FLASH VACUUM PYROLYSIS STUDIES .1. STRUCTURE AND ORIGIN OF THE ONION LACHRYMATORY FACTOR - MICROWAVE STUDY

A variety of structures have been proposed for the lachrymatory factor (LF) of the onion (Allium cepa) since the molecular formula C3H6SO was first determined in 19564and the cellular precursor t-(+)-S-(l-propenyl)-L-cysteine sulfoxide (la) identified in 1961.5Among the possibilities suggested for the LF have been β-hydroxypropanethial (2),4(E)-l-propenesulfenic acid S-H tautomer (3),6(2T)-propanethial S-oxide (4),7and an interconverting mixture of the latter two structures.10Recently we reported the application of flash vacuum pyrolysis (FVP) spectroscopic approaches to the study of structures related to 2-4, namely thioformaldehyde, CH2S,13methanesulfenic acid, CH3SOH,14and sulfine, CH2SO.2We now report the application of microwave (MW) and FVP-MW techniques to the characterization of the onion LF, for which we report a revised structure together with a unifying proposal for its genesis. We also report a new synthesis of sulfines discovered during the course of these studies. © 1979, American Chemical Society. All rights reserved.