The presence of bicarbonate had a strong effect on the rate of oxidation of methyl phenyl sulfide (MPS) by hydrogen peroxide. At different concentrations of bicarbonate and hydrogen peroxide, we have observed different proportional amounts of methyl phenyl sulfoxide (MPSO) and methyl phenyl sulfone (MPSO2). With equimolar amounts of hydrogen peroxide, bicarbonate and methyl phenyl sulfide, the two oxidation products coexisted, and it was very difficult to isolate methyl phenyl sulfoxide. With a large excess of hydrogen peroxide and bicarbonate ion (10-fold), methyl phenyl sulfone appeared as the sole oxidation product, and we never observed methyl phenyl sulfoxide. Other possible activating agents such as H2PO4-, HSO4- and urea have also been used. It has been observed that comparative values of k(1) and k(2) for bicarbonate in H2O were similar and very high, whereas they were distant from one another and lower for other potential activating agents. The same method using H2O/EtOH (50:50) produced methyl phenyl sulfoxide as the sole reaction product after 2 h at RT. (C) 2010 Elsevier B.V. All rights reserved.