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