A convenient and efficient method for the preparation of N-sulfonyl aldimines from aromatic aldehydes under solvent-free conditions

Article abstract of DOI:10.1080/10426500601087400

Condensation of a variety of aromatic aldehydes with sulfonamides in the presence of silica chloride by heating afforded novel functionally varied aromatic N-sulfonyl aldimines in good to excellent yields. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500601087400

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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A Convenient and Efficient
Method for the Preparation
of N-Sulfonyl Aldimines from
Aromatic Aldehydes under
Solvent-Free Conditions
Alireza Hasaninejad a & Hashem Sharghi b
a Department of Chemistry , Persian Gulf
University , Bushehr, I. R. Iran
b Department of Chemistry , Shiraz University ,
Shiraz, I. R. Iran
Published online: 24 Feb 2007.
To cite this article: Alireza Hasaninejad & Hashem Sharghi (2007) A Convenient
and Efficient Method for the Preparation of N-Sulfonyl Aldimines from Aromatic
Aldehydes under Solvent-Free Conditions, Phosphorus, Sulfur, and Silicon and the
Related Elements, 182:4, 873-880, DOI: 10.1080/10426500601087400
To link to this article: http://dx.doi.org/10.1080/10426500601087400
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Phosphorus, Sulfur, and Silicon, 182:873–880, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601087400
A Convenient and Efficient Method for the Preparation
of N-Sulfonyl Aldimines from Aromatic Aldehydes under
Solvent-Free Conditions
Alireza Hasaninejad
Department of Chemistry, Persian Gulf University, Bushehr, I. R. Iran
Hashem Sharghi
Department of Chemistry, Shiraz University, Shiraz, I. R. Iran
Condensation of a variety of aromatic aldehydes with sulfonamides in the presence
of silica chloride by heating afforded novel functionally varied aromatic N-sulfonyl
aldimines in good to excellent yields.
Keywords N-sulfonyl aldimine; sulfonamides; silica chloride; solvent-free
INTRODUCTION
Sulfonyl imines are versatile synthetic intermediates in organic syn-
thesis and have industrial applications.1,2 They are activated imines
in which the limitations of aldimine functionality such as low elec-
trophilicity of azomethine carbon and the tendency of enolizable imines
to undergo deprotonation rather than addition can be circumvated.3
They are excellent substrates in aziridination,4 oxaziridination,5 olefi-
nation reactions,6 nucleophilic additions,7 reductions,8 and aza Diels-
Alder reactions.9 Several synthetic methods for the preparation of
N-sulfonyl imines have been found in the literature.5,10−19 Most of
them involve the condensation of aldehydes with sulfonamides in the
presence of strong Lewis acids.10,12,17,18 In many cases such strongly
acidic conditions are not compatible with other functionality present
in a given substrate, and some methods need a two-step proce-
dure or they are expensive methods and generate toxic byproducts.
Received July 12, 2006; accepted September 20, 2006.
We gratefully acknowledge the support of this work by the Persian Gulf Research
Council.
Address correspondence to Alireza Hasaninejad, Department of Chemistry, Faculty
of Science, Persian Gulf University, Bushehr, 75169 I. R. Iran. E-mail: ahassaninejad@
yahoo.com
873

874
A. Hasaninejad and H. Sharghi
However, some methods require prior preparation such as oxime,
sulfinyl imine, and/or aziridine.11,15,19 Therefore, it seems highly desir-
able to find simple, efficient, economical, and green chemistry protocols
for synthesis of a wide range of N-sulfonyl imines without the require-
ment of toxic or otherwise hazardous reagents. Solvent-free organic
reactions have been applied as useful protocol in organic synthesis.20
A solid-state technique under thermal conditions often leads to shorter
reaction times, increased yields, and easier work-up; it matches with
green chemistry protocols; and it may enhance the regio- and stereose-
lectivity of reactions.20
Because of the convenience of solid reagents, such as ease of han-
dling, low costs, and ease of work-up of the reaction products, the use
of heterogeneous reagents from functional group transformation is of
value to synthetic organic chemists.21 Nevertheless, a literature survey
shows that little attention has been paid to the use of heterogeneous
reagents for preparation of N-sulfonyl imines.
RESULTS AND DISCUSSION
In extension of our previous studies on the application of silica chloride
and developing solvent-free conditions in organic synthesis,22,23 we de-
scribe here an efficient and operationally simple method for synthesis
of N-sulfonyl aldimines in one step without any solvent. In this method,
various N-sulfonyl imines were obtained from the reaction of aryl alde-
hyde and sulfonamide (Scheme 1). Silica chloride was obtained from
the reaction of silica gel (item 7731 for TLC from Merck, Darmstadt,
FRG) and thionyl chloride according to a literature procedure.24
SCHEME 1
We found heating (110–120◦C) an approximately equimolar mixture
of an aldehyde and sulfonamide in the presence of silica chloride
between 3–5 h resulted in the formation of sulfonyl aldimines in good
to excellent yield. The results of the reaction of aryl aldehydes with
sulfonamides in the presence of silica chloride are summarized in
Table I.
Aromatic aldehydes containing both electron-withdrawing and
-donating substituents afforded the corresponding sulfonyl imines in
high yields (Table I). The lower reactivity of the arylaldehydes contain-
ing electron-withdrawing or hindered substituents (Table I, entries 9

Preparation of N-Sulfonyl Aldimines
875
TABLE I Conversion of Aldehydes into N-Sulfonyl Imines in
the Presence of Silica Chloride at 120◦C
Entry
1
R
Ar
Product
Time (h)
3
Yield (%)a
75
p-tolyl
2
3
phenyl
3.5
3
70
76
p-tolyl
4
5
6
7
p-tolyl
p-tolyl
p-tolyl
p-tolyl
3
3
78
71
68
73
3.5
3
8
9
p-tolyl
p-tolyl
3
4
70
56
10
11
p-tolyl
p-tolyl
3.5
3
65
61
12
p-tolyl
3
69
aIsolated Yield.

876
A. Hasaninejad and H. Sharghi
and 11) generally necessitated longer reaction times. These indicate
that electron-donating groups increased the reaction speed as well as
reaction yields. Mention must be made here that the conversion rate of
p-toluenesulfonamide with aldehydes was a little higher than benzene
sulfonamide (for comparison, see Table I, entries 1 and 2).
The N-sulfonyl imines were readily separated from the byproducts
of the reaction, allowing their isolation in a high state of purity and in
good yield.
The crude products could be purified by recrystallization (see Table I
and Experimental section).
This chemistry was applied unsuccessfully toward the synthesis of
enolizable N-sulfonyl aldimines, and unfortunately this method shares
a common limitation with several other methods of N-tosylaldimine
synthesis10,12,17,18 in that it does not appear to be applicable to the
synthesis of N-tosyl aldimines derived from aldol condensations being
obtained instead. Methods of overcoming this limitation are currently
under investigation.
This method possesses advantages of facile work-up, it is nonpol-
luting and of low cost, and it has easy availability of the catalyst and
good yield.
EXPERIMENTAL
Melting points determined in open capillary tubes in a Buchi-535 circu-
lating oil melting point apparatus without further corrections. Infrared
spectra were obtained using a Perkin Elmer 781 and a Shimadzu FT-IR
8300 spectrophotometer, and NMR spectra were recorded on a Bruker
Avance DPX-250 (1H NMR 250 MHz and 13C NMR 62.9 MHz) spectrom-
eter in pure deuterated solvents with tetramethyl silane as an internal
standard. Elemental analyses were performed at the National Oil Co.
of Iran, Tehran Research Center, Iran.
Typical Procedure
General Procedure for Preparation of Silica Chloride (SiO2-Cl)24
To an oven-dried (120◦C, vaccum) silica gel (10 g) in a round bottomed
flask (250 mL) equipped with a condenser and a drying tube was added
thionyl chloride (40 mL), and it was refluxed for 48 h. The unreacted
thionyl chloride was distilled off. The resulting white-grayish powder
was flame dried and stored in a tightly capped bottle. This silica chloride
can be used for months without loosing its activity.

Preparation of N-Sulfonyl Aldimines
877
General Procedure for Synthesis of N-Sulfonyl Imines
In a 100-mL single-necked flask equipped with magnetic stirring bar
and short-path distilling head were placed equivalent amounts (typi-
cally 5 mmol) of the appropriate sulfonamide and aldehyde. The reac-
tion mixture was heated at about 120◦C in an oil bath, and after 10 min
the appropriate amount of silica chloride (3 g) was added to it, stirring
was continued for about 3 h, at which time the reaction was allowed
to cool to r.t. The solid mixture and the solid materials were removed
through a Celite pad and washed with acetone (50 mL). The solvent
was evaporated with a rotary evaporator, and the solid product was
dissolved in warm ethylacetate (10 mL), treated with n-hexane (35–
50 mL), and allowed to stand at r.t. for 5–6 h. During this time crystals
formed, which were collected by filtration, washed with n-hexane, and
dried.
Selected Spectral Data for Sulfonyl Imines
N-Benzylidene-4-methyl-benzenesulfonamide (1) 25
1
White solid; m.p. 108◦C (lit.,25 109◦C); H NMR (CDCl3, 250 MHz):
2.33 (s, 3H), 7.25 (d, J = 8.2 Hz, 2H), 7.48 (t, J = 7.8 Hz, 2H),
7.51(t, J = 6.2 Hz, 1H), 7.80–7.84 (m, 4H), 8.99 (S, 1H). 13C NMR
(CDCl3, 62.9 MHz): 21.97, 128.42, 129.89, 130.26, 131.61, 135.39,
140.21, 145.07, 170.69. IR (KBr): 1650, 1570, 1380, 1320, 1160 (cm−1).
N-Benzylidenebenzenesulfonamide (2) 25
m.p. 77–80◦C 1H NMR (CDCl3, 250 MHz): 7.61 (m, 6H), 8.02 (m, 4H),
9.05 (s, 1H).
N-(4-chlorobenzylidene)-4-methyl-benzenesulfonamide (3) 10
White needles; m.p. 172–173◦C (lit.,10 172–173◦C); 1H NMR (CDCl3,
250 MHz): 2.46 (s, 3H), 7.15 (d, J = 9.1 Hz, 2H), 7.38 (d, J = 9.0 Hz, 2H),
7.86 (dd, J = 8.9 Hz, 4H), 9.01 (s, 1H). 13C NMR (CDCl3, 62.9 MHz):
22.04, 128.53, 129.98, 130.25, 131.24, 132.73, 135.32, 141.80, 145.17,
169.02.
N-(4-bromobenzylidene)-4-methyl-benzenesulfonamide (4) 17
1
White powder; m.p. 181–183◦C; H NMR (CDCl3, 250 MHz): 2.50
(s, 3H), 7.26–7.85 (m, 8H), 9.04 (s, 1H). 13C NMR (CDCl3, 62.9 MHz):
22.69, 125.02, 128.60, 129.48, 131.18, 131.26, 133.87, 167.69.
N-(4-methyl-benzylidene)-4-methyl-benzenesulfonamide (5) 25
White powder; m.p. 112–114◦C; 1H NMR (CDCl3, 250 MHz): 2.42 (s,
6H), 7.26 (d, J = 7.5 Hz, 2H), 7.34 (d, J = 7.8 Hz, 2H), 7.82 (d, J = 7.5 Hz,

878
A. Hasaninejad and H. Sharghi
2H), 7.90 (d, J = 7.5 Hz, 2H), 8.96 (S, 1H). 13C NMR (CDCl3, 62.9 MHz):
22.01, 126.78, 128.38, 129.98, 130.17, 130.33, 131.80, 135.74, 144.87,
170.42.
N-(4-methoxy-benzylidene)-4-methyl-benzenesulfonamide
(6) 25
White powder; m.p. 126–128◦C; 1H NMR (CDCl3, 250 MHz): 2.36 (s,
3H), 3.78 (s, 3H), 6.93 (d, J = 8.5 Hz, 2H), 7.29 (d, J = 7.8 Hz, 2H),
7.81 (d, J = 7.5 Hz, 2H), 7.85 (d, J = 7.6 Hz, 2H), 8.90 (s, 1H). 13C NMR
(CDCl3, 62.9 MHz): 22.44, 56.58, 115.51, 125.95, 128.69, 130.40, 134.55,
136.59, 145.17, 166.20, 170.15.
4-methyl-N−thiophen-3-ylmethylene-benzenesulfonamide (7)
1
White needles; m.p. 127–129◦C; H NMR (CDCl3, 250 MHz): 2.43
(s, 3H), 7.29–8.15 (m, 7H), 9.01 (s, 1H). 13C NMR (CDCl3, 62.9 MHz):
22.02, 126.85, 128.20, 128.39, 130.19, 135.72, 137.42, 138.63, 144.91,
163.55. Anal. calcd for C12H11NO2S2: C, 54.32; H, 4.18, N, 5.28; found:
C, 54.43; H, 4.09, N, 5.46.
N-Furan-2-ylmethylene-4-methyl- benzenesulfonamide (8) 25
Brown powder; m.p. 100–101◦C; 1H NMR (CDCl3, 250 MHz): 2.32 (s,
1H), 6.76-7.75 (m, 7H), 8.83 (s, 1H). 13C NMR (CDCl3, 62.9 MHz): 22.53,
112.57, 115.42, 126.65, 128.63, 130.98, 148.36, 151.59, 154.39, 157.07.
N-(2, 5-dimethoxy-benzylidene)-4-methyl-
benzenesulfonamide (9)
1
M.p. 124–126◦C H NMR (DMSO-d6, 250 MHz): 2.39 (s, 3H), 3.69
(s,3H), 3.93 (s, 3H), 7.14–7.82 (m, 7H), 9.30 (s, 1H). 13C NMR (DMSO-
d6, 62.9 MHz): 21.00, 55.53, 56.24, 110.16, 114.28, 119.78, 125.17,
127.58, 130.01, 134.88, 144.47, 153.08, 156.44, 165.54. Anal. calcd. for
C16H17NO4S: C, 60.17; H, 5.37, N, 4.39; found: C, 60.03; H, 5.49; N, 4.46.
N-(2-chloro-benzylidene)-4-methyl-benzenesulfonamide (10) 10
White needles; m.p. 126–128◦C (lit.10; 128–129◦C); 1H NMR (CDCl3,
250 MHz): 2.43 (s, 3H), 7.29–7.90 (m, 8H), 9.13 (s, 1H). 13C NMR
(CDCl3, 62.9 MHz): 22.64, 126.90, 128.54, 129.10, 129.51, 131.17,
131.86, 134.48, 137.06, 168.12.
N-(4-Cyanobenzylidene)-4-methyl-benzenesulfonamide (11) 19
1
White needles; m.p. 172–173◦C; H NMR (CDCl3, 250 MHz): 2.35
(s, 3H), 7.28 (d, J = 10.2 Hz, 2H), 7.66–7.96 (m, 6H) 8.97 (s, 1H). 13C

Preparation of N-Sulfonyl Aldimines
879
NMR (CDCl3, 62.9 MHz): 21.68, 117.70, 126.32, 128.29, 129.92, 130.01,
131.34, 132.76, 135.89, 145.30, 168.16.
N-(4-Isoperopyl-benzylidene)-4-methyl-benzenesulfonamide
(12)
1H NMR (CDCl3, 250 MHz): 1.20 (d, j = 7 Hz, 6H), 2.33 (s, 3H), 2.93
(m, 1H), 7.18–7.80 (m, 8H), 8.91 (s, 1H). 13C NMR (CDCl3, 62.9 MHz):
22.43, 22.45, 32.91, 126.08, 126.70, 128.59, 129.32, 130.31, 130.95,
132.91, 156.73, 171.43. Anal. calcd. for C17H19NO2S: C, 67.74; H, 6.35;
N, 4.65; found: C, 67.81; H, 6.26; N, 4.52.
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