Process for the selective synthesis of silylalkyl disulfides

Preparation of bis(silylalkyl)disulphanes of formula (R R R SiR )2S2 (I) comprises (1) reacting silylalkyl polysulphide(s) of formula (R R R SiR )2Sn (II) with a nucleophilic compound (III) of formula MCN (IIIA), M2SO3 (IIIB) or R R R P (IIIC) in an amount equimolar to the number of sulphur atoms to be removed from (II); (2) filtering the resultant solid; and (3) purifying (I). In the formulae, R -R , R -R = 1-8C alkyl and/or alkoxy, H or monovalent aryl, preferably phenyl, toluyl or benzyl; R = divalent 1-8C, preferably 2-4C alkylidene or a group of formula (IV); n = 3-20, preferably 3-10; and M = an alkali cation, optionally substituted ammonium ion or half alkaline earth or zinc ion. Preferably a mixture of (IIIA), (IIIB) and (IIIC) is used. Reaction is carried out in the presence of a solvent for (III) at a temperature between 20 degrees C and the b.pt. of the solvent, especially in a 2-phase system in the presence of a phase transfer catalyst.