A novel one-step synthesis of symmetrical dialkyl trithiocarbonates in the presence of phase-transfer catalysis

Article abstract of DOI:10.1002/jccs.200800094

Symmetrical trithiocarbonates were directly obtained, in moderate to excellent isolated yields, by the reaction of various primary, secondary, allylic and benzylic halides or alkyl tosylates with a suspension of granulated KOH and alumina in CS₂ under phase-transfer catalysis. In this manner, cyclic trithiocarbonates such as 1,3-dithiolane-2-thione can also be prepared without formation of any polymeric by-products.

Full text of DOI:10.1002/jccs.200800094

Journal of the Chinese Chemical Society, 2008, 55, 639-642
639
A Novel One-step Synthesis of Symmetrical Dialkyl Trithiocarbonates in
the Presence of Phase-Transfer Catalysis
Ali Reza Kiasat* and Mehdi Fallah Mehrjardi
Chemistry Department, College of Science, Shahid Chamran University, Ahvaz 61357-4-3169, Iran
Symmetrical trithiocarbonates were directly obtained, in moderate to excellent isolated yields, by the
reaction of various primary, secondary, allylic and benzylic halides or alkyl tosylates with a suspension of
granulated KOH and alumina in CS2 under phase-transfer catalysis. In this manner, cyclic trithiocarbo-
nates such as 1,3-dithiolane-2-thione can also be prepared without formation of any polymeric by-prod-
ucts.
Keywords: Trithiocarbonate; Alkyl halide; Alkyl tosylate; Carbon disulfide; Phase-transfer ca-
talysis.
INTRODUCTION
Symmetrical dialkyl trithiocarbonates constitute an
(6) use of an inert atmosphere, and (7) unavailability of the
reagents.
important class of compounds which have been used for
various applications, especially as pesticides in agriculture
and as lubricating additives.1 For another application, di-
benzyl trithiocarbonate (DBTTC) derivatives are employed
as reversible addition-fragmentation chain transfer (RAFT)
agents,2 which enables controlled free-radical polymeriza-
tion of various vinyl monomers to afford polymers with
narrow polydispersities and controlled molecular weights.
Apart from other less important methods, the usual
Phase-transfer catalysis is now established as a versa-
tile and important synthetic technique in organic chemis-
try.9-11 Phase-transfer catalysis (PTC) is a very useful tech-
nique, which is widely used in industrial applications in
synthesis of dyes, pharmaceutics/perfumes, flavorants, ag-
ricultural chemicals, monomers, and polymers,12 and it has
been widely used for organic synthesis, particularly for
nucleophilic substitution.13 The PTC systems have several
advantages over single-phase systems, including improved
reaction rates, lower reaction temperature and absence of
expensive anhydrous or aprotic solvents.14
syntheses of dialkyl trithiocarbonates involve reactions of
thiols with either thiophosgene3 or chlorodithiofarmates4
and two-step reactions of thiols with carbon disulfide and
alkyl halides in basic conditions.5 Another general method
involves the dialkylation of the trithiocarbonate anion with
halides, using phase-transfer catalysts as the media.6 Leung
et al. discovered that the reaction between alkyl halides,
granulated KOH and carbon disulfide in anhydrous THF
occurs smoothly to give symmetrical trithiocarbonates.7
Recently, a novel procedure for preparation of symmetrical
dialkyl trithiocarbonates was reported.8 In this procedure,
alkyl halide was reacted with an equivalent of CS2 and ce-
sium carbonate in polar aprotic solvent. Each of the above
methods has at least one of the following drawbacks: (1)
long reaction time, (2) low yields of products, (3) difficulty
in separating product from the original reagent and PTC,
(4) use of aqueous media, (5) use of toxic chemicals with
unpleasant odors such as alkane thiols and thiophosgene,
In continuation of our efforts to synthesize trithiocar-
bonates,15 we describe a new approach to an easy and one-
step synthesis of symmetrical dialkyl trithiocarbonates di-
rectly from carbon disulfide and alkyl halides or tosylates
using tetrabutylammonium bromide (TBAB) as phase-
transfer catalysis (PTC).
RESULTS AND DISCUSSION
The trithiocarbonate anion is known to be prepared
by reacting ammonium sulfide, strong aqueous ammonia,
aqueous alkali-metal hydroxide or alkali-metal sulfide with
carbon disulfide.16 To increase the yield and reaction rate, a
PTC has often been used to promote the reactions in two-
phase systems.1 In the presence of PTC the trithiocarbonate
anion will be carried into the organic media and reacts with
alkyl halides to afford dialkyl trithiocarbonates. The re-
* Corresponding author. E-mail: akiasat@scu.ac.ir

640 J. Chin. Chem. Soc., Vol. 55, No. 3, 2008
Kiasat and Mehrjardi
markable ability of the quaternary ammonium salts as PTC
to promote the various reactions17 together with reported
insecticidal and fungicidal activities of symmetrical trithio-
carbonats gave us impetus for planning the synthesis of
various types of dialkyl trithiocarbonates in a one-pot pro-
cedure using tetrabutylammoniumbromide as PTC (Scheme
I).
Table 1. Optimization of conditions on trithiocarbonation of
benzyl bromide (1 mmol)
Entry
Condition
Time (min)
Conversion
1
2
3
4
5
A
B
C
D
E
300
030
025
120
120
Not completed
100%
100%
Not completed
Not completed
A: KOH (3 mmol), TBAB (1.0 mmol), CS2 (10 mL), reflux
B: KOH (10 mmol), TBAB (0.3 mmol), CS2 (10 mL), reflux
C: KOH (3 mmol), TBAB (0.3 mmol), neutral alumina (1 gr),
CS2 (10 mL), reflux
Scheme I
D: KOH (3 mmol), PEG (0.1 gr), neutral alumina (1 gr), CS2 (10
mL), reflux
E: basic alumina (2 gr), TBAB (0.3 mmol), CS2 (10 mL), reflux
We first optimized the conditions for the reaction, us-
ing benzyl bromide as a model alkyl halide (Table 1). As
shown in Table 1, the best result for benzyl bromide (1.0
mmol) is obtained with KOH (3.0 mmol), TBAB (0.3
mmol), neutral alumina (1.0 gr), and CS2 (10 mL) under re-
flux conditions. Thus, several symmetrical dialkyl trithio-
carbonates were easily and rapidly prepared by the simple
mixing of alkyl halides or tosylates with a suspension of
alumina, KOH and TBAB in CS2 under reflux conditions
(Scheme II).
Table 2. Conversion of alkyl halides and tosylates to the
corresponding symmetric trithiocarbonatea
d (ppm)
Time
(min)
Yieldb
(%)
Entry
Substrate
C NMR
C=S
1
C6H5CH2Br
25
60
94
93
95
93
94
95
90
90
69
72
82
85
74
55
65
74
83
60
62
222.2
222.1
223.0
222.8
223.6
225.1
224.1
214.2
221.9
224.6
222.4
222.7
227.5
226.2
226.3
223.0
223.5
252.8
232.4
2
C6H5CH2Cl
3
2-FC6H4CH2Cl
4-BrC6H4CH2Br
2-ClC6H4CH2Cl
2,4-Cl2C6H3CH2Cl
C10H7CH2Cl
45
4
45
5
50
6
90
Scheme II
7
100
120
5 h
120
60
8
C6H5CH2CH2Br
(C6H5)2CHBr
CH3(CH2)2CH2Cl
CH2=CHCH2Cl
CH2=CHCH2Br
ClCH2CH2Cl
9
10
11
12
13
14
15
16
17
18
19
60
60
CH3I
20
CH3OTs
15
To establish the generality and applicability of this
method, various primary, secondary, allylic, benzylic halides
and some alkyl tosylates are converted into corresponding
dialkyl trithiocarbonates as exclusive and virtually pure
products according to TLC and 1H-NMR in moderate to ex-
cellent isolated yields (Table 2). In addition, cyclic trithio-
carbonates such as 1,3-dithiolane-2-thione can also be pre-
pared without formation of any polymeric by-products
(Scheme III).
C2H5OTs
90
CH3(CH2)6CH2Ots
Phth-CH2CH2CH2Brc
Phth-CH2CH2Brc
180
10 h
14 h
a Dialkyl trithiocarbonates were identified by their IR and NMR
spectra and also by comparison of their other physical data with
those reported.15
b Isolated yield
c PhthH = Phthalimide
A notable point of this method is that in case the alkyl
halide or tosylate is not soluble in CS2, it is necessary to
carry out the reaction in the presence of a few drops of THF.
It is worth nothing that in this method, methyl tosylate eas-
ily and rapidly converts to dimethyl trithiocarbonate. Be-
Scheme III

Preparation of Symmetrical Dialkyltrithiocarbonates
J. Chin. Chem. Soc., Vol. 55, No. 3, 2008 641
cause of the high toxicity of methyl iodide, methyl tosylate
can be used for preparation of dimethyl trithiocarbonate.
More interestingly, base-sensitive functional groups
such as amides can also be tolerated under the reaction con-
ditions. Therefore, N-(2-bromoethyl)phthalimide and N-
(3-bromopropyl)phthalimide can be used to provide the
corresponding trithiocarbonates in moderate yields.
In summary, the present procedure provides a simple
and efficient general access to pure symmetrical trithiocar-
bonates from alkyl halides or tosylates. Our explored method
has the following advantages: (1) short reaction time, (2)
high yields of products, (3) simplicity of work-up, (4) elim-
ination of aqueous media, (5) availability of the reagents,
and (6) the reactions are remarkably clean, and no chro-
matographic separation is necessary to get the spectra-pure
compounds except in a few cases (Table 2, Entries 9, 18 and
19).
Bis(phenylmethyl) Trithiocarbonate 1, 2.7,8,15 IR:
1
1063 cm-1 (C=S). H-NMR (400 MHz, CDCl3): d = 4.68
(4H, s), 7.32-7.41 (10H, m). 13C-NMR (100 MHz, CDCl3):
d = 41.62, 128.34, 128.58, 128.80, 134.99, 222.26.
Bis(2-fluorophenylmethyl) Trithiocarbonate 3. IR:
1
1062 cm-1 (C=S). H-NMR (400 MHz, CDCl3): d = 4.66
(4H, s), 7.12-7.49 (8H, m). 13C-NMR (100 MHz, CDCl3): d
= 33.20, 116.42, 125.69, 126.71, 129.59, 130.30, 161.65,
223.04.
Bis(4-bromophenylmethyl) Trithiocarbonate 4. IR:
1
1065 cm-1 (C=S). H-NMR (400 MHz, CDCl3): d = 4.63
(4H, s), 7.55-7.71 (8H, m). 13C-NMR (100 MHz, CDCl3): d
= 38.55, 122.96, 130.02, 131.55, 137.88, 222.78.
Bis(2-chlorophenylmethyl) Trithiocarbonate 5. IR:
1
1058 cm-1 (C=S). H-NMR (400 MHz, CDCl3): d = 4.77
(4H, s), 7.21-7.47 (8H, m). 13C-NMR (100 MHz, CDCl3): d
= 38.02, 127.44, 128.27, 128.98, 129.75, 130.04, 138.11,
223.58.
EXPERIMENTAL
Bis(2,4-dichlorophenylmethyl) Trithiocarbonate 6.
1
General
IR: 1067 cm-1 (C=S). H-NMR (400 MHz, CDCl3): d =
IR spectra were obtained on a BOMEM MB-Series
1998 FT-IR spectrometer. NMR spectra were recorded in
CDCl3 using TMS as internal standard on a Bruker Avance
DPX instrument spectrometer (400 MHz). Alkyl halides
and tosylates were purchased from Fluka and Merck or pre-
pared in our laboratory from corresponding alcohols ac-
cording to known procedures. The products are known
compounds and are identified by comparison of their phys-
ical and spectral data with those previously reported. CAU-
TION:Care should be taken in using CS2 due to its toxicity
and low flash point.
4.83 (4H, s), 7.22-7.51 (6H, m). 13C-NMR (100 MHz,
CDCl3): d = 37.70, 128.38, 131.11, 132.43, 132.81, 134.02,
134.65, 225.13.
Bis(naphthylmethyl) Trithiocarbonate 7. IR: 1072
cm-1 (C=S). 1H-NMR (400 MHz, CDCl3): d = 4.80 (4H, s),
7.33-8.13 (14H, m). 13C-NMR (100 MHz, CDCl3): d =
35.14, 127.14, 127.41, 127.83, 128.20, 128.41, 128.97,
129.31, 132.14, 132.22, 138.21, 224.10.
Bis(phenylethyl) Trithiocarbonate 8. IR: 1075 cm-1
(C=S). 1H-NMR (400 MHz, CDCl3): d = 3.24 (4H, m), 3.71
(4H, t), 7.21-7.43 (10H, m). 13C-NMR (100 MHz, CDCl3):
d = 35.21, 36.37, 127.25, 127.68, 130.11, 143.22, 214.19.
Bis(diphenylmethyl) Trithiocarbonate 9. IR: 1069
cm-1 (C=S). 1H-NMR (400 MHz, CDCl3): d = 5.73 (2H, s),
7.17-7.33 (20H, m). 13C-NMR (100 MHz, CDCl3): d =
49.28, 127.89, 128.04, 131.62, 138.17, 221.93.
Dibutyl Trithiocarbonate 10.7,8,15 IR: 1052 cm-1
(C=S). 1H-NMR (400 MHz, CDCl3): d = 0.97 (6H, t), 1.48-
1.62 (4H, m), 1.76-1.83 (4H, m), 3.41 (4H, t). 13C-NMR
(100 MHz, CDCl3): d = 13.62, 21.97, 30.05, 36.55, 224.63.
Di-2-propenyl Trithiocarbonate 11, 12.7,8,15 IR: 1061
cm-1 (C=S). 1H-NMR (400 MHz, CDCl3): d = 4.15 (4H, d),
5.20 (2H, d), 5.32 (2H, d), 5.77-5.85 (2H, m). 13C-NMR
(100 MHz, CDCl3): d = 39.48, 119.83, 131.11, 222.48.
1,3-Dithiolane-2-thione 13.7,15 IR: 1063 cm-1 (C=S).
1H-NMR (400 MHz, CDCl3): d = 3.97 (4H, s). 13C-NMR
(100 MHz, CDCl3): d = 45.06, 227.49.
General procedure for the synthesis of symmetrical
dialkyl trithiocarbonate
The mixture of KOH (3.0 mmol, ~0.17 gr), TBAB
(0.3 mmol, ~0.1 gr) and neutral alumina (1.0 gr) was
ground in a mortar by a pestle and added to a mixture of
alkyl halide or tosylate (1.0 mmol) in CS2 (10 mL), (in
cases that alkyl halide or tosylate wasn’t soluble in CS2, a
few drops of THF was added to the reaction mixture). The
reaction mixture was stirred under reflux conditions. Prog-
ress of the reaction was followed by TLC (n-hexane). On
completion of the reaction, the remaining CS2 was evapo-
rated. Product was extracted by CCl4 (2 ´ 10 mL) and
washed with water (2 ´ 10 mL). The solvent was dried with
CaCl2 and evaporated under reduced pressure. The desired
trithiocarbonate was obtained in good to excellent isolated
yields.

642 J. Chin. Chem. Soc., Vol. 55, No. 3, 2008
Kiasat and Mehrjardi
Dimethyl Trithiocarbonate 14, 15.15 IR: 1071 cm-1
(C=S). 1H-NMR (400 MHz, CDCl3): d = 2.68 (6H, s). 13C-
NMR (100 MHz, CDCl3): d = 21.36, 226.27.
894 and references cited therein.
2. You, Y.-Z.; Hong, C.-Y.; Pan, C.-Y. Chem. Commun. 2002,
2800.
3. Duus, F. In Comprehensive Organic Chemistry; Barton, D.;
Ollis, W. D.; Ed.; Pergamon: New York, 1979; Vol. 3, p 432.
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Diethyl Trithiocarbonate 16.8 IR: 1068 cm-1 (C=S).
1H-NMR (400 MHz, CDCl3): d = 1.48 (6H, t), 3.49 (4H, q).
13C-NMR (100 MHz, CDCl3): d = 12.94, 30.98, 223.04.
Dioctyl Trithiocarbonate 17.8 IR: 1069 cm-1 (C=S).
1H-NMR (400 MHz, CDCl3): d = 0.86 (6H, t), 1.25-1.48
(20H, m), 1.69-1.74 (4H, m), 3.29 (4H, t). 13C-NMR (100
MHz, CDCl3): d = 14.12, 21.82, 26.63, 28.86, 29.32, 30.97,
36.72, 223.52.
6. (a) Sugawara, A.; Hasegawa, K.; Suzuki, K.-I.; Takahashi,
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Bis-[3-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-ethyl]
1
Trithicarbonate 18. IR: 1070 cm-1 (C=S). H-NMR (400
8. Aoyagi, N.; Ochiai, B.; Mori, H.; Endo, T. Synlett 2006, 636.
9. Mahdavi, H.; Tamami, B. React. Funct. Polym. 2005, 64,
179 and references cited therein.
MHz, CDCl3): d = 2.44 (4H, m), 3.62 (4H, t), 3.97 (4H, t),
7.35 (4H, m), 7.44 (4H, m). 13C-NMR (100 MHz, CDCl3):
d = 25.61, 30.12, 32.01, 124.72, 133.62, 134.08, 174.63,
252.84.
10. Xue, S.; Ke, S.; Wei, T.; Duan, L.; Guo, Y. J. Chin. Chem.
Soc. 2004, 51, 983.
Bis-[2-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-ethyl]
1
11. Aly, E.; Abdo, M.; El-Gharably, A. J. Chin. Chem. Soc.
2004, 51, 1013.
Trithicarbonate 19. IR: 1068 cm-1 (C=S). H-NMR (400
12. Mahdavi, H.; Haghani, E.; Malakian, B. React. Funct.
Polym. 2006, 66, 1033 and references cited therein.
13. Iliescu, S.; Ilia, G.; Pascariu, A.; Popa, A.; Plesu, N. Polymer
2006, 47, 6509 and references cited therein.
MHz, CDCl3): d = 3.93 (4H, t), 4.02 (4H, t), 7.66 (4H, m),
7.83 (4H, m). 13C-NMR (100 MHz, CDCl3): d = 35.20,
43.17, 124.22, 135.05, 136.91, 172.00, 232.36.
14. Siva, A.; Murugan, E. J. Mol. Catal. A: Chem. 2005, 241,
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ACKNOWLEDGEMENT
We gratefully acknowledge the support of this work
by the Shahid Chamran University Research Council.
15. Tamami, B.; Kiasat, A. R. J. Chem. Res. 1998, 454.
16. Wertheim, E. J. Am. Chem. Soc. 1926, 48, 836.
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He, L.-N. Appl. Catal., A. 2006, 301, 215. (b) Sugawara, A.;
Hasegawa, K.; Suzuki, K.-I.; Takahashi, Y.; Sato, R. Bull.
Chem. Soc. Jpn. 1987, 60, 435. (c) Sugawara, A.; Shirahate,
M.; Sato, S.; Sato, R. Bull. Chem. Soc. Jpn. 1984, 57, 3353.
Received November 19, 2007.
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