Nucleophilic Substitution Reactions of 2,4-Dinitrophenyl X-Substituted-Benzenesulfonates and Y-Substituted-Phenyl 4-Nitrobenzenesulfonates with Azide Ion: Regioselectivity and Reaction Mechanism

Article abstract of DOI:10.1002/bkcs.10259

The second-order rate constants for reactions of 2,4-dinitrophenyl X-substituted-benzenesulfonates (4a-4f) and Y-substituted-phenyl-4-nitrobenzenesulfonates (5a-5f) with N₃^- ion have been measured spectrophotometrically. The reactions of 4a-4f proceed through S-O and C-O bond fission pathways competitively. Fraction of the S-O bond fission decreases rapidly as the substituent X in the benzenesulfonyl moiety changes from an electron-withdrawing group to an electron-donating group. The Hammett plots for reactions of 4a-4f are linear with ρ_X=1.87 and 0.56 for the S-O and C-O bond fission, respectively. The fact that the substituent X is further away from the reaction site of the C-O bond fission than that of the S-O bond fission is one reason for the smaller ρ_X value. The nature of the reaction mechanism (i.e., a stepwise mechanism in which expulsion of the leaving group occurs after the rate-determining step) is also responsible for the smaller ρ_X value obtained from the C-O bond fission. The Bronsted-type plot for the reactions of 5a-5f is linear with β_lg=-0.63, which is typical for reactions reported previously to proceed through a concerted mechanism. Effects of substituents X and Y on regioselectivity and reaction mechanism are discussed in detail.

Full text of DOI:10.1002/bkcs.10259

Article
DOI: 10.1002/bkcs.10259
BULLETIN OF THE
J.-H. Moon et al.
KOREAN CHEMICAL SOCIETY
Nucleophilic Substitution Reactions of 2,4-Dinitrophenyl X-Substituted-
Benzenesulfonates and Y-Substituted-Phenyl 4-Nitrobenzenesulfonates
with Azide Ion: Regioselectivity and Reaction Mechanism
*
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 December 15, 2014, Accepted January 7, 2015, Published online April 23, 2015
The second-order rate constants for reactions of 2,4-dinitrophenyl X-substituted-benzenesulfonates (4a–4f)
and Y-substituted-phenyl-4-nitrobenzenesulfonates (5a–5f) with N3− ion have been measured spectrophoto-
metrically. The reactions of 4a–4f proceed through S O and C O bond fission pathways competitively. Frac-
tion of the S O bondfission decreasesrapidly as the substituent Xin the benzenesulfonylmoietychanges from
an electron-withdrawing group to an electron-donating group. The Hammett plots for reactions of 4a–4f are
linear with ρX = 1.87 and 0.56 for the S O and C O bond fission, respectively. The fact that the substituent
X is further away from the reaction site of the C O bond fission than that of the S O bond fission is one reason
for the smaller ρX value. The nature of the reaction mechanism (i.e., a stepwise mechanism in which expulsion
of the leaving group occurs after the rate-determining step) is also responsible for the smaller ρX value obtained
fromtheC Obondfission. TheBrønsted-typeplotforthereactionsof5a–5fislinearwithβlg = −0.63, whichis
typical for reactions reported previously to proceed through a concerted mechanism. Effects of substituents
X and Y on regioselectivity and reaction mechanism are discussed in detail.
Keywords: Aryl benzenesulfonates, Azidolysis, Regioselectivity, Yukawa-Tsuno plot, SNAr reaction
Introduction
mechanism on the basis of excellent linear Yukawa-Tsuno
plots with ρY = 0.95 0.04 and r = 0.55 for the reactions with
OH− and ρY = 1.98 0.06 and r = 0.41 for those with
C2H5O−.9
Nucleophilic substitution reactions of esters have been inten-
sively investigated due to their importance in synthetic appli-
cations and biological processess.1–12 Reactions of C O
centered esters with amines have often been reported to pro-
ceed through a stepwise mechanism in which the rate-
determiningstep (RDS) is dependent on basicityof the leaving
group and attacking amine.2–7 A curved Brønsted-type pot
observed for reactions of esters possessing a weakly basic
leaving group (e.g., 2,4-dinitrophenoxide) has been taken as
evidence for a stepwise mechanism with a change in the
RDS upon changing amine basicity.2–7 In contrast, reactions
of primary and secondary amines with P O centered esters
(e.g., 2,4-dinitrophenyl diphenylphosphinate) have been
reported to proceed through a concerted mechanism on the
basis of the kinetic result that the Brønsted-type plots are linear
with βnuc = 0.5 0.1.7
Similar results have been reported for the corresponding
reactions with anionic nucleophiles (e.g., OH− and
C2H5O−). Alkaline hydrolysis of Y-substituted-phenyl benzo-
ates (1) has been suggested to proceed through a stepwise
mechanism in which formation of an addition intermediate
is the RDS, as the Hammett plot correlated with σo constants
resulted in a much better linear correlation than that correlated
with σ− constants.8 However, reactions of Y-substituted-
phenyl diphenylphosphinates (2) with OH− and C2H5O−
anions have been concluded to proceed through a concerted
O
O
Ph P O
Ph
Ph C O
Y
Y
1
2
Reactions of O S O centered esters have also been stud-
ied.10–13 We have reported that reactions of sulfonate esters
are regioselective and that regioselectivity is dependent on
basicity of nucleophiles and structure of the substrate.11,12
The reaction of 3 with strongly basic OH− has been reported
to proceed through an E1cb (reversible) mechanism from lin-
ear-free energy relationships such as Brønsted-type and Ham-
1
mett plots together with H D exchange experiments by H
NMR spectroscopy.11 In contrast, the reactions of 3 with mod-
erately basic aryloxides and HOO− have been concluded
to proceed through an SN2 (S) mechanism on the basis of
Brønsted analysis,11 indicating that regioselectivity is gov-
erned by basicity of the nucleophile. A similar result has been
reported for reactions of 2,4-dinitrophenyl X-substituted-
benzenesulfonates(4a–4f)withamines.12 Wehavepreviously
reported that the reactions proceed S O and C O bond fis-
sion pathways competitively and that the regioselectivity is
dependent on nature of the substituent X and basicity of the
Bull. Korean Chem. Soc. 2015, Vol. 36, 1360–1365
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Wiley Online Library
1360

BULLETIN OF THE
Article
Azidolysis of Aryl X-Substituted-Benzenesulfonates
KOREAN CHEMICAL SOCIETY
attackingamine, e.g., theS Obondfissionoccursdominantly
for reactions with highly basic amines or with substrates pos-
sessing a strongly electron-withdrawing group (EWG) in
the benzenesulfonyl moiety while the C O bond fission
occurs considerably for reactions with weakly basic amines
or with substrates bearing a strongly electron-donating group
(EDG) in the benzenesulfonyl moiety.12 However, reactions
of 4a–4f with anionic nucleophiles (e.g., dissociated
C2H5O− and ion-paired C2H5O−Na+) have been reported to
proceed exclusively through the S O bond fission.13
constant obtained in this way corresponds to the overall sec-
ond-order rate constant (ktot). The second-order rate constants
for the S O bond fission (kS O) and those for the C O bond
fission (kC
) were calculated from the following
O
relationships:
kS O = ktot × the fraction of S Obond fission
ð1Þ
ð2Þ
kC O = ktot kS
O
Effect of Substituent X on Regioselectivity and Reactivity.
As shown in Table 1, the fraction of the S O bond fission for
the reactions of 4a–4f decreases rapidly as the substituent
X changes from a strong EWG to an EDG, e.g., up to 87%
C O bond fission when X = 4 OMe. Consequently, the
C O bond fission becomes the major reaction pathway when
the substituent X is an EDG. This demonstrates that the regios-
electivity is strongly governed by the electronic nature of the
substituent X in the benzenesulfonyl moiety of substrates 4a–
4f. One might expect that electrophilicity of the reaction center
is also influenced by the electronic nature of the substituent
X in the benzenesulfonyl moiety through an inductive effect.
However, such an inductive effect would be more significant
for the S O bond fission than for the C O bond fission, since
the substituent X is closer to the sulfonyl group (i.e., a prox-
imity effect). Thus, one can expect that electrophilicity of
the S atom of the sulfonyl moiety is strongly dependent on
electronic nature of the substituent X. It is apparent that an
EDG in the benzenesulfonyl moiety would decrease electro-
philicity of the S atom and the decreased electrophilicity of
the reaction site would retard attack of the nucleophile (i.e.,
N3−). This idea accounts for the kinetic result that the fraction
of the S O bond fission decreases rapidly upon changing the
substituentXfromanEWGtoanEDG, andthattheC Obond
fission becomes the major reaction pathway when the substit-
uent X is an EDG.
NO2
O
H3C S O
O
O
S O
O
NO2
Y
X
3
4a-4f
This study has now been extended to reactions of 4a–4f and
Y-substituted-phenyl-4-nitrobenzenesulfonates (5a–5f) with
azide ion (N−3) to obtain further information on regioselectivity
and reaction mechanism (Scheme 1). We report that electronic
nature of the substituents X and Y affects the regioselectivity
and reactivity but not the reaction mechanism.
Results and Discussion
Allofthereactionsinthisstudywerecarriedoutunderpseudo-
first-order reaction conditions (e.g., the N3− concentration was
kept in excess over the substrate concentration). Pseudo-first-
order rate constants (kobsd) were obtained from the equation,
ln(A∞ − At) = −kobsdt + C. Correlationcoefficients ofthelinear
regressions were usually higher than 0.9995. Generally, five
different N3− concentrations were used to obtain second-order
rate constants from the slope of the linear plot of kobsd vs. N3−
concentration. Thereactionsof4a–4fproceededthroughS O
and C O bond fission pathways competitively. The S O
bond fission led to formation of 2,4-dinitrophenoxide ion
and X-substituted-benzenesulfonyl azide, while the C O
bond fission yielded 1-azido-2,4-dinitrobenzene and X-sub-
stituted-benzenesulfonate anions. The fractions of the S O
bond fission are summarized in Table 1. The second-order rate
As mentioned above, the C O bond fission becomes
the major reaction pathway for substrates possessing an
EDG (e.g., 4e and 4f). This is consistent with the reports
that the C O bond fission occurs considerably for the reac-
tions of 4a–4f with weakly basic primary and secondary
amines (e.g., 2,2,2-trifluoroethylamine and piperazinium
O
S
O
O
S
kS–O
O
N3
O
N3
Table 1. Summary of kinetic data for the reactions of 2,4-
dinitrophenyl X-substituted-benzenesulfonates (4a–4f) with N3− in
80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC.
X
Y
X
O
Y
4a-4f or 5a-5f
kC–O
X
ktot/M−1 −1
s
kS O/M−1 −1
s
kC O/M−1 −1
s
O
S
0.406 (0.84)a
0.314 (0.75)a
0.0538 (0.46)a
0.0379 (0.33)a
0.0278 (0.24)a
0.0233 (0.13)a
0.341
0.236
0.0247
0.0125
0.00667
0.00303
0.0650
0.0780
0.0291
0.0254
0.0211
0.0203
Y
4a
4b
4c
4d
4e
4f
4-NO2
3-NO2
4-Cl
H
4-Me
4-OMe
N3
SO3
O
X
X
Y
N3
O
Y = 2,4-(NO2)2; X = 4-NO2(4a), 3-NO2(4b), 4-Cl(4c), H(4d), 4-Me(4e),
4-OMe(4f).
X = 4-NO2;
Y = 2,4-(NO2)2(5a), 4-NO2(5b), 4-CHO(5c), 4-CN(5d),
4-COMe(5e), 3-CHO(5f).
Scheme 1. Reactions of aryl benzenesulfonates with azide ion.
a The data in parenthesis are the fraction of the S O bond fission.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1360–1365
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1361

BULLETIN OF THE
Article
Azidolysis of Aryl X-Substituted-Benzenesulfonates
KOREAN CHEMICAL SOCIETY
ion, respectively),12 but is in contrast to the reports that
the reactions with strongly basic C2H5O− ion proceed exclu-
sively through the S O bond fission.13 It is noted that N3−
is a weakly basic nucleophile as the pKa of HN3 is 4.72.
Thus, one might suggest that a weak basicity of N3− is also
responsible for the fact that the reactions proceed largely
through the C O bond fission especially when the substituent
X is an EDG.
O
O
S
S
OAr
MeO
OAr
OAr
MeO
MeO
O
O
IR
IIR
O
C
O
C
OAr
MeO
IIIR
IVR
Table 1 shows that reactivity of the substrate decreases as
the substituent X changes from a strong EWG to an EDG,
e.g., the kS value decreases from 3.41 × 10−1 to 3.03 ×
Thus, one might suggest that GS stabilization of substrates
4c and 4f is responsible for the negative deviation from the
Hammett plot shown in Figure 1. To probe this idea, the
Yukawa-Tsuno equation has been introduced to the current
study. Equation (3) was originally derived to account for the
kinetic results obtained from solvolysis of benzylic systems
in which a partial positive charge develops.14,15 However,
we have previously shown that Eq. (3) is also highly effective
to clarify ambiguities in reaction mechanisms for nucleophilic
substitution reactions of esters with various nucleophiles (e.g.,
neutral amines as well as anionic nucleophiles such as N3−,
CN−, and OH−).5–9,11–13
O
10−3 M−1 s−1 as the substituent X changes from 4-NO2 to 4-
OMe, respectively. This is consistent with the preceding argu-
ment that electrophilicity of the reaction center decreases as
the substituent X changes from a strong EWG to an EDG.
The rate constant for the C O bond fission (i.e., kC O) also
decreases as the substituent X changes from an EWG to an
EDG. However, the kC value is much less dependent on
O
the electronic nature of the substituent X (e.g., it decreases
from 0.0650 to 0.0203 M−1 s−1 as X changes from 4-NO2 to
4-OMe, respectively). This is consistent with the fact that
the substituent X is further away from the reaction site of
the C O bond fission than from that of the S O bond fission.
Because the inductive effect exerted by the substituent
X should decrease with increasing the distance between the
substituent X and the reaction site.
Deduction of Reaction Mechanism (S O Bond Fission).
Nucleophilic substitution reactions of aryl benzenesulfonates
have been reported to proceed either through a stepwise mech-
anism or via a concerted pathway depending on reaction con-
ditions.12,13 Reaction of 2,4-dinitrophenyl benzenesulfonate
(4d) with amines have previously been suggested to proceed
through a stepwise mechanism with a change in the RDS upon
changing basicity of the incoming amine on the basis of a
curved Brønsted-type plot.12 In contrast, reactions of Y-sub-
stituted-phenyl benzenesulfonates with OH− and C2H5O−
have been reported to proceed through a concerted mechanism
since the Hammett plots correlated with σo constants exhibited
highlyscatteredpointswhiletheYukawa-Tsunoplotsresulted
in excellent linear correlations with ρY = 1.83 and r = 0.52 for
the reactions with OH− and ρY = 2.61 and r = 0.29 for the reac-
tions with C2H5O–.13
To investigate the reaction mechanism for the S O bond fis-
sioninthisstudy,Hammettplothasbeenconstructed.Asshown
in Figure 1, the Hammett plot is linear with ρX = 1.87 (R2 =
0.996). However, scrutiny of the Hammett plot reveals that
4c and 4f exhibit slightly negative deviation from the linearity.
This is consistent with our previous reports that substrates pos-
sessing a substituent, which can donate an electron pair through
resonance interactions, exhibit negative deviation from linear
Hammett plots for reactions of aryl X-substituted-benzoates
and related esters with amines as well as anionic nucleophiles
such as N3−, CN−, and OH−.8 We have attributed such negative
deviation to stabilization of the substrate in the ground state
(GS) through resonance interactions as modeled by the reso-
nance structures IR$IIR and IIIR$IVR.8,12
Â
À
ÁÃ
logkX=kH = ρX σXo + r σX+ – σXo
ð3Þ
As shown in Figure 2, the Yukawa-Tsuno plot exhibits
excellent linearity (R2 = 0.999) with ρX = 1.72 and r = 0.40.
The r value in Eq. (3) 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.14,15 Thus, the linear Yukawa-
Tsuno plot with r = 0.40 clearly supports the idea that the
0.0
4a
4b
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
4c
4d
4e
ρX = 1.87 0.08
R2 = 0.996
4f
–0.5
0.0
0.5
1.0
σX
Figure 1. Hammett plot for the reactions of 2,4-dinitrophenyl X-sub-
stituted-benzenesulfonates(4a–4f)withN3−(theS Obondfission) in
80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1360–1365
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1362

BULLETIN OF THE
Article
Azidolysis of Aryl X-Substituted-Benzenesulfonates
KOREAN CHEMICAL SOCIETY
negative deviation shown by substrates 4c and 4f in the
Hammett plot is caused by stabilization of their GS through
resonance interactions as modeled by the resonance structures
IR$IIR.
X-substituted-benzenesulfonate anions) from the Meisenhei-
mer complex occurs in the RDS. Because the electronic nature
of the substituent X could affect basicity and nucleofugality of
the leaving group through an inductive effect. On the contrary,
if expulsion of the leaving group occurs after the RDS, reac-
tivity of substrates 4a–4f would be independent of the basicity
and nucleofugality of the leaving group. It is notable that the
Hammett plot for the C O bond fission exhibits many scat-
tered points with a small ρX value (Figure 3). Thus, one can
suggest that expulsion of the leaving group from the Meisen-
heimer complex occurs rapidly after the RDS. This argument
can be further supported by the fact that (1) benzenesulfonates
are much less basic and better nucleofuges than azide and (2)
aromaticity, which is absent in the Meisenheimer complex,
can be restored by expulsion of the leaving group from the
Meisenheimer complex.
Brønsted-Type Analysis for S O Bond Fission Process.
Analysis of the Yukawa-Tsuno plot shown in Figure 2 does
not give conclusive information on the reaction mechanism.
Thus, second-order rate constants for the reactions of Y-substi-
tuted-phenyl 4-nitrobenzenesulfonates (5a–5f) with N3− have
been measured to obtain more conclusive information on
the reaction mechanism. It is noted that the reactions proceed
exclusively through the S O bond fission except for the reac-
tion of 5a, which proceeds through the S O and C O bond
fission competitively as mentioned earlier. Table 2 shows that
Deduction of Reaction Mechanism (C O Bond Fission).
The C O bond fission that leads to X-substituted-
benzenesulfonate anions and 1-azido-2,4-dinitrobenzene is a
typical SNAr reaction. It is well known that SNAr reactions
proceed through a stepwise mechanism with a Meisenheimer
complex, in which the RDS is dependent on reaction condi-
tions. For example, we have recently reported that SNAr reac-
tions of 1-(Y-substituted-phenoxy)-2,4-dinitrobenzenes with
C2H5O− in anhydrous ethanol proceed through an anionic
Meisenheimer complex, in which expulsion of the leaving
group occurs after the RDS.16a In contrast, we have shown that
SNAr reactions of the same substrates with secondary amines
proceed through a stepwise mechanism with a zwitterionic
Meisenheimer complex in which expulsion of the leaving
group occurs at the RDS.16b
To investigate the reaction mechanism for the C O bond
fission process, Hammett plot has been constructed. As shown
in Figure 3, the Hammett plot is linear with ρX = 0.56 with
many scattered points (R2 = 0.974). It is also noted that the
ρX value obtained for the C O bond fission process is much
smaller than that of 1.72 found for the S O bond fission reac-
tion (Figure 2). One might suggest that the smaller ρX value
observed for the C O bond fission is in accord with the dis-
tance effect as mentioned in the preceding section since the
substituent X is further away from the reaction site of the
C O bond fission.
the kS
value decreases as the leaving-group basicity
O
increases, e.g., it decreases from 3.41 × 10−1 to 5.68 × 10−5
M−1 s−1as the pKa of the conjugate acid of the leaving group
increases from 3.94 to 10.12. Thus, one might suggest that
expulsion of the leaving group is involved in the RDS either
in a concerted mechanism or in a stepwise pathway.
However, we propose that nature of the reaction mechanism
is also responsible for the small ρX value. One might expect
a large ρX value if expulsion of the leaving group (i.e.,
To investigate the reaction mechanism, Brønsted-type plot
has been constructed. As shown in Figure 4, the Brønsted-type
0.0
0.0
4a
4b
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–0.5
4b
–1.0
–1.5
–2.0
–2.5
–3.0
4a
4c
4c
4d
4e
4f
4d
4e
ρX = 1.72
r = 0.40
R2 = 0.999
4f
ρX = 0.56 0.06
R2 = 0.974
–0.5
0.0
0.5
1.0
–0.5
0.0
0.5
1.0
σXo + r (σX+ – σX
)
σX
o
Figure 2. Yukawa-Tsuno plot for the reactions of 2,4-dinitrophenyl
X-substituted-benzenesulfonates (4a–4f) with N3− (the S O bond fis-
sion) in 80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC.
Figure 3. Hammett plot for the reactions of 2,4-dinitrophenyl X-sub-
stituted-benzenesulfonates (4a–4f) with N3− (the C O bond fission)
in 80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1360–1365
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1363

BULLETIN OF THE
Article
Azidolysis of Aryl X-Substituted-Benzenesulfonates
KOREAN CHEMICAL SOCIETY
Table 2. Summary of second-order rate constants (kS O) for the
reactions of Y-substituted-phenyl 4-nitrobenzenesulfonates (5a–5f)
with N3− in 80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC.
bond fission competitively. The C O bond fission becomes
the major reaction pathway when the substituent X is an
EDG, indicatingthat regioselectivityisgovernedbyelectronic
nature of the substituent X. (2) Substrates possessing an EDG
(e.g., 4c and 4f) deviate negatively from the Hammett plot. GS
stabilization of the substrates is responsible for the negative
deviation as the Yukawa-Tsuno plot results in a much better
linear correlation with ρX = 1.72 and r = 0.40. (3) The Ham-
mett plot for the C O bond fission is linear but exhibits many
scattered points with ρX = 0.56, implying that the SNAr reac-
tion proceeds through a stepwise mechanism with a Meisen-
heimer complex, in which expulsion of the leaving group
occurs after the RDS. (4) The Brønsted-type plot for the reac-
tions of 5a–5f (the S O bond fission) is linear with βlg =
−0.63, indicating that the S O bond fission proceeds through
a concerted mechanism. (5) The substituent X and Y governs
the regioselectivity and reactivity but does not affect the reac-
tion mechanism in this study.
Y-C6H4OHa
Entry
Y
pKa
kS O/M−1 −1
s
5a
5b
5c
5d
5e
5f
2,4-(NO2)2
4-NO2
4-CHO
4-CN
4-COMe
3-CHO
3.94
7.79
8.45
8.82
8.94
10.12
0.341
0.000793
0.000184
0.000506
0.000132
0.0000568
a The pKa value of phenols in 20 mol% DMSO was calculated from the
relationship, pKa20 mol% DMSO = 1.27 × pKawater − 1.28 with the known
pKa values of phenols in water (see Ref. 18).
0
5a
Experimental
Materials. Substrates 4a–4f and 5a–5f were readily prepared
by reactions of the respective Y-substituted-phenol and X-
substituted benzenesulfonyl chloride under presence of
triethylamine in anhydrous ether as reported previously.13
Sodium azide and other chemicals were of the highest quality
available. Due to low solubility of substrates 4a–4f and 5a–5f
inpureH2O, aqueousdimethyl sulfoxide (DMSO) wasusedas
the reaction medium (i.e., 20 mol% DMSO/80 mol% H2O).
Doubly glass distilled water was further boiled and cooled
under nitrogen just before use.
–2
5b
5d
5c
5f
–4
–6
5e
β
lg = − 0.63 0.06
R2 = 0.982
4
6
8
10
pKa
Kinetics. The kinetic studies were performed at 25.0 0.1 ꢀC
with
a UV–Vis spectrophotometer equipped with a
Figure 4. Brønsted-type plot for reactions of Y-substituted-phenyl 4-
nitrobenzenesulfonates (5a–5f) with N3− in 80 mol% H2O/20 mol%
DMSO at 25.0 0.1 ꢀC.
constant temperature circulating bath. The reactions were fol-
lowed by monitoring the appearance of Y-substituted-
phenoxide ion, an S O bond fission product. All the reactions
were carried out under pseudo-first-order conditions in
which the N3− 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 the substrate solution
in MeCN by a 10 μL syringe into a 10 mm UV cell containing
2.50 mL of the reaction medium and N3−. All the transfers of
reaction solutions were carried out by means of gas-tight
syringes.
plot is linear with βlg = −0.63, although the correlation coeffi-
cient is not excellent (e.g., R2 = 0.982). One might expect a
curved Brønsted-type plot if the reactions of 5a–5f proceed
through a stepwise mechanism with a change in the RDS upon
changing the leaving-group basicity. In fact, a curved
Brønsted-type plot has been reported for reactions of Y-sub-
stituted-phenyl benzoates and O-Y-substituted-phenyl thio-
nobenzoates with N3−.17 The linear Brønsted-type plot
shown in Figure 4 indicates that the reactions proceed without
changing the RDS. Furthermore, a βlg value of −0.63 is typical
for reactions reported previously to proceed through a con-
certed mechanism.2–7 Thus, we propose that the reactions of
5a–5f proceed through a concerted mechanism.
Products Analysis. The amount of 2,4-dinitrophenoxide
formed during the S O bond fission process for the
reactions of 4a–4f was determined quantitatively by measur-
ing the optical density using a UV–Vis Spectrophotometer at
25.0 0.1 ꢀC. Y-Substituted-phenoxide ion (and/or its conju-
gate acid Y-substituted-phenol) was liberated quantitatively
and identified as one the reaction products for the reactions
of 5a–5f.
Conclusions
Thecurrentstudyhasallowedustoconcludethefollowing:(1)
Acknowledgment. The publication cost of this paper was
The reactions of 4a–4f proceed through the S O and C O
supported by the Korean Chemical Society.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1360–1365
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1364

BULLETIN OF THE
Article
Azidolysis of Aryl X-Substituted-Benzenesulfonates
KOREAN CHEMICAL SOCIETY
2007, 72, 3823; (c) I. H. Um, Y. H. Shin, J. Y. Han, M. Mishima,
J. Org. Chem. 2006, 71, 7715.
References
8. I. H. Um, H. J. Han, J. A. Ahn, S. Kang, E. Buncel, J. Org. Chem.
2002, 67, 8475.
1. (a)E. V. Anslyn, D. A. Dougherty, Chapter10:ModernPhysical
Organic Chemistry, University Science Books, California,
2006; (b) M. I. Page, A. Williams, Chapter 7: Organic and
Bio-organic Mechanisms, Longman, Singapore, 1997; (c) T.
H. Lowry, K. S. Richardson, Chapter 8.5: Mechanism and The-
ory in Organic Chemistry, 3rd ed., Harper Collins Publishers,
New York, 1987; (d) W. P. Jencks, Chapter 10: Catalysis in
Chemistry and Enzymology, McGraw Hill, New York, 1969.
2. Reviews:(a)E. A. Castro, PureAppl. Chem. 2009, 81, 685;(b)E.
A. Castro, J. Sulfur Chem 2007, 28, 401; (c) E. A. Castro, Chem.
Rev. 1999, 99, 3505; (d) W. P. Jencks, Chem. Rev. 1985, 85, 511;
(e) W. P. Jencks, Chem. Soc. Rev. 1981, 10, 345.
9. (a) H. J. Hong, J. Lee, A. R. Bae, I. H. Um, Bull. Korean Chem.
Soc. 2013, 34, 2001; (b) I. H. Um, J. E. Park, Y. H. Shin, Org.
Biomol. Chem. 2007, 5, 3539; (c) I. H. Um, Y. H. Shin, J. E. Park,
J. S. Kang, E. Buncel, Chem. Eur. J. 2012, 18, 961.
10. (a) F. Eroglu, D. Kahya, E. Erdik, React. Kinet. Catal. Lett. 2009,
98, 365; (b) L. Zhang, J. Wu, Adv. Synth. Catal. 2008, 350, 2409;
(c) C. Cai, N. R. Rivera, J. Balsells, R. R. Sidler, J. C. McWil-
liams, C. S. Shultz, Y. Sun, Org. Lett. 2006, 8, 5161; (d) M. J.
Pregel, E. J. Dunn, E. Buncel, J. Am. Chem. Soc. 1991,
113, 3545.
11. I. H. Um, L. R. Im, E. Buncel, J. Org. Chem. 2010, 75, 8571.
12. (a) I. H. Um, J. Y. Hong, J. A. Seok, J. Org. Chem. 2005,
70, 1438; (b) I. H. Um, S. M. Chun, O. M. Chae, M. Fujio,
Y. Tsuno, J. Org. Chem. 2004, 69, 3166; (c) I. H. Um, J. Y.
Hong, J. J. Kim, O. M. Chae, S. K. Bae, J. Org. Chem. 2003,
68, 5180.
13. (a)L. R. Im, Y. M.Park, I. H. Um, Bull. KoreanChem. Soc. 2008,
29, 2477; (b) I. H. Um, J. S. Kang, Y. H. Shin, E. Buncel, J. Org.
Chem. 2013, 78, 490.
14. (a) Y. Tsuno, M. Fujio, Adv. Phys. Org. Chem. 1999, 32, 267; (b)
Y. Tsuno, M. Fujio, Chem. Soc. Rev. 1996, 25, 129; (c) Y.
Yukawa, Y. Tsuno, Bull. Chem. Soc. Jpn. 1959, 32, 965.
15. (a) M. Zhang, M. Badal, R. Mizanur, M. Pasikowska, T. Sonoda,
M. Mishima, H. Fukaya, T. Ono, H.-U. Siehl, J.-L. M. Abboud, I.
A. Koppel, Bull. Chem. Soc. Jpn. 2014, 87, 825; (b) M. Badal, R.
Mizanur, M. Zhang, S. Kobayashi, M. Mishima, Bull. Chem.
Soc. Jpn. 2013, 86, 856; (c) M. Zhang, M. Badal, R. Mizanur,
I. A. Koppel, M. Mishima, Bull. Chem. Soc. Jpn. 2013, 86,
813; (d) M. Badal, R. Mizanur, M. Zhang, S. Kobayashi, M. Mis-
hima, J. Phys. Org. Chem. 2013, 26, 1071; (e) S. Than, M. Badal,
S. Itoh, M. Mishima, J. Org. Chem. Phys. Org. Chem. 2010, 23,
411; (f ) S. Itoh, M. Badal, M. Mishima, J. Phys. Org. Chem.
2009, 113, 10075; (g) S. Than, H. Maeda, M. Irie, K. Kikukawa,
M. Mishima, Int. J. Mass. Spectrom. 2007, 263, 205; (h) H.
Maeda, M. Irie, S. Than, K. Kikukawa, M. Mishima, Bull. Chem.
Soc. Jpn. 2007, 80, 195.
3. (a) E. A. Castro, M. E. Aliaga, M. Gazitua, P. Pavez, J. G. Santos,
J. Phys. Org. Chem. 2014, 27, 265; (b) P. Pavez, D. Millan, J. I.
Morales, E. A. Castro, J. Org. Chem. 2013, 78, 9670; (c) R.
Aguayo, F. Arias, A. Canete, C. Zuniga, E. A. Castro, P. Pavez,
J. G. Santos, Int. J. Chem. Kinet. 2013, 45, 202; (d) R. Ormaza-
bal-Toledo, E. A. Castro, J. G. Santos, D. Millan, A. Canete,
R. Contreras, P. R. Campodonico, J. Phys. Org. Chem. 2012,
25, 1359; (e) E. A. Castro, D. Ugarte, M. F. Rojas, P. Pavez,
J. G. Santos, Int. J. Chem. Kinet. 2011, 43, 708; (f ) E. Castro,
M. Aliaga, P. R. Campodonico, M. Cepeda, R. Contreras,
J. G. Santos, J. Org. Chem. 2009, 74, 9173; (g) E. A. Castro,
M. Ramos, J. G. Santos, J. Org. Chem. 2009, 74, 6374.
4. (a) H. K. Oh, Bull. Korean Chem. Soc. 2012, 33, 2427; (b) H. K.
Oh, Bull. Korean Chem. Soc. 2011, 32, 137; (c) H. Lee, H. K. Oh,
Bull. KoreanChem. Soc. 2010, 31, 475;(d)H. K. Oh, J. Y. Oh, D.
D. Sung, I. Lee, J. Org. Chem. 2005, 70, 5624;(e)H. K. Oh, Y. C.
Jin, D. D. Sung, I. Lee, Org. Biomol. Chem. 2005, 3, 1240; (f ) I.
Lee, D. D. Sung, Curr. Org. Chem. 2004, 8, 557; (g) J. F. Kirsch,
A. Kline, J. Am. Chem. Soc. 1969, 91, 1841; (h) T. H. Fife,
L. Chauffe, J. Org. Chem. 2000, 65, 3579; (i) W. J. Spillane,
C. Brack, J. Chem. Soc. Perkin Trans. 1998, 2, 2381.
5. (a) I. H. Um, M. J. Kim, A. R. Bae, J. M. Dust, E. Buncel, J. Org.
Chem. 2015, 80, 217; (b) I. H. Um, A. R. Bae, T. I. Um, J. Org.
Chem. 2014, 79, 1206; (c) I. H. Um, A. R. Bae, J. Org. Chem.
2012, 77, 5781; (d) I. H. Um, A. R. Bae, J. Org. Chem. 2011,
76, 7510; (e) I. H. Um, L. R. Im, E. H. Kim, J. H. Shin, Org. Bio-
mol. Chem. 2010, 8, 3801.
6. (a)I. H. Um, S. E. Lee, H. J. Kwon, J. Org.Chem. 2002, 67, 8999;
(b) I. H. Um, S. J. Hwang, S. R. Yoon, S. E. Jeon, S. K. Bae,
J. Org. Chem. 2008, 73, 7671; (c) I. H. Um, J. A. Seok, H. T.
Kim, S. K. Bae, J. Org. Chem. 2003, 68, 7742.
16. (a) I. H. Um, H. J. Cho, M. Y. Kim, E. Buncel, Chem. Eur. J.
2014, 20, 13337;(b)I. H. Um, M. Y. Kim, T. A. Kang, J. M.Dust,
J. Org. Chem. 2014, 79, 7025.
17. (a) I. H. Um, E. H. Kim, J. Y. Lee, J. Org. Chem. 2009, 74, 1212;
(b)I. H. Um, E. H. Kim, J. Y. Lee, Bull. KoreanChem. Soc. 2008,
29, 580.
7. (a)I. H. Um, J. Y. Han, Y. H. Shin, J. Org. Chem. 2009, 74, 3073;
(b) I. H. Um, K. Akhtar, Y. H. Shin, J. Y. Han, J. Org. Chem.
18. E. Buncel, I. H. Um, S. Hoz, J. Am. Chem. Soc. 1989, 111, 971.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1360–1365
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1365