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Kilburn, Keith Douglas (1955) Preparation and properties of phenyl substituted alkoxysilanes. Doctoral thesis, Northern Polytechnic.
The formation and proporties of tetra-alkoxysilanes, (RO)4Si, where R contains one or two phenyl groups, have been studied to obtain information relating to the effect of the position of the phenyl group in the alkyl group, and so to provide data for correlation with phosphorus halide and thionyl halide systems, already studied in some detail. In those examples where the phenyl group is not attached to the alcoholic carbon atoms, the alcohols behaved in a general way as does n-butanol when silicon tetrachloride (1 mol.) is allowed to react with alcohol (4 mols.). Under these conditions, those alcohols in which the phenyl is directly attached to the alcoholic carbon atom tend to yield alkyl chloride and silica, although benzyl alcohol tends, to behave like n-butanol. Cinnamyl alcohol was exceptional. In phenyl group in the alkyl group, and so to provide data for correlation with phosphorus halide and thionyl halide systems, already studied in some detail. In those examples where the phenyl group is not attached to the alcoholic carbon atoms, the alcohols behaved in a general way as does n-butanol when silicon tetrachloride (1 mol.) is allowed to react with alcohol (4 mols.). Under these conditions, those alcohols in which the phenyl is directly attached to the alcoholic carbon atom tend to yield alkyl chloride and silica, although benzyl alcohol tends, to behave like n-butanol. Cinnamyl alcohol was exceptional.
In the presence of pyridine all the primary and secondary alcohols studied, gave tetraester and no alkyl chloride: 4ROH + 4C5H5N + SiC14 = 4C5H5N.HC1. With tertiary alcohols, alkoxylation was limited because of steric hindrance.
In the examples of tetra-alkoxysilanes derived from alcohols of ordinary reactivity, i.e. those with a phenylgroup not attached directly to the alcoholic carbon atom, dealkylation by hydrogen chloride and hydrogen bromide was slow and resulted in the formation of alcohol. However, the silanes or reactive alcohols gave alkyl chloride, although it was not discerned whether this was produced via the alcohol (which reacted with hydrogen halide) or by a direct reaction.
(RO)4Si + 4HC1 = 4ROH + (SiC14) and ROH + HC1 RC1 + H2O with SiC14 + 4H2O ROH + HC1 RC1 + H2O or (RO)4Si + 4HCl Si(oH)4 4HC1 4HC1 + Si(OH)4
Proportionation of the tetra-alkoxysilanes with silicon tetrachloride were quite uniformly slow, giving either a mixture of chlorosilanes or alkyl chloride and silica.
In order to study these effects more conveniently the trimethylalkoxysilanes were examined:- with hydrogen chloride they gave trimethylalkoxysilanes and alcohol, the latter in a some cases reacting further to give alkyl chloride and water, and with silicon tetrachloride the pure alcohol-free trimethylalkoxysilanes gave alkoxychlorosilanes or tetraester and trimethylchlorosilane.
This last process led to a study of what appears to be a general reaction whereby phosphorus sulphur, silicon and boron may be alkoxylated under mild conditions by the interaction of a trimthylalkoxysilane and the appropriate non-metalic halide.
A few triphenylalkoxysilanes were investigated for a similar purpose but found to be inferior.
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