Intermediate compound theories

The Intermediate Compound Theory in Homogeneous and Heterogeneous Catalysis. 51... 

All the advantages of the intermediate compound theory without most of the disadvantages are possessed by what may be called the- chemical adsorption theory. 

Catalysis, enzyme-substrate and intermediate compound theory in homo-and heterogeneous, V, 51 Catalysts, for acetonation, III, 51 for acetylation of starch, I, 284, 286 Bourguel s, II, 109, 110, 113 for esterification of cellulose, I, 312 in oxidation of carbohydrates by halogens, III, 177... 

Intermediate compound theory of enzymatic action, V, 51 identification of intermediate compound, V, 53... 

The intermediate compound theory (Ashmor, 1963) proposed that the reaction took place between the bulk solid and the reactant to give an intermediate compound. This intermediate compound decomposed or reacted with any other necessary reactant to give the product of the main reaction and to regenerate the catalyst. As long as the intermediates were considered as bulk compounds, the intermediate compound theory was of limited applicability. 

This theory, known as the intermediate-compound theory,2 has... 

The intermediate compound theory of catalysis was extended and clarified by Mercer and Playfair. ... 

A. A. De la Rive extended this intermediate compound theory to the action of platinum. The catalytic actions are ... 

The two main theories of catalysis are (i) intermediate compound formation theory and (ii) adsorption theory. 

The reasoning which led the author to make this first shot in the dark regarding the usefulness of combinations of solid compounds as ammonia catalysts was as follows If we assume that a labile iron nitride is an interminate in the catalytic ammonia synthesis, every addition to the iron which favors the formation of the iron nitride ought to be of advantage. In other words, the hypothesis was used that surface catalysis acts via the formation of intermediate compounds between the catalyst and one or more of the reactants. An experimental support for this theory was the fact that a stepwise synthesis via the formation and successive hydrogen reduction of nitrides had been carried out with calcium nitrides (Haber), and cerium nitrides (Lipski). Later, the author found molybdenum nitride as being the best intermediate for such a stepwise synthesis. 

Theory of the Action in the Lead Chambers.—The actual mechanism of the chemical process in the lead chambers has for years been a matter of much conjecture and controversy. The formation of unstable intermediate compounds which subsequently undergo decomposition with production of sulphuric acid is almost universally accepted, but unfortunately there is no general agreement as to the identity of the intermediate compound or compounds. 

The controversy between Huisgen and Firestone concerning the mechanism for 1,3-dipolar cycloaddition is longstanding.9,11 For nitrile oxide cycloadditions, experimental data have been interpreted either as supportive of a concerted mechanism9 or in favor of a stepwise mechanism with diradical intermediates.11 Theory has compounded, rather than resolved, this problem. Ab initio calculations on the reaction of fulmonitrile oxide with acetylene predict a concerted mechanism at the molecular otbital level,12,13 but a stepwise mechanism after inclusion of extensive electron correlation.14 MNDO predicts a stepwise mechanism with a diradical intermediate.13 The existence of an extended diradical intermediate such as (4 Scheme 2) has been postulated by Firestone in order to account for the occasional formation of 1,4-addition products such as the oxime (5).11 Of course, the intermediates (4) and (5) for the Firestone mechanism do not correspond to the initial transition states in Firestone s theory. These are attained prior to the formation of, and at higher energy than, the intermediates. 

According to this theory, a catalyst first combines with one of the reactants to form an intermediate compound of activity greater than that of the reactants. This intermediate compound then reacts with another reactant to form the product and so gives back the catalyst. If A and B are two reactants and C is a catalyst, then according to this theory. 

The theoretical investigation of these reactions requires quantum-mechanical methods, in particular, the study of chemical bonds in initial, final, and intermediate compounds, as well as the consideration of nuclear motions. Yet frequently the important information can be obtained without analysis of electronic structure of molecules and investigation of actual motion of nuclei, only resorting to the graph theory and employing the group-theoretical conceptions. Here we should define two terms permutation isomers and permutation isomerism reaction. 

In the earlier literature, jS-D-glucose (3) was considered to be an intermediate compound which, on subsequent dehydration, provides levoglucosan. Experimental evidence against this theory has been adduced by Golova and associates, who obtained small yields of levoglucosan from jS-D-glucose and from cellobiose, as compared to a 54—60% yield from cellulose. 

Another school of thought attempts to define the nature of such addition products somewhat more exactly by supposing that they represent perfectly definite though very unstable chemical compounds which result from the interaction of the catalyst with one or more of the components of the reacting system and which later decompose with the liberation of the catalyst and the formation of the end products of the reaction. This theory, based as it is upon the assumption of the formation of intermediate compounds, is primarily concerned in defining and demonstrating the actual existence of such substances. 

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