Electrochemical and spectral analysis of oxidized products of 10-3'-bis(hydroxyethyl)aminopropyl-2-chlorophenoxazine redox indicator

摘要

10-(3'-Chloropropyl)-2chlorophenoxazine was obtained by N~(10)-alkylation of 2-chlorophenoxazine with 1-bromo-3-chloropropane via phase transfer catalysis. Nucleophilic substitution of N~(10)-propyl chloride with N,N-diethanolamine resulted in the formation of 10-3'-N-bis(hydroxyethyl)aminopropyl-2-chlorophenoxazine BPCP, which was characterized by UV, IR ~1H - and ~(13)C -NMR and mass spectral analysis. Cerium(IV) sulfate oxidazeds BPCP reversibly to a pink coloured radical cation BPCP~(+·) in the presence of stoichiomeric amounds (BPCP:Ce(IV) = 1:1) of the reactants. The radical cation undergoes a second one-electron oxidation to form a brownish yellow coloured dication BPCP~(2+) in the presence of more than one equivalent of Ce(IV), which was identified by UV-Vis, infrared and mass-spectral methods. The cyclic voltammogram of BPCP exhibited two anodic waves at 640 mV and 1057 mV and two cathodic waves at 582 mV and 930 mV at a scan rate of 24 mV/sec. The peak at 640 mV corresponds to the oxidation of BPCP to the radical cation BPCP~(+·) and second anodic peak at 1057 mV stands for oxidation of radical cation to dication BPCP~(2+). Other cyclic voltammetric parameters such as E_p~(01) and E_p~(02) (anodic peak potentials), E_p~(r1) and E_p~(r2) (cathodic peak potentials) E_(f1) and E_(f2) (formal redox potentials), i_p~(01) and i_p~(02) (anodic peak currents), i_p~(r1) and i_p~(r2) (cathodic peak currents) and D_1~(1/2) and D_2~(1/2) (diffusion coefficients) have been determined. Bromine, which is liberated due to oxidation of potassium bromide with bromamine- T (BAT) in acid medium, oxidizes BPCP to three products as evidenced by HPLC. The tentatively predicted structures based on the mass-spectral data support the formation of brominated oxidized products. The respectively first and second formal potentials of BPCP were found to be 782-771 mV and 936-842 mV and the transition potential of BPCP in the titration of ascorbic acid with BAT was found to be 770 mV in 0.5 M sulphuric acid. The optimum conditions for the successful use of BPCP as a redox indicator in the macro and micro determination of ascorbic acid, methionine, isoniazid, phenylhydraine hydrochloride and biotin using BAT as an oxidant have been developed.. The indicator gives sharp and stoichiometric end-points. The importance of this method was the utilization of BPCP as an indicator for oxidation-reduction reactions for the volummetric determination of bioanalytically important species such as ascorbic acid, methionine and isoniazid in real samples.