Phenothiazine Derivatives as Antioxidants for Engine Oils

Abstract

Phenothiazine derivatives have been known to function as antioxidants for engine oils, transmission fluids and industrial lubricants. Alkylated phenothiazines are amines which contain sulfur and have lower bond dissociation energy, i.e. a higher rate constant than their “parent” alkylated diphenylamines. They are highly reactive towards radicals and are therefore excellent inhibitors against autoxidation and polymerisation. Since alkylated phenothiazines can provide superior oxidation stability, help to prolong the useful life of lubricants and significantly improve the durability and resistance of lubricants when exposed to high temperatures, they are of increasing importance. Performance requirements have become more stringent in the past 10 to 20 years and the demand for longer drain intervals has grown steadily. Also, the use of Group II, III and IV base oils is becoming more wide spread. Such base oils have very little sulfur content since natural sulfur-containing antioxidants are either absent or removed during the severe refining process. These evolutions in performance and base oil chemistry can be well handled by the use of phenothiazine chemistry