Reaction between epoxides and carbon disulfide under hydrotalcite catalysis: Eco compatible synthesis of cyclic dithiocarbonates

Article abstract of DOI:10.1055/s-2007-1000820

Cyclic dithiocarbonates were prepared in good yield and excellent selectivity through an environmental acceptable methodology involving the reaction of substituted epoxides with carbon disulfide under hydrotalcite catalysis. The catalyst can be recovered by filtration and reused several times. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-1000820

PAPER
53
Reaction between Epoxides and Carbon Disulfide under Hydrotalcite
Catalysis: Eco Compatible Synthesis of Cyclic Dithiocarbonates
Reaction between
a
E
poxides
i
and Ca
m
rbon
D
isulfide unde
o
r
H
ydrotalc
i
n
te Catalysis do Maggi,* Clara Malmassari, Chiara Oro, Roberto Pela, Giovanni Sartori, Laura Soldi
‘Clean Synthetic Methodologies Group’, Dipartimento di Chimica Organica e Industriale , Università and Consorzio Interuniversitario
‘La Chimica per l’Ambiente’ (INCA) UdR di Parma 2, Viale G.P. Usberti 17A, 43100 Parma, Italy
Fax +39(0521)905472; E-mail: raimondo.maggi@unipr.it
Received 11 July 2007; revised 10 October 2007
geneous catalysis.4,5 Based upon these insights and due to
the fact that, to the best of our knowledge, this process has
never been studied under heterogeneous catalysis, the pur-
pose of this work was to test the ability of commercially
available basic solid catalysts to selectively promote the
synthesis of dithiocarbonates 3; the reaction shows 100%
atom economy:6 all the atoms of the two starting reagents
are incorporated into the final product.
Abstract: Cyclic dithiocarbonates were prepared in good yield and
excellent selectivity through an environmental acceptable method-
ology involving the reaction of substituted epoxides with carbon
disulfide under hydrotalcite catalysis. The catalyst can be recovered
by filtration and reused several times.
Key words: catalysis, green chemistry, heterocycles, heteroge-
neous catalysis, ring expansion.
The activity of two kinds of hydrotalcites,7 namely Pural
MG30 and MG70, and two basic oxides, namely alumina
and magnesium oxide (1.0 g each) was tested in a model
reaction between 1,2-epoxy-3-phenoxypropane (1a, 10
mmol) and carbon disulfide (2, 3 mL, utilized as solvent
and reagent) at 50 °C for three hours. The results are re-
ported in Table 1.
The explosive development of heterogeneous catalysis
over the past several years has led to a detailed re-exami-
nation of the most important synthetic processes by organ-
ic chemists.1 In fact, the use of heterogeneous catalytic
systems shows undoubted advantages from both an eco-
nomic and environmental point of view;2 these advantag-
es are more noteworthy if the heterogeneous catalysis is
applied to the preparation of fine chemicals, a chemistry
sector showing an E-factor value (kg of byproducts/kg of
product) up to 50.3
Table 1 Synthesis of 5-(Phenoxymethyl)-1,3-oxathiolane-2-thione
(3a) Promoted by Heterogeneous Basic Catalysts
S
O
basic catalyst
50 °C, 3 h
Cyclic dithiocarbonates 3 are important compounds uti-
lized for the preparation of polymers;4 usually they are
synthesized by reacting epoxides and carbon disulfide.
The process can also afford the two isomers 4 and 5, the
trithiocarbonate 6, and the episulfide 7 (Scheme 1).
O
S
+
CS2
PhO
PhO
1a
2
3a
Entry
Catalyst
none
Yield (%)
Selectivity (%)
S
1
2
3
4
5
6
2
84
67
21
16
33
99
99
98
98
99
98
O
O
S
hydrotalcite MG30
hydrotalcite MG70
alumina
+
CS2
+
R1
R2
R1
R2
1
2
3
S
O
S
MgO
S
S
O
S
S
S
S
+
+
+
R1
R2
MgO/alumina (30:70)
R1
R2
R1
R2
R1
R2
4
5
6
7
All the catalysts were able to promote the reaction with
high selectivity affording exclusively isomer 3a, whose
structure was assigned based on FT-IR, 1H NMR, and MS
data. Interestingly hydrotalcites MG30 and MG70, mate-
rials with magnesium oxide/alumina ratios of 30:70 and
70:30 respectively, performed the reaction in better yields
than alumina, magnesium oxide, and a 30:70 mixture of
magnesium oxide and alumina, confirming a synergic ef-
fect of the two oxides inside the hydrotalcite framework.
In our opinion the plausible mechanism involves activa-
tion of carbon disulfide by nucleophilic attack from hy-
Scheme 1 Possible products formed in the reaction between epox-
ides and carbon disulfide
By choosing convenient reaction conditions and by carry-
ing out the process in the presence of basic catalysts, the
selective production of 3 has been performed using homo-
SYNTHESIS 2008, No. 1, pp 0053–0056
x
x
.
x
x
.2
0
0
7
Advanced online publication: 07.12.2007
DOI: 10.1055/s-2007-1000820; Art ID: T10707SS
© Georg Thieme Verlag Stuttgart · New York

54
R. Maggi et al.
PAPER
drotalcite giving a supported xanthate anion that
subsequently adds to the epoxide moiety.5c
Table 2 Effect of the Amount of Catalyst in the Synthesis of
5-(Phenoxymethyl)-1,3-oxathiolane-2-thione (3a) at 50 °C
Before carrying out experiments to optimize the reaction
conditions, we decided to perform the Sheldon test8 on the
reaction carried out with hydrotalcite MG30 in order to
verify the real heterogeneity of the process. Thus the reac-
tion mixture was filtered at 50 °C after 1.5 hours (when 3a
was produced in 44% yield) and the filtrate was further
heated at 50 °C for 1.5 hours. Product 3a was detected in
46% total yield (44% + 2%). In contrast, addition of both
1,2-epoxy-3-phenoxypropane (1a, 10 mmol) and carbon
disulfide (3 mL) to the recovered solid catalyst and heat-
ing at 50 °C for three hours afforded the dithiocarbonate
3a in 83% yield: these results confirm that the reaction re-
ally occurs on the surface of the hydrotalcite catalyst.
Entry
MG30
amount (g)
Yield (%)
of 3a
Selectivity (%)
of 3a
1
2
3
4
0.25
0.50
0.75
1.00
72
89
99
99
98
98
99
99
The process was then applied to various epoxides
(Table 3) using 0.75 g of hydrotalcite MG30 for 10 mmol
of epoxide and performing the reactions at 50 °C for five
hours with carbon disulfide as solvent reagent (3 mL).
The next step was to optimize the reaction conditions; to
this end the following three parameters were considered:
reaction time, reaction temperature, and amount of cata-
lyst.
The corresponding dithiocarbonates 3a–d,g were ob-
tained in good yields without the formation of possible
byproducts 4–7. Only 1,2-epoxydodecane (1f) gave 3f in
low yield (Table 3, entry 6); the low reactivity of such ep-
oxides was already evidenced for reactions carried out un-
der homogeneous conditions.5c Interestingly, selective
monofunctionalization of 1,2,3,4-diepoxybutane (1g) was
observed and the corresponding 5-oxiran-2-yl-1,3-oxa-
thiolane-2-thione (3g) was isolated in 87% yield and with
100% selectivity (Table 3, entry 7).
Firstly the model reaction was analyzed by examining the
yield of product 3a versus time; the reaction was carried
out over six hours and GC analysis was performed every
30 minutes (Figure 1).
Table 3 Synthesis of Variously Substituted Dithiocarbonates Pro-
moted by Hydrotalcite MG30
S
S
O
MG30
+
CS2
O
S
+
S
O
R1
R2
50 °C, 5 h
R1
R2
R1
R2
1
2
3
4
Entry R1
R2
Products Yield
Ratio
3/4
Figure 1 Reactivity of 1,2-epoxy-3-phenoxypropane (1a) and car-
bon disulfide in the presence of hydrotalcite MG30 at 50 °C as a
function of time
3, 4
(%)
99
94
80
75
83
25
87
1
2
3
4
5
6
7
CH2OPh
CH2OBn
CH2Oi-Pr
–(CH2)4–
Ph
H
H
H
a
100:0
100:0
100:0
Results show that the maximum production of 3a occurs
during the first three hours (~84% yield, 99% selectivity);
then the reaction proceeds slowly and the yield reaches its
maximum value (~99% yield, 99% selectivity) after five
hours.
b
c
d
e
H
H
H
62:38a
100:0
In a second series of experiments the reaction temperature
was examined. To this end the process was carried out at
both 40 °C and 30 °C for five hours, but a dramatic drop
in yield was observed (58% and 8%, respectively).
n-C10H21
O
f
g
100:0
Finally, the effect of the amount of catalyst on the reaction
yield was also taken into account with the aim of examin-
ing the possibility of using the minimum amount of hy-
drotalcite catalyst. To this end, comparative experiments
a The isomers could not be separated. Ratio of 3e/4e was estimated by
1H NMR spectra.
with different amounts of MG30 were performed Styrene oxide 1e exhibited a particular reactivity, which
(Table 2).
can be ascribed to the presence of the phenyl group that
accelerates ‘a cleavage’ through the formation of a stable
benzylic cation.9 This reactivity is strongly dependent on
the reaction temperature (Scheme 2).
As can be concluded from the results depicted in Table 2,
lowering the amount of hydrotalcite MG30 from 1.00 to
0.75 g gives the same quantitative yield of 3a, however,
lowering the amount of catalyst further reduces the yield.
Synthesis 2008, No. 1, 53–56 © Thieme Stuttgart · New York

PAPER
Reaction between Epoxides and Carbon Disulfide under Hydrotalcite Catalysis
55
3J = 10.8, 4.5 Hz, 1 H, OCH2CH), 3.84 (dd, 3J = 10.8, 4.9 Hz, 1 H,
OCH2CH), 4.58 (d, J = 11.9 Hz, 1 H, CH2Ph), 4.63 (d, J = 11.9
Hz, 1 H, CH2Ph), 5.2–5.3 (m, 1 H, CH), 7.2–7.4 (m, 5 H, Harom).
13C NMR (75 MHz; CDCl3/TMS): d = 36.1, 68.5, 73.7, 89.2, 127.8,
128.1, 128.5, 137.1, 211.9.
S
S
3
3
S
S
O
S
S
O
S
+
+
O
S
S
O
+
3e
4e
Ph
Ph
S
Ph
Ph
3e
4e
MS (EI, 70 eV): m/z (%) = 91 (100), 107 (40), 147 (10), 240 (3)
S
S
[M+].
50 °C
75 °C
Ph
Anal. Calcd for C11H12O2S2: C, 43.60; H, 5.04; S, 26.72. Found: C,
43.42; H, 4.98; S, 26.56.
Ph
O
6e
7e
+ CS2
100 °C
S
Ph
25 °C
5-(Isopropoxymethyl)-1,3-oxathiolane-2-thione (3c)
Bp 135–137 °C.
1H NMR (300 MHz, CDCl3/TMS): d = 1.12 (dd, 3J = 6.1, 1.2 Hz, 6
H, 2 CH3), 3.5–3.8 (m, 5 H, OCH2CHCH2S), 5.1–5.3 [m, 1 H,
CH(CH3)2].
13C NMR (75 MHz, CDCl3/TMS): d = 21.9, 36.1, 66.7, 72.7, 89.9,
212.4.
S
S
NO REACTION
6e
Ph
Scheme 2 Product distribution as a function of temperature in the
reaction between styrene oxide and carbon disulfide
MS (EI, 70 eV): m/z (%) = 57 (100), 74 (91), 131 (51), 192 (79)
At 50 °C 3e and 4e are obtained in 83% total yield (3e/
4e = 62:38), by carrying out the reaction at 75 °C, byprod-
ucts 6e and 7e were also produced (91% total yield, 3e/4e/
6e/7e = 43:13:22:22) and by increasing the temperature
up to 100 °C, the trithiocarbonate 6e was isolated as the
sole reaction product (98% yield).
[M+].
Anal. Calcd for C7H12O2S2: C, 43.79; H, 6.30; S, 33.40. Found: C,
43.60; H, 6.38; S, 33.45.
5-Oxiran-2-yl-1,3-oxathiolane-2-thione (3g)
Bp 118–119.5 °C.
Finally, we faced the problem of catalyst recycling; at the
end of the model reaction the crude was filtered and the
catalyst, after washing with carbon disulfide, was reused
for at least four times affording product 3a with the same
high yield (reaction: 99%; 1st recycle: 98%; 2nd recycle:
97%; 3rd recycle: 99%; 4th recycle: 98%).
1H NMR (300 MHz, CDCl3/TMS): d = 2.9–3.0 (m, 2 H, OCH2),
3.3–3.4 (m, 1 H, OCH2CH), 3.6–3.7 (m, 2 H, SCH2), 5.0–5.2 (m, 1
H, SCH2CH).
13C NMR (75 MHz, CDCl3/TMS): d = 35.9, 44.2, 51.0, 89.1, 210.9.
MS (EI, 70 eV): m/z (%) = 57 (35), 71 (39), 162 (100) [M+].
Anal. Calcd for C5H6O2S2: C, 37.03; H, 3.73; S, 39.59. Found: C,
36.96; H, 3.65; S, 39.68.
In conclusion we have shown for the first time that a het-
erogeneous catalyst, namely commercially available hy-
drotalcite MG30, can be successfully and efficiently
utilized for the highly selective synthesis of cyclic dithio-
carbonates. Moreover, the use of carbon disulfide as sol-
vent–reagent, the high atom economy, and the possibility
of recycling the catalyst for several runs, make this ap-
proach practical and environmentally acceptable.
Acknowledgment
The authors thank the support of the Ministero dell’Istruzione,
dell’Università e della Ricerca (MIUR), Italy. The authors are also
grateful to the Centro Interdipartimentale Misure (CIM) for the use
of NMR instruments. The authors are indebted with Dr. Alexander
Malyschew (SASOL-Germany) for donation of the hydrotalcite
samples.
All compounds were purchased from Aldrich and used without fur-
1
ther purification. H (300 MHz) and 13C (75 MHz) NMR spectra
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Synthesis 2008, No. 1, 53–56 © Thieme Stuttgart · New York

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PAPER
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