Second order rate constants for reaction of a series of symmetrical, substituted diaryl- phosphine oxides and several dialkyphosphine oxides with diphenyl disulfide and acidities of the former in t-butanol and 95% ethanol were measured. Catalysis of the disulfide cleavage by base was observed. Correlation with Hammett substituent constants of both rate and acidity data is reported. A mechanism in which a rapid equilibrium “enolization” of the ...