 (Table IV). In ortho-substituted ph en -
yl ben zoates, th e steric effects in th e acyl com pon en t of esters are ca. 2.7
tim es stron ger th an th e steric effects from th e ph en yl com pon en t of esters
(δorth o = 1.0, Table VI). In Fig. 2 th e relation sh ip between th e steric effects in
0.0
2-CN
H
–0.5
2-F
2-CH
3
–1.0
2-Cl
2-I
2-OCH
3
2-NO
2
–1.5
–2.0
–2.5
2-CF
3
–1.2
–0.8
–0.4
0.0
log k
– 1.10σ° – 1.54σ (PhCO C H -X)
R I 2 6 4
ortho
FIG. 2
Relation sh ip between th e steric effects in alkalin e h ydrolysis of ph en yl esters of ortho-substi-
tuted ben zoic acids, X-C6H4CO2C6H5, calculated as log korth o – 0.31σ°R – 2.12σI an d th e steric
effects in alkalin e h ydrolysis of ortho-substituted ph en yl ben zoates, C6H5CO2C6H4-X, calcu-
lated as log korth o – 1.10σ°R – 1.54σI for water at 25 °C
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

124
Nummert, Piirsalu, Mäemets, Koppel:
alkalin e h ydrolysis of ph en yl esters of ortho-substituted ben zoic acids,
X-C6H4CO2C6H5, represen ted as (log korth o – 0.310.3σ°R – 2.12σI) an d th e
steric effects in alkalin e h ydrolysis of ortho-substituted ph en yl ben zoates,
C6H5CO2C6H4-X, calculated as (log korth o – 1.10σ°R – 1.54σI), for water at
25 °C is sh own . Slope of th is depen den ce is ca. 2.7.
Wh en th e Ch arton steric υ con stan ts (Table VII) were used, th e values of
(ρ)m ,p, (ρ°)m ,p, (ρI)orth o an d (ρ°R)orth o were foun d to be approxim ately th e
sam e as in th e case of th e EsB scale. On ly in n eat water δorth o = –1.2 for alka-
lin e h ydrolysis of ph en yl esters of ortho-substituted ben zoic acids (Table III)
an d δorth o = –0.45 for alkalin e h ydrolysis of ortho-substituted ph en yl ben z-
oates (Table VI). Wh en th e Ch arton steric υ con stan ts were used, th e steric
effects in th e acyl com pon en t of esters also appeared to be ca. 2.7 tim es
stron ger th an th e steric effects from th e ph en yl com pon en t of esters.
Effect of Solvent
Th e ρm ,p values calculated in th e presen t work for alkalin e h ydrolysis of eth -
yl esters of meta- an d para-substituted ben zoic acids in 56% (w/w) aqueous
aceton e (ρm ,p = 2.33), 85% (w/w) aqueous eth an ol (ρm ,p = 2.54) an d 65%
aqueous aceton e (ρm ,p = 2.38), appeared to be n early th e sam e as reported
in th e literature previously9,10
.
In alkalin e h ydrolysis of ph en yl esters of substituted ben zoic acids, th e
variation of th e meta an d para polar effect with solven t is com parable with
th at for eth yl ben zoates. Th e polar effect of meta an d para substituen ts in
alkalin e h ydrolysis of ph en yl esters of meta- an d para-substituted ben zoic
acids at 25 °C in creases by 0.6 un its of ρ wh en goin g from n eat water to
50% aqueous DMSO. In tran sition from 5% aqueous eth an ol to 65% aque-
ous DMSO, th e value of ρm ,p for alkalin e h ydrolysis of eth yl ben zoates in -
creases by 0.9 un its of ρ.
Wh en goin g from water to bin ary aqueous solven ts, th e differen ce be-
tween th e ortho in ductive an d th e meta an d para in ductive term s n early dis-
appears as th e in crease in th e ortho in ductive term due to solven t was foun d
to be essen tially lower th an th at of meta an d para substituen ts (see Tables III
an d IV). Previously5, in alkalin e h ydrolysis of substituted ph en yl ben zoates
th e variation of th e ortho in ductive term with th e solven t electroph ilicity
was foun d to be 3 tim es sm aller th an th at for para substituen ts.
Th e (ρ°R)orth o values for ph en yl an d eth yl esters of ortho-substituted ben -
zoic acids in tran sition from water to bin ary aqueous solven ts appeared to
in crease approxim ately to th e sam e exten t as th e reson an ce term of para de-
rivatives, th ough th e con tribution of reson an ce in th e case of ortho sub-
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
125
stituen ts in water was n egligible (0.3 un its of ρ). For alkalin e h ydrolysis of
ph en yl esters of substituted ben zoic acids in pure water ρm ,p – (ρ°R)orth o
=
1.4, in 50% aqueous DMSO ρm ,p – (ρ°R)orth o = 1.5. For eth yl esters of substi-
tuted ben zoic acids in 5% aqueous eth an ol, 56% aqueous aceton e, 85%
aqueous eth an ol an d 65% aqueous DMSO th e values of ρm ,p – (ρ°R)orth o were
1.3, 1.5, 1.3 an d 1.2, respectively.
Steric Effects in Acid Hydrolysis and Esterification
Th e steric E°s con stan ts for ortho substituen ts proposed by Taft14 gave excel-
len t correlation usin g Eq. (4) (Table V):
E°s = 0.52(±0.18) – 0.14(±0.12)σI – 1.26(±0.28)σ°R + 2.52(±0.47)EsB
R = 0.993, s = 0.062, so = 0.112, n = 7 .
(5)
Sim ilar to th e Taft steric E°s con stan ts, th e correlation of th e log k values
for acid esterification of substituted ben zoic acids in m eth an ol at 25 °C,
acid h ydrolysis of substituted m eth yl esters in 80% (v/v) aqueous m eth an ol
at 100.8 °C an d in acid esterification of substituted ben zoic acids in
cycloh exan ol at 55 °C with Eq. (3) (Table V) proved th at th e steric con tribu-
tion in th e acid esterification of ortho-substituted ben zoic acids or in th e
acid h ydrolysis of ortho-substituted ben zoates (th e value of δorth o ran gin g
from 1.8 to 3.0) is approxim ately equal to th e steric term in alkalin e h ydro-
lysis of esters of ortho-substituted ben zoic acids (th e m ean value of δorth o is
2.6). Th is con clusion is in accordan ce with th e Taft–In gold assum ption in
establish in g th e Taft polar substituen t con stan ts scale, σ*o, for ortho sub-
stituen ts accordin g to
σ*o = 1/2.48[log (k/ko)B – log (k/ko)A]
(6)
wh ere subscripts A an d B refer to ester h ydrolysis catalyzed by h ydrogen ion
an d h ydroxide ion , respectively.
A con tribution of th e reson an ce factor appeared to be sign ifican t in addi-
tion to steric effects in th e Taft steric substituen t con stan ts E°s ((ρ°R)orth o
=
–1.26, Eq. (5)), as well as in acid esterification of ortho-substituted ben zoic
acids an d acid h ydrolysis of esters of ortho-substituted ben zoic acids (th e
value of (ρ°R)orth o in th e ran ge from –1.0 to –1.8) (Eq. (5), Table V). Con se-
quen tly, th e con tribution of th e reson an ce term in alkalin e h ydrolysis of
esters of ortho-substituted ben zoic acids (th e (ρ°R)orth o value in th e ran ge
0–1.2) an d in acid esterification of ortho-substituted ben zoic acids or acid
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

126
Nummert, Piirsalu, Mäemets, Koppel:
h ydrolysis of ortho-substituted esters is quite differen t, even in sign . Th is is
in good accordan ce with th e m ech an ism of both reaction types con sidered:
th e electron don atin g substituen ts stabilize th e positively ch arged com plex
in acid h ydrolysis, but destabilize th e n egatively ch arged com plex in alka-
lin e h ydrolysis. Th e value of ρm ,p – (ρ°R)orth o ≈ 1.3 for acid esterification of
ortho-substituted ben zoic acids an d acid h ydrolysis of ortho-substituted es-
ters is n early th e sam e as th at foun d for alkalin e h ydrolysis of esters of
ortho-substituted ben zoic acids (th e ρm ,p – (ρ°R)orth o value in th e ran ge from
1.2 to 1.5). Equality of both steric effects an d th e values of (ρm ,p – (ρ°R)orth o
)
in alkalin e h ydrolysis an d acid h ydrolysis on ce again sh ows th at wh en cal-
culatin g th e Taft σ*o con stan ts usin g th e In gold–Taft equation (6), th e polar
con stan t for ortho substituen ts, σ*o, does n ot con tain an y con tribution of
th e steric effects an d th e overall con tribution of th e reson an ce effect be-
com es equal to th at for para substituen ts.
Conclusions
In alkalin e h ydrolysis of ph en yl an d eth yl esters of ortho-, meta- an d para-
substituted ben zoic acids th e depen den ce of th e reaction rates on th e
substituen t effects was foun d to be precisely correlated with th e Ham m ett–
Ch arton equation (3) usin g for meta an d para derivatives th e Ham m ett po-
lar substituen t con stan ts, σm ,p, an d for ortho derivatives th e Taft in ductive,
σI, th e reson an ce, σ°R, an d steric, EsB or υ con stan ts. R > 0.99 an d s < 0.1 for
,
th e reaction series con tain in g all ortho-substituted derivatives (X = F, Cl,
Br, I, CH3, CF3, NO2, OCH3, NH2, N(CH3)2, C(CH3)3) in n eat water at 25 °C
(Tables III an d VI). From th e acyl com pon en t of esters, th e polar effect of
meta an d para substituen ts was foun d to be 1.6 tim es an d th e in ductive ef-
fect of ortho substituen ts 1.5 tim es stron ger th an th e correspon din g in flu-
en ces from th e aryl com pon en t. Th e reson an ce factor of ortho substituen ts
in acyl com pon en t in water was foun d to be n egligible (ρ°R = 0.3). Th e con -
tribution s of th e steric effects in alkalin e h ydrolysis of esters of ortho-substi-
tuted ben zoic acids were approxim ately th e sam e as in acid h ydrolysis of
esters of ortho-substituted ben zoic acids an d in acid esterification of ortho-
substituted ben zoic acids. In ortho-substituted ph en yl ben zoates th e steric
effects in th e acyl com pon en t of esters were 2.7 tim es stron ger th an th e
steric effects from th e aryl com pon en t of esters. Th is could be assign ed to
th e n on -plan ar s-trans con form ation proposed for ph en yl ben zoates43. In
ph en yl esters th e plan e of ph en yl rin g in th e aryl com pon en t assum ed to
be n early perpen dicular to th e carbon yl bon d plan e an d th e ph en yl plan e
in th e acyl part of ester is coplan ar with th e carbon yl bon d plan e.
Collect. Czech. Chem. Commun. 2006, Vol. 71, No. 1, pp. 107–128

Kinetic Study of Hydrolysis of Benzoates
127
This work was supported by the grant No. 5226 of the Estonian Science Foundation.
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