Role of the Hydroxyl Group in the Gelation of Aluminium Soaps in Hydrocarbons

Abstract

IN most of the early investigations, aluminium soaps were prepared by aqueous metathesis between a soluble soap and an aluminium salt. As pointed out by McBain¹, the result of reaction between a weak acid and a weak base is not likely to produce a stable salt. The tendency of aqueous solutions of aluminium salts to precipitate aluminium hydroxide over a range of pH is well known, so some at least of soap prepared by aqueous metathesis is likely to consist of fatty acid adsorbed on to precipitated aluminium hydroxide. Analogous to the alumino silicates, alums, etc., one could associate a co-ordination number of four or six with aluminium, giving many different possibilities of co-ordination with fatty acid radical, undissociated fatty acid and water. When the effect of pH, heat and method of preparation on such a heterogeneous system² is considered, it is not surprising that results are difficult to duplicate.