DECARBOXYLATION OF 6-NITROBENZISOXAZOLE-3-CARBOXYLATE IN BENZENE CATALYZED BY CROWN ETHERS AND THEIR POLYMERS

Rate constants and activation parameters of decarboxylation of potassium 6-nitrobenzisoxazole-3-carboxylate (1) were measured in benzene in the presence of 4’-methylbenzo-18-crown-6, 18-crown-6, cryptand 2.2.2, and the homopolymer (P18C6) and styrene copolymers of 4’-vinylbenzo-18-crown-6. The crown-complexed ion pairs of 1 decompose with rate constants in the order of 0.1-1.0 s-1 at 25°C, depending on the crown compound. The rate constant for the cryptated ion pair (4.78 s-1 at 25°C) is nearly identical with that found for the decarboxylation of I in dimethyl sulfoxide and more than a thousand times higher than previously found for the tetramethylguanidinium salt of I in benzene. The crown ethers are believed to be externally complexed to the tight potassium carboxylate ion pair. For polymers with a high content of crown ligands, the rate constant of decarboxylation increases, probably as a result of an enlargement in the interionic distance of the crown complexed ion pair. © 1979, American Chemical Society. All rights reserved.