Characterization of artefacts produced by treatment of organic acids with diazomethane

When alpha, beta-unsaturated acids and alpha-keto acids react with diazomethane not only are the corresponding methylates produced, but also diazomethane is added to the C = C double bond or to the oxo group. The gas chromatographic and mass spectral behaviour of these undesired products and some further artefacts produced in the hot inlet lines of a gas chromatograph are described. The mass spectra and retention indices allowed the structural assignment of several "unknown" compounds found previously in the methylated acid fraction of urine. A detailed analysis of the reaction of alpha-oxo acids with diazomethane revealed that, besides the already known oxirane methyl esters, homologous esters are also produced by an insertion reaction.