On the mechanism of contact eliminations: IX. HCl elimination from gaseous 2,3-dichlorobutane on CaCl2, CaO, and Al2O3

Abstract The reaction was studied in the temperature range from 150 ° to 370 °C with the aid of the microcatalytic or pulse technique. The products are cis - and trans -2-chloro-2-butene, 2-chloro-1-butene, 1,3-butadiene, 1-butyne, and 2-butyne. These are all primary products. Furthermore an isomerization of the reactants takes place. No stereospecificity can be detected with CaCl 2 and CaO as catalysts. The ratio of cis -2-chloro-2-butene to trans -2-chloro-2-butene obtained from the meso form of the reactant is equal to that obtained from the dl form. The results can best be interpreted by a two-step mechanism comparable to E1 in liquid phase. With alumina more cis -2-chloro-2-butene is produced from the meso form, whereas the dl form gives more trans -2-chloro-2-butene, indicating that there is at least a partial stereospecificity corresponding to a trans mechanism.