To obtain an extreme pressure cleaner being excellent oil solubility and based on a sulfided hydroxyalkylbenzoic acid/alkyl phenol alkaline earth metal salt mixture.
A reactant mixture comprising a phenol having a 4-6C aliphatic hydrocarbon side chain, a dihydric alcohol, and an alkaline earth metal reagent in an amount corresponding to a gram equivalent ratio of the phenol of 0.99 or below is reacted. Next, carbon dioxide is reacted with a distillation bottom obtained by distilling the reaction mixture until at least a major amount of the water is removed, and the amount of the dihydric alcohol is reduced to 0.6 mol or below per mol of the alkaline earth metal reagent. The obtained product is reacted with above 0.5 to below 4.0 mol, per mol of the alkaline earth metal reagent, elemental sulfur. A 16-36C higher fatty carboxylic acid is added in an amount of 0.1-1.0 mol, per mol of the alkaline earth metal reagent between the reactant preparation step and the sulfidation step.
YAMAOKA SHINJI
UEKI HIROYUKI
COSMO OIL CO LTD