Catalysis by water

In this paper the author presents some of his contributions to the theory and practice of the cationic polymerisation (CP) of alkenes since 1944. The first phase of his work at the University of Manchester comprises the discovery of co-catalysis by water with TiCl4, the invention of the pseudo-Dewar reaction vessel, the use of trichloroacetic acid as co-catalyst, and the disproof of the alleged cationic isomerisation of cis-stilbene. 

Systems in which several chemically different chain carriers coexist constitute another type of enieidic polymerization. One example of this would be a polymerization in which concurrent co-catalysis by water and by alkyl halide solvent produced anions MtXBOH and MtX B+1. In that case one must assume a priori that the cations forming pairs with the two different anions will have different kinetic constants. 

Martinek, K., Levashov, A. V, Klyachko, N. L., Pantin, V. L, and Berezin, I. V. (1981). The principles of enzyme stabilization. 6. Catalysis by water-soluble enzymes entrapped into reversed micelles of surfactants in organic solvents. Biochem. 

In contrast, investigating the reaction of chelated protohemin chloride with H202, peracids, and fert-BuOOH, respectively, in buffered solution, suggested that general acid catalysis by water in the active site may facilitate the... 

Wolfe S, Kim CK, Yang K. Ab initio molecular orbital calculations on the neutral hydrolysis and methanolysis of azetidinones, including catalysis by water. Relationship to the mechanism of action of P-lactam antibiotics. Can J Chem 1994 72 1033-1034. 

The large negative entropies of activation and the large solvent isotope effects are no doubt intimately related. It is quite conceivable that these effects arise from a general catalysis by water of the water reaction. General base catalysis is known to occur in the hydrolysis of acetic anhydride by acetate, acetylp3rridinium ion by acetate (Bunton et al., 1961), acetylimidazole by imidazole, N-methyl,N -acetylimidazolium ion by N-methylimidazole, l-(N,N-dimethylcarbamoyl)pyridinium ion by pyridine (Johnson and Rumon, 1965), and ethyl haloacetates by weak bases (Jencks and Carriuolo, 1961). It is most reasonable then that the water reaction be similarily a base-catalyzed process. The isotope effects... 

Catalysis by Water-Soluble Imidazole-Containing Polymers... 

Research by Overberger [13], Kabanov [14,15], Klotz [16], Kunitake [17] and others [18, 19] has contributed much to development of the catalysis by water-soluble polymers. Among numerous synthetic polymer catalysts, imidazole derivatives are cited in particular because they are constituents of hydrolytic enzymes [1, 20-22]. Polyvinylimidazole (PVI) is several times more catalytically effective than imidazole because of its polyfunctional nature. Let us consider three possible mechanisms of cooperative catalysis (see p. 2). 

Catalysis by Water-Soluble Polymer-Metal Complexes... 

The first chapter of the book deals with enzyme-like eatalysis by synthetic polymers - catalysis by polymeric acids and bases, amphoteric polyelectrolytes and nonionic polymers. Because coordination compounds of metal ions with macromolecular ligands are interesting with regard to bioinorganic chemistry, this book elucidates some problems involving the catalysis by water-soluble polymer-metal complexes. Ester hydrolysis, hydrogen peroxide decomposition, oxidation of disubstituted phenols, hydroquinones, mercaptoalcohols and other types of reaction are chosen as model processes. A section devoted to interfacial catalysis is also included. 

These results highlight that for some aeid-eatalysed reactions in HTW and sew, the increase in the observed rate constant at weakly acidic and neutral pHs can be a consequence of an increase in general acid catalysis by water, as opposed to an increase in specific acid catalysis by H . This is a consequence of the substantive increase in thermal energy available in HTW and sew. The resulting increase in the heterolysis of water manifests itself more significantly in general acid catalysis than in the increase of K, for specific acid catalysis. 

Further examples of the importance of general acid catalysis by water in organic reactions in HTW have been reported. Savage et al. have shown that the observed rate constant for methyl benzoate ester hydrolysis in HTW is comprised of both a specific acid and a general acid-catalysed component (Scheme 3.5(a)). Previous studies on the hydrolysis of esters in HTW had... 

Turning to the kinetic studies, Bronsted and Pedersen found that in dilute solutions of strong acids the rate of decomposition at 15°C was independent of hydrogen ion concentration over a wide range (10 -0.4m). They attributed this rate to basic catalysis by water molecules, and concluded that there was no acid catalysis they also found that added neutral salts had little effect on the rate. Subsequent work in more... 

The example given in Figure 3 represents a case (19) when in the pH range from 7 to 8 (the slope of the line is -1), the rate of the reaction is proportional to the concentration of hydrated protons and the second term in equation 38 is predominant. The rate, in turn, is independent of the pH in the range 8-10 (neither the concentration of H3O+ nor that of OH affects the rate). In this region, the first term in equation 38 was shown to be predominant, that is catalysis by water occurs (general acid catalysis). Finally, the line from pH 10-12.5 has a slope of -1-1 (the predominant is the fourth term in eq. 38) showing specific base catalysis. 

As for the uncatalysed aminolysis of penicillins the reaction with oxygen anions could involve p-lactam C—N bond fission with or without assistance from general acid catalysis by water. The solvent isotope effect °H2o/ d20 fo " trifluoroethoxide ion reacting with benzylpenicillin is 3.9 (Davis et al., 1987). Although there are difficulties in the quantitative interpretation of solvent isotope effects (Gold and Grist, 1972) the values of... 

HO", to the enhancement of its activity in aqueous dimethyl sulfoxide as the concentration of water approaches low values.) Wang et al. (2011) demonstrated methylation of phenol and benzene-1,2-diol derivatives with 1,3,5-tiioxane (e.g.. Scheme A) in supercritical water, accelerated compared to the solvent-free reaction. The authors describe the reaction as uncatalyzed, though acid catalysis by water or by hydrogen ion is likely (see Section 3.6.1). 

Kiji, J. Okano, T. (1994) 2-Phase catalysis by water-soluble phosphine complexes of palladium, J. Synth. Org. Chem. Jpn., 52,276-84. 

Okano, T. Moriyama, Y. Konishi, H. Kiji, J. (1986) Counter phase transfer catalysis by water-soluble phosphine complexes. Catalytic reduction of allyl chlorides and acetates with sodium formate in two-phase system, Chem. Lett., 1463-6. 

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