Heterogeneously catalyzed gas phase oxidations of 1,3-pentadiene-cyclodimers and of related substances

Abstract

1,3-Pentadiene ( 1) has been thermally cyclodimerized to give a mixture of 3-methyl-4-(1-propenyl)-cyclohexene ( 6), 3-methyl-5-(1-propenyl)-cyclohexene ( 7), 3,5-dimethyl-4-vinylcyclohexene ( 8) and 3,4-dimethyl-5-vinylcyclohexene ( 9). They have been sequentially aromatized to give the correspondingly substituted benzenes ( 10– 13) and hydrogenated in the side chains to give the corresponding alkylated benzenes ( 14– 17). The mixture of the cyclodimers 6– 9, as well as the individual compounds 1-methyl-2-(1-propenyl)-benzene ( 10), 1-methyl-3-(1-propenyl)-benzene ( 11), 1-methyl-2-propylbenzene ( 14) and 1-methyl-3-propylbenzene ( 15) have been oxidized with air on a V/Mo/P/Al/Ti-oxide catalyst. At conversion levels of 92–98%, the 1,2-disubstituted benzenes 10 and 14 and the mixture of cyclodimers, which contains ca. 70% the 1,2-disubstituted cyclohexene 6, gave phthalic anhydride ( 4) as the major and 3-methyl phthalic anhydride ( 5) as the second major organic product. By contrast, the 1,3-disubstituted benzenes 11 and 15 gave approximately equal proportions of 3-methyl phthalic anhydride ( 5), 4-methyl phthalic anhydride ( 25) and maleic anhydride ( 2) as the major organic products.