DECOMPOSITION OF S-NITROSOTHIOLS BY MERCURY(II) AND SILVER SALTS

Rate measurements have been obtained for the reaction of a number of S -nitrosothiols (RSNO) in water with mercury(II) salts. Reaction is fir st order in both reactants, and the products are nitrous acid and the corresponding thiol-Hg-2+ complex. Decomposition is ca. 10(3) faster w hen mercury(II) nitrate, rather than mercury(II) chloride is used as t he source of mercury(II). This is consistent with the fact that wherea s the nitrate salt is fully ionised in water, the chloride exists almo st entirely in the undissociated molecular form. There is very little variation in the rate constant with RSNO structure. Silver ion reacts similarly, although less rapidly, and the kinetic order with respect t o [Ag+] is ca. 2. The results are discussed in terms of a mechanism in volving rate-limiting attack by water, at the nitrogen atom in the mer cury(II) (or silver) ion complex of the S-nitrosothiol, and are contra sted with the corresponding reactions of S-nitrosothiols with Cu+, whi ch generate nitric oxide.