Metal-ammonia reduction pathway

These results allow a complete description of metal-ammonia processes, as shown in Scheme IV. The upper pathway represents the classical Birch reduction (i.e., benzenes), whereas polynuclear aromatic compounds react by one of the lower routes. As indicated in Scheme IV, the protonation of dianions rather than radical anions by ammonia is favored. We previously suggested dianion protonation (8) because radical anions are not very basic (10). Recently, Mullen et al. (12) pointed out that, in some cases, dianions and radical anions of the same neutral precursor are protonated at different sites in the cases they investigated, protonation occurred with the dianions. 

The reduction of alkyl halides by solutions of dissolved metals like, e.g. sodium in ammonia or alkali metal naphthalenides in tetrahydrofuran, provides a convenient means of removing halogens to produce hydrocarbons or to prepare alkali metal organic compounds. It is generally accepted that these reductions involve free radical intermediates R pathway A, Scheme 12) . 

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