Homogeneous acid catalysis

The several attempts, published in the literature, to describe the kinetics of vapour phase olefin (mostly ethylene) hydration can be classified into two groups according to the basic model used. One model, for reactions catalysed by phosphoric acid supported on solids, treats the kinetics as if the process were homogeneous acid catalysis and takes into account the acid strength of the supported acid. Thus, a semiempirical equation for the initial reaction rate [288]... 

However, a direct relationship between the heterogeneous and homogeneous acid catalysis appears difficult since free carbocations have not been, so far, detected on zeolites [17-19]. Tliis is probably due to the solvation effect which will not be the same in strong liquid acids and zeolites. Moreover, if free carbocations were present on zeolites it would be... 

In aromatic alkylation with olefins, the solid acid catalyst based process has instead largely substituted the homogeneous acid catalysis process. This evidences that the change of substrate (isobutane vs. aromatic) could change completely the applicability of one technology with respect to another. 

Intramolecular heavy atom effects influence the photoisomerization derivatives of 5,5-diphenyl-1,3-cyclohexadiene The homogeneous acid catalysis of the photoisomerization of trans-3-(2-hydroxy-benzylidene)-4,5-dihydrofuran-2(3H)-one and model mechanisms for isomerization of carbocyanines have both been analyzed. The process of photoisomerization of the biologically important rhodopsin and bacteriorhodopsin has been examined by a theoretical ab initio study of retinal analogues. ... 

Izumi, Y, Matsuo, K., and Urabe, K. 1983. Efficient homogeneous acid catalysis of heteropoly acid and its characterization through ether cleavage reactions. /. Mol. Catal. 18 299-314. 

Etherification of alcohol (benzylic) 4a (homogeneous acidic catalysis)... 

Before we discuss characteristic features of a metal sulfate catalyst, it is to be noted that the model reaction should be one which has as straightforward a mechanism as possible, preferably in a homogeneously catalyzed reaction. This is the only way we can critically evaluate the efficiency of the present solid catalyst system. The depolymerization of paraldehyde was most extensively studied in view of the foregoing criterion. For the homogeneous acid catalysis of the depolymerization of paraldehyde, there are ample data given by Bell and his associates in nonaqueous solvent (by proton acid as well as Lewis acid) and also in aqueous solution (55,56). Since most Hammett indicators change their color when adsorbed on the surface acids of both Bronsted and Lewis type, it is fortunate that this depolymerization proceeds easily by acids of both types. Evidently the dotted line in Fig. 2 shows excellent... 

Catalysis by solid acids is of paramount importance in industrial chmnistry, namely due to its application in catalytic cracking, one of the most important processes in the world. However, despite its enormous importance, only recently have practical and quantitative relationship between the acidity of the catalyst and its catalytic activity began to appear, unlike homogeneous acid catalysis, which has made use of the Brdnsted relations for many years. The difficulties to be overcome are of various nature but it was found by some of the authors that Bronsted-like relationships also apply to solid acid catalysts [1]. 

Liu, Y., E. Lotero J. Goodwinjr (2006) A comparison of the esterification of acetic acid with methanol using heterogeneous versus homogeneous acid catalysis. Journal of Catalysis, 242, 278-286,ISSN 00219517. 

Fig. 8.16 Reaction network for tandem reaction of glucose conversion to HMF by CrCI3 and HCI in aqueous phase (FA- furfural, Lewis-catalyzed reaction network is shown by dashed line). (Modified from T. D. Swift, H. Nguyen, A. Anderko, V. Nikolalds, D.G. Vlachos, Tandem Lewis/Bronsted homogeneous acid catalysis conversion of glucose to 5-hydoxymethylfurfural in an aqueous chromium (III) chloride and hydrochloric acid solution. Green Chemistry 17 (2015) 4725—4735. Copyright 2015 Royal Society of Chemistry).

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