RP‐HPLC Method for Simultaneous Determination of Thiobenzanilide and its Oxidation Products: Monitoring the Oxidation of Thiobenzanilide with Jones' Reagent

Abstract

The reaction of thiobenzanilide with various oxidants leads to the formation of a few possible products such as benzanilide, 2‐phenylbenzothiazole, thiobenzanilide‐S‐oxide, bis(N‐phenylbenzimidoyl) disulfide, and bis(N‐phenylbenzimidoyl) sulfide. The formation of these products depends on the reaction conditions and liquid chromatography is a convenient method for monitoring the oxidation reaction. In the present study, a reversed‐phase HPLC method is developed for separation and simultaneous determination of thiobenzanilide and its oxidation products using an analytical column Lichrosorb RP18 (250×4 mm, particle diameter 5 µm) and gradient elution with acetonitrile and water with phosphoric acid (pH=3.0). The elution is monitored in the whole UV range (diode array detector) and detection at 254 nm is chosen for all examined analytes, except for thiobenzanilide‐S‐oxide, for which the wavelength of 344 nm is preferred regarding sensitivity and selectivity. The calibration curves for quantitative determination of thiobenzanilide and its oxidation products were constructed in the concentration range of 2×10−6 mol/L–1×10−3 mol/L. Linear dependence of the peak area versus concentration of each analyte was established with satisfactory values of the coefficient of correlation (R2>0.99). The proposed method was then applied for monitoring the reaction of oxidation of thiobenzanilide with Cr(VI), the so‐called Jones' reagent, and the results are presented and discussed.