Hydration and Hydrolysis

Evidence for a glycosyl-enzyme intermediate of finite lifetime with inverting a-D-glycosidases, and details of its reaction, came from studies with 2,6-anhydro-l-deoxyhept-l-enitols and glycosyl fluorides. - Analysis of hydration and hydrolysis products on the one hand, and of glycosyla-tion products on the other, indicated an intermediate that could be approached by water from the yff-face only of the ring, and by other glycosyl acceptors only from the a-face (see Schemes 4 and 5 This can be considered a proof of the principle of microscopic reversibility of chemical reactions. 

Under hydrothermal conditions, alumina suffers from increased rates of hydration and hydrolysis of the oxides, resulting in the weakening of conventional supports according to Equation 1. Silica can suffer a similar hydrothermal fate. Process pH can exacerbate the problem (Fig. 34.5). Hence hydrothermal stability is a paramount criterion. 

Boron trifluoride combines with atmospheric moisture to form a white mist containing hydration and hydrolysis products. The odor is detectable at 3.0ppm, but this does not serve as an adequate warning. ... 

Hydration and hydrolysis reactions. We have seen (Chapters 4 and 8) that large charge-to-size ratios for cations result in an increase in hydration energies. Closely related to hydration and, in fact, inseparable from it except in degree is the phenomenon of hydrolysis. In genera], we speak of hydration if no reaction beyond simple coordination of water molecules to the cation occurs ... 

Stacey and Turton61 showed that 2,3,4,6-tetra-O-acetyl-D-glucosone hydrate can be used in two of the established methods for the production of analogs of ascorbic acid. Methods of preparation, reactions, and importance of this class of compound have been reviewed previously.62 Addition of hydrogen cyanide to 2,3,4,6-tetra-O-acetyl-D-glucosone hydrate, and hydrolysis by the usual methods, led to a keto-acid (not isolated) which was converted by enolization and lactonization to D-gluco-ascorbic acid monohydrate, isolated in 50% yield. The product was identified by its (52) F. Smith, Advances in Carbohydrate Chem., 2, 79 (1946). 

E.N. Rizkalla and G.R. Choppin, Lanthanides and actinides hydration and hydrolysis 529... 

Hydration and Hydrolysis. The various oxidation states of plutonium form strong ion-dipole bonds with water to become strongly hydrated in aqueous solution. To a first approximation, we can expect the hydration numbers of the first coordination sphere to be the same as the most probable coordination numbers suggested in the preceeding section. This means values of 8 or 9 for Pu(lll), 7 or 8 for Pu(Vl), and, perhaps, 4 for PuOj and 6 for PuOj. However, the polarization of the water dipoles of the primary hydration layer leads to attraction of additional waters of hydration. Estimates of the total number of waters of hydration for trivalent lanthanides and actinides have been given as 12 - 15 model of a small number of... 

In single-species catalysis, the rate laws for noncatalytic reactions apply, the only difference being that the catalyst appears as both a reactant and a product. In catalysis by highly concentrated acids, anomalies may appear Protonated species other than H30+ (or protonated solvent in non-aqueous media) may arise and act as additional catalysts this can be accounted for with the Hammett acidity function. Also, the rates of reactions such as hydration and hydrolysis may decrease with further increase in acid concentration because of reduced availability of free water as reactant. 

Ion Hydration and Hydrolysis. All ions hydrate to some degree in water. Conceptually, the strength of hydration of an ion could be determined by measuring the heat released when the gaseous form of the ion is immersed in water. For a gaseous metal cation, (g), this reaction would be... 

However, the cations may also be involved in hydration and hydrolysis equilibria as a function of pH (Equations 8.33 and 8.34), which alters their charges and affinities for the surface groups. The surface hydroxyl groups may, of course, be involved in the competition of the ligand sites in... 

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