THE CHEMICAL CONSTITUTION OF ITS UNITS 29 



sugar of gelatin, as there were other substances like it with a sweet taste 

 and which were not fermentable, its name of glycocoll (y\v/cv$, sweet, 

 Ko\\a, glue) originated and was first used by Horsford, who made an 

 extensive study of it and its derivatives, whilst working in Liebig's 

 laboratory where much of the early work on proteins was carried out. 

 Laurent regarded glycocoll as belonging to the ammonia type of or- 

 ganic compounds ; it was supposed by Cahours to be a derivative of acetic 

 acid, which supposition was only proved by its synthesis from brom- 

 acetic acid and ammonia by Perkin and Duppa, and from chloracetic 

 acid and ammonia by Cahours, both in 1858 : 



CH 2 C1 . COOH + NH 3 = HC1 + CH 2 . NH 2 . COOH. 



About this time the terms glycocine and glycine were used for 

 glycocoll as it was then recognised as a homologue of alanine and leucine. 

 The whole of this series of compounds were termed the glycines. 



A very interesting synthesis of glycine was described by Emmerling, 

 in 1873, by the action of hydriodic acid upon cyanogen; here the 

 hydriodic acid acts both as a reducing agent and as a hydrolysing 

 agent : 



CN CH 2 .NH 2 



I + 5 HI + 2H 2 = | + NHJ + 2 I 2 , 



CN COOH 



and, in 1877, Wallach obtained it by the reduction of cyanoformic ester 

 with zinc : 



COOC 2 H 5 COOC 2 H 5 



I + 4H = | 



CN CH 2 .NH 2 



Lubavin, in 1882, stated that glycine was formed by the action of 

 ammonium cyanide upon glyoxal, which probably first breaks down 

 into formaldehyde and then by the cyanhydrin reaction yields glycine : 



C H + HCN + NH 3 = C H - C H 



^^ \VJ TT 



o 2 



CN COOH 



NH 2 



The direct synthesis of glycine from formaldehyde was only carried 

 out in 1894 by Eschweiler. This method, as well as the method from 

 chloracetic acid and ammonia, by which both Nencki and Mauthner 

 and Suida by slight modifications in technique attempted to obtain 

 larger yields, only gives about 20 per cent, but the method described by 

 Gabriel and Kroseberg, in 1 889, who made use of Gabriel's phthalimide 

 reaction, as first shown by Goedeckemayer, gives an almost theoretical 

 yield of glycine ; this reaction takes place in the following stages : 



