C3H7)(CH3) S0, and (n-C3H7), S0, have been studied in 955 vol% methanol/water at 25 OC and p= 1.0 (LiCI). In all cases the reaction is the simple replacement of one chloride by a sulfoxide. The second-order rate constants are insensitive to the change in inductive effect on changing the substituents but decrease with increasing bulk. An interpretation is proposed in terms of the intimate mechanism of the substitution, and a comparison is ...