Quinoxalinol derivatives of aliphatic 2-oxocarboxylic acids. Infrared and mass spectra of theO-trimethylsilylated compounds

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Abstract
In acidic media o-phenylenediamine and 2-oxoacids react to yield quinoxaline derivatives. On derivatization in pyridine with silylating reagents quinoxalinol-O-TMS ethers or O-TMS-ether-TMS-esters are formed exclusively as shown by gas chromatography infrared spectrometry and gas chromatography mass spectrometry. These derivatives have very favourable properties for gas chromatographic detection and quantitation of the parent 2-oxoacids. The mass spectra have characteristic fragments which facilitate easy identification. In addition, ‘single ion monitoring’ of all aliphatic 2-oxoacids can be performed with only three fragments at m/e 217, 232 and 245. In some aspects the mass spectra resemble those of other heterocyclic compounds which contain an O-alkyl sidechain. The fragmentation mechanisms were deduced by low resolution mass spectrometry with and without deuteration, high resolution mass spectrometry and metastable ion evidence. A new type of rearrangement α-β-elimination of ethylene or propylene from the aliphatic sidechain, is proposed for some O-TMS quinoxalinols.