An investigation of organic compounds that inhibit iron corrosion in sulphuric acid by way of oxidative addition to iron was carried out by electrochemical measurements and time-dependent analysis of chemical species in solution to which iron powder was added. Benzyl thiocyanate exhibited high corrosion inhibition effects by formation of a protective film on the iron surface via the oxidative-addition reaction. Characteristics of oxidative-addition corrosion inhibitors, represented as R—X, were discussed in terms of the facility of cutting the R—X bond and the stability of X− by using force constants of the CH3X bonds and pKa values of HX as the respective parameters.