Synthesis of S-aryl/alkyl thiolcarbonates from disulfides and chloroformates in the presence of the Zn/AlCl3 system

Article abstract of DOI:10.1007/s00706-007-0778-z

A simple, general, and high yielding method has been developed for the synthesis of S-aryl/alkyl-O-aryl/alkyl thiolcarbonates from various chloroformates and disulfides by reductive cleavage of the S-S bond with a Zn/AlCl₃ system in dry acetonitrile at 80°C.

Full text of DOI:10.1007/s00706-007-0778-z

Monatsh Chem 139, 251–253 (2008)
DOI 10.1007/s00706-007-0778-z
Printed in The Netherlands
Synthesis of S-Aryl=Alkyl Thiolcarbonates from Disulfides
and Chloroformates in the Presence of the Zn=AlCl3 System
Barahman Movassagh1;2;ꢀ and Maryam Tavoosi1
1
Department of Chemistry, K.N. Toosi University of Technology, Tehran, Iran
2
Kermanshah Oil Refining Company, Kermanshah, Iran
Received July 10, 2007; accepted July 14, 2007; published online February 12, 2008
# Springer-Verlag 2008
Summary. A simple, general, and high yielding method has
been developed for the synthesis of S-aryl=alkyl-O-aryl=alkyl
thiolcarbonates from various chloroformates and disulfides by
reductive cleavage of the S–S bond with a Zn=AlCl3 system in
dry acetonitrile at 80ꢁC.
cohols and 2,2,2-trihaloethanols with ethyl chlor-
othiolformate in the presence of anhydrous iron(III)
chloride [13], nucleophilic addition of potassium
monothiocarbonates to epoxides or alkyl halides [14],
selenium catalyzed reaction of alcohols, carbon
monoxide, sulfur, and alkyl halides [15], and sulfur-
assisted O-carbonylation of alcohols with carbon mon-
oxide in the presence of DBU [16]. Unfortunately,
most of the reported methods suffer from serious
drawbacks such as difficultly available reagents, low
yields, the use of poisonous phosgene and carbonyl
sulfide, the need of intolerable odorous thiols, the
use of moisture sensitive chlorothioformate, prep-
aration of certain thiolcarbonate derivatives, and
multi-step procedures. Very recently, a new seleni-
um-catalyzed reaction of alcohols with carbon mon-
oxide and diaryl disulfides was introduced for
synthesis of S-aryl-O-alkyl thiolcarbonates [17].
Keywords. Thiolcarbonates; Disulfides; Chloroformates;
Zinc thiolates.
Introduction
Thiolcarbonates are an important class of com-
pounds, being useful as synthesis intermediates in
the preparation of other valuable substances [1, 2],
polymerization inhibitors [3], heat stabilizers for
polymers [4], precursors to polymercaptanes [5], bio-
active compounds [6], radiographic contrast agent
[7], and as biological toxicants, particularly as nema-
tocides [8]. Of classical methods for the preparation
of thiolcarbonates, we can cite those involving the
reaction of primary and benzyl alcohols with carbon
dioxide, methanesulfonic anhydride, and thiols un-
der basic conditions [9], the rearrangement of diaryl
thioncarbonates [ArOC(S)OAr] [10], the treatment
of thiols with chloroformates [7], the reaction of
aryloxide salts, carbonyl sulfide and alkyl halides
[11], the reaction of trimethylsilyl enol ethers with
phenyl thiofluoroformate in the presence of a naked
fluoride ion catalyst [12], the reaction of ꢀ-nitroal-
Results and Discussion
As part of our ongoing work on the Zn=AlCl3 sys-
tem, we describe a useful and general method for the
synthesis of various S-aryl=alkyl-O-aryl=alkyl thiol-
carbonates 3 from disulfides 1 and chloroformates
2 by reductive cleavage of the S–S bond with a
Zn=AlCl3 system in dry acetonitrile at 80ꢁC accord-
ing to Scheme 1.
A series of symmetrical alkyl and aryl disulfides
were treated with phenyl and benzyl chloroformates
ꢀ
Corresponding author. E-mail: bmovass1178@yahoo.com

252
B. Movassagh et al.
IR spectra were obtained using an ABB FTLA 2000 instru-
ment. Mass spectra were recorded with a Hewlett-Packard
model 5973 instrument. Melting points and boiling points
were determined by a Bu¨chi B-540 melting point=boiling
point capillary apparatus.
Scheme 1
General Procedure for Synthesis of Thiolcarbonates
from Disulfides and Chloroformates
A mixture of 0.5 mmol disulfide, 130mg Zn powder
(2.0mmol), 134 mg finely ground anhydrous AlCl3 (1.0mmol),
and 6 cm3 dry acetonitrile was stirred at 80ꢁC for 1.5 h until
the zinc powder had almost disappeared. The chloroformate
(1.5mmol) was then added at once to the solution and stirring
was continued at that temperature for the appropriate time
(Table 1). After completion of the reaction as indicated by
TLC, the solution was filtered, acetonitrile was evaporated,
20 cm3 CHCl3 was added, the mixture washed with water
(2ꢂ10 cm3), and the organic layer was dried (Na2SO4). The
solvent was evaporated under reduced pressure, and the
crude mixture was purified by preparative TLC (silica gel;
eluent, n-heptane:EtOAc ¼ 6:1) to obtain the pure product.
All products were characterized by infrared, 1H and 13C
NMR spectroscopy, and finally by comparison with authen-
tic samples.
Table 1. Synthesis of various thiolcarbonates 3 from disul-
fides 1 and chloroformates 2
Entry
R1
R2
Reaction Product Isolated
time=min
yield=%
1
2
3
4
5
6
7
8
9
10
Ph
Ph
Ph
PhCH2
Ph
45
60
60
60
90
45
45
60
90
60
3a
3b
3c
3d
3e
3f
3g
3h
3i
90 [2g]
65 [20]
88
89 [10]
85
86
4-BrC6H4
4-ClC6H4
4-ClC6H4 PhCH2
4-MeC6H4
4-MeOC6H4
PhCH2
Ph
Ph
Ph
Ph
PhCH2
Ph
86
72 [19]
66 [19]
87 [11]
PhCH2
CH3
3j
Phenyl S-(4-bromophenyl) thiocarbonate (3c, C13H9BrO2S)
1
Mp 89–91ꢁC; IR (KBr): ꢁꢀ¼ 1735 (C¼O) cmꢃ1; H NMR
in the presence of the Zn=AlCl3 system with a molar
ratio of disulfide:AlCl3:chloroformate ¼ 0.5:1:1.5.
The disappearance of zinc powder during the prelim-
inary treatment of disulfides with Zn=AlCl3 is attrib-
uted to the formation of a zinc thiolate intermediate
[18], which further undergoes nucleophilic attack to
the chloroformate to afford the thiolcarbonates in
high yields.
The results are summarized in Table 1. Reactions
are very clean and thiolcarbonates are obtained as
the sole product during short times. The work-up
of the reaction is accomplished by simple filtration
and evaporation of the organic solvent (CH3CN) and
final purification.
In conclusion, the present method introduces
a simple, more general, and high yielding route to
a wide variety of thiolcarbonate derivatives with
shorter reaction times to the ones reported previous-
ly. Also, it offers some advantages over earlier re-
ported procedures, in that it avoids the need to apply
foul-smelling thiols, multi-step procedures, and the
use of complex starting materials.
(CDCl3): ꢂ ¼ 7.20 (dd, J ¼ 8.4, 8.2 Hz, Ph), 7.27 (t, J ¼
8.3 Hz, Ph), 7.42 (d, J ¼ 8.4 Hz, Ph) ppm; 13C NMR
(CDCl3): ꢂ ¼ 121.1, 125.7, 126.3, 129.54, 129.56, 136.03,
136.37, 151.2, 168.3 ppm; EIMS: m=z (%) ¼ 310 (M þ 2)þ
(51), 308 (Mþ, 49), 282 (81), 280 (78), 189 (73), 187 (72),
108 (100), 77 (53), 65 (44), 39 (47).
Benzyl S-(4-chlorophenyl) thiocarbonate (3e, C14H11ClO2S)
1
Mp 55–56ꢁC; IR (KBr): ꢁꢀ¼ 1730 (C¼O) cmꢃ1; H NMR
(CDCl3): ꢂ ¼ 4.10 (s, CH2), 7.26 (d, J ¼ 8.6 Hz, Ph), 7.30
(d, J ¼ 8.6 Hz, Ph) ppm; 13C NMR (CDCl3): ꢂ ¼ 39.3,
127.3, 128.54, 128.78, 128.94, 129.1, 131.4, 134.6, 137.1,
168.2 ppm; EIMS m=z (%) ¼ 280 (Mþ 2)þ (0.2), 278 (Mþ,
0.6), 236 (19), 234 (51), 108 (14), 91 (100), 65 (33), 39 (14).
Phenyl S-(4-methylphenyl) thiocarbonate (3f, C14H12O2S)
1
Mp 84–86ꢁC; IR (KBr): ꢁꢀ¼ 1730 (C¼O) cmꢃ1; H NMR
(CDCl3): ꢂ ¼ 2.41 (s, CH3), 7.18–7.28 (m, Ph), 7.38 (t,
J ¼ 8.1 Hz, Ph), 7.49 (d, J ¼ 8.1 Hz, Ph) ppm; 13C NMR
(CDCl3): ꢂ ¼ 21.4, 121.2, 123.6, 126.1, 129.4, 130.1, 134.8,
140.3, 151.3, 169.1ppm; EIMS m=z (%) ¼ 244 (Mþ, 44), 216
(52), 151 (28), 123 (100), 77 (32), 65 (20), 39 (19).
Phenyl S-(4-methoxyphenyl) thiocarbonate (3g, C14H12O3S)
1
Mp 52–53ꢁC; IR (KBr): ꢁꢀ¼ 1735 (C¼O) cmꢃ1; H NMR
(CDCl3): ꢂ ¼ 3.84 (s, CH3), 6.98 (d, J ¼ 8.8 Hz, Ph), 7.19–
7.28 (m, Ph), 7.40 (t, J ¼ 7.8 Hz, Ph), 7.55 (d, J ¼ 8.8 Hz, Ph)
ppm; 13C NMR (CDCl3): ꢂ ¼ 55.4, 114.9, 117.7, 121.2,
126.1, 129.5, 136.7, 151.4, 161.1, 169.5 ppm; EIMS m=z
(%) ¼ 260 (Mþ, 35), 232 (5), 139 (100), 124 (4), 95 (9), 77
(9), 65 (7), 39 (9).
Experimental
1H (300 MHz) and 13C (75 MHz) NMR spectra were
recorded using a Bruker AQS-300 Avance spectrometer.

Synthesis of S-Aryl=Alkyl Thiolcarbonates
253
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Acknowledgements
We thank the K.N. Toosi University of Technology
Research Council and Kermanshah Oil Refining
Company for financial assistance to this work.
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