Asghar, B. H. M. and Crampton, M. R. (2005) 'Rate-limiting proton-transfer in the sigma-adduct forming reactions of 1,3,5-trinitrobenzene and 4-nitrobenzofuroxan with substituted anilines in dimethyl sulfoxide.', Organic & biomolecular chemistry., 3 (21). pp. 3971-3978.
Kinetic and equilibrium results are compared for the reactions in dimethyl sulfoxide of 1,3,5-trinitrobenzene, 1, and 4-nitrobenzofuroxan, 4, with a series of substituted anilines in the presence of Dabco or in, some cases, quinuclidine. pKa values for the corresponding anilinium ions are reported. The reactions of 1 and 4 are likely to proceed through nucleophilic attack by the aniline to yield zwitterionic intermediates which may transfer an acidic proton to the bases present to yield the anionic adducts 9 or 12 respectively. In the formation of 9 from 1 the proton transfer step is rate-limiting; however, the slower interconversion of 4 and its zwitterion leads to only partial rate-limiting proton transfer in the formation of 12. Results with substituted anilines including 2-substituted and N-methyl aniline indicate that steric effects are not a major factor in determining rates of proton-transfer in these systems. Contrary to previous reports no evidence was found for a strong interaction between 1 and Dabco in DMSO.
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|Publisher Web site:||http://dx.doi.org/10.1039/b511644a|
|Record Created:||21 Sep 2007|
|Last Modified:||08 Apr 2009 16:35|
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