PURPOSE: To obtain a lubricant additive obtd. by reacting an surfurized olefin with a branched chain dialkyl hydrogen phosphite and an amine at a specified temp. and providing improved corrosive life of copper.

CONSTITUTION: An aimed additive is obtd. by reacting a surfurized olefin (A) most suitably prepd. of isobutylene and contg. pref. 40-50 wt.% sulfur with dialkyl hydrogen phosphites (B) pref. contg. a 4-8C branched chain alkyl group and pref. 4-22C primary alkyl or alkenyl amines (C) at 45-75°C (pref. 50-65°C) ordinarily for 30 min-2 hr.