The redox properties of Nicotinamide Methohalides

Abstract

The reversible reduction of nicotinamide methiodide and methochloride has been studied using cathodic reduction at a mercury surface, sodium dithionite, hydrogen and colloidal platinum, and various leuco-dyes. The method of cathodic reduction was the most satisfactory. Polarography showed a 2-step reduction. Macro-reductions at a mercury surface suggested dimerization of the intermediate free radical. The behaviour of dihydromethylnicotinamide towards hydrogen ions, oxygen, iodine, potassium ferricyanide, ferric iron, and various dyes has been examined. Although it is not readily oxidized by oxygen it is capable of reducing most other systems with a higher E_o?:. Two methods of estimating the reduced compound are suggested and involve (a) the potentiometric titration of potassium ferricyanide at pH 9.1 and (b) the reduction and decolourization of 2.6-dichlorophenolindophenol at pH 4.7. The oxidation-reduction potential of nicotinamide methiodide has been measured by oxidative titration of the dihydro-compound at pH 9.1 and 30±0.01 °C and found to be -0.36 ± 0.02 V against the normal hydrogen electrode. The titration curve does riot show a separation of the two reduction steps. Evidence is discussed for the production of both o- and p-dihydromethylnicotinamide during reduction.