Spontaneous electron transfer in the reaction between methylgiyoxal and methylamine

The reactions of glyoxal, methylglyoxal, and diacetyl with methylamine were investigated by electron spin resonance (esr) spectroscopy. Methylgiyoxal rapidly underwent condensation reactions with methylamine to form deeply colored products such as substituted pyrazines and complex polymers. Glyoxal underwent similar condensations but more slowly. Diacetyl spontaneously underwent ring condensation to form 2,5-dimethyl-1,4-semidione at alkaline pH; however, it did not react with methylamine to form colored condensation products. It appears that a critical step in such condensations of glyoxals with amines is the ability to form ene diols. Time-resolved esr studies of the first few seconds of the methylglyoxal and methylamine reaction showed that methylgiyoxal anion radicals were formed, confirming that methylgiyoxal can act as a charge acceptor in this system. No such radicals could be formed from trimethylamine, however, suggesting that the free radicals observed in the methylamine reaction probably formed by electron transfer from a condensation product to methylglyoxal rather than directly from the methylamine itself.