Increased Concentration of the Nitromethyl Aci-Anion in nitromethane-amine mixtures

We have investigated the concentration of the nitromethyl aci‐anion in nitromethane and nitromethane‐diethylenetriamine mixtures. Ultra‐violet absorption spectroscopy and electrical conductivity measurements have given direct experimental evidence that the aci‐anion concentration is increased as compared to that in pure nitromethane. The increase is consistent with a shift in the acid‐base equilibrium. In any one mixture that is in contact with air, we have also observed a subsequent decrease in the aci‐anion concentration as a function of time. A newly observed band in the vibrational spectrum of nitromethane has been assigned to the aci‐anion and was used to confirm the decrease in its concentration with time. We discuss the previously suggested link between the aci‐anion and the sensitivity of nitromethane and conclude that it is unlikely that there exists any correlation.