Thermal decomposition of 1,3-dimethyl derivative of phenobarbital in trimethylanilinium hydroxide

Extensive degradation of the 1,3-dimethyl derivative of phenobarbital occurs when it is injected with trimethylanilinium hydroxide in methanol into a gas chromatograph. The application of mass spectrometry demonstrated that the major products are N-methyl-2-phenylbutyramide, N,N-dimethyl-2-phenylbutyramide, methyl 2-phenylbutyrate, N,N,N'-trimethylethylphenylmalondiamide, and N,N,N',N'-tetramethylethylphenylmalondiamide. The methyl group of the ester arises from the methanol solvent, whereas the methyl groups of the substituted amides arise from the parent compound or the methylating reagent. Tetramethylammonium hydroxide causes much more degradation than trimethylanilinium hydroxide under comparable conditions.