A Photometric Titration Method for the Determination of Thiourea Function and Its Application to the Analysis of Some Thiourea-based Commercial Products

Organic compounds containing thiourea function find many industrial, agricultural, pharmaceutical and analytical applications. Consequently, convenient, reliable, rugged and cost-effective methods for ensuring the quality of commercial products based on it are highly desirable. The case with which hydrogen peroxide in the presence of an excess of sodium hydroxide oxdatively desulphurise the thiocarbonyl sulphur of thiourea into sodium sulphate and residual alkali is instantaneously transformed into bright yellow sodium benzyl trithiocarbonate (through reaction with carbon disulphide and benzyl mercaptan) showing maximum absorbance at 430mm, has been made the basis of a photometric titration method The method consists in adding a known excess of sodium hydroxide and hydrogen peroxide to thiourea solution in aqueous test-butanol (2:8v/v) followed by the addition of sodium sulphite and carbon disulphide and titrating the resulting solution photometrically at 430mm against standard benzyl mercaptan. The absorbance increases till it attains maximum value corresponding to the quantitatively transformation of sodium hydroxide into yellow sodium trithio-carbonate and thereafter, it attains almost constant values. The end-point is formed from extrapolation of two linear segments. The methods has been applied with success to the analysis of commercial formulations of thiophanate methyl (fungicide) and thiopentone sodium (drug) with recoveries in the range 99%-99.6% of the nominal content with relative standard durations in the range 0.4-0.6%.