Kinetic investigation on the reactions of p-toluenesulfonyl chloride with p-substituted benzoic acid(s) in the presence of triethylamine in aprotic solvents

Article abstract of DOI:10.1002/kin.20400

Second-order rate constants of the reactions of p-toluenesulfonyl chloride with p-substituted benzoic acids in the presence of triethylamine in acetonitrile/acetone under equimolar and pseudo-first-order conditions have been determined by the conductometric method using the Guggenheim principle at 25, 30, 35, and 40°C. The reactions follow second order with respect to the whole and first order with respect to each of the reactants. The order of reactivity of the substituents in benzoic acid is rationalized. Activation parameters are obtained by applying the usual methods. The Hammett plot has been found nonlinear, whereas the Bronsted plot shows good correlation. This may be explained on the basis of electronic effects of substituents on the reaction center. Kinetic data and the product analyses indicate that the reaction proceeds through direct nucleophilic attack on the sulfur center. Int J Chem Kinet 41: 303-308, 2009

Full text of DOI:10.1002/kin.20400

Kinetic Investigation on the
Reactions of
p-Toluenesulfonyl Chloride
with p-Substituted Benzoic
Acid(s) in the Presence of
Triethylamine in Aprotic
Solvents
SUBBIAH ANANTHALAKSHMI, M. NALLU
School of Chemistry, Bharathidasan University, Tiruchirappalli, 620 024, India
Received 9 August 2006; revised 21 February 2007, 21 September 2007, 13 April 2008, 4 September 2008,
15 October 2008; accepted 15 October 2008
DOI 10.1002/kin.20400
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Second-order rate constants of the reactions of p-toluenesulfonyl chloride with
p-substituted benzoic acids in the presence of triethylamine in acetonitrile/acetone under
equimolar and pseudo-first-order conditions have been determined by the conductometric
method using the Guggenheim principle at 25, 30, 35, and 40◦C. The reactions follow second
order with respect to the whole and first order with respect to each of the reactants. The
order of reactivity of the substituents in benzoic acid is rationalized. Activation parameters are
obtained by applying the usual methods. The Hammett plot has been found nonlinear, whereas
the Bronsted plot shows good correlation. This may be explained on the basis of electronic
effects of substituents on the reaction center. Kinetic data and the product analyses indicate
that the reaction proceeds through direct nucleophilic attack on the sulfur center. ꢀ 2009 Wiley
C
Periodicals, Inc. Int J Chem Kinet 41: 303–308, 2009
involving metal carboxylates/triethylammonium
carboxylates and active organic halide containing
saturated carbon atom. The reactivity of metal car-
boxylates/triethylammonium carboxylates, the effect
of solvents, formation of O C bond, and cleavage of
C X bond in the transition state (TS), etc., have been
discussed [1–7]. Much work has not been done on
the organic compounds containing S as a heteroatom
INTRODUCTION
A number of kinetic investigations have been car-
ried out on the nucleophilic substitution reactions
Correspondence to: M. Nallu; e-mail: nallu46@rediffmail.com.
2009 Wiley Periodicals, Inc.
c
ꢀ

304
ANANTHALAKSHMI AND NALLU
and triethylamine (25 mL, 0.05 mol dm3) in ace-
tone were mixed under kinetic conditions and were
kept overnight at about 30◦C. The needle-shaped crys-
talline solid formed was filtered. This solid product
was washed well with acetone; yield 0.229 g (67%),
melting point 254–256◦C [11]. Thin-layer chromatog-
raphy tests on this solid, using methanol as an elu-
ent showed a single spot. The solid product was also
identified as triethylammonium chloride on the basis
like arenesulfonyl chloride, which is found to be a
good substrate for nucleophilic substitution reactions
[8–12]. However, Banjoko and Okwuive have reported
the kinetics of nucleophilic substitution reaction of
sodium benzoate(s) with benzenesulfonyl chloride in
methanol [13]. They concluded that the substitutions
at sulfonyl sulfur would take place through the SN2
mechanism. We have also made similar investiga-
tion on the reaction of p-toluenesulfonyl chloride
with triethylammonium benzoate(s) in acetonitrile
(ACN)/acetone with a view to study the substituent
effects and the solvation behavior of these solvents.
We report here our findings on the title reaction.
1
of IR (KBr) and H NMR (200 mHz, CDCl3) data.
IR: In IR spectrum, the bands observed at 2731 and
2677 cm−1indicate the presence of N+ H bond. Very
weak bending band at 1475 cm−1is due to triethylam-
monium ion. The CH2 group absorbs at 2971 and
2939 cm−1 for stretching and bending, respectively. H1
NMR: δ = 11.9 (broad hump, 1H, N+ H), 3.00–3.18
(q, 6H, N+ (CH2 CH3)3 ) and 1.38–1.45 (t, 9H, N+
(CH2 CH3)3 ppm.
EXPERIMENTAL
Materials
p-Toluenesulfonyl chloride, p-substituted benzoic
acid(s), triethylamine, ACN, and acetone (analytical
grade) were purified before use by recrystallization
or distillation until their physical constants (melting
point/boiling point) agreed with the literature values
[14,15].
The filtrate was completely evaporated in vac-
uum to get residue, which was dissolved in di-
ethyl ether and dried over anhydrous Na2SO4. The
solid product was obtained by the slow evaporation
of the solvent and was recrystallized from toluene,
yield = 0.53 g (77%), melting point = 103–105◦C.
The product was identified as p-toluenesulfonyl ben-
Kinetic Measurements
1
zoate (Fig. 1) from IR (KBr) and H and 13C NMR
The solutions of p-toluenesulfonyl chloride and the
mixture of benzoic acid(s) and triethylamine (25 mL,
5 × 10−3 mol dm3) were prepared in ACN/acetone. The
rates were followed by the conductometric method as
reported elsewhere [16,17]. The conductivity is due to
triethylammonium cation (formed by the interaction
between benzoic acids and triethylamine) and chlo-
ride anion (liberated from p-toluenesulfonyl chloride
by the attack of triethylammonium benzoate). Second-
order rate constants (k2) under equimolar conditions in
ACN/acetone with different concentrations of the sub-
strate (TsCl) and the nucleophile (mixture of benzoic
acid and triethylamine) have been determined. Rate
constants of the reaction of p-toluenesulfonyl chloride
with a mixture of benzoic acid and triethylamine in
ACN were determined under pseudo-first-order condi-
tions. The activation parameters were computed from
the rate constants at 25, 30, 35, and 40◦C by the usual
method [18,21] by least squares analysis.
(CDCl3) spectral data. IR: 3070 υC H(aromatic), 2833
υC H(aliphatic), 1685 υC
COAr), 1324 υS O(asy.), 1176
O(
υS O(sym.) cm−1; 1H NMR: δ = 8.20–8.00 (d, 2H, C2
and C6 H, SO2C6H4CH3(p)), 7.65–7.55 (d, 2H,
C3 and C5 H, SO2C6H4CH3(p)), 7.53–7.40 (m,
5H, COC6H5) and 2.48, (s, 3H, SO2C6H4CH3(p))
ppm. 13C NMR: δ = 172, 145, 141, 133, 130, 129, 128,
125, and 21 ppm. Similar procedures were followed for
4-OH, 4-NH2 and identified the products by spectral
1
(IR, H, and 13C NMR) data as p-toluenesulfonyl 4-
hydroxybenzoate and p-toluenesulfonyl 4- aminoben-
zoate, respectively.
IR: 3493 υOH,3061 υC
,
2822
H(aromatic)
υC H(aliphatic), 1658 υC
COAr), 1374 υS
,
O(
O(asy.)
1178υS
cm−1
,
1H NMR: δ = 7.79–7.77 (d,
O(sym.)
2H, C2 and C6 H, COC6H4OH(p)), 7.52–7.50 (d,
2H, C3 and C5 H, COC6H4OH(p)), 7.15–7.13
(d, 2H, C2 and C6 H, SO2C6H4CH3(p)), 6.84–
6.82 (d, 2H, C3 and C5 H, SO2C6H4CH3(p)),
6.0 (s, 1H, COC6H4OH(p) and 2.50, (s, 3H,
SO2C6H4CH3(p)) ppm. IR: 3363 υN H,3061
It was observed from the control experiments that
conductance of the solution of TsCl with benzoic acid
or TEA did not increase with the increase of time in
ACN/acetone. It indicates that ions responsible for con-
ductance are not liberated from the above solution.
O
S
O
C
X
CH3
O
Product Analyses
O
Equal volumes of equimolar solutions of p-
toluenesulfonyl chloride and a mixture of benzoic acid
Figure 1 p-Toluenesulfonyl benzoate (X = 4-H, 4-NH2,
and 4-OH).
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KINETIC INVESTIGATION ON THE REACTIONS OF p-TOLUENESULFONYL CHLORIDE
305
Table II Rate Constants of the Reaction of TsCl with
BA–TEA under Pseudo-First-Order Conditions in ACN at
30◦C
υC H(aromatic), 2921 υC H(aliphatic), 1665 υC
,
O( CO Ar)
1374 υS O(asy.), 1175 υS
cm−1 1H NMR:
;
O(sym.)
δ = 10.81 (s, 2H, COC6H4NH2(p)), 7.51–7.49 (d,
2H, C2 and C6 H, COC6H4OH(p)), 7.17–7.15
(d, 2H, C3 and C5 H, COC6H4OH(p)), 7.30
(m, 4H, SO2C6H4CH3(p)), and 2.50, (s, 3H,
SO2C6H4CH3(p)) ppm.
103×
k2 = k1/
[Nu]a(dm3
mol−1 min−1
)
104× [TsCl] [BA − TEA] 103 × k1
(mol dm−3
)
(mol dm−3
)
(min−1
)
8.0
8.0
8.0
8.0
8.0
5.0
6.0
7.0
9.0
1.0
2.0
3.0
4.0
5.0
2.0
2.0
2.0
2.0
4.638
9.508
13.670
18.990
23.950
0.092
0.092
0.091
0.094
46.38
47.54
45.59
47.47
47.90
45.97
45.82
45.54
47.10
RESULTS AND DISCUSSION
The rate constant for the reaction of p-toluenesulfonyl
chloride with the equimolar mixture of benzoic acid(s)
and triethylamine in ACN/acetone has been determined
by the conductometric method under equimolar con-
centrations at 30◦C (Table I). The reaction was also
carried out under pseudo-first-order conditions in ACN
at 30◦C for benzoic acid alone (Table II). The rate data
indicate that the reaction is second order with respect
to the whole and first order with respect to the individ-
ual reagents. The rate of the reaction in ACN is found
to be 13 times greater than that in acetone. This may
be due to the less solvation of benzoate ion by ACN.
The reactions were studied at different temperatures
in ACN/acetone (Table III). It is seen from Table III
that the reactivity order of the substituents in ben-
zoic acid(s) is 4-Cl > 4-NO2> 4-OH > 4-OCH3 > 4-
NH2 > 4-CH3 > 4-H in ACN, whereas the reactivity
order in acetone is 4-Cl > 4-NO2 > 4-OH > 4-H > 4-
CH3 > 4-OCH3 > 4-NH2. Electron-withdrawing and
electron-donating groups in benzoic acid in ACN
medium show a higher order of reactivity than the
parent compound. The order of reactivity in acetone is
also found different from the expected reactivity order.
This order of nucleophilic reactivity in ACN may be
explained on the basis of the relation between basicity/
polarizability of benzoate’s solvation and the charge
Abbreviations: TsCl, p-toluenesulfonyl chloride; BA, benzoic acid;
TEA, triethylamine.
a[Nu] = [BA − TEA].
on the sulfur atom of tosylate in the TS [20]. Electron-
attracting sulfonyl group induces the polarizability on
S Cl bond. This may facilitate the usual backside at-
tack by the benzoate. The residual positive charge on
S atom may lead to the strong interaction with the ben-
zoate anion. This interaction may depend on the basic
strength of benzoate anion and the magnitude of sol-
vation by ACN. The less basic benzoate anion will be
solvated less. Thus, the order of reactivity of benzoate
anion falls in the order of basic strength. However, it is
found difficult to understand the order of the reactivity
of benzoates in acetone. The hydrogen-bonding inter-
action between acetone and unionized benzoic acid(s)
as well as the TS may be the factor for the variation in
the reactivity.
Activation parameters have been evaluated by the
usual methods (Table III) [18–20]. The values of
ꢀH‡in ACN are slightly higher than those in acetone.
This can be explained on the basis of solvation. Tri-
ethylammonium benzoate ion may be desolvated more
in ACN than in acetone due to the protogenic char-
acter of ACN [7,22]. This may raise the energy of
benzoate ion and diminish the energy gap between the
reactants and TS, which increases the rate. The en-
tropies of activation are negative as we expected for
nucleophilic bimolecular reactions. The high negative
ꢀS‡ observed with respect to all the substituents stud-
ied support the operation of “electrostriction” in these
compounds pointing to more polar TS. The average
values are −40.43 (ACN) and −61.41 in (acetone)
J mol−1 deg−1, respectively. The difference in the val-
ues of entropy can be explained on the basis of solvent
participation in the TS of the reaction. Acetone may
highly solvate the TS by H bonding than ACN, which
results in the decrease of entropy (Table III).
Table I Second-Order Rate Constants of the Reaction
of TsCl with BA–TEA in ACN/Acetone at 30◦C
[TsCl]
(mol dm−3
[BA]
(mol dm−3
[TEA]
(mol dm−3
k2 (dm3
)
)
)
mol−1 min−1
)
0.005
(0.05)
0.004
(0.04)
0.003
(0.03)
0.002
(0.02)
0.001
(0.01)
0.005
(0.05)
0.004
(0.04)
0.003
(0.03)
0.002
(0.02)
0.001
(0.01)
0.005
(0.05)
0.004
(0.04)
0.003
(0.03)
0.002
(0.02)
0.001
(0.01)
49.29
(3.67)
49.17
(3.53)
47.01
(3.58)
45.67
(3.61)
48.17
(3.71)
Abbreviations: TsCl, p-toluenesulfonyl chloride; BA, benzoic acid;
TEA, triethylamine.
Values in parentheses are for acetone.
International Journal of Chemical Kinetics DOI 10.1002/kin

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ANANTHALAKSHMI AND NALLU
Table III Rate Constants and Activation Parameters at 30◦C [TsCl] = [4X − BA] = [TEA] = 0.02 mol dm−3
(Acetone) = 0.0025 mol dm−3 (ACN)
k2 (dm3 mol−1 min−1
)
E
ꢀH‡
(kJ mol−1
−ꢀS‡
ꢀG‡
(kJ mol−1
)
a
Substituent X
4-H
25◦
30◦
35◦
40◦C
(kJ mol−1
)
)
(J mol−1 deg−1
)
35.47
(2.329)
38.51
(2.249)
51.64
(1.920)
60.48
(2.955)
43.22
(1.555)
98.64
(3.802)
83.44
(3.885)
45.67
(3.611)
49.36
(3.132)
66.80
(2.740)
85.52
(3.929)
59.90
(2.370)
126.28
(5.637)
112.49
(5.381)
77.45
(4.597)
80.01
(4.665)
102.80
(4.089)
123.90
(5.540)
90.80
(3.118)
205.68
(7.755)
164.55
(8.371)
87.65
(7.351)
105.10
(6.215)
131.04
(5.450)
172.00
(7.888)
116.16
(4.991)
245.28
(10.986)
217.16
(10.628)
51.41
(56.06)
57.31
(54.04)
53.14
(54.22)
55.09
(54.97)
52.22
(58.73)
52.35
(52.61)
51.87
48.89
(53.54)
54.79
(51.52)
50.61
(51.70)
52.58
(52.45)
49.71
(56.21)
49.83
(50.09)
49.34
51.86
(57.67)
31.76
(65.74)
43.04
(65.99)
34.49
(60.53)
38.63
(52.35)
40.33
(65.35)
42.90
63.97
(71.03)
64.61
(71.44)
63.65
(71.70)
63.06
(70.79)
63.93
(72.07)
62.05
(69.89)
62.34
4-CH3
4-OCH3
4-OH
4-NH2
4-Cl
4-NO2
(53.66)
(51.14)
(62.24)
(70.02)
Values in parentheses are for acetone.
The Hammett plot is found to be nonlinear (Figs. 2
and 3). It is known that the correlation between log
k2/ko and the value of σ+ in these two solvents is
also very poor (Eqs. (1) and (2)). This nonlinearity
indicates that the electronic effects of substituents in
benzoic acid on the rate are considerably different.
found scattered (Figs. 2 and 3). This may be explained
on the basis of cross-conjugation (Figs. 4a and 4b)
[7,23]. That is, −R parasubstituents (4-NO2 and 4-
Cl) may not fully exhibit −R effect, and it may also
influence a small +R effect on the reaction center and
vice versa in the case of +R parasubstituents (4-OH,
4-NH2, and 4-OCH3).
log k2(ACN) = 0.128σ+ + 0.29
(1)
(2)
0.3
(r = 0.636, n = 6, s = 0.337)
4-Cl
4-NO2
0.2
0.1
0
log k2(acetone) = 0.164σ+ + 0.075
(r = 0.835, n = 6, s = 0.126)
4-OH
2
1.5
1
0.5
0
0.5
1
It is seen that the points for the substituents such
as the p-NO2,p-Cl, p-OH, p-NH2, and P-OCH3 are
0.1
0.2
0.3
4-OCH3
4-CH3
4-NH2
4-Cl
0.5
4-NO2
0.4
+
0.3
4-OH
Figure 3 The Hammett plot for the reaction of p-
toluenesulfonyl chloride with 4-subtituted benzoic acid(s)–
triethylamine in acetone at 30◦C. [Color figure can be viewed
in the online issue, which is available at www.interscience.
wiley.com.]
4-OCH3
0.2
4-NH2
0.1
0
4-CH3
+
2
1.5
1
0.5
0
0.5
1
X
X
..
COO HNEt3
COO HNEt3
+
Figure 2 The Hammett plot for the reaction of p-
toluenesulfonyl chloride with 4-substituted benzoic acid(s)–
triethylamine in ACN at 30◦C. [Color figure can be viewed
in the online issue, which is available at www.interscience.
wiley.com.]
(X= NO2 and Cl)
a. – R para-substituents
(X= OH, NH2 and OCH3)
b. + R para-substituents
Figure 4 Canonical structures of triethylammonium ben-
zoate: (a) −R parasubstituents and (b) +R parasubstituents.
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETIC INVESTIGATION ON THE REACTIONS OF p-TOLUENESULFONYL CHLORIDE
307
0.8
2.2
2.1
2
4-Cl
4-NO2
4-NO2
4-Cl
4-OH
4-OH
4-OCH3
4-H
0.6
0.4
1.9
1.8
1.7
1.6
4-CH3
4-CH3
4-OCH3
12.8
13
13.2
13.4
13.6
13.8
12.8
13
13.2
pKa
13.4
13.6
13.8
pKa
Figure 5 The Bronsted plot for the reaction of p-
toluenesulfonyl chloride with 4-subtituted benzoic acid(s)–
triethylamine in ACN at 30◦C. [Color figure can be viewed
in the online issue, which is available at www.interscience.
wiley.com.]
Figure 6 The Bronsted plot for the reaction of p-
toluenesulfonyl chloride with 4-subtituted benzoic acid(s)–
triethylamine in acetone at 30◦C. [Color figure can be viewed
in the online issue, which is available at www.interscience.
wiley.com.]
0.8
4-NO2
4-Cl
The extent of S O bond formation in the TS
when the benzoate ion approaches the sulfur atom of
p-toluenesulfonyl chloride is gauged from the
Bronsted coefficient value (β). The values of log k2
were plotted against the pKa values of the benzoate
except 4-NH2 (Figs. 5 and 6). It is found that the cor-
relation is fair (Eqs. (3) and (4)).
0.7
0.6
0.5
0.4
0.3
4-OH
4-OCH3
4-NH2
1.7
1.8
1.9
2
2.1
2.2
log k2(ACN) = −0.541 pKa + 9.120
(r = 0.972, n = 5, s = 0.240)
log k2(acetone) = −0.427 pKa
+ 6.278(r = 0.839)
(3)
log k2 (ACN)
Figure 7 Plot log k2 (ACN) with log k2 (acetone) for the
reaction of p-toluenesulfonyl chloride with 4-subtituted ben-
zoic acid(s)–triethylamine in ACN/acetone at 30◦C. [Color
figure can be viewed in the online issue, which is available
at www.interscience.wiley.com.]
(4)
(r = 0.923, n = 6, s = 0.153)
Mechanism
O
O
O
O
_
O
O
X-C6H4
C
Cl
O
S
------- -------Cl
O
S
X-C6H4
C
+
+
+
Et3NH
Et3NH
CH3
CH3
TS
O
S
O
_
+
Et3NHCl
+
C
X-C6H4
CH3
O
O
Scheme 1
International Journal of Chemical Kinetics DOI 10.1002/kin

308
ANANTHALAKSHMI AND NALLU
The values of log k2 (ACN) were plotted against
the values of log k2 (acetone), and the linear line was
obtained (Fig. 7) with (r = 0.995, n = 5, s = 0.054).
This is one of the probes for the operation of the same
mechanism in both the solvents.
Based on the kinetic data and the product anal-
yses, the synchronous direct nucleophilic displace-
ment mechanism of benzoate ion at the S atom of
p-toluenesulfonyl chloride has been proposed for the
reaction studied (Scheme 1).
2. Krishna Pillay, M.; Kannan, K.; Ramasubramanian, P.
Tetrahedron 1983, 39, 3899.
3. Detar, D. F.; Novak, R. W. J Am Chem Soc 1970, 92,
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CONCLUSION
Rate constants for the reactions of p-toluenesulfonyl
chloride with benzoic acid(s)–triethylamine have been
determined in ACN and /acetone at different concentra-
tions and temperatures by the conductometric method.
The order of reactivity of the substituents is discussed
in terms of basicity and polarity of benzoates and the
positive charge on S atom of tosylate in TS. Activation
parameters have been evaluated from the rate data.
The negative values of ꢀS‡ indicate the formation of
rigid TS. The nonlinearity of the Hammett plot is ex-
plained in terms of cross-conjugation. The Bronsted
plot shows good correlation. A plot of log k2(ACN)
with log k2(acetone) gives a straight line, indicating
the operation of similar mechanism in both the sol-
vents. We proposed the SN2 mechanism based on the
kinetic data and product analyses.
13. Banjoko, D.; Okwuiwe, R. J Org Chem 1980, 45,
4966.
14. Vogel, A. I. A Text Book of Practical Organic Chemistry,
4th ed; ELBS: London, 1978.
15. The Merck Index, 10th ed; Merck: Rahway, NJ,
1983.
16. Krishna Pillay, M.; Jeyaraman, R.; Nallu, M.;
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International Journal of Chemical Kinetics DOI 10.1002/kin