184 ABIOGENIC ORGANIC-CHEMICAL EVOLUTION 



The primary photochemical reaction seems to be the 

 breakdown of ammonia according to the equation: nh3-> 

 NHj + H.^'"' A number of derivatives can be formed from nHo, 

 especially hydrazine, NH2-NH2, which itself absorbs ultraviolet 

 radiation at 2,400 A and can then take part in chemical 

 reactions with other substances or be broken down according 

 to the equation 2 NoH4-^2 NH3 + N2 + H2.^^^ Molecular nitro- 

 gen could also have been formed in the primaeval atmo- 

 sphere by the direct oxidation of ammonia by the oxygen 

 liberated by the photolysis of water and the escape of 

 hydrogen. Reactions between nitrogen and hydrocarbons, 

 particularly methane, give rise to cyanogen derivatives. 



When ammonia reacts photochemically with carbon mon- 

 oxide it gives formamide, with ethylene it gives vinylamine 

 and so forth. As a rule unsaturated hydrocarbons react 

 photochemically with ammonia to give cyclic compounds of 

 the nature of pyrrolidine or pyridine. ^^^ 



In the primaeval atmosphere of the Earth the hydro- 

 carbons could also react with hydrogen sulphide. This gas 

 was evolved during the formation of the lithosphere when 

 metallic sulphides were hydrolysed by the constitutional 

 water of the mineral formations. When it was given off into 

 the atmosphere it was enabled to react with the hydrocarbons 

 present there by the action of both electric discharges and 

 ultraviolet radiations. This must have led to the formation 

 of mercaptans and various products of their polymerisation, as 

 was observed by S. M. Losanitsch and M. Z. Jowitschitsch^^^ 

 when they passed silent discharges through a mixture of HoS 

 and ethylene: 



C2H4 -f H2S->CH3.CH2SH 

 6 CH3.CH2SH^(C2H4S)6 4- 6H2 



In their book, to which reference has already been made, 

 C. Ellis and A. A. Wells^^ showed that on ultraviolet irradia- 

 tion from a quartz mercury lamp mercaptans (rsh) lose 

 their hydrogen and are converted into the corresponding 

 alkyl disulphides (r-s-s-r). Ultraviolet irradiation can also 

 bring about the formation and further alteration of thio- 

 glycolic acid, cysteine and other complicated organic com- 

 pounds of sulphur, particularly heterocyclic ones. 



