Knowledge Bank

The pulsed-beam FT-MW technique utilizing a modified solenoid valve for continuous gas flow was adapted to detect the onion lachrymator (2) in the headspace above freshly prepared onion mecerate. A monodeuterated isotopomer of (2), $CH3CHDCH=SO$, was observed when the onion was processed with $D2O$. Pyrolysis of 2-methyl-2-propyl 1*-propenyl sulfoxide with $D2O$ affirds the same monodeuterated species, $CH3CHDCH=SO$. Since (2) has no exchangeable hydrogens, these results provide strong support for mechanisms, both in the pyrolysis and the onion, which invole a common intermediate, propenesulfenic acid. (1). The acidc hydrogen. $H\ast$. on (1) exchanges with $D2O$, leading to deuteration of (2) at the methylene hydrogen position.$$[CH_{3}CH=CHSOH^{}]\rightarrow CH_{3}CH_{2}^{}CH=SO$$ $H\ast$. Analogous results were obtained from the pyrolysis of 2-methyl-2-propyl vinyl sulfoxide with $D2O$ which produces $CH2DCH=SO$. This pyrolysis provides evidence for reversibility in the above mechanism because $CHD2CH=SO$ is found to be a minor product.