KINETIC-STUDY OF THE FAST STEP OF THE ALKALINE-HYDROLYSIS OF P-CHLORANIL USING STOPPED-FLOW TECHNIQUE

The alkaline hydrolysis of p-chloranil or 2,3,5,6-tetrachloro-1,4-benz oquinone (C6Cl4O2, O) was studied, using stopped flow spectrophotometr y and Electron Spin Resonance techniques (E.S.R.). In the present stud y it was shown for the first time, that a free radical is produced che mically and that it can account for the propagation of the reaction. I t was found that in alkaline conditions chloranil in a ''Michael'' fas hion undergoes 1,2 addition being hydrolyzed and in turn produces a ch loranil free radical (Q.). The hydrolysis then proceeds via a number o f intermediates yielded by this radical and a number of different prod ucts is formed. The formation of these products, both quantitatively a nd qualitatively has a strong dependence on the concentration of the O H- species and chloranil. The various possible routes of the hydrolysi s are studied either spectrophotometrically or by E.S.R. Two different intermediates are observed absorbing at 426 nm and at 540 nm, respect ively. Each species was formed and destroyed within 10 s to 30 min dep ending on the exact conditions. The reaction rate constants for the fo rmation and the decay of the intermediates was estimated using the Gug genheim method. At both wavelengths the rate constants seem to have a complex relation to the concentration of the anion. (C) 1997 John Wile y & Sons, Inc.