IN SITU DETECTION AND MECHANISM OF FORMATION OF THE ONION LACHRYMATOR, (Z)-PROPANETHIAL S-OXIDE, BY PULSED-BEAM FT-MW SPECTROSCOPY
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Date
1996
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Ohio State University
Abstract
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), $CH_{3}CHDCH=SO$, was observed when the onion was processed with $D_{2}O$. Pyrolysis of 2-methyl-2-propyl 1*-propenyl sulfoxide with $D_{2}O$ affirds the same monodeuterated species, $CH_{3}CHDCH=SO$. 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).$^{a}$ The acidc hydrogen. $H^{*}$. on (1) exchanges with $D_{2}O$, leading to deuteration of (2) at the methylene hydrogen position.$$[CH_{3}CH=CHSOH^{*}]\rightarrow CH_{3}CH_{2}^{*}CH=SO$$ $H^{*}$. Analogous results were obtained from the pyrolysis of 2-methyl-2-propyl vinyl sulfoxide with $D_{2}O$ which produces $CH_{2}DCH=SO$. This pyrolysis provides evidence for reversibility in the above mechanism because $CHD_{2}CH=SO$ is found to be a minor product.
Description
$^{a}$See the recent review, E. Block, Angew, Chem., Int. Edn. Engl. 31, 1135 (1992).
Author Institution: Department of Chemistry, Siena College; Department of Chemistry, Rensselaer Polytechnic Institute
Author Institution: Department of Chemistry, Siena College; Department of Chemistry, Rensselaer Polytechnic Institute