Kinetics and equilibria in the nitric acid–nitrous acid–sodium thiocyanate system

Abstract

The nature of the red species formed in acidic solutions containing nitrous acid and thiocyanate ion has been confirmed to be ONSCN. The alternative literature interpretation in terms of ONSCNH⁺ arises from neglect of activity coefficients and partial protonation of SCN^– to HNCS in moderately concentrated mineral acid. The kinetics of the nitrous acid-catalysed oxidation of thiocyanate in moderately concentrated nitric acid is controlled by rate-determining formation of N₂O₄ at even modest concentrations of thiocyanate. Literature work on this system is discussed.