CONDENSATION PRODUCTS OF AMINO ACIDS 17 



Anhydrides of Glycine and the Biuret Base. 



In 1883 Curtius first prepared glycine ester by decomposing glycine 

 ester hydrochloride with silver oxide. It was a colourless, strongly 

 basic oil, very unstable, and only capable of preservation in dry ether. 

 If it were allowed to stand in the air, it underwent decomposition and 

 was converted into an insoluble anhydride, 



and a soluble base, which gave the biuret reaction and was called the 

 biurel base. 



Further investigations upon the nature of these compounds were 

 made by Curtius and Goebel in 1888, who found that the glycine 

 anhydride separated when the ester was allowed to stand for a few days 

 with four volumes of water, and that from the analysis of its silver and 

 copper compounds it had the formula 



/NH ,N 



CH,\ or possibly CH,\ || 



\CO \C(OH) 



No result could be arrived at concerning the biuret base, which was 

 prepared by keeping pure glycine ester in a sealed tube, when it 

 changed into a white crystalline mass. 



Curtius and Schulze, in 1 890, by molecular weight determinations 

 found that the formula of the anhydride must be doubled, and it was 

 probably represented by 



/NH CO\ 



C <CO-NH> H ' 

 which was ultimately proved by Fischer and Fourneau in 1901. 



The biuret base was investigated again in 1 894 by Lilienfeld, who 

 prepared it by heating glycine ester with solid potassium bisulphate on 

 the water bath, and who gave it the formula C 4 H 9 N,O,, and the con- 

 stitution 



/CO . NH. : CH, 

 NH/ 



\CO.NH, :CH, 



since he also obtained dimethylamine, ethyl ether and carbonic acid in 

 its preparation. 



When he heated it with water, Lilienfeld obtained a flocculent pre- 

 cipitate, such as Curtius and Goebel had observed; this, formed a 

 gelatinous mass after filtering which contracted like gelatin and be- 

 haved, in fact, very like glutin. In a similar manner Lilienfeld con- 



PT. H. a 



