Solution phase interaction of nicotinamide with ascorbic acid



A study was made of what appears to be a charge-transfer interaction that is responsible for the instantaneous generation of a yellow color in aqueous solutions containing nicotinamide and ascorbic acid. Spectral studies were utilized to elucidate some of the factors that influence the interaction. Analysis, by the method of continuous variation, showed that a 1:1 complex was formed. The extent of association was pH dependent and exhibited a maximum at a pH of approximately 3.8. The pH dependency was compared with that of the 3-carbamyl-1-methyl-pyridinium chloride-ascorbic acid system and indicated that the interactants were protonated nicotinamide and ascorbate anion. Association constants, at a number of different temperatures, were determined by using the Benesi-Hildebrand treatment of spectral data. The standard enthalpy change that resulted from association was estimated to be −1,500 cal.