Pyrolysis Reaction of Carpronium Chloride and its Structurally Realated Compounds. 2-A Mass Spectrometric Study of The Lactonization Mechanism

Article abstract of DOI:10.1002/oms.1210180402

The mechanism of the pyrolysis reaction of carpronium chloride <(CH3)3N⁺-(CH2)3-COOCH3Cl^-> leading to γ-butyrolactone and tetramethylammonium chloride was investigated by means of thermal analysis, pyrolysis gas chromatography mass spectrometry and field desorption mass spectrometry, using deuterium labelling.The results indicated that carpronium chloride pyrolysed to yield equimolar amounts of γ-butyrolactone and tetramethylammonium chloride, methyl transfer occured between N and O during the pyrolysis process.The mechanism is discussed on the basis of the experimental results, and with the aid of the theoretical results calculated by the CNDO/2 method.The mechanism presented is as follows. γ-Butyrolactone is formed by the intramolecular migration of the ?-orbital of C=O to the carbon adjacent to <(CH3)3N>⁺ via a 5-membered ring transition state, accompained by a bimolecular reaction between <(CH3)3N>⁺ and the CH3 of O-CH3, resulting in the formation of tetramethylammonium chloride in an amount equimolar with γ-butyrolactone.