H N Kalpana
Articles written in Journal of Chemical Sciences
Volume 111 Issue 6 December 1999 pp 725-739 Physical And Theoretical
Synthesis of 10-[(3′-N-benzylamino)propyl]phenoxazine [BAPP] is accomplished in two steps. The first step involved N10-alkylation of parent phenoxazine via phase transfer catalysis (PTC) followed by iodide-catalysed nucleophilic substitution of the N10-propyl chloride with N-benzylamine. BAPP formed 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 cation undergoes a second one-electron oxidation to form a brownish yellow coloured dication [BAPP2+], which is characterized by UV-Vis, IR and mass-spectral methods. The biological functions of phenoxazines are connected to a great extent with their ability to undergo reversible redox conversion and therefore the electrochemical behaviour of BAPP is investigated by cyclic voltammetry. Other cyclic voltammetric parameters have also been determined. Bromine in acid medium oxidizes BAPP to three products as shown by HPLC. The tentatively predicted structures based on the mass-spectral data support the formation of three brominated oxidized products. In order to explore the analytical applications, the optimum conditions for the use of BAPP as redox indicator in the macro and micro estimation of ascorbic acid, methionine, isoniazid, phenylhydrazine hydrochloride and biotin using chloramine-T as an oxidant have been developed. The indicator gives sharp and stoichiometric end-points. During the titration, BAPP initially undergoes a reversible one-electron oxidation. With progress of titration, the radical pink cation is oxidized to a blue coloured dication with the loss of one more electron. The utilization of BAPP as an indicator for oxidation-reduction reactions for the volumetric determination of bioanalytically important species such as ascorbic acid, methionine and isoniazid in real samples is significant.
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