THE INFLUENCE OF CHEMICAL-STRUCTURE ON THE OXIDATIVE STABILITY OF ORGANIC SULFIDES

Several organic sulfides were carefully selected to relate alkyl/cycli c substitution chain length, and polysulfide functionality to oxidativ e performance in a solvent-refined base oil and a hydrotreated base oi l. The organic sulfides were tested in the modified Groupement Francai s de Coordination (GFC) oxidation test at 160 degrees C. Samples were drawn at 96, 144, and 192 hours and characterized for viscosity increa se, total acid number (TAN), and weight percent insolubles in hexane. The viscosity increase, TAN, and insolubles were generally lower in th e hydrotreated base oil. Using the solvent-refined mineral base oil, t he data indicates alkyl/cyclic substitution, polysulfide functionality and, to a lesser degree, chain length were governing factors for oxid ative stability. Collectively, the oxidative stability of the polysulf ides tested based on the modified GFC oxidation test in decreasing ord er of stability is as follows: primary/tertiary alkyl monosulfides > p rimary/tertiary alkyl disulfides > cyclic disulfides and alkyl trisulf ides. Bond dissociation energies of C-S, S-S and S-n were used to rati onalize the observed ranking.