116 Biological Chemistry. 



This substance contains both an alcoholic hydroxy and a 

 carboxyl group, and its constitution, apart from its for- 

 mation from glycol, is also established by the following 

 synthesis. When acetic acid is chlorinated, it yields, 

 amongst other products, the mono-chlor derivative. This 

 on warming with water gives rise to glycollic acid 



CH 2 C1 CH 2 OH 



I +H 2 0= I 

 COOH CO OH 



Glycollic acid is, therefore, hydroxy acetic acid. It is 

 a monobasic acid, containing as it does only one carboxyl 

 group, and it gives rise to esters of the general formula 



CH,-OH 



io. 



I OR 



The acid itself is a hygroscopic crystalline product, melting 

 point 82. 



Lactic acid, CH 3 - CH(OH) - CO - OH, is a more im- 

 portant product, which is constantly met with in biological 

 research. It is a product of fermentation of sugars, 

 starches, etc., and is known to occur in various isomeric 

 forms, some of which exhibit optical activity. The nature 

 of this isomerism, which is different to any so far discussed, 

 will be considered in detail later (Chapter IV.). The 

 sarcolactic acid of muscle is one of these forms. 



The ordinary lactic acid, as prepared synthetically in 

 the laboratory, is, however, optically inactive. Amongst 

 the synthetical methods for its preparation two may be 

 mentioned : (a) When propionic acid is treated with 

 bromine under certain conditions, the substance 



CH,-CHBr CO-OH 

 is obtained. This on treatment with water yields lactic 



acid 



CH. CHBr CO-OH f H.O- CH, CH(OH) CO OH + HBr 



