An efficient, one-pot, Triton-B catalyzed synthesis of O-alkyl-S-methyl dithiocarbonates

Article abstract of DOI:10.1007/s00706-006-0514-0

A novel process for the one-step conversion of a variety of primary and secondary alcohols into their O-alkyl-S-methyl dithiocarbonates using methyl iodide catalyzed by the Triton-B/CS₂ system was developed. Thus, O-alkyl-S-methyl dithiocarbonates were obtained in very good to excellent yields. This protocol is mild and efficient compared to other methods.

Full text of DOI:10.1007/s00706-006-0514-0

Monatshefte f€ur Chemie 137, 1219–1223 (2006)
DOI 10.1007/s00706-006-0514-0
An Efficient, One-Pot, Triton-B Catalyzed
Synthesis of O-Alkyl-S-methyl
Dithiocarbonates1
ꢀ
Devdutt Chaturvedi and Suprabhat Ray
Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow, India
Received December 14, 2005; accepted (revised) December 19, 2005
Published online August 23, 2006 # Springer-Verlag 2006
Summary. A novel process for the one-step conversion of a variety of primary and secondary alcohols
into their O-alkyl-S-methyl dithiocarbonates using methyl iodide catalyzed by the Triton-B=CS2 sys-
tem was developed. Thus, O-alkyl-S-methyl dithiocarbonates were obtained in very good to excellent
yields. This protocol is mild and efficient compared to other methods.
Keywords. Triton-B; Carbon disulfide; Alcohols; Methyl iodide; O-Alkyl-S-methyl dithiocarbonates.
Introduction
O-Alkyl-S-methyl dithiocarbonates (xanthates) are a versatile source of radicals
[1], versatile intermediates in the synthesis of thiols [2], thiocarbonates [3], alkenes
[4], alkanes [5], S-activated carbanions [6], and photosensitizers [7] for the poly-
merization of vinyl monomers. They have also been used in the synthesis of natural
products [8], Claisen rearrangements [9], and are also important for their biological
activities [10]. Traditionally, they are prepared from alcohol in a three-step process
[11]. The reaction involves the use of strong bases such as sodium hydride, sodium
amide, or potassium t-butoxide in polar aprotic solvents like DMSO [12], DMF
[13], or diglyme [14]. Phase transfer catalysis and crown ethers have also been used
with strong bases, specifically for the preparation of dithiocarbonates from unfunc-
tionallized alcohols [15]. However, most of these methods suffer from limitations
such as longer reaction times, use of expensive strongly basic reagents, and tedious
work-up. Consequently, there is continued interest in developing new and conve-
nient methods for the synthesis of dithiocarbonates using mild reaction conditions.
Recently, we found that benzyltrimethylammonium hydroxide (Triton-B) is the
best reagent for the preparation of carbamates and dithiocarbamates using cheap,
ꢀ
Corresponding author. E-mail: ddchaturvedi002@yahoo.co.in
þ
CDRI Communication No.: 6358

1220
D. Chaturvedi and S. Ray
abundantly available, and safe reagents like CO2 and CS2 [16]. In the present com-
munication, we report an efficient, one-pot synthesis of O-alkyl-S-methyl dithio-
carbonates from corresponding alcohols and methyl iodide using the Triton-B=CS2
system.
Results and Discussion
During the course of our recent studies for the synthesis of carbamates and dithio-
carbamates, Triton-B has been found to be an efficient and mild basic catalyst [16].
Taking these observations as a guide, we tried a reaction of an alcohol with methyl
iodide using the Triton-B=CS2 system at room temperature. The desired product
was isolated and further confirmed by different spectroscopic and analytical tech-
niques. Thus, various alcohols were reacted (Scheme 1) with methyl iodide using
the Triton-B=CS2 system at room temperature for 1.5–5 h yielding O-alkyl-S-
methyl dithiocarbonates in high to excellent yields (70–98%) as shown in Table 1.
We tried several solvents like n-pentane, n-hexane, n-heptane, DMF, DMSO, acet-
onitrile, HMPA, etc. and found dry DMSO most suitable for good yields of the
required products at room temperature.
Scheme 1
Table 1. Conversion of alcohols into O-alkyl-S-methyl dithiocarbonates 1
Product
R1
R2
R3
Time=h
Yield=%
1a
1b
1c
1d
1e
1f
CH3
CH3(CH2)6
H
H
H
H
H
H
H
H
H
2.5
2
90
93
95
98
92
85
91
88
82
80
94
92
90
79
70
78
CH3(CH2)10
CH3(CH2)14
(CH3)2CHCH2
CH3
H
2
H
1.5
2.5
2.5
2.5
3
H
CH3
H
1g
1h
1i
Ph
R1 ¼ R2 ¼ R3 ¼ Ph
R1 ¼ R2 ¼ R3 ¼ Cyclohexyl
PhCH¼CH
3
1j
H
H
H
H
2.5
2.5
3
1k
1l
PhCH2CH2
PhCH2
CH3
H
CH3
H
1m
1n
1o
1p
1q
n-C3H7
2
R1 ¼ R2 ¼ R3 ¼ Menthyl
R1 ¼ R2 ¼ R3 ¼ Cholesteryl
n-C4H9
4
5
n-C4H9
n-C4H9
H
3
n-C4H9
n-C4H9
not formed

Synthesis of O-Alkyl-S-methyl Dithiocarbonates
1221
In conclusion, we have developed a convenient and efficient protocol for a one-
pot, three components coupling of the various alcohols with methyl iodide in the
presence of the Triton-B=CS2 system. This reaction generates the corresponding O-
alkyl-S-methyl dithiocarbonates in good to excellent yields. Further, our method
exhibits substrate versatility, mild reaction conditions, and experimental conveni-
ence. This synthetic protocol is believed to offer a more general method for the
formation of C–S bonds, essential for numerous organic syntheses.
Experimental
Chemicals were obtained from Merck, Aldrich, and Fluka. IR spectra were recorded on a Bomem MB-
1
104 FTIR spectrometer and H NMRs were scanned on an AC-300F NMR (300 MHz) instrument
using CDCl3 as solvent and TMS as internal standard. Elemental analyses were made by a Carlo-Erba
EA1110 CNNO-S analyzer and agreed favorably with calculated values.
Procedure
A mixture of 6 mmol alcohol and 6 mmol CS2 were taken in 40 cm3 dry DMSO and were allowed
to stir for 20 min at rt. Triton-B (6 mmol) was added and the reaction was continued at rt for 1 h.
Now 6 mmol methyl iodide were added. The reaction was further continued until completion (cf.
Table 1). The reaction mixture was poured into 50 cm3 distilled H2O and extracted with ethyl
acetate thrice. The organic layer was separated, dried (Na2SO4), and concentrated to give the de-
sired compound.
O-Ethyl-S-methyl dithiocarbonate (1a, C4H8OS2)
1
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2900, 1230, 1065 cmꢁ1; H NMR (CDCl3): ꢁ ¼ 1.40–1.43 (t, OCH2CH3),
2.54–2.57 (s, 3H, SCH3), 4.54–4.57 (m, 2H, OCH2CH3) ppm; MS: m=z ¼ 136.
O-Octyl-S-methyl dithiocarbonate (1b, C10H20OS2)
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2860, 1231, 1080 cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.96–1.56 (m, 15H), 2.52 (s,
3H), 4.55–4.59 (t, 2H) ppm; MS: m=z ¼ 220.
O-Dodecyl-S-methyl dithiocarbonate (1c, C14H28OS2)
Oil; IR (neat):ꢀꢀ ¼ 3000ꢁ2850, 1240, 1082cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.94–1.57 (m, 23H), 2.54 (s,
3H), 4.60–4.63 (t, 2H) ppm; MS: m=z ¼ 276.
O-Hexadecyl-S-methyl dithiocarbonate (1d, C18H36OS2)
1
Mp¼ 28.5ꢂC; IR (KBr): ꢀꢀ ¼ 3000ꢁ2855, 1238, 1081 cmꢁ1; H NMR (CDCl3): ꢁ ¼ 0.95–1.67 (m,
31H), 2.53 (s, 3H), 4.61–4.64 (t, 2H) ppm; MS: m=z ¼ 332.
O-(3-Methylbutyl)-S-methyl dithiocarbonate (1e, C7H14OS2)
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2850, 1236, 1079cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.96 (d, 6H), 1.70–1.73 (m,
H), 2.53 (s, 3H), 4.60–4.63 (t, 2H) ppm; MS: m=z ¼ 178.
O-(1-Methyethyl)-S-methyl dithiocarbonate (1f, C5H10OS2)
1
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2900, 1238, 1070cmꢁ1; H NMR (CDCl3): ꢁ ¼ 1.36 (d, 6H), 2.53 (s, 3H),
5.76–5.79 (m, H) ppm; MS: m=z ¼ 150.
O-Phenylmethyl-S-methyl dithiocarbonate (1g, C9H10OS2)
Oil; IR (neat): ꢀꢀ ¼ 3100ꢁ2900, 1245, 1084 cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 2.56 (s, 3H), 5.62–5.64 (m,
2H) 7.30–7.38 (m, 5H) ppm; MS: m=z ¼ 198.

1222
D. Chaturvedi and S. Ray
O-Phenyl-S-methyl dithiocarbonate (1h, C8H8OS2)
1
Oil; IR (neat): ꢀꢀ ¼ 3100, 2950, 1600, 1500, 1200, 1060 cmꢁ1; H NMR (CDCl3): ꢁ ¼ 2.57 (s, 3H),
7.20–7.25 (m, 5H) ppm; MS: m=z ¼ 198.
O-Cyclohexyl-S-methyl dithiocarbonate (1i, C8H14OS2)
1
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2850, 1230, 1070cmꢁ1; H NMR (CDCl3): ꢁ ¼ 1.44–1.59 (m, 10H), 2.54
(s, 3H), 5.60 (m, H) ppm; MS: m=z ¼ 190.
O-Styryl-S-methyl dithiocarbonate (1j, C10H10OS2)
Oil; IR (neat): ꢀꢀ ¼ 3100, 2940, 1228, 1065 cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 2.55 (s, 3H), 5.60 (s, H), 6.6
(s, H), 7.15–7.30 (m, 5H) ppm; MS: m=z ¼ 210.
O-(3-Phenylpropyl)-S-methyl dithiocarbonate (1k, C11H14OS2)
1
Oil; IR (neat): ꢀꢀ ¼ 3100ꢁ2955, 1232, 1072cmꢁ1; H NMR (CDCl3): ꢁ ¼ 1.80–1.82 (m, 2H), 2.52
(s, 3H), 2.60–2.63 (t, 2H), 3.85–3.90 (t, 2H), 7.08–7.25 (m, 5H) ppm; MS: m=z ¼ 226.
O-(1,1-Dimethyl-2-phenylethyl)-S-methyl dithiocarbonate (1l, C12H16OS2)
1
Oil; IR (neat): ꢀꢀ ¼ 3100ꢁ2950, 1234, 1075 cmꢁ1; H NMR (CDCl3): ꢁ ¼ 1.26 (s, 6H), 2.54 (s, 3H),
2.66 (s, 2H), 7.10–7.20 (m, 5H) ppm; MS: m=z ¼ 240.
O-Butyl-S-methyl dithiocarbonate (1m, C6H12OS2)
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2900, 1235, 1072cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.93–0.96 (m, 3H), 1.33–1.48
(m, 4H), 2.54 (s, 3H), 4.20–4.25 (m, 2H, OCH2) ppm; MS: m=z ¼ 164.
O-Menthyl-S-methyl dithiocarbonate (1n, C12H22OS2)
Oil; IR (neat): ꢀꢀ ¼ 3000ꢁ2950, 1233, 1075 cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.85–0.87 (d, 3H), 0.90–0.95
(d, 6H), 1.15–2.20 (m, 8H), 2.50 (s, 3H), 5.45–5.50 (m, H) ppm; MS: m=z ¼ 246.
O-Cholesteryl-S-methyl dithiocarbonate (1o, C28H46OS2)
Mp¼ 125ꢂC; IR (KBr): ꢀꢀ ¼ 3000ꢁ2850, 1241, 1082 cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.84–0.86 (s, 3H),
0.90–0.95 (d, 6H), 1.10 (s, 3H), 1.15 (s, 3H), 1.21–2.20 (m, 31H), 2.54 (s, 3H), 3.50–3.53 (m, H),
5.50–5.55 (m, H) ppm; MS: m=z ¼ 246.
O-sec-Butyl-S-methyl dithiocarbonate (1p, C10H20OS2)
Oil; IR(neat): ꢀꢀ ¼ 3000ꢁ2950, 1237, 1070cmꢁ1; 1H NMR (CDCl3): ꢁ ¼ 0.93–0.96 (t, 3H), 1.20–1.23
(d, 3H), 1.60–1.63 (m, 2H), 2.55 (s, 3H), 5.50–5.55 (m, H, CH) ppm; MS: m=z ¼ 220.
Acknowledgements
Authors are grateful to Dr. N. Anand for fruitful discussion and SIAF Division of CDRI for providing
spectroscopic and analytical data.
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Synthesis of O-Alkyl-S-methyl Dithiocarbonates
1223
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