Hammett Correlation in the Accelerated Formation of 2,3-Diphenylquinoxalines in Nebulizer Microdroplets |
| |
| Authors: | Nathan W Fenwick Richard Telford Amie Saidykhan William H C Martin Richard D Bowen |
| |
| Institution: | Faculty of Life Sciences, School of Chemistry and Biosciences, University of Bradford, Bradford BD7 1DP, UK; (N.W.F.); (R.T.); (A.S.); (W.H.C.M.) |
| |
| Abstract: | The accelerated formation of 2,3-diphenylquinoxalines in microdroplets generated in a nebulizer has been investigated by competition experiments in which equimolar quantities of 1,2-phenylenediamine, C6H4(NH2)2, and a 4-substituted homologue, XC6H3(NH2)2 X = F, Cl, Br, CH3, CH3O, CO2CH3, CF3, CN or NO2], or a 4,5-disubstituted homologue, X2C6H2(NH2)2 X = F, Cl, Br, or CH3], compete to condense with benzil, (C6H5CO)2. Electron-donating substituents (X = CH3 and CH3O) accelerate the reaction; in contrast, electron-attracting substituents (X = F, Cl, Br and particularly CO2CH3, CN, CF3 and NO2) retard it. A structure–reactivity relationship in the form of a Hammett correlation has been found by analyzing the ratio of 2,3-diphenylquinoxaline and the corresponding substituted-2,3-diphenylquinoxaline, giving a ρ value of −0.96, thus confirming that the electron density in the aromatic ring of the phenylenediamine component is reduced in the rate-limiting step in this accelerated condensation. This correlation shows that the phenylenediamine acts as a nucleophile in the reaction. |
| |
| Keywords: | microdroplets diphenylquinoxalines condensation competition experiments nebulizer Hammett relationship |
|
|
