Document Detail


Carbon Kinetic Isotope Effects Reveal Variations in Reactivity of Intermediates in the Formation of Protonated Carbonic Acid.
MedLine Citation:
PMID:  24256305     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Kinetic evidence suggests that acid-catalyzed decarboxylation reactions of aromatic carboxylic acids can occur by a hydrolytic process that generates protonated carbonic acid (PCA) as the precursor of CO2. Measurements of reaction rates and carbon kinetic isotope effects (CKIE) for decarboxylation of isomeric sets of heterocyclic carboxylic acids in acidic solutions reveal that C-C cleavage to form PCA is rate-determining with significant variation in the magnitude of the observed CKIE (1.018-1.043). Larger values are associated with the more reactive member in each isomeric pair. This variation is consistent with stepwise mechanisms in which C-C cleavage is competitive with C-O cleavage, leading to reversion to the protonated reactant to varying degrees with an invariant intrinsic CKIE for C-C cleavage. Thus, the relative barriers to reversion and formation of PCA control the magnitude of the observed CKIE in a predictable manner that correlates with reactivity. Application of the proposed overall mechanism reveals that carboxylation reactions in acidic solutions will proceed by way of initial formation of PCA.
Authors:
Adelle A Vandersteen; Scott O C Mundle; Georges Lacrampe-Couloume; Barbara Sherwood Lollar; Ronald Kluger
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-11-20
Journal Detail:
Title:  The Journal of organic chemistry     Volume:  -     ISSN:  1520-6904     ISO Abbreviation:  J. Org. Chem.     Publication Date:  2013 Nov 
Date Detail:
Created Date:  2013-11-21     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  2985193R     Medline TA:  J Org Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Davenport Research Laboratories, Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.
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