An investigation into the molecular stability of zinc di-alkyl-di-thiophosphates (ZDDPs) in relation to their use as anti-wear and anti-corrosion additives in lubricating oils

The electronic energies and structures of the monomeric, neutral and basic forms of the important lubricating oil additive zinc di-alkyl-di-thiophosphate (ZDDP) are examined by molecular optimisation techniques using semi-empirical quantum chemistry calculations (MNDO). The optimised geometries reveal good agreement with known crystallographic data. The molecular stability is found to be highest for the basic form of ZDDP. For all forms, the variation of the chain length of the alkyl groups does not significantly change the overall molecular structure. © 1997 Elsevier Science S.A.