How Acid-Catalyzed Decarboxylation of 2,4-Dimethoxybenzoic Acid Avoids Formation of Protonated CO2.

J Am Chem Soc

Davenport Chemical Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.

Published: June 2016


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Article Abstract

The decarboxylation of 2,4-dimethoxybenzoic acid (1) is accelerated in acidic solutions. The rate of reaction depends upon solution acidity in a manner that is consistent with the formation of the conjugate acid of 1 (RCO2H2(+)), with its higher energy ring-protonated tautomer allowing the requisite C-C bond cleavage. However, this would produce the conjugate acid of CO2, a species that would be too energetic to form. Considerations of mechanisms that fit the observed rate law were supplemented with DFT calculations. Those results indicate that the lowest energy pathway from the ring-protonated reactive intermediate involves early proton transfer from the carboxyl group to water along with C-C bond cleavage, producing 1,3-dimethoxybenzene and CO2 directly.

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http://dx.doi.org/10.1021/jacs.6b01770DOI Listing

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