Reactions of Benzyne with Deuteriated Benzenes

To confirm reaction scheme (4) for the formation of naphthalene and biphenyl, phthalic anhydride was allowed to react with benzene-dx (Fields and Meyerson, 1966c). Barring an appreciable isotope effect, two-thirds of the naphthalene should contain a deuterium atom and one-third only protium. Biphenyl arises in two ways insertion of benzyne into a C—H bond of benzene and pyrolysis of benzene. Biphenyl from benzyne insertion should form with retention of the deuterium atom biphenyl from benzene pyrolysis should—again ignoring any isotope effect—be d0, dlt and dz on the statistical basis of losing two, one, or zero deuterium atoms from a total of twelve protiums and deuteriums in the over-all reaction of two benzene molecules. The amount of biphenyl- 

Produots from Pyrolysis of Phthalic Anhydride in Benzene-dj 

The observed naphthalene results did not agree well with those calculated. Further, a considerable amount of both naphthalene and biphenyl contained more deuterium than could arise by the simple postulated reactions. To help clarify these results, benzene-d x was pyrolyzed alone at 690°, and both the benzene recovered and the biphenyl produced were analyzed for deuterium content. The results, shown in Table 3, reveal a 

Number of D atoms Calculated from Calculated from 

The data suggest that hydrogen exchange among benzene molecules is much faster than biphenyl formation, and that the process by which benzene molecules undergo exchange leaves them in an activated state for the reaction to form biphenyl. 

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