Value hydrolytic processes

Using the same approach again, both hydrolytic processes seen above will be expected to occur and the pH of the solution will depend on the relative values of pKa and pAb, but be independent of the... 

The hydrolytic processes of cations, which give the upper value of the pH... 

Hydroxides of transuranium elements (TUE) can be obtained as amorphous precipitates from aqueous solutions with certain pH values. This process is preceded by hydrolysis that can be considered as a stepwise removal of H from H2O molecules from the first coordination sphere of the TUE ions. In order to characterize hydrolytic behavior of the TUE ions, one can use hydrolysis constants according to the following reactions ... 

Such an enzyme under normal steady-state conditions tends to have the concentrations of its substrates and products at or near to their equilibrium values. Any enzyme enhances equally both the forward and the reverse rates of its catalyzed reaction. Those enzymes that catalyze seemingly irreversible reactions usually involve hydrolysis and since the water concentration in cells and tissues is thousands of times greater than metabolites, the equilibrium position of these reactions is poised in favor of the forward or hydrolytic process. In reactions not involving water, the net direction of the reactions depends on the relative concentration of the substrates and products. If the activity of the enzyme is sufficiently high, relative to others in a metabolic pathway, altering the activity of the enzyme simply makes both the forward and reverse reactions go faster, thus maintaining a pseudo-equilibrium. 

The deoxygenation is general and proceeds at every position of hexoses except at the anomeric carbon where a hydrolytic process is favored over the expected reduction. It should also be noted that satisfactory yields can be obtained when unprotected alcohols, silylethers, or ketal groups are present. Furthermore, the deoxygenation of diesters is still of preparative value even if small amounts of monoesters arise from the deoxygenation of either of the ester groups. 

Independently of strictly enzymatically caused cleavages, hydrolytic processes are often catalyzed in the polymer by a reduction in pH-value. This value can shift to a pH range < 7 due to secondary chemical reactions caused by microorganisms, if low-molecular acids are simultaneously formed by anaerobic metabolism. A principle distinction is made between two mechanisms of enzymatic action hydrolysis and oxidation [889]. 

The same strategy has been employed successfully for the KR of mono-2- or mono-3-substituted indolines [214] and 2,3-disubstituted indolines [215] using CAL-A or CAL-B (Figure 9.30). Similarly, cyclic a-amino esters derived from the 2,3-dihydroindole and octahydroindole cores have also been resolved successfully using allyl carbonates and CAL-A, attaining excellent selectivity and conversion values [216]. Although less explored, complementary hydrolytic processes have also been reported, as, for instance, Ostaszewski and coworkers used "homemade" animal liver acetone powders for the KR of 2-acetyl-4-phenyl-l,4-dihy-dro-2H-isoquinolin-3-one [217]. 

Since base catalysis plays an important role in the hydrolytic breakdown of carbamates, this process has been investigated quite extensively. However, very few data are available on the neutral reaction, which, in some cases, may be significant at ambient pH values. The acid-catalyzed reaction, on the other hand, can generally be neglected. This is presumably because so many electron-withdrawing atoms surround the central carbon that protonation of the carboxyl oxygen insignificantly enhances its susceptibility to nucleophilic attack. 

Since the alcohol is regenerated and the net result is the same as though the original silicon halide had been hydrolyzed directly, it is obvious that the esters may be regarded as hydrolytic intermediates which allow the over-all process of hydrolysis to be controlled and directed. The commercial value of the esters therefore lies in their ability to deposit silica in a desired form and at a well-defined rate. Besides their use as stone preservatives, esters like ethyl silicate are used as sources of pure ion-free silica and as additives to organic paints and lacquers to provide a harder, more resistant film. A disperse sol of silica in n-propanol (possibly derived from propyl silicate) is available commercially for related applications. 

---