Kinetics and mechanism of reduction of hexacholoroiridate (IV) by carcinogenic nicotine as alkaloid in aqueous solutions with determination of ionization constant of nicotine

Abstract

Nicotine (NIC) is a lipid soluble alkaloid found predominately in tobacco and tobacco products including cigarettes, cigars and oral tobacco products such as snuff and chewing tobacco. Since nicotine substrate is the major constituent of tobacco smoke, it may cause negatively impacted problems to the human healthcare which keeps many users hooked. A spectrophotometric technique has been applied for investigating the kinetics of reduction of hexachloroiridiate (IV) as inert one-equivalent oxidant by carcinogenic nicotine (NIC) in aqueous perchlorate solutions. First-order in [IrCl6]2- and fractional-first-order with respect to the nicotine concentration has been revealed. Kinetic evidence for formation of 1: 1 intermediate complex between the NIC and [IrCl6]2- prior to the rate-determining step was confirmed. The ionization constants of nicotine was evaluated from the kinetic data and has been found to be 8.57x10-4 and 4.57 x 10-4 moldm-3 at ionic strength of 0.5 moldm-3 and at 30˚C and 40˚C, respectively. The activation parameters have been deduced from the kinetic results of the temperature-dependence of rate constants and a plausible reaction mechanism of the redox reaction is suggested and discussed. Nicotinic acid (Vitamin B3) was formed as oxidation product of nicotine oxidation.