Acetals, acid catalyzed coefficient

The acid-catalyzed hydrolysis of orthoesters is very much faster than that of esters. The second-order rate coefficient for the hydrolysis of ethyl acetate is of the order of 10"4 1-mole-1-sec1 at 25°C, whereas that for the hydrolysis of ethyl orthoacetate103 is of the order of 104 l-mole-1-sec 1, and that for the breakdown of a monoalkyl orthoester must be faster still. If the breakdown of the tetrahedral intermediate is partially rate-determining in acid-catalyzed ester hydrolysis, therefore, its concentration must be very small that is, the equilibrium for its formation must be highly unfavourable. This... 

Rate coefficients and Arrhenius parameters of the acid catalyzed hydrolyses of acetals, ketals, and orthoesters in water at 20 °C... 

It was found by Skrabal et al. [176] that substituent effects on the rate of acid catalyzed acetal hydrolysis are additive. Rate coefficients for a series of aliphatic acetals obey the simple equation... 

The factor q depends on the alkyl group R and the constants p, and p2 depend on the alkyl groups R and R" in RCH(OR )(OR ). The standard reaction with the rate coefficient k0 is the hydrolysis of dimethyl formal. According to the more recent study by Kreevoy and Taft [162], the structure—reactivity relationship for the acid catalyzed hydrolyses of 21 diethyl acetals and ketals of non-conjugated aldehydes and ketones in... 

According to the findings of Kreevoy and Taft [162], the rate coefficients for the acid catalyzed hydrolyses of acetals and ketals can be fitted into the same structure—reactivity relationship. Therefore it is to be expected that the same A1 mechanism is operative for acetals and for ketals, at least as far as they are non-conjugated. 

Catalytic supercritical water oxidation is an important class of solid-catalyzed reaction that utilizes advantageous solution properties of supercritical water (dielectric constant, electrolytic conductance, dissociation constant, hydrogen bonding) as well as the superior transport properties of the supercritical medium (viscosity, heat capacity, diffusion coefficient, and density). The most commonly encountered oxidation reaction carried out in supercritical water is the oxidation of alcohols, acetic acid, ammonia, benzene, benzoic acid, butanol, chlorophenol, dichlorobenzene, phenol, 2-propanol (catalyzed by metal oxide catalysts such as CuO/ZnO, Ti02, MnOz, KMn04, V2O5, and Cr203), 2,4-dichlorophenol, methyl ethyl ketone, and pyridine (catalyzed by supported noble metal catalysts such as supported platinum). ... 

Numerous workers have examined the rate constants for the mutaro-tation of D-glucose in the presence of acetic acid and sodium acetate in an attempt to ascertain whether equation 9 or 10 applies. Although the two equations differ widely, it is not easy to distinguish experimentally between them. It is probable that the concerted mechanism is of no significance in the mutarotation of sugars in aqueous solution, with the possible exception of reactions catalyzed by the water molecule, as will be discussed later. In solvents of low dielectric constant, the formation of ionic intermediates becomes less favored, and the concerted mechanism may apply. Some of the methods that have been used for studying these reactiqns and for determining the catalytic coefficients will be considered next. 

It is sometimes found that acidic species other than hydrogen ions and basic species other than hydroxide ions are capable of catalyzing reactions. One then speaks of general acid-base catalysis. For example, in an aqueous solution containing acetic acid and sodium acetate the rate coefficient A (=u/[S]) can be expressed as... 

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