Kinetics and mechanism of uncatalyzed and selenium dioxide catalyzed oxidation of nicotinic acid hydrazide by bromate

70-76The uncatalyzed and selenium dioxide catalyzed oxidation of nicotinic acid hydrazide, (NIH) by bromate has been studied in hydrochloric acid medium. The –NH2 of hydrazoic moiety and pyridine nitrogen of the NIH forms protonated species which are involved in two ion pair complexes with the oxidant in prior equilibria. In case of uncatalyzed reaction the complex with the protonated hydrazoic moiety decomposes to give corresponding acyl diimide intermediate while that of the pyridine nitrogen decreases the rate of reaction. In presence of selenium dioxide as catalyst, the NIH reduces the catalyst to H2SeO2 species which is oxidized by the oxidant to complete its catalytic cycle. The product of the reaction is found to be nicotinic acid and there is no intervention of any free radicals. A rate law derived for both the reactions satisfy the kinetic data obtained and UV-spectrophotometer examination of the reaction mixture also support the mechanisms proposed