Synthesis of triethoxysilanol

Article abstract of DOI:10.1007/s11172-005-0409-y

Triethoxysilanol was isolated for the first time by hydrolysis of chloro(triethoxy)silane in an organic solvent in the presence of a heterogeneous base and identified as an individual compound. The synthesis of this compound made it possible to study its physicochemical properties and substantially extended its potentialities for the synthesis of hyperbranched polyethoxysiloxanes and functional oligomers.

Full text of DOI:10.1007/s11172-005-0409-y

1350
Russian Chemical Bulletin, International Edition, Vol. 54, No. 5, pp. 1350—1351, May, 2005
Synthesis of triethoxysilanol
ꢀ
V. V. Kazakova, O. B. Gorbatsevich, S. A. Skvortsova, N. V. Demchenko, and A. M. Muzafarov
N. S. Enikolopov Institute of Synthetic Polymeric Materials, Russian Academy of Sciences,
70 ul. Profsoyuznaya, 117393 Moscow, Russian Federation.
Fax: +7 (095) 335 9000. Eꢀmail: valent@ispm.ru
Triethoxysilanol was isolated for the first time by hydrolysis of chloro(triethoxy)silane in an
organic solvent in the presence of a heterogeneous base and identified as an individual comꢀ
pound. The synthesis of this compound made it possible to study its physicochemical properties
and substantially extended its potentialities for the synthesis of hyperbranched polyꢀ
ethoxysiloxanes and functional oligomers.
Key words: chloro(triethoxy)silane, triethoxysilanol, hyperbranched polyethoxysiloxane.
The synthesis of triethoxysilanol was mentioned1 for
thionyl chloride15 in the presence of catalytic amounts
of DMF.
It is known16 that the condensation of hydrolysis prodꢀ
the first time in the late XIX century. However, the reꢀ
ported results were not substantiated and triethoxysilanol
was regarded in scientific literature only as a reactive inꢀ
termediate in the hydrolysis of tetraethoxysilane almost
for the next hundred years.2—5 Progress in analytical techꢀ
niques and especially in 29Si NMR spectroscopy made it
possible to detect the presence of triethoxysilanol in reacꢀ
tion mixtures. The reported6 chemical shift for the Si atom
in triethoxysilanol (δ –76.95) gives some objective grounds
for numerous assumptions. The value obtained agrees with
the previous7,8 assignments and is now universally acꢀ
cepted. As a major intermediate that is stable for at least
several hours in THF, triethoxysilanol is used as the reꢀ
agent AB3 in the synthesis of hyperbranched polyethoxyꢀ
siloxanes.9—11 It should be emphasized that triethoxyꢀ
silanol was isolated as an individual compound in none of
the above studies.
ucts from chlorosilanes is mainly due to heterofunctional
condensation of chlorosilyl groups with hydroxyl ones.
To suppress this process, an excess of water was used for
hydrolysis. The hydrolysis of chloro(triethoxy)silane
(c ≤ 5%) was carried out in THF at 0 °C in the presence of
(NH4)2CO3 as a heterogeneous base. A dilute solution of
chloro(triethoxy)silane was added to a mixture of THF,
water, and the base to give the target triethoxysilanol,
which was isolated by distillation in vacuo in 70% yield
(Scheme 1).
Scheme 1
The instability of triethoxysilanol is associated with
the presence of functional groups of two types (—OH
and —OEt) in its molecule, which can undergo subseꢀ
quent transformations and interact with each other. It is
well known that the reactivities of such functional groups
are determined by the presence of ionic impurities; withꢀ
out them, silanols very sluggishly interact with both the
hydroxy and ethoxy groups of other molecules.12 Even
reactive silanols can be distilled in the absence of ionic
impurities.13
Owing to its chemical structure,12 triethoxysilanol
should be relatively stable in a neutral medium containing
no ionic impurities. The goal of the present work was to
select an appropriate starting reagent and conditions for
its conversion into silanol.
Triethoxysilanol is a transparent mobile liquid,
b.p. 52 °C (1 Torr). Its structure was confirmed by
1H and 19Si NMR and mass spectra and elemental analyꢀ
sis data.
The synthesis and isolation of triethoxysilanol subꢀ
stantially extends the possibilities of obtaining siliconꢀ
containing compounds, including hyperbranched polyꢀ
ethoxysiloxanes. The fact itself of the stability of triethoxyꢀ
silanol is also important, which makes it promising to
develop simpler routes to this compound.
Experimental
We started from chloro(triethoxy)silane prepared in
85% yield by chlorination of tetraethoxysilane14 with
GLC analysis was performed on a 3700 chromatograph (Rusꢀ
sia) with a katharometer as a detector (helium as a carrier gas,
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1309—1310, May, 2005.
1066ꢀ5285/05/5405ꢀ1350 © 2005 Springer Science+Business Media, Inc.

Synthesis of triethoxysilanol
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
1351
column dimensions 2 m × 3 mm, SEꢀ30 stationary phase (5%)
on ChromatonꢀHꢀAW). H NMR spectra were recorded on a
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(32 Torr)).
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1
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This work was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ
08080), the Council for Grants of the President of the
Russian Federation (Program for Support of Leading
Scientific Schools of the Russian Federation, Grant
NSh 1878.2003.3), the Ministry of Industry and Science
(Project No. 41.002.1.1.1403), and the Russian Academy
of Sciences (Program of the Presidium of the Russian
Academy of Sciences "Targeted Synthesis of Compounds
with Desired Properties and Creation of Functional Maꢀ
terials on Their Basis").
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Received March 14, 2005