Water-soluble sulfonated diphosphines

A water-soluble diphosphine prepared by a process comprising reacting a biaryl compound of the formula ##STR3## in which the A's are individually alkyl, cycloalkyl, phenyl, tolyl, or naphthyl, the R.sup.1 's are individually hydrogen, or alkyl or alkoxy radicals having 1 to 14 carbon atoms, cycloalkyl, aryl, or aryloxy radicals having 6 to 14 carbon atoms, or a fused benzene ring, the m's are individually integers from 0 to 5 and the n's are individually integers from 0 to 4;

• at initial temperatures of 0.degree. C. to 60.degree. C., with oleum, to form an initial mixture, allowing said initial mixture to subsequently react with vigorous stirring at a reaction temperature of 20.degree. C. to 60.degree. C. over a period of 1 to 60 hours to form a reaction mixture, diluting said reaction mixture with water while maintaining a dilution temperature of from 0.degree. C. to 20.degree. C. to form a dilution mixture.