Colorimetric determination of C-2 unsubstituted phenothiazines, using morpholine and N-bromosuccinimide

A colorimetric method for quantitative determination of 6 C-2 unsubstituted phenothiazine derivatives is described. The method is based on reaction of phenothiazine derivative with morpholine and N-bromosuccinimide reagents in aqueous methanol at 60 degrees C to produce a blue color. Beer's law is obeyed in a wide range of concentrations for all 6 compounds at 660 nm. Optimum analytical conditions were determined and the produced color is stable for at least 24 h. Analytical data for determination of the pure compounds are presented together with the application of the proposed method to analysis of some pharmaceutical preparations. The results compare favorably with those of official methods. Furthermore, the method is specific for intact drug in the presence of oxidative decomposition products. The reaction product has been isolated and identified and a possible reaction mechanism is suggested.