PREPARATION OF DIMETHYL CARBONATE FROM METHANOL AND CARBON DIOXIDE IN THE PRESENCE OF ORGANOTIN COMPOUNDS

Article abstract of DOI:10.1135/cccc19942116

Dibutyltin dialkoxides react with methanol and carbon dioxide to give dimethyl carbonate in 60 to 220 mole percent yields with respect to organotin compound.The higher yields of the carbonate (150 up to 330 mole percent) have been achieved with the use of chemical scavengers of the reaction water.

Full text of DOI:10.1135/cccc19942116

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116
Kizlink, Pastucha:
PREPARATION OF DIMETHYL CARBONATE FROM METHANOL AND
CARBON DIOXIDE IN THE PRESENCE OF ORGANOTIN COMPOUNDS
Juraj KIZLINK and Ivan PASTUCHA
Department of Organic Technology,
Slovak Technical University, 812 37 Bratislava, The Slovak Republic
Received January 26, 1994
Accepted June 7, 1994
Dibutyltin dialkoxides react with methanol and carbon dioxide to give dimethyl carbonate in 60 to
2
20 mole % yields with respect to the organotin compound. The higher yields of the carbonate (150
up to 330 mole %) have been achieved with the use of chemical scavengers of the reaction water.
1
2
In the preceding study the synthesis of dimethyl carbonate by the title reaction was
effected in the presence of a series of organotin compounds. Their effectiveness has
been compared with the use of solid carbon dioxide (dry ice) as one of the reaction
components. As the relatively low yields of dimethyl carbonate obtained by this way
might result from the moisture introduced by the dry ice, in the present work the di-
methyl carbonate synthesis was carried out with the use of gaseous carbon dioxide and
3
,4
in the presence of chemical scavengers of water .
EXPERIMENTAL
Chemicals. Methanol (p. a., 99.8% and 0.2% H O, Lachema Brno, The Czech Republic) was dried
2
over sodium sulfate and calcium hydride and distilled through a column filled with sodium, yielding
the product containing max. 0.01% H O. Pressurized carbon dioxide (pure, min. 98.5%, max. 0.5%
2
H O, Tetragas Sala, The Slovak Republic) was used as obtained. The water content in both reagents
2
was determined by the Fischer method. Dicyclohexylcarbodiimide (DCC) and trimethyl phosphate
(
TMP) (both chemical purity grade, min. 99%, Aldrich, U.K.) were used as chemical scavengers of
1
water. The other chemicals were the same as in our previous work .
Procedure. All the experiments were carried out in a 150 ml-stainless steel autoclave equipped
with magnetic stirring. The reactor was immersed into the electrically heated and temperature con-
trolled silicone bath. The autoclave was charged with 40 ml (32 g, 1 mol) of methanol, followed by
1
0 mmol of organotin compound, 8 g of drying agent (Na SO , MgSO , molecular sieve and others),
2 4 4
eventually by 5 mmol of iodine as the initiator or 50 mmol of the water scavenger (DCC or TMP).
After purging with carbon dioxide, the autoclave was pressurized to 0.5 MPa, warmed up to 150 °C
(
by which the pressure increased to 2.5 MPa), and the reaction mixture was stirred at this tempera-
ture for 20 h. After that, the reaction mixture cooled to room temperature was filtered and analyzed
by GLC, using toluene as the internal standard. Chromatographic analyses were carried out under the
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

Short Communication
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same conditions as in the previous work1 (SE-30, SE-31, SE-30l, and Reoplex-400 as stationary
phases). The results are presented in Table I.
RESULTS AND DISCUSSION
The inspection of data presented in Table I shows that when compared to our previous
1
work the use of gaseous carbon dioxide, the lower pressure and the longer reaction
time results in the dimethyl carbonate yields greater by 30 to 50 per cent, and that in
TABLE I
Activity of organotin compounds in the reaction of carbon dioxide with methanol to give dimethyl
carbonate
a
(MeO)2CO
yield , %
Compound
Addend
b
150 °C, 2.5 MPa (total pressure), 20 h
Bu Sn(OMe)
none
TMP
DCC
none
TMP
DCC
none
TMP
DCC
none
TMP
DCC
81
103
118
115
118
170
90
2
2
Bu Sn(OEt)
2
2
Bu Sn(OPr)
2
2
130
170
220
180
317
Bu Sn(OBu)
2
2
180 °C, 2.8 MPa (total pressure), 20 h
Bu Sn(OMe)
none
none
none
TMP
DCC
none
TMP
DCC
100
133
110
140
177
222
235
333
2
2
Bu Sn(OEt)
2
2
Bu Sn(OPr)
2
2
Bu Sn(OBu)
2
2
a
b
TMP, DCC, 50 mmol of each, the reaction activated by adding 5 mmol of iodine as the activator.
Expressed as mole % per mol of organotin compound. The dibutyl tin alkoxide is partially decom-
posed to Bu SnO (Eq. (A)) during the reaction.
2
Collect. Czech. Chem. Commun. (Vol. 59) (1994)

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Kizlink, Pastucha:
the 60 to 220 mole % range with respect to the organotin compound. Nevertheless, the
2
yields are still lower compared to those reported earlier by other authors . The use of
iodine as the initiator turned out to be advantageous also in the present reaction (for
1
1
further compounds see ref. ). The favourable effect of increased temperature was here
less pronounced. The formation of alcohols by the decomposition of dibutyltin dialkoxides
by water (Eq. (A)) was within the range 16 to 55 mole % for dibutyltin diethoxide, 17
to 62 mole % for the dipropoxide, and 22 to 77 mole % for the dibutoxide. Besides
formation of dimethyl carbonate, any other thermal decomposition of dibutyltin dialkoxides
such as formation of the ethers according to Eq. (B) has not been observed.
Bu Sn(OR) + H O
Bu SnO + 2 ROH
(A)
(B)
2
2
2
2
Bu Sn(OR)
Bu SnO + R O
2
2
2
2
The main problem of the synthesis is the removal of the reaction water. Of the inor-
ganic drying agents, MgSO proved to be suitable, the less so Na SO and molecular
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2
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sieves of different types (Calsit, Nalsit, Potasit). Calcium oxide induced a considerable
decomposition of the dimethyl carbonate formed. The yields of dimethyl carbonate can
however be significantly increased in the presence of chemical scavengers of the reac-
tion water. The best ones turned out to be trimethyl phosphate (TMP), giving 100 up to
2
30 mole % yields (also with added cation exchanger) and especially dicyclohexyl-
carbodiimide (DCC), with 160 up to 330 mole % yields (Table I). These water
scavengers should be used in at least twofold molar excess with respect to the organotin
compound. The fivefold amount of the scavengers has not any additional favourable
effect. The water content in the reaction mixture after completion of the reaction was
0
.05 to 0.10 wt.% with the use of inorganic drying agents, while the above scavengers
reduced it to max. 0.05% with TMP and to max. 0.02% with DCC. By this way of
water removal, the results comparable with – and in some respects even better than –
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those reported earlier by other authors have been achieved in the present study.
REFERENCES
1
2
3
. Kizlink J.: Collect. Czech. Chem. Commun. 58, 1399 (1993).
. Yamazaki N., Nakahama S.: Ind. Eng. Chem., Prod. Res. Dev. 18, 249 (1979).
. Parkins A. W., Poller R. C.: An Introduction to Organometallic Chemistry. MacMillan, London
1
986.
. Elsenbroich C., Salzer A.: Organometallics, a Concise Introduction. VCH Verlag, Weinheim
992.
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1
Translated by J. Hetflejs.
Collect. Czech. Chem. Commun. (Vol. 59) (1994)