Oxidative degradation of isoniazid (INAH) with Mn
2+ was examined and the result from the analysis of reaction products shows that the main products are isonicotinic acid and isonicotinamide, and a small amount of by-products are 1, 2-diisonicotinoylhydrazine and isonicotinaldehydeisonicotinoylhydrazone. It was found that INAH makes chelates with Mn
2+ in the ratio of 1 : 1 and 1 : 2, these chelates are oxidized to Mn
3+ compounds by oxygen and then degraded, and that apparent degradation velocity of INAH is determined by the concentration and degradation rate of each of the chelates. The activation energy of the degradation reaction of chelate compounds, INAH-Mn
+ and INAH-Mn-INAH, was 11.7 and 10.0 kcal/mole, respectively. The degradation of INAH with Mu
2+ is accomplished by a three-step process ; first Mn
2+ forms a chelate with INAH, then Mn
2+ of the chelate is oxidized to Mn
3+ by oxygen, and then the high electron affinity of Mn
3+ cleaves the C=N and N-N bonds.
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