Over-based magnesium salts of sulphonic acids

A process for preparing an over-based, oil-soluble magnesium salt of a sulfonic acid comprising contacting carbon dioxide at a temperature ranging from 50.degree. F. to 200.degree. F. with a mixture comprising:

• (a) an oil-soluble magnesium salt of a sulfonic acid,
• (b) from approximately 10 up to approximately 40 equivalents of a light magnesium oxide per equivalent of sulfonic acid,
• (c) a promoter system comprising
• (1) from approximately 0.5 to approximately 5 equivalents of an essentially oil-insoluble carboxylic compound per equivalent of sulfonic acid, said compound being selected from the group of compounds consisting of lower carboxylic acid, lower carboxylic anhydrides, substituted lower carboxylic acids, metal salts and esters of lower carboxylic acids and mixtures thereof, all having 1 to 5 carbon atoms,
• (2) from approximately 2 to approximately 8 equivalents of water per equivalent of sulfonic acid, and
• (3) an amount of alcohol up to approximately 8 equivalents of alcohol per equivalent of sulfonic acid, said alcohol being selected from the group consisting of lower alkanols, lower alkoxy alkanols, and mixtures thereof, all having from 1 to 5 carbon atoms,
• (d) an inert solvent for lowering the viscosity of said mixture to facilitate mixing,
• additional water and alcohol being added to the reaction mixture during a portion of the time that carbon dioxide is being contacted with said mixture where the total amount of water in said mixture is less than 30 equivalents and the total amount of alcohol in said mixture is less than 35 equivalents, the volatile components being stripped from the reaction mixture after absorption of the carbon dioxide by the reaction mixture is at a desired level to give an over based oil-soluble magnesium salt of a sulfonic acid having a metal ratio of equivalents of magnesium to equivalents of sulfonic acid ranging from approximately 10 to approximately 40.