N-Oxidation of 2-substituted pyridines by dimethyldioxirane: Kinetics and activation parameters

ORGN 147

W. Rucks Winkeljohn, wwinkeljohn@student.gsu.edu1, Pamela Leggett-Robinson, pmrobinson@tuskegee.edu2, Brian S. Crow1, Pedro C. Vasquez1, Paul J. Franklin1, Lucjan Strekowski, lucjan@gsu.edu1, and A. L. Baumstark1. (1) Department of Chemistry, Georgia State University, University Plaza, Atlanta, GA 30303, (2) Department of Chemistry, Tuskegee University, 102 Armstrong Hall, Tuskegee University, Tuskegee, AL 36088
Oxidation of aryl azines by dimethyldioxirane has been shown to give the corresponding N-oxides in quantitative yields. Recently, we have reported the first kinetic study of the N-oxidation of a series of substituted pyridines by dimethyldioxirane. In the current study, the oxidation of 2-alkylpyridines 1a-f by dimethyldioxirane is investigated. The N-oxidation was found to be of the second-order with k2's (M-1s-1) of 0.70 (1a), 0.39 (1b), 0.38 (1c), 0.16 (1d), 0.14 (1e) and 0.000001 (1f). A plot of log k2 for 1a-e showed an excellent correlation with Taft constants. The data for 1f did not correlate. The activation parameters for N-oxidation of pyridine in dried acetone were obtained by the Arrhenius method [ΔH‡ = 9.9 kcal/mol, ΔS‡ = -28.6 eu, ΔG‡ = 18.1 kcal/mol, k2 (23 °C) = 0.78 M-1s-1]. The results are consistent with an electrophilic oxygen transfer mechanism.

 

Heterocycles, Aromatics, Materials, Devices, Switches, Combinatorial Chemistry, Metal-Mediated Reactions
8:00 PM-10:00 PM, Sunday, 13 March 2005 Convention Center -- Hall D, Poster

Division of Organic Chemistry

The 229th ACS National Meeting, in San Diego, CA, March 13-17, 2005