Kinetic study on alkaline hydrolysis of Y-substituted phenyl X-substituted benzenesulfonates: Effects of changing nucleophile from azide to hydroxide ion on reactivity and transition-state structure

Article abstract of DOI:10.1002/bkcs.10297

Second-order rate constants (k_OH-) for alkaline hydrolysis of 2,4-dinitrophenyl X-substituted benzenesulfonates (1a-1f) and Y-substituted phenyl 4-nitrobezenesulfonates (2a-2g) have been measured spectrophotometrically. Comparison of k_OH

Full text of DOI:10.1002/bkcs.10297

Article
DOI: 10.1002/bkcs.10297
BULLETIN OF THE
J.-H. Moon et al.
KOREAN CHEMICAL SOCIETY
Kinetic Study on Alkaline Hydrolysis of Y-substituted Phenyl
X-substituted Benzenesulfonates: Effects of Changing Nucleophile from
Azide to Hydroxide Ion on Reactivity and Transition-State Structure
*
Ji-Hyun Moon, Min-Young Kim, So-Yeop Han, and Ik-Hwan Um
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
*E-mail: ihum@ewha.ac.kr
Received January 15, 2015, Accepted February 6, 2015, Published online May 26, 2015
Second-order rate constants (kOH ) for alkaline hydrolysis of 2,4-dinitrophenyl X-substituted benzenesulfo-
nates (1a–1f) and Y-substituted phenyl 4-nitrobezenesulfonates (2a–2g) have been measured spectrophoto-
metrically. Comparison of kOH with the kN3 values reported previously for the corresponding reactions
with N3 has revealed that OH is only 103-fold more reactive than N3 , although the former is 11 pKa units
more basic than the latter. The Yukawa–Tsuno plot for the reactions of 1a–1f results in an excellent linear cor-
relation with ρX = 2.09and r=0.41. TheBrønsted-typeplot forthereactions of 2a–2g islinearwith βlg = −0.51,
which is typical for reactions reported to proceed through a concerted mechanism. The Yukawa–Tsuno plot for
the reactions of 2a–2g exhibits excellent linearity with ρY = 1.85 and r = 0.25, indicating that a partial negative
charge developson theOatomof theleaving groupin thetransition state. Thus, the alkalinehydrolysis of 1a–1f
and 2a–2ghas been concludedtoproceedthrougha concerted mechanism. Comparison ofthe ρX and βlg values
for the reactions with OH and N3 ions suggests that the reactions with hydroxide ion proceed through a tighter
transition-state structure than those with azide ion.
Keywords: Aryl benzenesulfonates, Alkaline hydrolysis, Sulfonyl-group transfer, Yukawa–Tsuno plot,
Concerted mechanism
Introduction
of the kinetic result that the Yukawa–Tsuno plot exhibits an
excellent linear correlation with ρY = 2.61 and r = 0.29.13
The reaction mechanism for alkaline hydrolysis of aryl ben-
zenesulfonates is also controversial. From a kinetic study,
Babtie et al. have concluded that nucleophilic substitution
reactions of Y-substituted phenyl benzenesulfonates (Y = 3-
F-4-NO2, 4-NO2, 4-CN, 3-NO2, 3-CN, 4-Cl, H, and 3,4-
Me2) with OH proceed through a stepwise mechanism invol-
ving a pentavalent intermediate.14 Theevidenceprovided for a
stepwise mechanism was a biphasic Brønsted-type plot (e.g.,
βlg = −0.27 when the leaving group pKa < 8.5 but βlg = −0.97
whentheleavinggrouppKa > 8.5).14 Thestepwisemechanism
has also been supported their quantum/molecular mechanics
(QM/MM) calculations.14 In contrast, Duarte et al. have
found no computational evidence for a thermodynamically
stable intermediate for any of the above sulfonate esters
from a detailed computational study using HF/6-31++G∗.15
Furthermore, inclusion of the experimental data for the reac-
tions of 3-pyridyl benzenesulfonate and its N-oxide and
N-methylpyridinium derivatives gave a very good Hammett
correlation.15 Thus, the reactions have been concluded to pro-
ceed through a concerted mechanism, in which expulsion
of the leaving group is advanced only a little in the transition
state (TS).15
Acyl-group and phosphoryl-group transfer reactions have
been intensively investigated because of their importance in
biological processes as well as in synthetic applications.1–9
In contrast, sulfonyl-group transfer reactions have received
much less attention, although bacteria can use sulfonate esters
as sulfur sources when sulfate concentration is low in their
environment.10 Thus, their reaction mechanisms have not
been completely understood, e.g., nucleophilic substitution
reactions of aryl benzenesulfonates have been reported to
proceed through a concerted mechanism or via a stepwise
pathway.11–17
Williams and coworkers have reported that reactions of 4-
nitrophenyl 4-nitrobenzenesulfonate with a series of substi-
tuted phenoxides proceed through a concerted mechanism
on the basis of a Brønsted-type plot with absence of a
break (or curvature) when the pKa of the aryloxide nucleophile
corresponded to that of the leaving 4-nitrophenoxide.11 How-
ever, Buncel and coworkers have suggested that reactions
of Y-substituted phenyl benzenesulfonates (Y = 4-NO2, 3-
NO2, 4-CF3, 3-Br, 4-Cl, and H) with C2H5O proceed through
a stepwise mechanism, since the Hammett plot correlated with
σo constants resulted in much better linearity than
σ−constants.12 On the other hand, we have recently reported
that alkaline ethanolysis of Y-substituted phenyl benzenesul-
fonates proceed through a concerted mechanism on the basis
We have reported that nucleophilic substitution reactions of
aryl benzenesulfonates are regioselective, e.g., reactions of
2,4-dinitrophenyl X-substituted benzenesulfonates (1a–1f)
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Alkaline Hydrolysis of Aryl Benzenesulfonates
KOREAN CHEMICAL SOCIETY
with primary and cyclic secondary amines proceed through
S O and C O bond fission competitively.16 The S O bond
fission, which leads to the formation of 2,4-dinitrophenoxide
ion and X-substituted benzenesulfonamides, was found to be
the major reaction pathway for the reactions with strongly
basic amines (e.g., piperidine or ethylamine) or for those of
substrates possessing a strong electron withdrawing group
(EWG) in the benzenesulfonyl moiety.16 In contrast, the
C O bond fission, which yields 2,4-dinitroaniline derivatives
and X-substituted benzenesulfonates, increased significantly
for the reactions with weakly basic amines (e.g., piperazinium
ion or 2,2,2-trifluoroethylamine) or for those of substrates
bearing a strong electron donating group (EDG) in the benze-
nesulfonyl moiety.16
could not be compared with the current data because of the dif-
ference in the reaction medium.
Results and Discussion
The kinetic study was carried out under pseudo-first-
order conditions (e.g., the OH concentration was kept at least
20 times in excess over the substrate concentration) in 80 mol
% H2O/20 mol% DMSO at 25.0 0.1 ꢀC. All the reactions in
this study obeyed pseudo-first-order kinetics with quantitative
liberation of 2,4-dinitrophenoxide ion for the reactions of
1a–1f and Y-substituted phenoxide ion for those of 2a–2g.
The pseudo-first-order rate constants (kobsd) were calculated
from the equation: ln (A∞ – At) = − kobsdt + C. The correlation
coefficients of the linear regressions were usually higher than
0.9995. Generally, five different OH concentrations were
used to calculate the second-order rate constants (kOH ) from
the slope of the linear plot of kobsd vs. [OH ]. The uncertainty
in the kOH values is estimated to be less than 3% from rep-
licate runs. The kOH values calculated in this way are summar-
ized in Tables 1 and 2 for the reactions of 1a–1f and 2a–2g,
respectively. ThekN3 valuesreportedpreviously17 forthecor-
responding reactions with weakly basic N3 are also listed for
comparison.
O
S
O
Y
O
X
1 or 2
Y = 2,4-(NO2)2 ; X = 4-NO2(1a), 3-NO2(1b), 3-Cl(1c), H(1d),
4-Me(1e), 4-MeO(1f)
X = 4-NO2 ;
Y = 2,4-(NO2)2(2a), 4-NO2(2b), 4-CHO(2c),
4-CN(2d), 4-COMe(2e), 3-CHO(2f), 4-Cl(2g).
A similar result has been reported for the reactions of 1a–1f
with weakly basic N3 ; e.g., reactions of substrates possessing
an EWG produced mainly the S O bond fission products, while
those of substrates bearing an EDG yielded mostly the C O
bondfissionproducts.17 Incontrast, wehavepreviouslyreported
that the corresponding reactions with strongly basic C2H5O in
anhydrous ethanol proceed exclusively through the S O bond
fission.13 Thesedemonstrateconvincinglythattheregioselectiv-
ityinthe nucleophilic substitutionreactionsof1a–1fisgoverned
by the electronic nature of the substituent X in the benzenesul-
fonyl moiety and by the basicity of the nucleophiles.
Our study has now been extended to alkaline hydrolysis of
1a–1f and Y-substituted phenyl 4-nitrobenzenesulfonates
(2a–2g) in 80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC
to obtain further information on the reaction mechanism
(Scheme 1). The kinetic results obtained from the current
study have been compared with those reported recently17
for the corresponding reactions with weakly basic N3 to
investigate effects of changing the nucleophile from the azide
iontothehydroxideiononreactivity andTSstructures. Nucle-
ophilic substitution reactions of 1a–1f and 2a–2g with
strongly basic C2H5O in anhydrous ethanol have previously
been carried out to investigate the effects of the alkali metal
ions on reactivity (e.g., catalysis or inhibition).13 However,
the kinetic data obtained previously in anhydrous ethanol
Effect of Substituent X on Reactivity and Reaction Mech-
anism. As shown in Table 1, reactivity of substrates 1a–1f
toward OH decreases steeply as the substituent X changes
from a strong EWG to an EDG; e.g., the kOH value decreases
from 442 to 7.80 and 1.30 M−1s−1 as the substituent X changes
from 4-NO2 to H and 4-MeO, in turn. A similar result is
demonstrated for the corresponding reactions with N3 ,
although the azide ion is ~103-fold less reactive than the
hydroxide ion. It is noted that N3 is a weak base since the
pKa of HN3 is 4.72.18 Thus, one might suggest that the weak
basicity of the azide ion is responsible for the kinetic result that
N3 is less reactive than OH .
However, the difference in their basicity cannot be solely
responsible for the kinetic result shown in Table 1, since
OH is only ~103-fold more reactive than N3 although the
former is ~11 pKa units more basic than the latter. This appears
to be consistent with the report that OH often deviates
Table 1. Summary of second-order rate constants for the reactions
of 2,4-dinitrophenyl X-substituted benzenesulfonates (1a–1f) with
OH (kOH ) and N3 (kN3 ) in 80 mol % H2O/20 mol % DMSO
at 25.0 0.1 ꢀC.a
X
kOH /M−1 −1
s
103kN3 /M−1 −1
s
1a
1b
1c
1d
1e
1f
4-NO2
3-NO2
4-Cl
H
4-Me
4-MeO
442
234
22.0
7.80
3.20
1.30
341
236
24.7
12.5
6.67
3.03
O
S
O
S
O
2OH
O
O
H2O
Y
Y
X
O
X
O
1a-1f or 2a-2g
a The data for the reactions with N3 were taken from Ref. 17.
Scheme 1.
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Alkaline Hydrolysis of Aryl Benzenesulfonates
KOREAN CHEMICAL SOCIETY
negatively from linear Brønsted-type plots for nucleophilic
substitution reactions of esters with various anionic nucleo-
philes.19 Jencks has attributed the negative deviation shown
by OH from the linear Brønsted-type plot to a solvation
effect, since OH is known to be strongly solvated in H2O
through H-bonding interactions.19 Thus, solvation effects
would be also responsible for the kinetic results men-
tioned above.
O
O
S OAr
MeO
MeO
S OAr
O
O
IR
IIR
To examine the validity of the above idea, the Yukawa–
Tsuno plot has been constructed in Figure 2. Eq. (1) was orig-
inally derived to account for the kinetic results for the solvo-
lysis of benzylic systems in which a positive charge develops
partially in the TS.20 We have shown that Eq. (1) is also
highly effective in clarifying the ambiguities in reaction
mechanisms for nucleophilic substitution reactions of esters
with various nucleophiles (e.g., neutral amines as well as ani-
onic nucleophiles such as OH , N3 and CN ).6,7,13 As shown
in Figure 2, the Yukawa–Tsuno plot for the reactions of
1a–1f with OH exhibits excellent linearity (R2 = 0.9998)
The reactions of 1a–1f with a weakly basic N3 have been
suggested to proceed through the S O and C O bond fission
competitively.17 The fraction of the C O bond fission has
been reported to increase significantly as the substituent
X in the benzenesulfonyl moiety changes from a strong
EWG to an EDG (e.g., the percentage of C–O bond fission
increases from 16 to 87% as X changes from 4-NO2 to 4-
MeO, respectively).17 Accordingly, the C O bond fission
becomes the major reaction pathway when the substituent
X is an EDG. In contrast, we have previously reported that
the reactions of 1a–1f with strongly basic C2H5O proceed
exclusively through the S O bond fission on the basis of
the product analysis (e.g., the 2,4-dinitrophenoxide ion was
found as one of the S O bond fission products but not 1-
ethoxy-2,4-dinitrobenzene, one of the C O bond fission pro-
ducts).13 It is noted that the reactions of 1a–1f with OH yield
the 2,4-dinitrophenoxide ion as one of the reaction products
whether or not the reactions proceed through the S O bond
fissionorviatheC Obondscission. Accordingly, regioselec-
tivity is not discussed in this study.
The effect of the substituent X on reactivity is shown in
Figure 1. The Hammett plot for the reactions of 1a–1f with
OH− is linear with ρX = 2.27 and R2 = 0.997. However, a scru-
tiny of the linear Hammett plot reveals that substrates 1c and 1f
deviate negatively from the linear plot. It is notable that 1c
and 1f possess a substituent in the benzenesulfonyl moiety
(i.e., 4-Cland4-MeO, respectively) thatcandonateanelectron
pair through resonance interactions as modeled by the reso-
nance structures IR $ IIR. Since such resonance interactions
could stabilize the ground state (GS) of the substrate, one
might suggest that the negative deviation shown by 1c and
1f from the linear Hammett plot is due to the GS stabilization
of substrates 1c and 1f.
3
ρX = 2.27 0.08
1a
R2 = 0.997
1b
2
1
0
1c
1d
1e
1f
-0.5
0.0
0.5
1.0
σX
Figure 1. Hammett plot for the reactions of 2,4-dinitrophenyl X-
substituted benzenesulfonates (1a–1f) with OH in 80 mol % H2O/
20 mol % DMSO at 25.0 0.1 ꢀC. The identity of the points is given
in Table 1.
3
1a
1b
2
Table 2. Summary of second-order rate constants for the reactions of
Y-substituted phenyl 4-nitrobenzenesulfonates (2a–2g) with OH
and N3 in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 oC.a
1c
1d
1
Y-PhOH
1e
Entry
Y
pKa
kOH /M−1 −1
442
3.06
s
103kN3 /M−1 −1
341
0.793
s
1f
2a
2b
2c
2d
2e
2f
2,4-(NO2)2
4-NO2
4-CHO
4-CN
4-COMe
3-CHO
4-Cl
3.94
7.79
8.45
8.82
8.94
ρ = 2.09
rX= 0.41
0
R2 = 0.9998
0.811
1.67
0.610
0.299
0.174
0.184
0.506
0.132
0.0568
-
-0.5
0.0
0.5
1.0
σXo + r (σX+ − σ Xo )
10.12
10.63
Figure 2. Yukawa–Tsuno plot for the reactions of 2,4-dinitrophenyl
X-substituted benzenesulfonates (1a–1f) with OH in 80 mol% H2O/
20 mol% DMSO at 25.0 0.1 ꢀC.
2g
a The kN3 values were taken from Ref. 17.
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Alkaline Hydrolysis of Aryl Benzenesulfonates
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with ρX = 2.09 and r = 0.41. A similar linear Yukawa–Tsuno
plot has been reported for the corresponding reactions with
N3 (e.g., R2 = 0.999, ρX = 1.72 and r = 0.40).17
coefficient for the plot is not excellent (i.e., R2 = 0.985).
A similar linear Brønsted-type plot has been reported for the
corresponding reactions with N3 (e.g., βlg = −0.63 and R2 =
0.982).17 A βlg value of −0.6 0.1 is typical for reactions
reported previously to proceed through a concerted mechan-
ism.2–7 In fact, the reactions of 2a–2g with the azide ion have
been reported to proceed through a concerted mechanism on
the basis of the βlg value of −0.63.17 Thus, one might propose
that the reactions with OH− also proceed through a concerted
mechanism.
Useful information on the reaction mechanism can be
obtained from Hammett plots correlated with σo and σ− con-
stants. If the reactions of 2a–2g with OH− proceed through
a concerted mechanism, a negative charge would develop par-
tially on the O atom of the leaving Y-substituted phenoxide in
the TS. Since such a negative charge could be delocalized to
the substituent Y through resonance interactions, σ− constants
shouldresultinabetterHammettcorrelation thanσo constants.
In contrast, if the current reactions proceed through a stepwise
mechanism, expulsion of the leaving group would occur after
the rate-determining step (RDS). This is because OH is much
more basic and a poorer nucleofuge than aryloxide ions.
Accordingly, if the reactions of 2a–2g with OH proceed
throughastepwise mechanism, inwhichexpulsion oftheleav-
ing group occurs after the RDS, no negative charge would
develop on the O atom of the leaving group in the TS. In this
case, σo constants should exhibit a better linear correlation
than σ− constants.
Â
À
ÁÃ
logkX=kH = ρX σXo + r σX+ – σXo
ð1Þ
The r value in Eq. (1) represents the resonance demand of
the reaction center or the extent of resonance contribution,
while the term (σX+ −σXo ) is the resonance substituent constant
that measures the capacity for π-delocalization of the
π-electron donor substituent.20,21 Thus, the linear Yukawa–
Tsuno plot shown in Figure 2 is consistent with the above idea
that the negative deviation shown by substrates 1c and 1f from
the linear Hammett plot (Figure 1) is caused by GS stabiliza-
tion through resonance interactions, as modeled by the reso-
nance structures IR $ IIR.
Effect of Substituent Y on Reactivity and Reaction Mech-
anism. The linear Yukawa–Tsuno plot shown in Figure 2 sug-
gests that the reactions of 1a–1f proceed through the same
reaction mechanism. However, it does not give any further
information on the reaction mechanism. Thus, second-order
rate constants for the reactions of Y-substituted phenyl 4-
nitrobenzenesulfonates (2a–2g) with OH have been measured
to obtain more conclusive information on the reaction mechan-
ism. The kOH values are summarized in Table 2 together with
the kN3 values reported previously17 for the corresponding
reactions with N3 for comparison. As shown in Table 2, kOH
decreases as the substituent Y in the leaving group becomes a
weaker EWG; e.g., it decreases from 442 to 3.06 and 0.174
M−1s−1 as the substituent Y changes from 2,4-(NO2)2 to 4-
NO2 and 4-Cl, in turn. A similar result is demonstrated for
the corresponding reactions with N3 , although the azide ion
is ~103-fold less reactive than the hydroxide ion.
To examine the above idea, Hammett plots were con-
structed using σo and σ− constants. As shown in Figure 4, both
Hammett plots exhibit highly scattered points although the
plot correlated with σo constants results in a slightly better cor-
relation (R2 = 0.964) than that with σ− constants (R2 = 0.921).
Thus, one cannot obtain any useful information from the poor
Hammett plots.
The effect of the substituent Y on the reactivity is illustrated
in Figure 3. The Brønsted-type plot for the reactions of 2a–2g
with OH is linear with βlg = −0.51, although the correlation
To elucidate the reaction mechanism, Yukawa–Tsuno
plots have been constructed for the reactions of 2a–2g with
4
βlg = − 0.51 0.04
(a)
(b)
3
R2 = 0.985
2a
1
0
1
0
2b
2b
2
2d
2d
2c
2e
1
2c
2b
2d
2e
2f
2f
0
2c
2f
2e
2g
2g
-1
-2
-1
-2
2g
ρY = 1.03
-1
ρY = 2.11 0.29
R2 = 0.921
R2 = 0.964
-2
0.0
0.5
1.0
1.5
0.2
0.4
0.6
σYo
0.8
1.0
3
6
9
12
σY−
pKa
o
−
Figure 3. Brønsted-type plot for reactions of Y-substituted phenyl 4-
nitrobenzenesulfonates (2a–2g) with OH in 80 mol % H2O/20 mol
% DMSO at 25.0 0.1 ꢀC. The identity of the points is given in
Table 2.
Figure 4. Hammett plots correlated with σY (a) and σY (b) constants
for reactions of Y-substituted phenyl 4-nitrobenzenesulfonates (2b–
2g) with OH in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 ꢀC.
The identity of the points is given in Table 2.
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Alkaline Hydrolysis of Aryl Benzenesulfonates
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OH and with N3 . As shown in Figure 5(a), the plot for the
reactions of 2a–2g with OH exhibits an excellent linear cor-
relation with ρY = 1.85 and r = 0.25. A similar result is shown
for the corresponding reactions with N3 (e.g., ρY = 2.10 and r
= 0.22). As mentioned above, the r value in the Yukawa–
Tsuno equation represents the extent of resonance contribu-
tion.20,21 Thus, the r value of 0.25 implies that a negative
charge develops partially on the O atom of the leaving group,
which can be delocalized to the substituent Y through reso-
nance interactions. This is possible only when the reactions
proceed through a concerted mechanism but not possible if
the reactions proceed through a stepwise mechanism as dis-
cussed earlier. Thus, it is concluded that the alkaline hydroly-
sis of 2a–2g proceeds through a concerted mechanism.
Effect of Changing Nucleophile from N3 to OH on Reac-
tion Mechanism. It is generally understood that ρX and ρY
values represents a relative degree of bond formation between
the nucleophile and the electrophilic center in the TS and a rel-
ative degree of expulsion of the leaving group, respectively.
As mentioned earlier, the ρX value of 2.09 obtained from
the reactions with OH is larger than that reported for the cor-
responding reactions with N3 (i.e., ρX = 1.72). This implies
that bond formation in the TS is more advanced for the reac-
tions with OH than for those with N3 . In contrast, Figure 5
shows that the ρY values are 1.85 and 2.10 for the reactions
with OH and N3 , respectively, indicating that expulsion of
the leaving group is less advanced for the reactions with
OH than for those with N3 . Thus, one can suggest that the
reactions with OH proceedthrough a tighter TSthanforthose
with N3 (i.e., a TS with more bond formation but with less
leaving-group expulsion).
ion toward substrates 1a–1f and 2a–2g, although the former
is 11 pKa units more basic than the latter. (2) Substrates 1c
and 1f deviate negatively from the linear Hammett plot,
while the Yukawa–Tsuno plot results in an excellent linear
correlation with ρX = 2.09 and r = 0.41, indicating that GS
stabilization of the substrates 1c and 1f is responsible for
the negative deviation. (3) The Brønsted-type plot for reac-
tions of 2a–2g with OH− is linear with βlg = −0.51, a typical
value reported for reactions that proceed through a concerted
mechanism. (4) The Yukawa–Tsuno plot for the reactions of
2a–2g with OH− exhibits excellent linearity with ρY = 1.85
and r = 0.25, a clear indication that a negative charge devel-
ops partially on the O atom of the leaving group. (5) The
reactions with OH proceed through a concerted mechanism
with a tighter TS than those with N3 .
Experimental
Materials. Substrates 1a–1f and 2a–2g were readily pre-
pared from reactions of the respective Y-substituted phenol
and X-substituted benzenesulfonyl chloride in the presence
of triethylamine in anhydrous ether as reported previ-
ously.13,16 The crude products were purified by recrystalliza-
tion or column chromatography. DMSO and other chemicals
were of the highest quality available. Because of the low sol-
ubility of the substrates in pure H2O, aqueous DMSO was
used as the reaction medium (i.e., 20 mol% DMSO/80 mol
% H2O). Double-distilled water was further boiled and
cooled under nitrogen just before use. Sodium hydroxide
stock solution was titrated using potassium hydrogen
phthalate.
Kinetics. The kinetic studies were performed at 25.0 0.1 ꢀ
C with a UV–vis spectrophotometer for slow reactions (e.g.,
t1/2 > 10 s) or with a stopped-flow spectrophotometer for
fast reactions (e.g., t1/2 ≤ 10 s) equipped with a constant-
temperature circulating bath. The reactions were followed
by monitoring the appearance of 2,4-dinitrophenoxide ion
for the reactions of 1a–1f (or Y-substituted phenoxide ion
for those of 2a–2 g). All the reactions were carried out
under pseudo-first-order conditions in which the sodium
hydroxide concentration was at least 20 times greater than
the substrate concentration. Typically, the reaction was
initiated by adding 5 μL of 0.02 M of a substrate solution
in MeCN by a 10-μL syringe into a 10-mm UV cell con-
taining 2.50 mL of the reaction medium and NaOH. All
transfers of reaction solutions were carried out by means
of gas-tight syringes.
Conclusions
The current study has allowed us to conclude the following:
(1) Hydroxide ion is only 103-fold more reactive than azide
-2
(a)
(b)
1
0
2b
2b
-3
-4
-5
2d
2d
2c
2c
2e
2e
2f
2f
2g
-1
ρ = 1.85
rY= 0.25
ρ = 2.10
rY= 0.22
Products Analysis. 2,4-Dinitrophenoxide or Y-substituted
phenoxide ion was liberated quantitatively and identified as
one of the reaction products after completion of the reaction
with that of authentic sample under the same kinetic
conditions.
R2 = 0.997
R2 = 0.990
-2
0.0
0.5
1.0
0.0
0.5
1.0
σYo + r (σY− − σYo)
σYo + r (σY− − σYo)
Figure 5. Yukawa–Tsuno plots for the reactions of Y-substituted
phenyl 4-nitrobenzenesulfonates (2b–2g) with OH (a) and N3 (b)
ions in 80 mol %H2O/20 mol % DMSOat 25.0 0.1 ꢀC. The identity
of the points is given in Table 2.
Acknowledgment. The publication cost of this paper was met
by the Korean Chemical Society.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1563–1568
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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BULLETIN OF THE
Article
Alkaline Hydrolysis of Aryl Benzenesulfonates
KOREAN CHEMICAL SOCIETY
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Bull. Korean Chem. Soc. 2015, Vol. 36, 1563–1568
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1568