Russian Journal of General Chemistry, Vol. 75, No. 12, 2005, pp. 1927 1929. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 12, 2005,
pp. 2018 2020.
Original Russian Text Copyright
2005 by Voronkov, Boyarkina, Gebel’, Albanov, Basenko.
Cleavage of the C Si bond in Trifluoro(phenyl)silane
with Aliphatic Alcohols
M. G. Voronkov, E. V. Boyarkina, I. A. Gebel’, A. I. Albanov, and S. V. Basenko
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
Received May 25, 2005
Abstract Trifluoro(phenyl)silane reacts with aliphatic alcohols under reflux. The reaction involves not
only Si F bond cleavage to form ethoxyfluoro(phenyl)silanes, but also C Si bond cleavage to form benzene
and alkoxyfluoro- and tetraalkoxysilanes. The formation of the latter products was proved by 19F and 29Si
NMR spectroscopy and also by model disproportionation reactions of trifluoro(phenyl)silane with trimethoxy-
(phenyl)-, tetramethoxy-, or tetraethoxysilanes.
It has long been believed that alcoholysis of tri-
fluoro(phenyl)silane involves no other processes than
Si F bond cleavage. Thus, as shown in [1], the reac-
tion of trifluoro(phenyl)silane with ethanol results in
exclusive formation of diethoxy(phenyl)silane,
whereas the third fluorine atom remains completely
intact.
simultaneously with ethoxydifluoro(phenyl)silane.
The latter was identified after prolonged boiling of
the reaction mixture (7 14 h) even with a double
excess of ethanol. The reaction with methanol occurs
in a similar way.
With higher alcohols (hexanol and octanol), the
yield of C Si cleavage products, i.e. alkoxyfluoro-
silanes, is much higher. This is probably explained
not only by steric reasons, but also by the fact that
higher alcohols (R = C6H13, C8H17) are stronger bases
and weaker Lewis acids than lower alkanols (R = CH3,
C2H5), according to Komlett Taft parameters [4].
The potentiometric titration curve of trifluoro-
(phenyl)silane in DMSO with 0.1 N sodium ethylate
in ethanol contains three potential jumps correspond-
ing to successive substitution of all the thee fluorine
atoms by ethoxy groups [2].
We found that the reaction of trifluoro(phenyl)-
silane with aliphatic alcohols under reflux involves
no only Si F [scheme (1)], but also C Si bond
cleavage to form benzene and alkoxyfluoro- and tetra-
alkoxysilanes by scheme (2).
In the case of R = CH3, C2H5, prolonged (7 14 h)
boiling of the reaction mixture cause alkoxyfluoro-
silanes formed together with alkoxyfluoro(phenyl)-
silanes in 10 15% yield to disproportionate to form
the most stable trialkoxyfluorosilanes and SiF4.
C6H5SiF(OR)2 + C6H5SiF2(OR),(1)
C6H5SiF3 + ROH
By contrast, in a low-boiling polar solvent, such as
HCCl3, the reaction of trifluoro(phenyl)silane with
hexanol gives rise to fluoro(hexyloxy)phenylsilanes
C6H5Si(OC6H13)nF3 n, n = 1, 2.
(2)
(RO)nSiF4 n + C6H6,
R = CH3, C2H5, C4H9, C8H17; n = 1, 2; m = 0 4.
In all the cases studied, catalytic amounts of tri-
ethylamine (0.01 0.1 mol%) accelerate the reactions
not changing their direction.
Excess alcohol does not change the composition of
the products, that depends on the nature of alkyl
substituent R. Thus, the reactions of trifluoro(phenyl)-
silane with methanol and ethanol primarily take path
(1) and give rise to alkoxyfluoro(phenyl)silanes. Small
amounta of alkoxyfluorosilanes are present in the re-
action mixture only the initial period of the reaction.
On prolonged boiling of the reaction mixture (14
28 h), gaseous tetrafluorosilane evolves. The latter is
trapped with DMSO and converts into a crystalline
adduct 2(Me2SO) SiF4 we described previously [3].
The above-described reactions all involve forma-
tion of a white powdery precipitate insoluble in or-
dinary solvents. The composition of the precipitate
corresponds to the formula (F2SiO)n. Therewith, as
the length of the hydrocarbon chain in the alcohol
increases (from R = CH3 to R = C8H17), the yield of
this polymer increases to reach 20 wt% of the start-
ing trifluoro(phenyl)silane at R = C6H13. With R =
CH3 and C2H5, the yield of the polymer is as low as
Diethoxyfluoro(phenyl)silane is formed almost
1070-3632/05/7512-1927 2005 Pleiades Publishing, Inc.