GB789264A - Polysiloxanes - Google Patents

Abstract

A composition useful as a lubricant comprises a mixture of lower polyalkoxypolysiloxanes, the alkoxy groups containing from 1 to 16 carbon atoms. The mixture, prepared by hydrolysing a mixture of alkoxyhalosilanes (see Group IV (a)), comprises mainly hexa-alkoxy disiloxane with minor proportions of tri-, tetra- and higher siloxanes and orthosilicates. In the examples, the alkoxy group is 2-ethylbutoxy.ALSO:Mixtures of lower polyalkoxypolysiloxanes are prepared by reacting an alkyl alcohol containing 1 to 16 carbon atoms with a silicon tetrahalide to form a mixture of alkoxy halosilanes, the molar ratio of alcohol to halide being more than 2 : 1, but less than 4 : 1, removing hydrogen halide formed in the reaction, reacting the mixture of alkoxy halosilanes with water in the presence of a - or b -picoline in amounts stoichiometrically equal to the halogen of the alkoxyhalosilanes, and separating the polyalkoxypolysiloxanes from the liquid picoline hydrohalide salt formed in the reaction. The products comprise mainly hexa-alkoxydisiloxanes, with minor proportions of tri-, tetra- and higher siloxanes and orthosilicates. Preferred alcohols in the reaction are primary and secondary, and mixtures thereof may be employed. Silicon tetrachloride, bromide or iodide may be used. Reaction between them in the initial stage is preferably effected below 0 DEG C., e.g. from - 20 DEG to - 10 DEG C. The hydrogen halide may be removed by blowing through nitrogen. Temperatures in the second stage are preferably from 70 DEG to 250 DEG C. but may be considerably lower. A solvent such as benzene or toluene may be present. The picoline hydrohalide salt must be in the liquid state when separated and this is ensured by maintaining the temperature above its melting-point, e.g. above 71 DEG C. for a -picoline. It is separated by decantation. In the examples: (1) SiCl4 (3 mols.) is reacted with 2-ethylbutanol (9.6 mols.) and the product is hydrolysed as above to give a mixture containing 64 per cent hexa-(2-ethylbutoxy)-disiloxane, 16 per cent 2-ethylbutyl silicate, 8 per cent octa-(2-ethylbutoxy) trisiloxane and 1 per cent heavier distillate. The remaining examples employ the same reactants in varying proportions, all being batch operations. The Specification also describes, with a schematic flow diagram, a continuous process wherein excess materials are recovered and recycled to the reaction.