1070-4272/02/7507-1196$27.00C2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 7, 2002, pp. 1196 !1197. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 7,
2002, pp. 1219!1220.
Original Russian Text Copyright + 2002 by Gorshkov, Kopylov, Markacheva, Polivanov.
Solvent Regeneration in Direct Synthesis of Alkoxysilanes
A. S. Gorshkov, V. M. Kopylov, A. A. Markacheva, and A. N. Polivanov
State Research Institute of Chemistry and Technology of Organoelement Compounds,
State Scientific Center of the Russian Federation, Moscow, Russia
Received July 6, 2001; in final form, April 2002
Abstract-A procedure was developed for regeneration of Termolan, solvent used in synthesis of alkoxy-
silanes, involving its treatment with ethanol to remove alkoxysilanes.
Alkoxysilanes are synthetic precursors of various
organosilicon products. They are used for preparing
organosilicon oligomers, carbofunctional products,
compounds, high-purity silicon dioxide for fiber
optics, etc. Triethoxysilane is also used for producing
monosilane and semiconductor-grade silicon. Tetra-
ethoxysilane and ethyl silicate prepared from it are
used as binders in fabrication of molds for precision
casting [1, 2].
Direct synthesis of alkoxysilanes is based on the
reaction of silicon with alcohols. With copper chloride
as catalyst, the major products are trialkoxysilanes
Si + 3ROH $ SiH(OR)
With base catalysts and with copper or silver salts
as cocatalysts, tetraalkoxysilanes Si(OR)
 (R is an alkyl group).
The reaction is performed in a high-boiling solvent,
e.g., in polyaromatic oils, alkylbenzene, etc. [6, 7].
In this work, direct synthesis of triethoxysilane was
performed in alkylated naphthalene (Termolan , an
analog of Therminol 59 and Therminol 60 [6, 9]).
Direct synthesis of alkoxysilanes is accompanied
by side processes yielding water, which inhibits the
main reactions and hydrolyzes alkoxysilanes:
(n + 1)Si(OR)
O $ Si
where n >1.
The occurrence of reaction (2) results in the accum-
ulation of oligoethoxysiloxanes. They should be re-
moved from the solvent at regular intervals for its
regeneration and reuse.
Procedures are known for the solvent regeneration
by treatment with boron derivatives [9, 10] or organic
acids . However, in this procedure, oligoethoxy-
siloxanes decompose to form solid silicon compounds.
Here we propose an extraction procedure for sol-
vent regeneration to remove ethoxysiloxanes after the
direct synthesis. The siloxanes were extracted with
ethanol. The procedure was optimized using model
systems alcohol3ethoxysiloxanes3Termolan. As a
source of ethoxysiloxanes we used ethyl silicate from
which the low-boiling fraction was preliminarily
removed by distillation. The silicon content in the
initial ethoxysiloxanes was 14322%.
First, we prepared a solution of siloxanes in the
solvent, and then added alcohol. The contents were
thoroughly mixed, with the subsequent phase separa-
tion. The siloxanes passed to the alcohol fraction.
Experiments were performed at 20oC.
The results are shown in the figure. It is seen that,
at the initial concentration of ethoxysilanes in Termo-
lan of up to 30%, the alcohol/Termolan volume ratio
of 0.630.8 is sufficient to virtually completely remove
the siloxanes from the solvent by extraction.
The density of siloxanes is higher than that of the
initial Termolan, and at low amounts of alcohol added
for extraction the concentration of siloxanes in the
alcohol becomes fairly high, with the density of the
alcohol phase becoming higher than the density of the
solvent phase. In this case, the lower layer was an
alcoholic solution of siloxanes, and the upper layer
was the regenerated solvent. With a larger amount of
alcohol taken for extraction, the concentration of
siloxanes in the alcohol phase was lower, and the al-
cohol phase having lower density formed the upper
layer, and the regenerated solvent, the lower layer.
The suggested regeneration procedure was tested