54 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



With phenyl hydrazine a compound of the following 



formula C 6 H 5 N NH 2 we have : 



R=C=0 + H 2 N NHC 6 H 5 = RCN NHC 6 H 5 + H 2 



Acids. Upon oxidation the CO group gives rise to an acid, 

 the exact composition of which depends on the elements or 

 groups attached to the carbon. Thus an aldehyde oxidises 

 as follows : 



R R 



l_ l_ 



I I 



H OH 



A ketone gives a mixture of acids according to a rather 

 more complex reaction. 



The group C0 2 H, which is a shortened form of the group 



OTT 

 """" " as written above, is known as the carboxyl group, 



and is characteristic of all organic acids which may be written 

 according to the general formula RCOOH ; thus in acetic acid 

 R is represented by the group CH 3 or methyl, and the formula 

 of the acid is CH 3 COOH. The substance used as an illustra- 

 tion of the determination of a molecular formula on p. 44 was 

 acetic acid. On reduction with nascent hydrogen the group 



/H 



C0 2 H is reconverted to C=0 and CH 2 OH, i.e., acids 



give on reduction aldehydes and alcohols. 



Esters. Alcohols combine with organic acids to form what 

 are known as esters or ethereal salts ; thus ethyl alcohol com- 

 bines with acetic acid according to the following equation : 



C 2 H 5 OH + CH 3 COOH = CH 3 COOC 2 H 5 + H 2 

 which may be generalised as follows : 



ROH + RCOOH = RCOOR + H 2 



