Additives to lubricating oils having extreme pressure, antiwear and antioxidant effects, process for preparation thereof and lubricating compositions containing said additives

A process for the preparation of dithiophosphorous disymmetric bisulfide of the formula:

• ##STR8## wherein X and Y can be identical or different, and represent an oxygen or sulphur atom or a methylene group, with the provisos that:
• (a) if X and Y represent an oxygen or sulphur atom, R.sub.1, R.sub.2 and R.sub.3 can be identical or different and represent a hydrocarbon acyclic or cyclic, saturated, unsaturated or aromatic radical or a chain of the general formula:
• ##STR9## wherein Z.sub.1 and Z.sub.2, can be identical or different, and correspond to an oxygen or sulphur atom, R.sub.4 corresponds to an alkyl group, R.sub.5 corresponds to an alkylene group and is an between 0 and 8, and
• (b) if X and Y represent a methylene group, R.sub.1 and R.sub.2, can be identical or different, and represent a hydrogen atom or a hydrocarbon radical and R.sub.3 represents a hydrocarbon radical, said process comprising condensing a compound of the general formula:
• ##STR10## with an S-alkylthiosulphate of the general formula
• R.sub.3 --S--SO.sub.3 M (III)
• in a two phase medium containing water and an organic solvent in the presence of a phase transfer agent, wherein R.sub.1 R.sub.2, R.sub.3, X and Y are as indicated and M represents an alkaline or alkaline earth metal or an ammonium ion.