Reaction of R (Ph) P (O) NHOSO2Bn (R= PhMeCH) with ButNH2 in CH2Cl2 gives a mixture of RP (O)(NHPh) NHBut and ButNHSO2Bn, the proportion of the sulfonamide increasing steadily (14.6% to 32.9%) as the concentration of amine is reduced (8.0 to 0.2 mol dm− 3).