1070-4272/01/7412-2091 $25.00 C 2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 12, 2001, pp. 2091!2094. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 12, 2001,
Original Russian Text Copyright + 2001 by Voronkov, Baryshok, Kuznetsova.
AND INDUSTRIAL ORGANIC CHEMISTRY
Recovery of Trimethylchlorosilane
from Its Azeotropic Mixture with SiCl
M. G. Voronkov, V. P. Baryshok, and G. A. Kuznetsova
Favorskii Institute of Chemistry, Siberian Division, Russian Academy of Sciences, Irkutsk, Russia
Received July 30, 2001
Abstract-Reaction of tetraethoxysilane with the azeotropic mixture Me
in the presence of cer-
tain cyclic (tetrahydrofuran, dioxane) and acyclic (diethyl ether) ethers, ethanol, or dimethylformamide was
studied with the aim of SiMe
Trimethylchlorosilane is one of the most important
organosilicon monomers. It is used to incorporate
inert terminal groups into oligoorganosiloxanes to be
applied as heat- and frost-resistant oils, lubricants,
liquid dielectrics, heat carriers, hydrophobizing com-
ponents, lacquers, and enamels; also, it is widely used
as trimethylsilylating agent in organic and organo-
metallic chemistry .
Direct synthesis of methylchlorosilane by reaction
Cl with the Si3Cu contact mass yields up to
10% of the azeotropic mixture Me
The majority of methods proposed for its separation
[azeotropic distillation with acetonitrile; partial hy-
drolysis or alcoholysis; chemical binding of SiCl
the form of solid complexes with tertiary aliphatic and
aromatic amines, formamide, and dimethylformamide
(DMF), insoluble in the reaction medium; fluorination
in aqueous solution] have a number of drawbacks: low
yield of Me
SiCl, strongly corrosive medium, gela-
tion, and formation of abundant by-products whose
utilization requires sophisticated procedures .
Simple procedures for Me
SiCl recovery from the
azeotropic mixture Me
have been devel-
oped only recently. They are based on binding of SiCl
with organylalkoxysilanes, ethyl silicate, and bottoms
from its synthesis in the presence of alcohols, traces
of moisture, metal salts, and acid catalysts [6, 7].
The reaction between alkoxy- and chlorosilanes
occurs either as exchange of an alkoxy group for a
halogen atom [scheme (1), a] or as heterofunctional
condensation [scheme (1), b] :
+ ROSiÄÄSiÄX+ÄSiÄOR 6 RX + ÄSiÄOÄSiÄ.
Both pathways, a and b, are accelerated in the pres-
ence of HCl. As a rule, the contribution of pathway b
becomes appreciable at elevated temperatures.
Reaction of SiCl
yields a mixture of OEt3Cl exchange products .
In the presence of 0.24 wt % ethanol, this reaction is
76397% complete in 20370 h at molar ratio SiCl
= 1 : 3 and 20322oC .
A procedure has been developed for separation of
a technical azeotropic mixture Me
impurities by binding
with tetraethoxysilane to form ethoxychloro-
silanes in a selective reaction in the presence of initi-
ators, with subsequent fractionation of the reaction
mixture [12, 13].
To this end, a technical azeotropic mixture was
brought into reaction with Si(OEt)
in the presence of
0.2310 wt % DMF, tetrahydrofuran (THF), dioxane,
diethyl ether, or ethanol. The reaction was performed
at 20325oC or at refluxing (60365oC) for 2372 h
until conversion of SiCl
into ethoxychlorosilanes and
-siloxanes was complete:
Si 6 Cl
3 ! k ! p
where n, m, k, p =133.
With the above initiators, it was possible to recover
6388% of Me
SiCl from the reaction mixture. In the
presence of DMF, the mixture undergoes partial tar-
ring due to low thermal stability of DMF3SiCl