Kinetics and Mechanistic Studies of the Bromination of some Substituted 2-Benzylidene-1,3-indandione

The rate of bromination of 2-benzylidene-1,3-indandione (I1) and its derivatives p-NO2 (I2), p-Cl (I3), furan ring (I4), and p-OCH3 (I5) have been studied in chloroform by means of U.V spectroscopy technique. The study indicated first order dependence on each of reactants with order of rates I2 > I3 > I4 > I1 > I5 at any temperature. The effect of substituents on the rate showed that electronic factors, inductive and resonance effects play reasonable role on the stability of the intermediates. Moreover, bromination processes showed a good free energy relationship with Hammett value of greater than "1.0" at 298 K. The kinetic studies for these reactions revealed that these reactions are of nucleophilic addition type which characterized by the formation of intermediates that transformed to the desired products (II). Suggested mechanisms, which are consistent with the results, have been postulated and suitable rate laws in consonance with the suggested mechanisms have been derived.