Analysis of oxidation products of 10-[3 '-N-benzylaminopropyl]phenoxazine redox indicator by spectral and cyclic voltammetric methods

Synthesis of 10-[(3'-N-benzylamino)propyl]phenoxazine [BAPP] is accomplishe d in two steps. The first step involved N-10-alkylation of parent phenoxazi ne via phase transfer catalysis (PTC) followed by iodide-catalysed nucleoph ilic substitution of the N-10-propyl chloride with N-benzylamine. BAPP form ed is purified by column chromatography. In the second stage BAPP undergoes one-electron oxidation with Ce(IV) to form a pink radical cation [BAPP(+.) ]. In the presence of more than one equivalent of Ce(IV), the radical catio n undergoes a second one-electron oxidation to form a brownish yellow colou red dication [BAPP(2+)], which is characterized by UV-Vis, IR and mass-spec tral methods. The biological functions of phenoxazines are connected to a g reat extent with their ability to undergo reversible redox conversion and t herefore the electrochemical behaviour of BAPP is investigated by cyclic vo ltammetry. Other cyclic voltammetric parameters have also been determined. Bromine in acid medium oxidizes BAPP to three products as shown by HPLC. Th e tentatively predicted structures based on the mass-spectral data support the formation of three brominated oxidized products. In order to explore th e analytical applications, the optimum conditions for the use of BAPP as re dox indicator in the macro and micro estimation of ascorbic acid, methionin e, isoniazid, phenylhydrazine hydrochloride and biotin using chloramine-T a s an oxidant have been developed. The indicator gives sharp and stoichiomet ric end-points. During the titration, BAPP initially undergoes a reversible one-electron oxidation. With progress of titration, the radical pink catio n is oxidized to a blue coloured dication with the loss of one more electro n. The utilization of BAPP as an indicator for oxidation-reduction reaction s for the volumetric determination of bioanalytically important species suc h as ascorbic acid, methionine and isoniazid in real samples is significant .