Reactions of one-electron reducing as well as oxidizing radicals with 4-mercaptopyridine (4-MPy) were studied in aqueous solutions at different pH values. One-electron oxidizing radicals such as N3 • and Br2 −•, react with 4-MPy by electron transfer reaction at pH 11 to give 4-pyridylthiyl radical. The reduction potential for the couple 4-PyS• /4-PyS− was estimated to be 0.93V vs. NHE by equilibrium reaction with I2 −• /2I− couple. At pH 6.8, where the compound is predominantly present in the thione form, the transient species formed is a cation radical. OH radicals react with 4-MPy by addition to the pyridine ring at pH 6.8 and 11. At pH 0, OH radicals as well as one-electron oxidants like Cl2 −• and Br2 −• radicals react with 4-MPy to produce the protonated form of 4-pyridylthiyl radical. At pH 6.8 and 11, eaq − reaction with 4-MPy gave an initial adducts which reacted with the parent molecule to give dimer radicals. Acetone ketyl radicals were unable to reduce 4-MPy at neutral pH. Reducing radicals like H-atoms and acetone ketyl radicals reacted with 4-MPy at acidic pH by H-abstraction reaction to give the same species as produced by oxidizing radicals.
Research on Chemical Intermediates – Springer Journals
Published: Oct 13, 2004
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