Investigation of the acid-catalyzed hydrolysis and reaction mechanisms of N,N′-diarylsulfamides using various criteria

Article abstract of DOI:10.1002/poc.3242

The mechanism of acid-catalyzed hydrolysis of a series of p-substituted N,N′-diarylsulfamides was investigated in aqueous mineral acid solutions. Rate profiles, reaction activation parameters, catalytic order of strong acids, solvent isotope effects, and analysis of the kinetic data by the excess acidity method suggest a change in the mechanism from A2 to A1. While the hydrolysis proceeds with an A2 mechanism in low acidity regions, an A1 mechanism takes place in high acid concentrations. Copyright

Full text of DOI:10.1002/poc.3242

Research Article
Received: 9 June 2013,
Revised: 18 September 2013,
Accepted: 29 September 2013,
Published online in Wiley Online Library: 4 November 2013
(wileyonlinelibrary.com) DOI: 10.1002/poc.3242
Investigation of the acid-catalyzed
hydrolysis and reaction mechanisms of
N,N′-diarylsulfamides using various criteria
a
b
c
Yunus Bekdemir , Aliye Gediz Erturk * and Halil Kutuk
The mechanism of acid-catalyzed hydrolysis of a series of p-substituted N,N′-diarylsulfamides was investigated in aqueous
mineral acid solutions. Rate profiles, reaction activation parameters, catalytic order of strong acids, solvent isotope effects,
and analysis of the kinetic data by the excess acidity method suggest a change in the mechanism from A2 to A1. While the
hydrolysis proceeds with an A2 mechanism in low acidity regions, an A1 mechanism takes place in high acid concentrations.
Copyright © 2013 John Wiley & Sons, Ltd.
Keywords: acid catalysis; diarylsulfamides; excess acidity; hydrolysis; mechanism
were performed on a GBC Cintra 20 model ultraviolet–visible (UV–VIS) spec-
trophotometer (Australia) with a fitted thermostated cell compartment.
INTRODUCTION
In the literature, the mechanism of the acid-catalyzed hydrolysis
[
1]
of the sulfonamides and the sultams (the corresponding cyclic
Preparation of sulfamides
[
2]
sulfonamides) has been studied in some detail. Both classes of
compounds are very stable and so their S–N bond cleavage oc-
curs in strong acid media at elevated temperatures. Protonation
of these compounds in aqueous acid solutions takes place on
the nitrogen and then, in slow steps, a water molecule attacks
the sulfur atom. Acid-catalyzed hydrolysis of a series of symmet-
rical N,N′-diarylsulfamides was studied in the pH range by
Spillane and his co-workers. They measured the rate of hydro-
lysis in a water–acetone, 9:1 (v/v) solvent system containing
added hydrochloric acid, and they suggested that the major
hydrolytic pathway involves a bimolecular water attack on the
unprotonated diarylsulfamide. However, the reaction mecha-
nism in strong aqueous mineral acid solutions has not yet been
investigated.
Our interests in the structure and reactivity of sulfur com-
pounds containing heteroatoms such as nitrogen and oxygen
have led us to study the sulfamides. We now report the kinetic
study of the acid-catalyzed hydrolysis of the N,N′-diarylsulfamides
The sulfamides 1a–d were prepared from the reaction of the correspond-
ing amines with sulfuryl chloride in the presence of dry pyridine at ꢀ78 °C
[5]
according to the method given by Parnell.
[6]
1
a.m.p. 109–111 °C (Lit. 111–112 °C); IR (KBr): 3276, 3057, 1602, 1341,
[3]
ꢀ1 1
1
156 cm ; H-NMR (200 MHz, CDCl
3
, 25 °C); δ = 6.90 (s, 2H), 7.00–7.50 (m,
1
3
10H); C-NMR (50 MHz, CDCl , 25 °C); δ = 121.3, 125.4, 129.4, 136.4 ppm.
3
[
4]
1b.m.p. 93–95 °C (Lit. 98–100 °C); IR (KBr): 3380, 3030, 2980, 1600,
[
4]
ꢀ1
1
1535, 1500,1450, 1340,1160, 1135 cm
C); δ = 2.30 (s, 6H), 6.40 (s, 2H), 6.90–7.10 (m, 8H); C-NMR (50 MHz, CDCl
; H-NMR (200 MHz, CDCl , 25 °
3
13
3
,
2
1
5 °C); δ = 21.1, 118.0, 129.1, 130.2, 133,4 ppm.
[6]
1
c.m.p. 118–120 °C (Lit. 119–120 °C); IR (KBr): 3299, 3101, 1601, 1330,
ꢀ
1 1
156, 917 cm ; H-NMR (200 MHz, CDCl
3
, 25 °C); δ = 6.68 (s, 2H), 7.00–7.40
, 25 °C); δ = 122.3, 129.6, 131.2, 134.4 ppm.
d.m.p. 195–197 °C (Lit. 195–197 °C); IR (KBr): 3380, 3035, 1600, 1540,
1
3
(
m, 8H); C-NMR (50 MHz, CDCl
3
[5]
1
ꢀ
1 1
1520, 1500, 1450, 1360, 1320, 1160, 1135 cm ; H-NMR (200 MHz, Acetone-
d
6
, 25°C); δ = 3.30 (s, 2H), 7.30 (d, J=10.12 Hz, 4H), 8.50 (d, J=10.00 Hz, 4H);
C-NMR (50 MHz, Acetone-d , 25°C); δ = 119.0, 123.4, 138.1, 141.2 ppm.
6
13
Kinetic procedure
1
a–d (Scheme 1) in concentrated aqueous mineral acid solutions
at elevated temperatures.
The rates of hydrolysis of the sulfamides were followed at 225–315 nm
using a UV–VIS spectrophotometer fitted with a thermostated cell
compartment (±0.05 °C). Good first-order behavior was observed with
EXPERIMENTAL
*
Correspondence to: Aliye Gediz Erturk, Faculty of Science and Arts, Department
of Chemistry, Ordu University, Cumhuriyet Campus, 52200 Ordu, Turkey.
E-mail: aerturk@att.net
Materials and instruments
Chemicals were purchased from Aldrich, Acros, and Merck and purified
by crystallization or distillation before use. Thin layer chromatography
was performed using Merck aluminum-backed plates (Kieselgel 60 F254),
and visualization was achieved by ultraviolet (UV) light. All products were
characterized by comparison of their physical data with samples prepared
a Y. Bekdemir
Canik Basari University, Gurgenyatak Campus, 55080 Canik/Samsun, Turkey
1
13
b A. Gediz Erturk
by conventional methods. The H and C NMR spectra were recorded on
a Bruker AC 200 MHz Spectrometer (Germany) at 200MHz and 50 MHz,
Faculty of Science and Arts, Department of Chemistry, Ordu University,
Cumhuriyet Campus, 52200 Ordu, Turkey
3
respectively, in CDCl using tetramethylsilane (TMS) as the internal stan-
dard. IR spectra were recorded with a MATTSON 1000 FTIR spectrophoto-
meter (USA). Melting points were determined on an Electrothermal 9100
Melting Point Apparatus (China). All kinetic measurements of sulfamides
c H. Kutuk
Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayis Univer-
sity, 55139 Atakum/Samsun, Turkey
J. Phys. Org. Chem. 2014, 27 94–98
Copyright © 2013 John Wiley & Sons, Ltd.

HYDROLYSIS MECHANISMS OF N,N′-DIARYLSULFAMIDES
Scheme 1. The N,N’-diarylsulfamides 1a-d
well-defined isosbestic points. The pseudo first-order rate constants’
values (k ) were calculated by plotting the log (A –A ) or log (A –A )
1 ∞ t t ∞
against time using the least squares procedure. All kinetic runs were
duplicated, and the average deviation from the mean was less than 5%.
Product analysis
Analysis of the product was also determined by comparing the UV
spectrum obtained after completion of the kinetic experiment with the
spectrum of the expected product with the same concentration and
under the same conditions. The UV–VIS spectra of the product of the
acid-catalyzed hydrolysis of compounds 1a–d were found to be identical
to the UV–VIS spectra of the corresponding amines recorded under the
same conditions. Also, the product of the hydrolysis of a typical
sulfamide (1d), which was isolated and recrystallized from ethanol, was
found to be p-nitroaniline with m.p. 146–149 °C. The structure of this
Figure 1. Plots of k1 for sulfuric acid-catalyzed hydrolysis of 1a–c at
85.0 ± 0.1 °C. ▲: p-CH3; ◊: p-H; and ○:p-Cl
1
increase sharply. The final increases are associated with a change-
over of mechanism from A2 to A1. Similar behavior has also been
observed for acid-catalyzed hydrolysis of secondary alkyl and
compound was confirmed by H and IR spectra.
[
16]
benzyl esters.
RESULTS AND DISCUSSION
Because of its high reactivity, the hydrolysis of the N,N′-di-(p-
nitrophenyl)sulfamides 1d could not be studied at 85.0 °C. How-
ever, a more detailed study of the hydrolysis of 1d at 50.0 °C in
sulfuric, perchloric, and hydrochloric acid shows that the cata-
lytic effectiveness of the added acids was HCl > H SO > HClO
Acid-catalyzed reactions can occur in two different ways: general
acid catalysis (Eqn 1) and specific acid catalysis (Eqns 2a, 2b). Both
mechanisms involve the proton transfer occurring before or during
the rate-determining step of the reaction (Scheme 2). In general acid
catalysis, each of the acidic species in the solution catalyzes the reac-
tion according to its own ability. Protonation of the substrate is the
rate-determining step and then the conjugate acid of the substrate
2
4
4
(Table 1). Bunton and his co-workers have suggested that such
an order is characteristic of a bimolecular (A2) mechanism
because the transition state of the positive character is being
preferentially stabilized by small anions of highly charged
undergoes reaction to products in a fast step (Eqn 1). In specific acid
+
ꢀ
catalysis, the only protonation source is H O . The catalysis proceeds
density such as Cl , whereas the converse is usually the case
3
[
17,18]
by fast, pre-equilibrium protonation before the rate-determining
step. The second step proceeds by either a monomolecular mecha-
nism – A1 (Eqn 2a) or a bimolecular mechanism – A2 (Eqn 2b)
for the unimolecular (A1) mechanism.
The kinetic data in sulfuric acid solution were analyzed by the
[
19–21]
excess acidity treatment of Cox and Yates,
according to
[7–10]
depending on the molecularity of the rate-determining step.
which the pseudo first-order rate constant, k
1
, obeys the equation
Profiles of the acid-catalyzed hydrolysis of the sulfamides 1a–c
in aqueous solutions of sulfuric acid at 85.0 ± 0.1 °C are shown in
Fig. 1. In the 1.00–8.00 M region, the rate of hydrolysis increased
with increasing acid concentration. All show a clearly defined rate
maximum (at 8.00 M) and then the rates decrease, pass a minimum
þ
þ
þ
log k ꢀ log C ꢀ log C =ðC þ C
1
H
S
S
SH
Þ
≠
¼ m*m X þ r log aNu þ logðko=KSK Þ
in the case of the A2 mechanism. In this equation, C
(3)
+
S
and CSH are
the concentrations of the unprotonated and protonated sub-
(ca. 10.00–11.00 M), and finally increase again (after 11.00 M). Sim-
+
ilar rate maxima have been observed for acid-catalyzed hydrolysis
strate in the aqueous acid with concentration C
Because of the extremely low basicity of the sulfamides studied,
the protonation correction term [log C
neglected in the low acidity region (up to 8.00 M). X is the excess
acidity, and aNu is the water activity (C
corrected according to temperature; the recent molarity-based
log aNu values by Cox were used because of their correct stan-
dard state), and r is the number of water molecules in the transi-
H 2 4
[=c(H SO )].
[
2]
[11]
of other compounds such as sultams, amides,
hydroxamic
[12,13]
[14]
+
acids,
primary acetate esters,
and N-acetylsulfonimidic
S S
/(C + CSH)] can be
[15]
esters. These rate maxima were attributed to an A2 mechanism
in which extensive protonation of the sulfamides occurs in the
regions of acidity in which the activity of the water is falling. The
rates of hydrolysis of the sulfamides at higher concentrations of
the sulfuric acid solutions pass through a minimum and then
+
H
[21,22]
[23]
, X,
and aNu
were
[
21]
[
21,22]
≠
tion state.
m* and m are the slope parameters, which give
information about the protonation site and the transition state,
respectively. k stands for the medium-independent rate con-
o
+
SH
stant of the rate-limiting step and K for the thermodynamic
dissociation constant of the protonated form of the substrate.
+
H
A plot of the log k –log C versus X is shown in Fig. 2 for the
1
hydrolysis of 1a–c in sulfuric acid solutions. If we focus on the
.00–8.00 M acidity region in Fig. 2, where the acidity is low, then
3
Scheme 2. Acid-catalyzed reactions. (1) General acid catalysis (2a, 2b)
Specific acid catalysis
the protonation can be almost neglected because of the low ba-
sicity of the sulfamides. The slightly downward curvature of this
J. Phys. Org. Chem. 2014, 27 94–98
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

Y. BEKDEMIR, A. GEDIZ ERTURK AND H. KUTUK
1
Table 1. Values of k for the hydrolysis of 1a–c at 85.0 ± 0.1 °C and 1d at 50.0 ± 0.1 °C
1
a
1b
1c
1d
+
4
ꢀ1
4
ꢀ1
4
ꢀ1
6
ꢀ1
6
ꢀ1
6
ꢀ1
[
H ]/(M)
k
1
(10 s
)
k
1
(10 s
)
k
1
(10 s
)
k
1
(10 s
)
k
1
(10 s
)
k
1
(10 s
)
H
2
SO (M)
4
H
2
SO
4
(M)
H
2
SO
4
(M)
H
2
SO (M)
4
HClO (M)
4
HClO (M)
4
1
2
3
4
5
6
7
7
8
8
9
9
1
1
1
1
1
1
.00
.00
.00
.00
.00
.00
.00
.50
.00
.50
.00
.50
0.00
1.00
2.00
3.00
4.00
5.00
0.660
0.190
0.233
0.428
0.666
1.18
1.83
2.39
3.00
2.63
2.21
1.66
0.955
0.479
0.977
1.75
2.37
-
0.330
0.127
0.157
0.279
0.493
0.813
1.30
-
1.43
-
1.10
-
0.758
1.23
2.93
4.76
-
1.31
52.20
48.80
44.60
40.60
36.00
30.70
24.30
-
18.00
-
15.40
-
11.40
9.25
6.62
6.56
9.95
-
50.50
43.50
37.10
28.80
23.90
18.10
13.40
-
10.80
9.27
9.37
8.87
8.55
-
61.6
63.2
69.5
77.4
88.4
102.0
112.0
-
106.0
-
79.0
-
10.10
10.70
-
-
-
0.238
0.327
0.530
0.991
1.48
2.14
-
3.28
-
2.86
-
1.75
1.05
0.739
0.931
1.24
2.09
-
-
-
-
-
-
Figure 2. Plots of log k
the acid-catalyzed hydrolysis of 1a–c at 85.0 ± 0.1 °C in 3.00–8.00 M
aqueous sulfuric acid solutions ▲: p-CH3, ◊: p-H, and ○: p-Cl
1
–log CH + versus X (temperature corrected) for
Figure 3. Excess acidity plot for hydrolysis of 1a–c in aqueous sulfuric
acid for the first part of the profile (3.00–8.00 M) ▲: p-CH3, ◊: p-H, and
○: p-Cl
≠
region implies A2 reactions that are typical when involving the
water rate-determining step. Similar behavior has been observed
given in Table 2. According to Ghosh and Cox, m*m >1 is for
≠
[13,26]
A1 processes and m*m <1 is for A2 processes.
For 1a–c,
[
24]
≠
for the hydrolysis of iminosulfonate esters, benzohydroxamic
values of m*m have been found, which are lower than 1, which
implies an A2 mechanism. Similar plots and slope values (m m*)
[13]
[25]
≠
acids, and sulfinylphthalimides.
In order to obtain a linear plot, increasing values of rlog aNu are
subtracted from the left-hand side of the equation until linearity
[
19]
against X is achieved.
Subtraction of log aH2O from the left-
Table 2. Excess acidity treatment of the hydrolysis of the
sulfamides 1a–c in aqueous sulfuric acid
hand side of Eqn 3 gives good straight line correlations, which
imply involvement of one water molecule in the transition state
for N,N′-diarylsulfamides (Fig. 3 and Eqn 3 where r = 1). In the
light of this evidence, we can say that the first parts of the pro-
files (3.00–8.00 M) proceed with an A2 mechanism involving
one water molecule in the transition state, where r is 1. The slope
and intercept values of the lines obtained in Fig. 3 for 1a–c are
≠
+
2
Compound Slope (m*m ) Intercept [log (k
o
/KSH)]
R
1
1
1
a
b
c
0.877
0.798
0.805
ꢀ7.29
ꢀ7.39
ꢀ7.09
0.9965
0.9949
0.9983
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Copyright © 2013 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2014, 27 94–98

HYDROLYSIS MECHANISMS OF N,N′-DIARYLSULFAMIDES
were obtained for the hydrolysis of benzohydroxamic acids,
classified as an A2 mechanism.
of water take place on the protonated substrate, the values of kD2O/
kH2O lie closer to unity than those observed for the A1 mechanism.
[
13,26]
The temperature dependence of the rate constants on the
hydrolysis reaction was analyzed by a least squares procedure
using a spreadsheet program (Eyring equation). The values of
Values of 1.02 and 1.19 were obtained for the acid-catalyzed
[25]
hydrolyses of N-(4-substituted-arylsulfinyl)phthalimides
and
[32]
arylsulfonyl phthalimides,
respectively. The kinetic solvent
k
1
at different temperatures and the calculated activation
isotope effect (kD2O/kH2O) observed for the hydrolysis of 1d is
shown in Table 4. In Table 4 in 1.00 M acid, kD2O/kH2O is 1.047, which
implies an A2 mechanism, whereas in high acid concentration (in
17.83 M), it is 1.60, which shows an A1 mechanism. The mechanistic
changeover is also supported by the values of the kinetic deute-
enthalpy and entropy values are shown in Table 3. For the
acid-catalyzed hydrolysis of the esters and amides,
ceed with an A1 mechanism, ΔS ~ 0–41.8 J mol
[
27]
they pro-
, whereas
≠
ꢀ1 ꢀ1
K
≠
those proceeding with an A2 mechanism have ΔS ~ ꢀ62.8 to
ꢀ
1
ꢀ1
[33]
ꢀ
125.5 J mol
K
. For the hydrolysis of 1a, in 1.00, 7.00, and
rium solvent isotope effect.
≠
1
4.00 M sulfuric acid, the values of ΔS are ꢀ18.17, 8.15, and
The slope of the Hammett Plot (logk/ko = ρα) gives the ρ value.
As a general convention, if the ρ value is positive, it implies that
electron-withdrawing groups accelerate the rate of reaction, and
electron releasing-groups retard the reaction (A2 mechanism). A
ꢀ
1
ꢀ1
≠
+
41.09 J mol
K , respectively. This change in ΔS is attrib-
uted to a distinct changeover in the mechanism, which is further
supported by other mechanistic criteria. The values for the
hydrolysis of 1b and 1c change in a similar way, as expected. It
is suggested that the negative values of ΔS for an A2 mecha-
nism are a reflection of the loss of rotational and translational
negative ρ value simply implies the opposite contribution of the
≠
[34,35]
substituent (A1 mechanism).
The substituent effects are
[
36]
well correlated by a satisfactory Hammett Plot.
acidity levels of up to 10.00 M [H ] (at 1.00 M H
[R : 0.9999]; at 7.00 M H SO , ρ = 0.538 [R : 0.9589]), the
2 4
At lower
, ρ = 1.65
+
freedom of water molecules in the transition state, where a water
molecule acts as a nucleophile. The positive values of ΔS in
2
SO
4
≠
2
2
1
4.00 M acid, for the hydrolysis of 1a–c, indicate that no water
electron-withdrawing substituents produce the highest rate of
hydrolysis (i.e., 1c > 1b in Fig. 1). Clearly at these acidities, the
electron-withdrawing substituents increase the positive charge on
the sulfur atom so the nucleophilicity of the water molecule
becomes more effective because of the positively charged sulfur
atom in the rate-determining transition state for the A2 mechanism.
molecule is involved in the rate-determining step, and so, a
unimolecular mechanism is proposed. Thus, the bimolecular
mechanism proposed for the hydrolysis at low acid concentra-
tions and the monomolecular mechanism for the high acid con-
centrations are further supported by the values of the entropies
[28]
+
of activation.
Changing the solvent from H O to D O in acid-catalyzed reac-
At acidity levels higher than 10.00 M [H ], however, (at 13.00 M
2
H SO , ρ = ꢀ1.77 [R : 0.9779]), the electron-donating substituents
2
2
2
4
tions, changes the environment of the reactants by forming
solvent–solvent and solvent–solute interactions. It also affects
the strength of the acids involved in the reaction. In the A1
mechanism, the rate-determining step is not affected signifi-
cantly by the change of solvent because it does not involve
the solvent or transfer of proton. Thus, the main effect of
changing the solvent from H O to D O lies in its influence on
produce the highest rate of hydrolysis (i.e., 1b > 1c in Fig. 1). With
these acidities, the electron-donating substituents increase the
basicity and facilitate protonation of the sulfamides. Electron-donating
Table 4. Deuterium solvent isotope effect for the hydrolysis
of 1d in sulfuric acid solutions at 85.0 ± 0.1 °C
2
2
the first step involving the protonation equilibrium. In the A1
mechanism, k ~ k and the ratio kD2O/kH2O are influenced by
the KSD/KSH ratio. In D O, the concentration of the conjugate acid
6
ꢀ1
6
ꢀ1
[
Acid]/M
10 k
1
(s
)
10 kave. (s
)
k
D2O/kH2O
D
H
+
+
2
1
1
1
1
.00 M D
2
SO
4
54.00
54.65
52.20
1.047
+
+
of the substrate [SD ] is higher than [SH ] in H
acids are stronger in H O than in D O. Therefore, the ratio is
expected to be around 2–4. For example, the kD2O/kH2O
ratios for the acid-catalyzed hydrolysis of ethylene oxide and
2
O because most
5
4.65
53.30
1.10
122.60
2
2
.00 M H
2
SO
4
[
29–31]
5
[
30]
7.83 M D
2
2
SO
4
121.40
76.03
1.60
[31]
t-butyl acetate are 2.2 and 2.0, respectively. The ratio kD2O/kH2O
120.20
+
+
is controlled not only by the KSD/KSH ratio but also by the difference
between the k and k rate constants. In general, for the A2 mech-
anism in the rate-determining step, when the nucleophilic attacks
7.83 M H
SO
4
75.00
7
D
H
7.03
4
ꢀ1
1
Table 3. Values of 10 k (s ) hydrolysis of the diarylsulfamides (1a–c) at different temperatures
≠
ꢀ1
≠
ꢀ1 ꢀ1
2
Compound
H
2
SO
4
80.0 °C
85.0 °C
90.0 °C
95.0 °C
ΔH (kJ mol
)
ΔS (J mol
K
)
R
1a
1b
1c
1.00
0.37
1.06
1.29
0.18
0.73
1.65
0.78
1.30
0.72
0.66
1.83
2.37
0.33
1.30
2.93
1.31
2.14
1.24
0.99
3.19
4.03
0.57
2.04
5.09
2.24
3.80
2.37
1.75
5.32
7.62
0.90
3.60
9.38
3.56
6.10
4.06
110.26 ± 0.43
116.50 ± 0.07
127.58 ± 0.32
115.49 ± 0.35
113.95 ± 0.33
125.43 ± 0.24
109.80 ± 0.15
112.38 ± 0.23
125.95 ± 0.29
ꢀ18.17 ± 1.20
+8.15 ± 0.20
+41.09 ± 0.87
ꢀ9.21 ± 0.98
ꢀ2.11 ± 0.91
+37.00 ± 0.67
ꢀ13.35 ± 0.42
ꢀ1.89 ± 0.64
+31.57 ± 0.80
0.9968
0.9999
0.9987
0.9981
0.9983
0.9992
0.9996
0.9991
0.9989
7.00
1
1
1
4.00
1.00
7.00
4.00
1.00
7.00
4.00
J. Phys. Org. Chem. 2014, 27 94–98
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

Y. BEKDEMIR, A. GEDIZ ERTURK AND H. KUTUK
Acknowledgement
This work was supported by Ondokuz Mayis
University (Grant No. EF-075).
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There is no direct evidence concerning the site of protonation
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[
3]
take place on nitrogen as observed for the sultams and sulfon-
[37]
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CONCLUSIONS
3
32–340.
On the basis of the overall evidence available, we have proposed that
the acid-catalyzed hydrolysis mechanism of the sulfamides 1a–d
proceeds with an A2 mechanism at lower acidities (1.00–8.00 M), as
shown in Scheme 3. In this first step, rapid pre-equilibrium pro-
tonation of the N,N′-diarylsulfamides takes place. It is assumed
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[
+
determining step. At acidity levels higher than 10.00 M [H ], the
acid-catalyzed hydrolysis mechanism of the sulfamides 1a–d SUPPORTING INFORMATION
proceeds with an A1 mechanism, as shown in Scheme 4. Rapid
protonation on the nitrogen atom is followed by S–N bond
cleavage in the rate-determining step.
Additional supporting information may be found in the online
version of this article at the publisher’s website.
wileyonlinelibrary.com/journal/poc
Copyright © 2013 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2014, 27 94–98