The use of enthalpimetric titration to study the reaction of thiourea and its N-substituted derivatives with cerium(IV)

Abstract

The oxidation of thiourea and its symmetrically N-substituted derivatives has been examined by enthalpimetric titrimetry. The initial reaction is considered to cause the formation of a disulphide and slower secondary oxidations of these products have been detected. Reaction rates are acid dependent and studies have been carried out in hydrochloric and sulphuric acids. In hydrochloric acid, thiourea and ethylenethiourea can be titrated to within ±0·3 per cent. of the theoretical value for the first reaction step over the acid range 0·3 to 0·2 M, while in sulphuric acid (0·3 to 0·6 M) the values for N,N′-diethylthiourea are within ±0·4 per cent. of the theoretical. Comparison is made with the titration method for the determination of thiourea by cerium(IV), which has been shown to be satisfactory within certain acidity ranges in sulphuric acid.