Sterischer Ablauf der Dehydratisierung von gasförmigem 2-Butanol-3-d1 an AlPO4, Ba3(PO4)2 und Ca3(PO4)2 / Stereo Mechanism of Dehydration of Gaseous 2-Butanol-3-d1 over AlPO4, Ba3(PO4)2 and Ca3(PO4)2

Abstract

Dehydration can proceed according to one (E2) or two (El, ElcB) step mechanisms. In the first case the leaving groups can be abstracted from the cis or trans (syn or anti) position. In order to get insight into the mechanism, the dehydration of 1-butanol, 2-butanol, D,L-erythro- and D,L-threo-2-butanol-3-d₁ as well as the isomerization of 1-butene and cis-2-butene were studied in the temperature range from 250 to 400°C, using microcatalytic and mass-spectrometric techniques. In order to distinguish between cis and trans elimination, erythro- and threo-2-butanol-3-d₁ were studied. Over AlPO₄, Ba₃(PO₄)₂ and Ca₃ (PO₄) ₂ a simultaneous trans and cis mechanism was found. The ratio of cis to trans mechanism was calculated to be 85/15 with Ca₃ (PO₄)₂, 70/30 with Ba₃ (PO₄)₂ and 45/55 with AlPO₄. The cis mechanism is highest for Me-O-distances of the catalysts of 2.5 A which coincides practically with the distance between - OH and -H (D) to be eliminated