NUCLEAR MAGNETIC RESONANCE MEASUREMENTS OF PROTON TRANSFERS IN ACETYLACETONE IN DIETHYLAMINE AND TRIETHYLAMINE

Solutions of acetylacetone in triethylamine are completely enolic at all dilutions studied (0.1 to 0.85 mole fraction). The nature of the proton resonance signals in the NMR spectrum indicates a proton exchange between the OH and ==CH— groups of the enol tautomer. Addition of diethylamine to acetylacetone results in the formation of a white crystalline 1:1 molecular complex which melts at 41.5 °C. The NMR spectrum of the complex reveals a simultaneous proton exchange between the amine NH group and the OH and ==CH— groups of the enol tautomer. The mechanism of this exchange is discussed. In effect the addition of amines to acetylacetone not only alters the keto–enol equilibrium very markedly, but also increases the keto–enol conversion rate. With diethylamine the conversion rate becomes sufficiently high to "average out" the individual NMR spectra of the two tautomers.