Mutarotation generalized acid-base catalysis

When a reaction is susceptible to catalysis by Bronsted acids and bases, the phenomenon is characterized as generalized acid or basic catalysis. One of the earliest reactions discovered to be subject to such generalized acid-base catalysis was the mutarotation of optically active glucose ... 

One of the first reactions to be examined in a reverse micelle was the mutarota-tion of 2,3,4,6-tetramethyl-a-D-glucose in solutions of dodecylammonium salts of carboxylic acids in benzene containing small amounts of water [134], The substrate is relatively hydrophilic, and should be partitioned into the aqueous interiors of the micelles where it is exposed to the ammonium and carboxylate groups of the surfactant which could act as general acid-base catalysts, (Mutarotation in water is subject to general acid-base catalysis,)... 

The depolymerization of dimeric dihydroxyacetone and glycollalde-hyde ° has been studied in aqueous solution, and again shows general acid-base catalysis. Qualitatively similar catalytic behaviour has been observed in the mutarotation of optically active a-keto-esters in alcoholic solution,and in exchange reactions between alcohols and esters, both of which presumably take place by the reversible addition of alcohol to the carbonyl group. 

EXAMPLE The mutarotation of glucose is a case of general acid-base catalysis, with the rate coefficient for the reaction in water having the form... 

The idea that simultaneous (i.e., concerted) acid and base catalysis could strongly accelerate reactions was probably introduced by T. M. Lowry in his considerations of general acid-general base catalysis of the mutarotation of glucose (Lowry and Faulkner, 1925). The concept was provided with strong experimental support by C. G. Swain and J. F. Brown (1952a,b), who used... 

General base and general acid catalysis. Base-catalyzed mutarotation might be formulated as follows A hydroxyl ion or some other base attacks the proton on the anomeric -OH group of the sugar, removing it to form an anion and the conjugate acid BH+ (Eq. 9-87,... 

A reaction exhibiting general acid catalysis, the ester hydrolysis (XXXVIII), has been discussed in Sect. 2.3. The present section deals with a classic reaction which is subject to both general acid and base catalysis in homogeneous media, the mutarotation of D-glucose. 

The mutarotation reaction exhibits general acid-and-base catalysis, the rate depending on the concentrations of all the acids and bases present. 

Lowry and co workers141,222 studied the mutarotation of tetra-O-methyl-a-D-glucopyranose, and found that the rate of reaction is low in dry pyridine or in dry cresol, but high in a mixture of the two solvents or in either solvent when moist. Lowry and Smith57 concluded that the mutarotation requires an acid catalyst and a base catalyst, and that amphoteric solvents are complete catalysts for the process, whereas aprotic solvents are not. They also showed that molecules of undissociated acids, cations of weak bases, and anions of weak acids have catalytic properties. Much the same concept was developed independently by Bronsted and Guggenheim,189,223 and came to be known as generalized acid and base catalysis. It was found that the rate of mutarotation of a sugar in the presence of a mixture of several catalysts may be represented by an equation of the type ... 

---