. Can. J. Chem. 54, 3364 (1976).The kinetics of the gas phase thermoiysis of Zvinyloxirane (4) have been studied over the temperature range 270-310 "C. The racemization of chiral 4 occurs six times faster than the structural ison~erization to 2,3-dihydrofiran, (E)-and (d)-2-butenai, and 3-butenal. The butenals undergo a slow ihermolysis to propene and carbon monoxide. cis-Deuterio-and frnr2s-3-deuterio-vhyioxirai1~ have been synthesized and their interconversion is slow. Deuterium kinetic isotope ezects on motzo-and dideurerio-4 suggest that for the formation of the kutenals the rate determining step involves rupture of the oxirane C-0 bond. The dihydrofuran is produced by thermolysis of the oxirane C-C bond. The preferred mechanistic interpretatiur, is that a carbon-oxygen diradical serves as an intermediate for butenal formation, and that a carbonyi-ylide is involved in the formation of the dihydrofuran.Tile relative rates, at 307.4 " C , of cis-irans-isomerizatim:diI1ydrofuran formation: racemization: butenal formation for 3-dcuterio-2-vinyloxirane are On a CtudiC, B des ten~pCratures ai!ant de 270-310 'C, la cinktique de ia thermolyse en phase gazeuse du vinyl-2 oxiranne (4). La racCrnisation du composk 4 chiral se pioduib 6 fois plus rapidemnt que I'isorn6risation de structure en dihydro-2,3 furanne, en butkne-2 als ( E ) et ( Z ) el en Sutkne-3 al. Les butenais subissent !me therinolybe lente conduisant au propkne et au monoxyde de carbone. On a aussi syntbCtisC les deutCrio-3 vinyloxirannes cis et trans et !cur interconversion est lente. Ees effets isotopiques cinktiques du deuterium sur les motlo-et diderlririo 4 suggkrent que, pour la formation des butknals, I'etape dCtermiriant la vitesse de la rCaction irnplique la rupture du lien C--0 de l'oxiranne. Le dihydrofuranne se produit par thermolyse du lien C-C de i'oxiranne. L9interprCtation mkcanistique prCf6rCe implique qu'il y a formation d'un diradical carbone-oxygkne comnle interinkdiaire pour la formation des butenais et qu'un carbonyl-yfide est irnplique dans la formation de la dihydrofuranne. kes vitesses relatives, B 307.4 "C, pour I'isomCrisation cis-tratzs: la formation de dilvdrohranne: la rackmisation: la formation de butenal B partir du de~lterio-3 vinyl-2 oxiranne sont respectivement de 1.0:0.88 :40.2:5.94.[Traduit par le journal]
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