Hydrogen Cyanide Dimer and Chemical Evolution.

The hypothesis that life originated by a process of slow chemical evolution has been the basis of many attempts to synthesize biochemical molecules under simulated primitive earth conditions. Since the primitive atmosphere is believed to have been strongly reducing, consisting essentially of the hydrides of hydrogen, carbon, nitrogen, and oxygen,'-3 experiments have been directed toward the synthesis of organic compounds from mixtures of simple hydrides.4-6 Among the many products obtained under a variety of conditions were amino acids and purines, which can be regarded as precursors of proteins and nucleic acids. . striking fact revealed by these experiments is the importance of hydrogen cyanide as a reaction intermediate, shown most clearly by experiments carried out in the laboratories of Miller, Calvin, and Oro'. Miller7 obtained amino acids and other products by passing electrical discharges through mixtures of hydrogen, methane, ammonia, and water. Hydrogen cyanide and aldehydes were shown to be direct products of the discharge. Calvin and Palm6 used high-energy electrons to bombard similar mixtures of gases, obtaining hydrogen cyanide and adenine among the products. Oro' and co-workers5' 8 treated hydrogen cyanide with aqueous ammonia and obtained amino acids and adenine, as well as a black polymer. This polymer was assumed to be the well-known but not well-characterized polymer which forms spontaneously from hydrogen cyanide in the presence of basic catalysts.9 The base-catalyzed polymerization of hydrogen cyanide also yields a tetramer, sometimes formed as the sole product,10 which has only recently been characterized unequivocally as 1,2-diaminomaleonitrile.11' 12 Because of the symmetry of this structure, Kliss"3 postulated that the tetramer is formed by the dimerization of a bivalent carbon species, aminocyanocarbene,14 according to the following mechanism: