MERCURY PHOTOSENSITIZED DIMERIZATION OF AMINES

Previous mercury photosensitized reactions failed for important classe s of compounds such as fluorocarbons, aromatic compounds and many amin es. We now find that the scope of the method is greatly expanded by th e use of ammonia as reactive gas. In the case of amine dimerization, d iscussed in this paper, ammonia prevents diversion of the product from the desired dehydrodimer to imine formation. In this way, a variety o f 1,2-diamines can be prepared simply and in high yield from the corre sponding amines. For example, isopropylamine is converted to 2,3-dimet hyl-2,3-diaminobutane. In this paper we consider a simple application of the Hg/NH3 method : the dehydrodimerization of amines. In the abse nce of NH3, (Hg-amine) exciplex formation can occur for amines, givin g unselective reactions or quenching the Hg without productive chemis try taking place at all. Ammonia has the advantage both of preventing (Hg-amine) exciplex formation and of preventing attack on the interme diate imine by the amine starting material, both processes that severe ly reduce yields of dehydrodimer. For primary, secondary and tertiary amines, different pathways all lead to the formation of a new C-C bond at the position alpha- to N in the amine. Recombination between N- an d C-centered radicals can also give C-N dimers. Cross-dimerization of amine-derived radicals with other classes of compounds lead to the cor responding mixed products. For example, an amine and trioxane give alp ha-aminoaldehyde derivatives.