Location of double bonds in long chain esters by mass spectroscopy of methoxyhalogeno derivatives prepared from methoxymercuriacetate adducts

Abstract

Methyl esters of mono-, di-, and triunsaturated long chain fatty acids react quantitatively with mercuric acetate in methanol to produce methoxyacetoxy-mercuri derivatives. Demercuration of these products with solutions of bromine or iodine in methanol yields methoxybromo or methoxyiodo derivatives readily isolable by thin layer chromatography. Mass spectra of the methoxyhalogeno derivatives of monounsaturated esters are characterized by intense peaks due to loss of halogen and cleavage adjacent to methoxy functions; the latter fragmentation allows the position of the original double bond to be established. The mass spectra of the methoxyhalogeno derivatives of polyunsaturated esters are more complex.