Properties of Mono-and Dialkyldiphenyl Sulfides for High Temperature Lubricants and Their Molecular Structures

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Mono and dialkyldiphenyl sulfides (MADPSs and DADPSs) were prepared from diphenyl sulfide and C 10 ～C 18 alpha olefins by Friedel Crafts synthesis. For MADPS the alkyl is mainly located on para or ortho position with higher π electron density, and for DADPS the two alkyls are mainly located on para and ortho position of two different benzene rings. These compounds exhibit low volatility, moderate to good flow and fire properties. Thermal stability of these compounds is much better than that of diesters and polyolesters. Their resistance to oxidation at 230℃ is markedly superior to that of poly alpha olefins, polyolesters and alkylated diphenyl ethers. In oxidation tests, the intermediate oxidized products, such as sulfoxides, sulfoacids, sulfinic acids and phenolic compounds, were detected. Alkyldiphenyl sulfides (ADPSs) show dual antioxidation functions, i. e., the sulfur containing compounds decompose hydroperoxides and the phenolic compounds capture the free radicals. Owing to their high thermal and oxidation stability, alkyldiphenyl sulfides are of interest to be further studied as basestocks for high temperature synthetic lubricant formulations.