Oxidation of Epinephrine to Adrenochrome by Cetyltrimethylammonium Dichromate: A Mechanistic Study

The present study reports the oxidation of epinephrine (adrenaline), a neurotransmitter by a lipid compatible lipophilic Cr (VI) oxidant, cetyltrimethylammonium dichromate (CTADC). The kinetics of the reaction is studied in organic media in the presence of acetic acid by UV-vis spectroscopic method. The rate of the reaction is measured by monitoring adrenochrome, the oxidized product of epinephrine at 455 nm. The reaction is fractional order with respect to CTADC and epinephrine. Acetic acid is found to retard the rate of the reaction. A suitable ionic mechanism is proposed based on the experimental findings where epinephrine is converted to adrenochrome through the intermediate, leucochrome. The proposed reaction mechanism is also supported by the effect of solvent, effect of temperature, and effect of surfactants on the rate of the reaction. The decrease in rate constant due to increase in polarity and hydrogen bond acceptor ability of the solvent indicates the existence of a less polar transition state and stabilization of the reactants through strong intermolecular hydrogen bonding. The addition of surfactants (cationic, anionic, and nonionic) decreased the rate of reaction, and the retardation is explained through the partition of oxidant and substrate in different microheterogeneous media.