Nonlinear Bronsted and Hammett Correlations Associated with Reactions of 4-Chloro-7-nitrobenzofurazan with Anilines in Dimethyl Sulfoxide Solution

作者：Jmaoui I; Boubaker T^*; Goumont R

来源：International Journal of Chemical Kinetics, 2013, 45(3): 152-160.

DOI：10.1002/kin.20751

The kinetics and mechanism of nucleophilic aromatic substitution reactions of 4-chloro-7-nitrobenzofurazan 1 with 4-X-substituted anilines 2ag (X = OH, OCH3, CH3, H, I, Cl, and CN) are investigated in a dimethyl sulfoxide (Me2SO) solution at 25 degrees C. The Hammett plot of log k1 versus s is nonlinear for all the anilines studied due to positive deviations of the electron-donating substituents. However, the corresponding YukawaTsuno plot resulted in a good linear correlation with s+r (s+-s). The corresponding Bronsted-type plot is also nonlinear, i.e., the slope (beta nuc) changes from 1.60 to 0.56 as the basicity of anilines decreases. These results indicate a change in a mechanism from a polar SNAr process for less basic nucleophiles (X = I, Cl, and CN) to a single electron transfer for more basic nucleophiles (X = OH, OCH3, and CH3). The satisfactory log k1 versus Eo correlation obtained for the reactions of 1 with anilines 2ad in the present system is consistent with the proposed mechanism. Interestingly, the beta nuc = 1.60 value measured for 1 in Me2SO reflects one of the highest coefficients Bronsted ever observed for SNAr reactions.

• 出版日期2013-3