Acid-catalyzed hydrolysis of some N, N-dibenzylalkanesulfinamides in 50% acetonitrile-water

Article abstract of DOI:10.1080/10426507.2012.704105

The hydrolysis of some N,N-dibenzylalkanesulfinamides (RSONH(CH2Ph)2; 1, R = Me; 2, R = ⁱPr; 3, R = ^tBu; 4, R = 1-adamantyl) has been studied in 50% (v:v) acetonitrile-water solutions of hydrobromic and hydrochloric acids, mainly at

Full text of DOI:10.1080/10426507.2012.704105

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Acid-Catalyzed Hydrolysis of Some N,N-
Dibenzylalkanesulfinamides in 50%
Acetonitrile–Water
Mrityunjoy Datta a & Alan J. Buglass a
a Department of Chemistry , Korea Advanced Institute of Science
and Technology , Daejeon , Republic of Korea
Accepted author version posted online: 26 Jun 2012.Published
online: 31 May 2013.
To cite this article: Mrityunjoy Datta & Alan J. Buglass (2013) Acid-Catalyzed Hydrolysis of Some N,N-
Dibenzylalkanesulfinamides in 50% Acetonitrile–Water, Phosphorus, Sulfur, and Silicon and the Related
Elements, 188:6, 691-700, DOI: 10.1080/10426507.2012.704105
To link to this article: http://dx.doi.org/10.1080/10426507.2012.704105
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Phosphorus, Sulfur, and Silicon, 188:691–700, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.704105
ACID-CATALYZED HYDROLYSIS OF SOME
N,N-DIBENZYLALKANESULFINAMIDES IN 50%
ACETONITRILE–WATER
Mrityunjoy Datta and Alan J. Buglass
Department of Chemistry, Korea Advanced Institute of Science and Technology,
Daejeon, Republic of Korea
GRAPHICAL ABSTRACT
O
S
O
S
H2O
+
NH(CH2Ph)2
R
N(CH2Ph)2
OH
R
HCl or HBr
in 50% MeCN:
H2O (v:v)
1 R = Me
2 R = iPr
3 R = tBu
4 R = 1-adamantyl
Abstract The hydrolysis of some N,N-dibenzylalkanesulfinamides (RSONH(CH2Ph)2; 1,
i
t
R = Me; 2, R = Pr; 3, R = Bu; 4, R = 1-adamantyl) has been studied in 50% (v:v)
acetonitrile–water solutions of hydrobromic and hydrochloric acids, mainly at 44.8 ◦C, us-
ing ultraviolet (UV) spectrophotometry to determine pseudo first-order rate constants. The
compounds were found to hydrolyze by concurrent bimolecular neutral, acid-catalyzed, and
acid-dependent nucleophilic (halide ion) catalysis pathways. The last-named is predominant
in reactions in HBr solutions, but in HCl solutions, the acid-catalyzed pathway is predominant.
The results indicate that both steric and electronic effects are important in these reactions.
There appears to be no mechanistic switchover in the series 1→4.
Keywords Acid-catalyzed hydrolysis; acid-dependent nucleophilic catalysis; alkanesulfi-
namides; electronic effects; reaction mechanism; steric effects
INTRODUCTION
Nucleophilic substitution reactions at sulfinyl sulfur (>S O) have received consider-
able attention in the 1970s1 and 1980s, including a number of mechanistic investigations.2–5
Received 1 May 2012; accepted 12 June 2012.
Thanks are due to Dr. J. G. Tillett for much fruitful discussion. Financial support from KAIST is gratefully
acknowledged.
Address correspondence to Alan J. Buglass, Department of Chemistry, Korea Advanced Institute of Science
and Technology, Daejeon 305-701, Republic of Korea. E-mail: ajbuglass@kaist.ac.kr
691

692
M. DATTA AND A. J. BUGLASS
The general chemistry of sulfinamides has been reviewed by Tillett,6 where it is clear that
they undergo hydrolysis under a range of conditions to the corresponding sulfinic acids and
amines.
Most previous mechanistic reports on the hydrolysis of sulfinamides are on N-
arylarenesulfinamides,3,4,7 with the exceptions of the work of Wagner et al., which reported
briefly on the neutral hydrolysis (in D2O) of MeSONMe2 (and a number of cyclic alkane-
sulfinamides),8 and the report of Baltas et al., which described the alkaline hydrolysis of
some N-aryl-β-sulfinamoyl esters.5 More recently, Kutuk et al. have described the hydroly-
sis of N-phthalimidoarenesulfinamides in aqueous mineral acids,9 Bozkurt and Kutuk have
studied the reaction of sulfinyl phthalamides with nucleophiles in dioxane,10 and we have
reported on the hydrolysis of N-phenylalkanesulfinamides in aqueous mineral acids.11
Of the sulfinamides reported in Asefi and Tillett3 and Datta et al.11, N-
arylarenesulfinamides (Ar1SONHAr2) hydrolyzed so rapidly at 25 ◦C that a stopped-flow
spectrophotometric method had to be used.3 In contrast, N-phenylalkanesulfinamides
(RSONHPh) hydrolyzed more slowly at 45 ◦C,11 but even here, MeSONHPh and
EtSONHPh were too reactive to be studied using conventional spectrophotometric
i
techniques, and PrSONHPh could be studied only at low acid concentrations. The
generally high reactivity of the N-arylsulfinamides can be ascribed, at least in part, to the
efficacy of aniline (or arylamine in general) as a leaving group.
A characteristic feature of the reactions of N-arylsulfinamides (both Ar1SONHAr2
and RSONHAr) in aqueous HCl and HBr is the existence of acid-dependent nucleophilic
catalysis, as well as bimolecular (A-2 type) acid-catalysis.3,11 Additionally, a slow sponta-
neous reaction was reported for RSONHAr in water.11
The major aim of the present work was to synthesize a number of N,N-
dialkylalkanesulfinamides and to study their reactions in mineral acid solutions, in the
expectation that they would be less susceptible to acid-catalyzed decomposition, thus
allowing study under ordinary conditions of substrates with a wider range of S-alkyl
groups, including methyl. Another objective was to determine whether acid-dependent
nucleophilic catalysis participates in the overall reaction scheme, as has been observed
in the hydrolysis of N-arylarenesulfinamides3 and N-arylalkanesulfinamides11 in acidic
media. We now report the synthesis of a series of N,N-dibenzylalkanesulfinamides
(1–4) and their reactions in 50% aqueous acetonitrile (v:v) solutions of HBr and HCl.
N,N-Dibenzyl derivatives were chosen to facilitate the monitoring of reaction progress
using ultraviolet (UV) spectrophotometry.
RESULTS AND DISCUSSION
Most previous kinetic studies on the hydrolysis of sulfinamides have been carried
out in purely aqueous or predominantly aqueous media,3,8,9,11 except, for example, Biasotti
and Andersen’s work with ethanol–water medium4 and Bozkurt and Kutuk’s work with
dioxane.10 However, compounds 1–4 produced precipitates after partial reaction times in
aqueous acids, making it difficult to use UV spectrophotometry for kinetic analysis. To
overcome this problem, reactions for kinetic study were performed in 50% (v:v) aqueous
acetonitrile.
Compound 4 was dissolved (∼10−4 M) in a 50% aqueous acetonitrile solution of
1.00 M HCl and its UV spectrum between 225 nm and 325 nm was monitored at 3 min
intervals at 58.6 ◦C. The results are shown in Figure 1, where it can be seen that there are

HYDROLYSIS OF SOME N,N-DIBENZYLALKANESULFINAMIDES
693
Figure 1 UV-vis spectral curves for the hydrolysis of 4 in 1.00 M HCl (50% v:v acetonitrile:water) at 58.6
0.1 ◦C (time interval 3.00 min).
two isosbestic points (at 247 nm and 309 nm), indicating the likelihood of the reactants
giving a single set of products in constant proportions.
The pseudo first-order plots for 1–3 were linear, with reasonable scatter and uncer-
tainty, as indicated by coefficient of determination (R2) values better than 0.990 and relative
standard deviations (%RSD) for pseudo first-order rate constants (k1) better than 5.0%. The
corresponding parameters for 4 were better than 0.999 and 2.0%, respectively. Figures 2
and 3 display the variation of k1 with acid concentration for 1–4 at 44.8 ◦C in 50% (v:v)
acetonitrile–water solutions of HBr and HCl, respectively. Two features of these data are
worthy of comment.
30.0
1
2
104k1/s−1
20.0
3
4
10.0
0
0
1.00 2.00 3.00 4.00
[HBr]/M
Figure 2 Pseudo first-order rate constant/acid concentration profiles of 1–4 in HBr media (50% (v:v) acetoni-
trile:water) at 44.8 ◦C. Curves drawn using OriginPro 7TM polynomial analysis tool. For k1, %RSD (n = 3) for
1–3 is better than 5.0%, R2 is better than 0.990; %RSD (n =3) for 4 is better than 2.0%, R2 is better than 0.999.

694
M. DATTA AND A. J. BUGLASS
15.0
2
104k1/s−1
1
10.0
4
3
5.0
0
0
1.00 2.00 3.00 4.00
[HCl]/M
Figure 3 Pseudo first-order rate constant/acid concentration profiles of 1–4 in HCl media (50% (v:v) acetoni-
trile:water) at 44.8 ◦C. Curves drawn using OriginPro 7TM polynomial analysis tool. For k1, %RSD (n = 3) for
1–3 is better than 5.0%, R2 is better than 0.990; %RSD (n = 3) for 4 is better than 2.0%, R2 is better than 0.999.
First, there is a slow neutral reaction for each substrate, as observed by Wagner
et al. for the hydrolysis of MeSONMe2 in D2O,7 although 1–4 are rather more reactive
than this compound ◦(e.g., 104ko (s−1) for 1, 2, 3, and 4 are 1.21, 1.15, 0.78, and 0.56,
respectively, at 44.8 C in 50% acetonitrile–water (v:v), compared with 0.28 × 10−4 s−1
◦
for MeSONMe2 at 55.0 C in D2O). Slow neutral reactions were also observed for N-
phenylalkanesulfinamides.11
Second, for all the substrates (1–4), there is a marked dependence of k1 on acid
concentration, and especially on [HBr], suggesting the existence of specific acid-catalysis,
as well as acid-dependent nucleophilic catalysis, as previously observed in the reactions
of N-arylarenesulfinamides3 and N-phenylalkanesulfinamides11 in aqueous mineral acid
solutions. It can be seen from Figures 2 and 3 that the general reactivity is in the order
1 > 2 > 3 > 4, in both HBr and HCl, and that HBr is generally a better catalytic medium
than HCl. These observations are in accord with the greater nucleophilicity of Br− over
Cl− in aqueous media and also suggest that steric and/or electronic effects are involved in
the reaction mechanism. Furthermore, reactions in HClO4, whose conjugate base ClO−4 is
of very low nucleophilicity, were very slow. For example, k1 for 1 (predicted to be the most
reactive of these substrates) in 3.00 M and 5.00 M HClO4 was found to be 2.33 × 10−4 and
4.01 × 10−4 s−1, respectively. The considerably lower reactivity in HClO4 is probably due
to the absence of nucleophilic catalysis, along with extensive hydration of ClO−4 , which
reduces the catalytic activity of water required for a bimolecular rate-limiting step.
Table 1 shows the variation of k1 with [HBr] for compound 1 at constant bromide
ion concentration of 1.00 M (made up with added LiBr). Limited solubility of LiBr in
the reaction medium prevented collection of data for [HBr] < 0.50 M ([LiBr] > 0.50 M).
These data are consistent with the participation of both acid catalysis and acid-dependent
nucleophilic catalysis in the overall reaction of 1 in HBr solutions and this conclusion can
be extended to compounds 2, 3, and 4, because of the observed similar kinetic behavior
(see also Table 2 and discussion of Arrhenius parameters).

HYDROLYSIS OF SOME N,N-DIBENZYLALKANESULFINAMIDES
695
Table 1 Rate constants (104k1/s−1) for hydrolysis of 1 in HBr (50% (v:v) acetonitrile:water) at 44.8 0.1 ◦
C
and constant bromide ion concentration of 1.00 M
[HBr]/M
104k1/s−1
0
0.50
15.9
0.80
23.3
1.00
29.7
1.21a
aExtrapolated value.
In order to analyze the reactions more closely, especially in terms of the relative
contributions of acid-dependent nucleophilic catalysis and acid-catalysis to the overall
reaction, we may write a general expression for the reactions of 1–4 as Equation (1),
k1 = ko + kX−[X−] + kH+[H+] + kHX[H+][X−]
(1)
as originally suggested in Ref. 3. The first specific rate constants, ko and k−X, relate to the slow
reactions in solutions without added acids (representing attack of H2O and X−, respectively,
on the neutral substrate) whereas kH+ and kHX are the rate constants for the acid-catalyzed
and acid-dependent nucleophile (halide ion)-catalyzed reactions, respectively. The latter
two relate to attack of water and specific nucleophile, respectively, upon the conjugate acid
of 1–4 (protonated substrates) in the rate-determining step.
In order to check for the presence of specific nucleophilic catalysis on the neutral
rate, reactions of 1 in 50% acetonitrile–water were carried out with added 0.20 M KCl and
0.20 M KBr, whence k1 was found to be 1.22 × 10−4 s−1 and 1.24 × 10−4 s−1
(
0.06 ×
10−4 s−1), respectively. Within experimental error, these values are indistinguishable from
ko, hence suggesting specific halide catalysis of the neutral reaction is insignificant, so that
the second term in Equation (1) can be neglected. This is supported by the data shown in
Table 1. Equation (1) thus reduces to Equation (2):
k1 = ko + kH+[H+] + kHX[H+][X−]
(2)
In an attempt to qualitatively determine the relative contributions of acid catalysis and
acid-dependent nucleophilic catalysis components of Equation (2), it is assumed that the
mineral acids HX are 100% ionized, then [HX] = [H+], and [H+] = [X−], so that Equation
(2) can be written as Equation (3):
k1 = ko + kH+[HX] + kHX[HX]2
(3)
Equation (3) predicts a linear dependence of k1 on [HX] for acid-catalysis, whereas
there is a quadratic dependence for acid-dependent nucleophilic catalysis. Therefore, a
distinct parabolic curvature in plots of k1 versus [HX] is expected where the acid-dependent
Table 2 Rate constantsa and activation parameters for the hydrolysis of 1 and 4 in 1.00 M HCl (50% (v:v)
acetonitrile:water) at various temperatures
T/oC ( 0.1 oC)
44.8
51.5
51.7
53.6
57.3
59.5
59.7
67.6
104k1/s−1 1b
104k1/s−1 4c
6.6
2.9
13.5
—
—
6.5
15.1
8.1
—
11.8
24.9
—
—
13.2
41.6
22.5
a%RSD for 1 and 4 (n = 3); better than 5.0% and 2.0%, respectively.
bꢀH= = 69 4 kJ mol−1; ꢀS= = −86 13 J mol−1 K−1
.
cꢀH= = 73 2 kJ mol−1; ꢀS= = −81 7 J mol−1 K−1
.

696
M. DATTA AND A. J. BUGLASS
nucleophilic catalysis component is important (i.e., where kHX > kH+). Distinct curves are
observed in plots of k1 versus [HBr] for all the substrates in HBr solutions (Figure 2),
reflecting the high nucleophilicity of Br−. The degree of curvature of such plots decreases
along the series 1→4, suggesting a diminution of the acid-dependent nucleophilic catalysis
component, in favor of the acid-catalysis component. The probable reason for this is
increased steric hindrance and/or increased electronic resistance (+I effect) along the
series to nucleophilic attack by Br− (as opposed to the smaller H2O nucleophile), on the
protonated substrate in the rate-determining step. Thus for 4, where steric hindrance and
the +I effect will be greatest, kHBr ∼ kH+ and the plot of k1 versus [HBr] here has the least
curvature. It can be concluded that the nucleophilicity of Br− is sufficiently high to ensure
that kHBr is significant for all the substrates, particularly 1–3.
On the other hand, plots of k1 versus [HCl] show less curvature than those of k1
versus [HBr] (Figure 3), reflecting the lower nucleophilicity of Cl− and suggesting that
the acid-dependent nucleophilic catalysis component is generally less significant in HCl
media. Indeed, the plot of k1 against [HCl] is a very shallow curve for 3 and is essentially
linear for 4, suggesting that kHCl < kH+ for both these substrates. Thus, it can be concluded
that the nucleophilicity of Cl− is insufficiently high to compete effectively with H2O in
nucleophilic attack on the protonated substrate, especially the more sterically hindered 3
and 4.
Table 2 displays the Arrhenius parameters for 1 and 4, in 50% aqueous acetonitrile
solutions of 1.00 M HCl, along with the data that were used to determine the parameters.
Given the concurrent nature of the reactions that comprise the hydrolysis of 1–4 (see
previous discussion) and the difficulty in extracting specific rate constants at different
temperatures, the thermodynamic parameters calculated from the Arrhenius equation will
be composite values and, hence, cannot be compared rigorously with literature data that
refer to single reactions. Nevertheless, the computed values of ꢀH= and ꢀS= are similar
to those reported for the acid3 and alkaline4 hydrolysis of N-arylarenesulfinamides (e.g.,
for N-p-tolyl-p-toluenesulfinamide3 in aqueous 0.500 M-HClO4, ꢀH= = +37.8 kJ mol−1
;
ꢀS= = −123.3 J K−1 mol−1 and for N-mesyl-p-chlorobenzenesulfinamide4 in 0.05 M
NaOH (95% ethanol:5% water), ꢀH= = +83.6 kJ mol−1 and ꢀS= = −37.2 J K−1 mol−1).
In particular, the quite large negative values of ꢀS= are in the range generally associated
with reactions that have bimolecular rate-determining steps.12 This can be taken as evidence
that the set of concurrent reactions that characterize the hydrolysis of 1 and 4 is essentially
bimolecular in character. Furthermore, since compounds 1 and 4 represent the structural
extremes of the series 1–4, the similar values of ꢀS= for these two substrates indicate
that all four compounds react by similar mechanisms and that there is no gross change in
mechanism somewhere along the series.
It is possible to depict the acid-catalyzed hydrolysis of sulfinamides occurring via dis-
crete sulfurane (hypervalent) intermediates (Scheme 1, pathway A) or by direct (SN2-like)
displacement at sulfinyl S (Scheme 1, pathway B). Okuyama and coworkers have provided
good evidence for the former in a study of the hydrolysis of N-arylarenesulfinamides in
dilute aqueous acid (HClO4).8 However, it is still unclear whether protonation occurs pri-
marily at O or N.13,14 Our results show that specific nucleophilic species (X− = Br− or
Cl− in Scheme 1) play an important role and are involved in the rate-determining step
of a generally significant (and in certain cases predominant) acid-dependent nucleophilic
catalysis route.
By comparison of our results with those for N-arylarenesulfinamides3,4,7,8 and N-
phenylalkanesulfinamides,11 it is also clear that the order of reactivity of sulfinamides toward

HYDROLYSIS OF SOME N,N-DIBENZYLALKANESULFINAMIDES
697
O
S
+OH
S
O
S
+
N(CH2Ph)2
N(CH2Ph)2
NH(CH2Ph)2
R
R
R
B
A
−HN(CH2Ph)2
Rate-
_
_
X
X
determining
step
O
S
H2O
Fast
HO
N(CH2Ph)2
Fast
S
Products
X
R
R
X
−HN(CH2Ph)2
Scheme 1
hydrolysis in acidic solutions is in general, R1SONR22 < RSONHPh < Ar1SONHAr2, where
R and Ar are alkyl and aryl groups, respectively. This order of reactivity can be explained
partly by relative leaving group ability from the N-protonated conjugate acid (ArNH2 >
R2NH) and partly by the different reactivities of the sulfinamide conjugate acids toward
nucleophilic attack (Schemes 2 and 3), which is related to the electron density at the sulfur
atom.
+OH
S
OH
S
+
N(CH2Ph)2
N(CH2Ph)2
R
R
Scheme 2
+OH
S
OH
S
+
NH
R
N
R
H
+OH
S
+
R
N
(etc)
H
_
Scheme 3
For 1–4, electron delocalization of the sulfinamide system (O S N) is max-
imized (Scheme 2), whereas for N-arylalkanesulfinamides11 (Scheme 3) and N-
arylarenesulfinamides,3 N-aryl delocalization competes with this, resulting in overall lower

698
M. DATTA AND A. J. BUGLASS
electron density at sulfinyl sulfur, thus making it more susceptible to nucleophilic attack,
thereby rendering N-arylsulfinamide conjugate acids more reactive than those of 1–4.
Although at the present time, there is no direct evidence for N-aryl delocalization in N-
arylsulfinamide conjugate acids (protonated substrate) as suggested above, existence of this
feature in the solid state neutral substrate is evident from the short N Caryl bond (1.408 Å)
in 2-methyl-N-phenylpropane-2-sulfinamide,15 as opposed to considerably longer N Calkyl
bonds (1.470–1.530 Å) found in N-alkylsulfinamides16–18 and also in an O-methylated N-
alkylarenesulfinamide.19
CONCLUSIONS
N,N-Dibenzylalkanesulfinamides (1–4) were shown to undergo hydrolysis in 50%
acetonitrile–water solutions of HCl and HBr by concurrent neutral, acid-catalyzed, and
acid-dependent halide ion-catalyzed pathways (all bimolecular), the last-named being the
most important for reaction in HBr media and generally significant (but not predominant)
for reaction in HCl media.
EXPERIMENTAL
Synthesis of Compounds 1–4: General Procedure
The general procedure is illustrated by the synthesis of N,N-dibenzylmethanesulfina-
mide (1). Methanesulfinyl chloride was prepared by the reaction of methyl disulfide and
sulfuryl chloride in acetic acid, according to the method of Youn and Herrmann.20 The
general procedure for the formation of sulfinamides from the sulfinyl chloride and amine is
based on that of Stetter et al.21 To our knowledge, there are no previous data in the literature
for compounds 1, 2, and 4.
N,N-Dibenzylmethanesulfinamide (1). To a solution of dibenzylamine (1.97 g,
10 mmol) in dry ether (20 mL) was added a solution of methanesulfinyl chloride (490 mg,
5 mmol) in dry ether (15 mL), dropwise, with stirring over a period of 20 min, at 0 ◦C. The
◦
reaction mixture was then stirred at 0 C for 3 h. The white solid amine salt was filtered
off and the solvent was removed under reduced pressure. The residue was purified by silica
gel column chromatography (dichloromethane) to provide 1 as a white solid (1.25 g, 97%),
mp 68–70 ◦C.
FTIR (KBr) νmax (cm−1): 3108, 3088, 3064, 3033, 3011, 1496, 1455, 1446, 1436,
1409, 1384, 1311, 1267, 1210, 1130, 1084, 1056, 1015, 949. 1H NMR (400 MHz, CDCl3,
ppm with respect to TMS): δ 7.34–7.29 (m, 10H), 4.33 (s, 4H), 2.76 (s, 3H). 13C NMR
(100 MHz, CDCl3, ppm with respect to TMS): δ 135.4, 128.8, 128.7, 128.0, 49.8, 40.3.
EIMS m/z (%): 259 (M+, 12), 196 (M+– CH3SO, 47), 184 (49), 91 (100). Anal. calcd. for
C15H17NOS: C, 69.50; H, 6.56; N, 5.40; S, 12.35. Found: C, 69.46; H, 6.58; N, 5.52; S,
12.28.
N,N-Dibenzyl-2-propanesulfinamide (2). Iso-propylsulfinyl chloride was prepared
by the reaction of iso-propyldisulfide and sulfuryl chloride in acetic acid.20 The general
procedure was followed by using dibenzylamine (1.24 g, 6.34 mmol), iso-propylsulfinyl
chloride (400 mg, 3.17 mmol), and dry ether (30 mL). The crude product was purified by
silica gel column chromatography (5% ethyl acetate in hexane) to give 2 as a white solid
(880 mg, 96%), mp 155–157 ◦C.

HYDROLYSIS OF SOME N,N-DIBENZYLALKANESULFINAMIDES
699
FTIR (KBr) νmax (cm−1): 3082, 3056, 1485, 1453, 1409, 1383, 1334, 1290, 1272,
1224, 1152, 1110, 1072, 1010, 950. 1H NMR (400 MHz, CDCl3, ppm with respect to TMS):
δ 7.45–7.24 (m, 10H), 3.91 (t, J = 5.3 Hz, 4H), 2.86–2.80 (m, 1H), 1.22 (d, 6H). 13C NMR
(100 MHz, CDCl3, ppm with respect to TMS): δ 130.5, 130.2, 129.2, 129.0, 50.9, 49.3,
17.7. EIMS m/z (%): 286 (M+–H, 12), 285 (54), 208 (63), 197 (MH+– iso-propylsulfinyl,
15), 167 (20), 149 (42), 141 (34), 134 (21), 106 (MH+– dibenzyl, 88), 91 (100).
N,N-Dibenzyl-2-methylpropane-2-sulfinamide (3). The general procedure was fol-
lowed by using dibenzylamine (1.20 g, 6.09 mmol), tert-butylsulfinyl chloride (obtained
from Aldrich-Sigma, 428 mg, 3.04 mmol), and CH2Cl2 (30 mL). The residue was purified
by silica gel column chromatography (EtOAc: hexane, 1:4) to afford sulfinamide 3 as a
white solid (896 mg, 98%), mp 55–57 ◦C (lit.21 54–56 ◦C).
1H NMR (400 MHz, CDCl3, ppm with respect to TMS): δ 7.31–7.22 (m, 10H), 4.27
(d, J = 15.36 Hz, 2H), 4.03 (d, J = 15.36 Hz, 2H), 1.19 (s, 9H). 13C NMR (100 MHz,
CDCl3, ppm with respect to TMS): δ 136.87, 128.71, 128.44, 127.40, 58.56, 51.56, 23.26.
EIMS m/z (%): 302 (MH+, 7), 301 (M+, 15), 247 (44), 246 (72), 245 (MH+– tBu, 95), 196
(MH+– tBuSO, 25), 195 (53), 106, (48), 91 (100).
N,N-Dibenzyl-1-adamantanesulfinamide (4). 1-Adamantanesulfinyl chloride was
obtained by the reaction of adamantane and thionyl chloride in the presence of AlCl3.21
The general procedure was followed by using dibenzylamine (1.20 g, 6.09 mmol), 1-
adamantanesulfinyl chloride (664 mg, 3.04 mmol), and dichloromethane (30 mL). The
residue was purified by silica gel column chromatography (dichloromethane-hexane, 1:1)
to afford sulfinamide 4 as a viscous liquid (1.1 g, 95%).
FTIR (neat) νmax (cm−1): 2907, 2851, 1591, 1487, 1449, 1351, 1295, 1075, 891, 815.
1H NMR (400 MHz, CDCl3, ppm with respect to TMS): δ 7.31–7.22 (m, 10H), 4.27 (d,
J = 15.3 Hz, 2H), 4.01 (d, J = 15.3 Hz, 2H), 2.08 (s, 3H), 1.91 (d, J = 11.3 Hz, 3H),
1.76–1.62 (m, 9H). 13C NMR (100 MHz, CDCl3, ppm with respect to TMS): δ 136.87,
128.68, 128.35, 127.31, 60.31, 51.93, 36.29, 35.26, 28.41. EIMS m/z (%): 379 (M+, 11),
280 (9), 253 (20), 136 (34), 135 [M+– (PhCH2)2NSO, 100], 129 (72), 91 (50).
Authentication of Products from Kinetic Experiments
Before commencing kinetic investigations, it was necessary to confirm the product
identity. The amine was chosen, since the sulfinic acid products are UV-inactive and are
unavailable as standards. A larger scale reaction of 2 (40 mg) in 2.00 M HCl (50%
◦
acetonitrile:water) (10.0 mL) was investigated at 44.8 C over a period of 12 h by TLC
(silica gel, ethyl acetate, UV visualization). A new spot at Rf ∼ 0.37 was observed after 1 h,
which was identified as dibenzylamine hydrochloride by comparison with a pure authentic
sample run on the same plate. Identical results were obtained for 1, 3, and 4. Also, under
the above TLC conditions, Rf values of 2 and dibenzylamine were found to be 0.64 and
0.80, respectively.
Kinetic Measurement
The rates of hydrolysis were measured by following the decrease in absorbance at
257 nm for compounds 1–3 and 267 nm for compound 4, using a JASCO V-530 UV/visible
spectrophotometer with a thermostatted cell holder. For all compounds, 0.1 M stock so-
lutions in methanol were prepared. Aliquots (4 μL) of the relevant stock solution were

700
M. DATTA AND A. J. BUGLASS
added by syringe to 4.0 mL of the reaction solution contained in a cuvette and already
equilibrated at the desired temperature. The reactions were monitored over at least three
half-lives and “infinity” values were measured in all cases, except the slowest reactions.
Pseudo first-order rate constants were calculated from plots of ln(A A∞) against time,
where A is absorbance at time t and A∞ is the absorbance at “infinity,” except for the
slowest reactions, whence the method of Guggenheim was used.22 All acid reaction solu-
tions were prepared from analytical grade concentrated acids, using deionized water and
HPLC grade acetonitrile, making appropriate allowance for the water content of the acid.
The reaction solutions were discarded after use, freshly made solutions being used for each
experiment, because of the appearance of crystals in some solutions after several weeks
standing at room temperature. These were identified as ammonium salts and were probably
the result of slow acetonitrile hydrolysis in some of the more concentrated acid solutions.
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