Kinetics and the Mechanism of Reduction of Hexacholoroiridate (IV) by Carcinogenic Nicotine as an Alkaloid in Aqueous Solutions with the Determination of Ionization Constant of Nicotine

Background: Nicotine (NIC) is a lipid-soluble alkaloid found predominantly in 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 for human healthcare, which keeps many users hooked. Methods: A spectrophotometric technique has been applied to investigate the kinetics of reductoin hexachloroiridate (IV) as an inert one-equivalent oxidant by carcinogenic nicotine (NIC) in aqueous perchlorate solutions. Results: First-order in [IrCl6]²- and fractional-first-order concerning the nicotine concentration has been revealed. Kinetic evidence for forming a 1:1 intermediate complex between the NIC and [IrCl6]2- before the rate-determining step was confirmed. Conclusion: The ionization constants of nicotine were evaluated from the kinetic data and are 8.57x10-4 and 4.57 x 10-4 moldm-3 at an ionic strength of 0.5 moldm-3 and 30°C and 40°C, respectively. The activation parameters have been deduced from the kinetic results of the temperature dependence of rate constants. A plausible reaction mechanism for the redox reaction is suggested and discussed. Nicotinic acid (Vitamin B3) was formed as an oxidation product of nicotine oxidation.