The Oxidation of Thiocyanate Ion by Hydrogen Peroxide. II. The Acid-catalyzed Reaction

The stoichiometry and kinetics of the acid-catalyzed reaction have been studied in the range 0.05 to 1.3 M perchloric acid. The main products are sulfate and hydrogen cyanide, but sulfur dicyanide, S(CN), is also formed. The reaction, as determined by iodometry, follows a rate law of the form R = k(H)(SCN)(HO)/[(HO) + α(HCN)] in which α is a constant. A mechanism of reaction is deduced, making use of carbon-14 and oxygen-18 tracer experiments as well as conventional rate data, and α is identified as a ratio of rate constants of secondary reactions. The rate constant of the third order primary reaction HO + SCN + HO →HOSCN + 2HO is fitted by the expression k = 1.75 × 10 exp(−11000/RT) 1. mole min. in the range 20 to 50°.