THERMAL REARRANGEMENT OF ARYLAZOTRIBENZOYLMETHANES IN SOLID STATE . EXAMINATION WITH DIFFERENTIAL THERMAL ANALYSIS

The rearrangements of phenylazotribenzoylmethane (H-I) to the corresponding enol benzoate (H-II) and the hydrazone (H-III), as well as the following rearrangement of the H-II first formed to H-III, have been studied with the aid of differential thermal analysis. The similar set of reactions of p-bromophenylazotribenzoylmethane (Br-I) and its relatives Br-II and Br-III have also been studied. The various thermal changes associated with melting and rearrangement evident from the thermograms have been correlated with chemical analysis of interrupted reaction mixtures. Examination of mixtures of these compounds (H-I, H-II, and H-III or Br-I, Br-II, and Br-III) has shown that their eutectic points are at 115-120°, well above the temperatures required for convenient study of the rearrangements. It is shown that the relative areas corresponding to the various thermal changes in a thermogram are quite reproducible from one experiment to another. A method is described for determining approximate values of the enthalpy changes associated with the processes evident from the thermograms. © 1969, American Chemical Society. All rights reserved.