Superoxide ion-promoted facile one-pot synthesis of O-alkyl-S-methyl dithiocarbonates from alcohol under mild reaction conditions

Article abstract of DOI:10.1080/10426507.2010.482545

A new, mild, and efficient protocol for the one-pot synthesis of O-alkyl-S-methyl dithiocarbonates (xanthates) has been described in reasonably good yields from a variety of alcohols employing carbon disulfide and methyl iodide using superoxide ion at room temperature. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2010.482545

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Phosphorus, Sulfur, and Silicon and the
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Superoxide Ion–Promoted Facile One-
Pot Synthesis of O-Alkyl-S-methyl
Dithiocarbonates from Alcohol Under
Mild Reaction Conditions
Satish Kumar Singh a & Krishna Nand Singh a
a Department of Chemistry, Faculty of Science , Banaras Hindu
University , Varanasi, India
Published online: 13 Jan 2011.
To cite this article: Satish Kumar Singh & Krishna Nand Singh (2010) Superoxide Ion–Promoted
Facile One-Pot Synthesis of O-Alkyl-S-methyl Dithiocarbonates from Alcohol Under Mild Reaction
Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, 186:1, 94-97, DOI:
10.1080/10426507.2010.482545
To link to this article: http://dx.doi.org/10.1080/10426507.2010.482545
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Phosphorus, Sulfur, and Silicon, 186:94–97, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.482545
SUPEROXIDE ION–PROMOTED FACILE ONE-POT
SYNTHESIS OF O-ALKYL-S-METHYL
DITHIOCARBONATES FROM ALCOHOL UNDER MILD
REACTION CONDITIONS
Satish Kumar Singh and Krishna Nand Singh
Department of Chemistry, Faculty of Science, Banaras Hindu University,
Varanasi, India
GRAPHICAL ABSTRACT
S
KO2/Et4NBr
R-OH + CS2
1a-j
R-O-C-SCH3
+ CH3I
DMF, RT
2a-j
75-86%
Abstract A new, mild, and efficient protocol for the one-pot synthesis of O-alkyl-S-methyl
dithiocarbonates (xanthates) has been described in reasonably good yields from a variety of
alcohols employing carbon disulfide and methyl iodide using superoxide ion at room tempera-
ture.
Keywords Alcohols; dithiocarbonates; phase-transfer catalyst; superoxide ion
INTRODUCTION
O-Alkyl-S-methyl dithiocarbonates (xanthates) have attracted a great deal of interest
due to their use as a versatile source of radicals,1 intermediates in organic synthesis,2–6
and photosensitisers.7 Their synthetic applications in natural products8 and Claisen re-
arrangement9 are also well documented in the literature. They have also received wide
attention due to their marked biological activities.10 Traditionally, xanthates are prepared
from an alcohol in a three-step process.11 The reaction involves the use of strong bases
such as sodium hydride, sodium amide, or potassium tert-butoxide in polar aprotic solvents
such as DMF,12 DMSO,13 or diglyme.14 Mitsunobu’s reagent,15 Cs2CO3-TBAI,16 and basic
resin17 have also been used for the preparation of dithiocarbonates from different alcohols.
Phase-transfer catalysis and crown ethers have also been used with strong bases specif-
ically for the preparation of dithiocarbonates from unfunctionalized alcohols.18 Recently
TBAH-catalyzed, one-pot synthesis of symmetrical trithiocarbonates from alkyl halides
and carbon disulfide under neat aqueous conditions has been reported.19 However, most
Received 23 February 2010; accepted 30 March 2010.
The authors are thankful to UGC, New Delhi, for financial support.
Address correspondence to K. N. Singh, Department of Chemistry, Faculty of Science, Banaras Hindu
University, Varanasi 221005, India. E-mail: knsinghbhu@yahoo.co.in
94

SYNTHESIS OF O-ALKYL-S-METHYL DITHIOCARBONATES
95
of these methods suffer from limitations such as long reaction times, use of expensive
reagents, strongly basic conditions, and tedious workup. Consequently, there is continued
interest in developing new and convenient methods for the synthesis of dithiocarbonate
using mild reaction conditions.
RESULTS AND DISCUSSION
In light of the above, and as a part of our ongoing research on the use of the superoxide
ion20 in organic synthesis, we report in this article a mild and efficient one-pot synthesis of
O-alkyl-S-methyl dithiocarbonates via a three-component coupling of an alcohol, carbon
disulfide, and methyl iodide using in situ–generated tetraethylammonium superoxide in dry
DMF at room temperature (Scheme 1).
S
KO2/Et4NBr
R-OH + CS2
R-O-C-SCH3
2a-j
+ CH3I
DMF, RT
1a-j
75-86%
Scheme 1 Superoxide-induced synthesis of dithiocarbonates.
In order to achieve the optimum yield of the product, the effect of various parameters such
as molar proportion of the reactants and effect of solvents (DMF, DMSO, and CH3CN)
were investigated in detail using 1c as a reference compound. The best result was obtained
using 1c, CS2, methyl iodide, KO2, and Et4NBr in the molar proportion 1:1.5:2:2:1 at room
temperature in dry DMF in 2.0 h. Under the optimized set of reaction conditions, various
alcohols (1a–j) were made to undergo smooth coupling with CS2 and methyl iodide in
the presence of tetraethylammonium superoxide (Et4NO2) at room temperature to afford
O-alkyl-S-methyl dithiocarbonates in very good yields (75–86%, Table 1).
Tetraethylammonium bromide behaves as an inexpensive phase-transfer catalyst to
generate tetraethylammonium superoxide (Et4NO2) in the presence of potassium superox-
ide. Superoxide is assumed to initiate the reaction by proton abstraction from the substrate
followed by nucleophilic attack and methylation under significantly mild reaction condi-
tions in aprotic medium.
A comparison of the existing methods for the synthesis of xanthates is described in
Table 2.
CONCLUSION
In conclusion, a new and mild approach for the one-pot synthesis of O-alkyl-S-
methyl dithiocarbonates has been achieved by using superoxide ion in non-aqueous medium
employing alcohols, CS2, and methyl iodide.
EXPERIMENTAL
Potassium superoxide and tetraethylammonium bromide were purchased from E.
Merck, Germany, and were used as received. Dry N,N-dimethylformamide (DMF) was
purchased from Aldrich, USA, and was stored over molecular sieves (4Å) prior to use. The
other reagents and solvents were of AR grade. NMR spectra were recorded on a JEOL

96
S. K. SINGH AND K. N. SINGH
Table 1 Et4NO2 induced one-pot synthesis of O-alkyl-S-methyl dithiocarbonates
Entry
1
Substrate
Product
Time (h)
Yield (%)a
82
Ref.
17
C4H9OH
(1a)
1.75
S
C4H9OCSCH3
(2a)
2
CH3(CH2)7OH
2.0
86
18b
S
(1b)
CH3(CH2)6CH2OCSCH3
(2b)
S
3
4
5
6
7
8
CH3(CH2)11OH
2.0
2.0
1.75
2.0
1.5
2.0
80
85
77
83
82
81
17
(1c)
CH3(CH2)10CH2OCSCH3
(2c)
S
CH3(CH2)15OH
18b
18b
18b
18b
18b
(1d)
CH3(CH2)14CH2OCSCH3
(2d)
S
(CH3)2CHOH
(1e)
(CH3)2CHOCSCH3
(2e)
S
(CH3)2CH(CH2)2OH
(1f)
(CH3)2CH(CH2)2OCSCH3
(2f)
S
C6H5OH
(1g)
C6H5OCSCH3
(2g)
S
C6H5CH2OH
(1h)
C6H5CH2OCSCH3
(2h)
S
9
C6H5(CH2)3OH
2.0
2.0
84
75
17
(1i)
C6H5(CH2)3OCSCH3
(2i)
S
10
18b
OH
OCSCH3
(2j)
(1j)
aIsolated yield.
Table 2 Comparison of different methods of synthesizing xanthates
Entry
Bases
Reaction conditions
Time (h)
Yield (%)
Ref.
1.
2.
3.
4.
5.
Pot. tert-butoxide
Mitsunobu’s reagent
Cs2CO3/TBAI
Basic resin
50% aq. NaOH/nBu4NHSO4
0◦C
–
4–8
3–12
2–6
0.5–1.5
60–65
76–98
57–96
72–98
80–95
14
15
16
17
18
rt
0◦C to rt
rt
rt

SYNTHESIS OF O-ALKYL-S-METHYL DITHIOCARBONATES
97
AL300 FTNMR spectrometer; chemical shifts are given in δ ppm, relative to TMS as
internal standard. Crude products were purified using column chromatography.
General Procedure for Synthesis of O-Alkyl-S-methyl Dithiocarbonates
(2a–j)
A mixture of potassium superoxide (0.568 g, 8 mmol) and tetraethylammonium
bromide (0.840 g, 4 mmol) (weighed under a nitrogen atmosphere using an atmosbag) in
dry DMF (20 mL) was stirred for 15 min and then CS2 (0.457 g, 6 mmol) was added
while continuing the stirring. After 10 min, the alcohols 1 (4 mmol) and methyl iodide
(1.14 g, 8 mmol) were introduced, and the stirring was continued. After the reaction was
over (1.5 to 2 h, TLC), cold brine solution (10 mL) was added to decompose the unreacted
potassium superoxide. The mixture was then extracted with diethyl ether (3 × 15 mL), and
the combined organic phase was dried over anhydrous Na2SO4, filtered, and evaporated to
give the product 2, which was purified by column chromatography.
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