Yasuo Yamazaki

Metathesis of α,ω-dienes over a CsNO3-Re2O7-Al2O3 catalyst in liquid phase

Abstract The metathesis of five kinds of α,ω-dienes containing from six to ten carbon atoms were investigated over CsNO 3 -Re 2 O 7 -Al 2 O 3 catalyst. The reactions were carried out in a continuous-flow system with a fixed catalyst bed at atmospheric pressure in the liquid phase. The α,ω-dienes were easily metathesized and all the reaction products were metathesis products. By-products resulting from double-bond isomerization of α,ω-diene were not found in the reaction products. Thus, the catalyst appeared to be a very active and selective catalyst for the metathesis of α,ω-dienes. 1,7-Octadiene underwent only intramolecular metathesis with quantitative yield of cyclohexene. On the contrary, 1,5-hexadiene and 1,9-decadiene underwent only intermolecular metathesis and both intra- and intermolecular metathesis took place for 1,6-heptadiene and 1,8-nonadiene. The relative reactivities of the α,ω-dienes were measured by both conventional and competitive reaction and the reactivity was obtained in decreasing order: 1,7-octadiene > 1,6-heptadiene > 1,8-nonadiene > 1,5-hexadiene > 1,9-decadiene. The reaction behavior and the relative reactivity were discussed and explained on the basis of the metal carbene mechanism.

Metathesis of 1, 4-alkadienes over a CsNO3-Re2O7-Al2O3 catalyst

Abstract The synthesis of 1, 4-cyclohexadiene (1, 4-CHD) by the metathesis of 1, 4-alkadiene (1, 4-AD) was investigated using a continuous-flow system over a CsNO 3 -Re 2 O 7 -Al 2 O 3 catalyst in liquid phase at atmospheric pressure. The effects of 1, 4-AD structure on the reactivity and reaction behavior were also studied. The reaction behaviors of 1, 4-hexadiene (1, 4-HD) and 1, 4-octadiene (1, 4-OD) were almost the same, but that of 1, 4-pentadiene (1, 4-PD) differed widely. The reactivity of 1, 4-ADs decreased in the following sequence: 1, 4-HD > 1, 4-OD > l, 4-PD. The order was mainly governed by the reactivity of carbenes. In the metathesis of 1, 4-PD, degenerative meta-thesis, which does not contribute to the conversion, occurred more than with other 1, 4-ADs, and this led to the lowest reactivity and a different reaction behavior. 1, 4-CHD could be obtained from either 1, 4-AD with fairly good selectivity and yield per pass at mild reaction conditions. It is considered that the 1, 4-CHD synthesis by metathesis provides a new and effective synthetic process.

Hydrogenolytic Behaviors of Asymmetric Diarylmethanes

Publisher Summary This chapter discusses the hydrogenolytic behaviors of asymmetric diarylmethanes (DAMs). The study of the hydrogenolytic behaviors of asym DAMs, in connection with their structures and the properties of the catalyst, leads to several fruitful conclusions. The position and the number of methyl substituents significantly affect the product selectivity between a methylene group and two aryl groups. The product selectivity can be estimated with high accuracy by using the relative values of the two phenylarylmethanes can be constituted. The methylene group insulates the interaction between two aryl groups; then the chemical properties of each individual aryl group are essentially independent of the other aryl group. The product selectivity of asym DAMs is closely related to the relative basicities of the two aryl groups as estimated from the corresponding methylbenzenes. The structure of asym DAM also affects the reactivity. The kinetic studies of the hydrogenolysis of diphenylmethane (DPM) indicate that both the DPM and hydrogen are adsorbed on the same kind of active sites on the catalyst. Also, the rate-determining step of the hydrogenolysis is a surface reaction between adsorbed DPM and dissociatively adsorbed hydrogen.