Catalysis 2+, aquation

Wastewaters containing chlorinated hydrocarbons (CHCs) are very toxic for aquatic system even at concentrations of ppm levels [1] thus, appropriate treatment technologies are required for processing them to non-toxic or more biologically amenable intermediates. Catalytic wet oxidation can offer an alternative approach to remove a variety of such toxic organic materials in wet streams. Numerous supported catalysts have been applied for the removal of aqueous organic wastes via heterogeneous wet catalysis [1,2]. 

Hydrolysis of coordinated ligands is a special case of nucleophilic attack. Two examples involving inorganic ligands have already been given in Section II. A on aquation of cobalt(III) complexes. Many further examples will be found in the following Section VII.B on catalysis of hydrolysis of organic substrates by metal ions and complexes. 

Hoffmann, M. R. (1990), "Catalysis in Aquatic Environments , in W. Stumm, Ed., Aquatic Chemical Kinetics Reaction Rates of Processes in Natural Waters, John Wiley and Sons, New York. 

The chemical reactivity of crown-ether complexes with neutral molecules has received little attention. Nakabayashi et al. (1976) have reported crown-ether catalysis in the reaction of thiols with l-chloro-2,4-dinitrobenzene. The catalytic activity was attributed to deprotonation of thiols by dicyclohexyl-18-crown-6 in acetonitrile solution. Blackmer et al. (1978) found that the rate of aquation of the cobalt(III) complex [333] increases on addition of... 

Because practically all aromatic organic pollutants that release phenols or anilines in the course of their degradation could bind HS through enzymatic catalysis, methods employing enzyme-catalyzed polymerization reactions minimizing their presence by partial removal in aquatic and terrestrial environments might be utilized in pollution control. This can have a remarkable effect in environmental engineering practice. 

The rapid anation reaction observed in the presence of I3 implies that 12 should be a very efficient catalyst for the aquation of Co(CN)5r-3. Qualitative observations confirm this prediction, but a careful study of the catalyzed aquation has not yet been completed. A study of the catalysis by other halogen molecules and Lewis acids will also be undertaken in future work. 

I think in the current paper, Dr. Wilmarth s paper worked on by Dr. Haim, the acid catalysis of the aquation of the azide system is an example of what I call an off-site reaction. The attachment of hydrogen to nitrogen, which is three atoms away from the cobalt atom bringing about a weakening of the cobalt nitrogen bond and—if I remember the figures correctly—a 3500-or 5800-fold increase in the rate of aquation. 

Hoffman, M., Catalysis in aquatic environments . In Aquatic Chemical Kinetics, W. Stumm, Ed., Wiley-Interscience, New York, 1990, pp. 71-111. 

Hoffmann, M. R. (1980).Trace metal catalysis in aquatic environments. Environ. Sci. Technol. 14,1061-1066. 

In the heterogeneous catalysis of gas reactions it is a commonplace that the products of a reaction depend upon the catalyst used. For instance, at 280°C ethanol is oxidised to CH3CHO over copper (a dehydrogenation catalyst) but is dehydrated to CH3CH2OCH2CH , over an alumina catalyst [135], The corresponding situation in solution catalysis is less well documented but an example from the author s laboratory will illustrate the point. It concerns the aquation of [Co(NH3)r)Br]Br2... 

Hydrolysis of monodentate phosphate is also very slow and Com-OP03H species (n = 3-0) can be considered inert at room temperature (ka, Table 44). As expected, hydrolysis occurs by substitution at the metal and without exchange into the phosphate (equation 117). Acid catalysis is interpreted in terms of aquation of the acid conjugate of the complexed phosphate (Table 44). [Co OP(OH)3 (NH3)5]3+ (p a — 0.7) hydrolyzes some 102 times slower than [Co OP(OMe)3 (NH3)5]3+, which suggests that protonation at the bound O atom is not important. Base hydrolysis is also very slow (Table 44), occurs via substitution at the metal, and an S lcb process is likely via prior deprotonation of an ammine ligand (equation 118). 

In our previous reports, we measured the kinetics of the covalent binding of aniline to soil and aquatic fulvic and humic acids from the IHSS, and used NMR to follow the incorporation of N-labelled aniline into these samples in the absence of catalysis by enzymes or metals (8,9). In this study, we use NMR to... 

The most important t5q)es of homogeneous catalysis in water are performed by acids, bases and trace metals. A wide variety of mechanisms have been outlined for acid/base catalysis and are presented in kinetics texts (e.g. Moore and Pearson, 1981 Laidler, 1965). A number of bases have been observed to catalyze the hydration of carbon dioxide (Moore and Pearson, 1981 Dennard and Williams, 1966). Examples are listed in Table 9.7 for OH and the base Co(NH3)gOH2. The most dramatic effect is the catalysis of HS-oxidation by cobalt-4,4, 4",4"-tetrasulfophthalocyanine (Co-TSP ). At concentrations of 0.1 nM Co-TSP the reaction rate was catalyzed from a mean life of roughly 50 h to about 5 min. The investigators attributed the reason for historically inconsistent experimentally determined reaction rates for the H2S-O2 system by different researchers partly to contamination by metals. Clearly, catalysis by metal concentrations that are present in less than nanomolar concentrations is likely to be effective in aquatic systems. We shall see that similar arguments apply to catalysis by surfaces and enzymes. 

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