BASE-INDUCED DIOXYGENATION OF SULFUR-DIOXIDE BY HYDROGEN-PEROXIDE

In the complete absence of water sulfur dioxide (SO2) does not react w ith anhydrous hydrogen peroxide (HOOH). When water or a base is presen t in an acetonitrile matrix the reaction rate has at least a first-ord er dependence on its concentration. The most reasonable mechanism is a base-induced (B) nucleophilic attack by HOOH(B) of an SO2 molecule to produce HOS(O)(2)OH after intramolecular rearrangement [HOS(OO- is no t reactive with HOOH in a primary process]. The general rate law is -d [SO2]/dt = k(B)[SO2][HOOH][B] [B = pyridine (k(B), 180+/-20 M(-2) s(-1 )); HOS(OO- (20+/-2 M(-2) s(-1)); [H2O](3) (3.7+/-0.4 M(-1) s(-1)); [H 2O](2) (0.46+/-0.005 M(-3) s(-1)); H2O (0.12+/-0.002 M(-2) s(-1))]. Th e results indicate that even under acidic conditions (pH 2) HOOH(B) ca n react as a nucleophile. An analogous mechanism is responsible for th e rapid reaction between tBuOOH and SO2 to give t-BuOS(O)(2)OH, but t- BuOOBu-t is unreactive under all conditions.