The chemical process accompanying the hydrogenation of fats I. Geometrical isomerization
Summary1. It has been shown for numerous examples that the catalytic hydrogenation of fats is accompanied by the cis-trans isomerization of the radicals of the unsaturated acids.2. A scheme is proposed which explains the mechanism of the isomerization through a process of the hydrogenation-dehydrogenation of the olefinic compounds.
Modern State of the Multiplet Theor of Heterogeneous Catalysis
Publisher Summary This chapter reviews the modern state of the multiplet theory of heterogeneous catalysis. The multiplet theory deals with numerical values of bond lengths and bond energies, as well as with the geometrical form of reacting molecules and the crystal lattices of catalysts. This allows definite results to be obtained for many reactions on an atomic level. This is how the multiplet theory differs from a number of other theories on catalysis. The theory of the structure of matter is based on both electronic theory and quantum mechanics—the basis for the multiplet theory. Bond lengths and energies represent a stable complex of electronic properties essential for catalysis. The multiplet theory proceeds from the premise that catalysis is a chemical phenomenon and that covalent bonds require catalytic activation.
4 The Stereochemistry of the Hydrogenation of the Isomers of Dimethylcyclohexene and Xylene
The hydrogenation of eight isomers of dimethylcyclohexene over Adams' platinum oxide in glacial acetic acid at two atmospheres of hydrogen gives mainly the cis-dimethylcyclohexane regardless of the positions of the methyl groups. Since 1,2-dimethylcyclohexene yields only 77% of the cis isomer, in this reaction there is a nonstereospecific process. It is neither the isomerization of the olefin to another which returns to the bulk phase or an isomerization of the product, the dimethylcyclohexane. The amount of cis isomer is increased to 86% when the pressure of hydrogen is raised to 150 atm. The ratio of isomers from the hydrogenation of 4-methylmethylenecyclohexane depends upon the catalyst, the percentage of the cis isomer is PtO2 54, Ni 46, and Pd 30. The xylenes also yield mixtures when reduced over PtO2 in acetic acid; the per cent of cis isomer is o 96, m 86, and p 74. The possibility that the trans isomer is formed by the isomerization of the cis isomer is excluded because only 5% of the trans isomer is contained in the equilibrium mixture of the 1,3-dimethylcyclohexanes. Apparently, the reduction of the aromatic compounds proceeds through a number of stages, the later ones in the sequence coinciding with stages in the reduction of the related olefins.