Benzisoxazole-3-carboxylic acids, formation

A second, related aspect of the medium effect is also likely to be important. Decarboxylation converts a polar, highly solvated -C02 group into a nonpolar, nearly unsolvated CO2. For the case of benzisoxazole-3-carboxylic acids, carboxyl desolvation has been demonstrated to be an important component of solvent catalysis of decarboxylation 113). Desolvation of the carboxyl group on binding to an enzyme may likewise be an important factor. Carbon isotope effects are consistent with this possibility (777). Oxygen isotope effects on formate dehydrogenase are also consistent with this mechanism 114). 

To estimate the impact of these molecular solvent effects the division of solvents into protic (H-bond donor and acceptor) and aprotic (at most H-bond acceptor) ones is very helpful since the formation of specific hydrogen bonds often increases or decreases the reaction rate drastically. The rate for Kemp decarboxylations of benzisoxazole-3-carboxylic acid derivatives accelerate by a factor of about 10 when the solvent character changes from polar protic to polar aprotic. Hydrogen bonds between the reacting anion and the protic solvent were determined to be the most important factor for this acceleration [655, 656]. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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