212 J. CHEM. RESEARCH (S), 1998
Solid Supported Reagents and Reactions. Part 21.1
Rapid and Clean Synthesis of Thiols from Halides
Using Polymer-supported Hydrosulfide$%
Babasaheb P. Bandgar*a and Sanjay B. Pawarb
J. Chem. Research (S),
1998, 212±213$
aOrganic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramanand Teerth
Marathwada University, Dnyanteerth, Vishnupuri Post Box No. 87, Nanded-431 602,
Maharashtra, India
bDepartment of Chemistry, R.B.N.B. College, Shrirampur-413 709, India
A variety of thiols are prepared from corresponding halides using polymer-supported hydrosulfide in excellent yields.
Isolation of pure products by simple filtration and evaporation is an important feature of this method.
Thiols are important not only for their use in the synthesis
of organosulfur compounds but also for their roles in cell
biochemistry. Therefore, many synthetic methods have been
developed.2,3 Although direct preparations of thiols from
alkyl halides and metal sul®des would be straightforward,
formation of dialkyl sul®des as by-products is avoided.
Tertiary alkyl halides (entries c and d in Table 1) are also
smoothly converted into corresponding thiols at 25 8C.
These reactions not only proceed with unique chemo-
selectivity but also give excellent yields of thiols compared
to those prepared by indirect methods.4±9 The isolation of
pure products by simple ®ltration and evaporation is an
important feature of this method. The recovered resin can
be recycled in the process after regeneration by treatment
with dilute HCl.
direct methods give only
a moderate yield of thiols
accompanying a considerable amount of dialkyl sul®de.2
Therefore, indirect methods involving thiourea,2 xanthate2
and thioacetate2 are commonly utilized for the synthesis
of thiols and other new indirect methods have been
reported.4±9 These indirect methods usually give around
80% yield and no dialkyl sul®des or other undesired by-
products; however, intermediates have to be transformed
to thiols by hydrolysis with base5±9 or by reduction with
lithium aluminium hydride.10,11 Recently thiols have been
prepared in quantitative yield from the corresponding thio-
acetates via Pd-catalyzed methanolysis with borohydride
exchange resin under mild and neutral conditions.2
Experimental
All reactions were conducted in oven-dried ¯asks. Solvents were
distilled before use. All chemicals were of analytical grade.
Reactions were monitored by TLC. The strongly anionic exchange
resin, Tulsion A-27 (Cl ) was procured from Thermax Chemicals,
Pune.
Preparation of Hydrosul®de Exchange Resin.ÐTo a solution of
NaSH (50 mmol) in MeOH (50 ml), Tulsion A-27 (chloride form)
(10 g) was added and the mixture was shaken for 1 h. The resin was
®ltered o and washed with distilled water until it was free from Cl
and excess NaSH. The resin was then washed with methanol,
diethyl ether and dried under vacuum at 50 8C for 2 h. The capacity
Table 1 Synthesis of thiols from halides at 25 8C
Yield mp/bp (Torr)
(%)
Entry
Halide
Product
(Lit.) (8C)
a
Me[CH2]2CH2Br Me[CH2]2CH2SH
98 97 (760 mm)
[96±97
(760 mm)]13
b
c
d
Me[CH2]2CH2I Me[CH2]2CH2SHa 93 97 (760 mm)
[96±97
(760 mm)]13
Scheme 1
Me3CBr
Me3CCl
Me3CSH
Me3CSH
96 63 (760 mm)
[61.60
(700.8 mm)]14
95 63 (760 mm)
[61.60
We now report on an exceedingly simple method for the
direct synthesis of thiols from halides using hydrosul®de
exchange resin (Scheme 1). It is important to note that this
method produces thiols in excellent yields (93±98%) without
any trace of dialkyl sul®des.3
The synthesis of thiols from alkyl halides and NaSH
always results in the formation of dialkyl sul®des12
because any alkyl thiols formed initially further react with
excess alkyl halides. However, Tulsion A-77-supported
hydrosul®de has more nucleophilic character than NaSH
and therefore alkyl halides react with hydrosul®de exchange
resin much faster than NaSH giving corresponding thiols
within a very short time (15 min) at 25 8C. Thus the
(700.8 mm)]14
e
98 194 (760 mm)
[192±194
(760 mm)]11
f
93 103 (12 mm)
[105
(10 mm)]15
97 121 (14 mm)
[123±125
g
(10 mm)]15
h
i
97 58
[58]16
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
%This paper has been dedicated to Professor M. S. Wadia
(University of Pune) on the occasion of his 60th birthday.
96 43
[44]17
aThe reaction was carried out at 0 8C.