48 PHYSIOLOGY 



With sodium hydrogen sulphite the following reaction takes place : 



CH 3 CH 3 



| + NaHSO 

 CHO 



SO 3 Na 



These compounds of aldehydes with sodium sulphite can be readily obtained in a 

 crystalline form and furnish a convenient means of separating the aldehydes from their 

 solutions. 



(4) All the aldehydes possess a strong tendency towards polymerisation. Ethyl 

 or acetic aldehyde treated with strong sulphuric acid gives the compound paraldehyde. 

 Thus: 



3C 2 H 4 C 6 H 12 3 . 



(acetic aldehyde) (paraldehyde) 



If warmed with strong potash the polymerisation occurs to a still further extent with 

 the formation of resinous substances of unknown composition, but at any rate of a 

 very high molecular weight, the so-called ' aldehyde resin.' Formic or methyl aldehyde, 

 CH 2 0, may in the same way undergo polymerisation with the formation of a mixture 

 of substances belonging to the group of sugars, namely, the hexoses, as follows : 



6CH 2 O = C 6 H 12 6 . 



This formation of sugar from formic aldehyde probably plays an important part in the 

 assimilation of the carbon from the carbonic acid of the atmosphere by the green parts 

 of plants. 



ACIDS. By the oxidation of the group CHO of the aldehydes we obtain the group 

 COOH, which is characteristic of an organic acid. Thus, formic aldehyde on oxidation 

 gives the compound HCOOH, formic acid. Ethyl or acetic aldehyde, CH 3 CHO, with 

 an atom of oxygen, gives the compound CH 3 COOH, acetic acid. 



CH S CH 3 



I +0= | 



CHO COOH. 



Since these acids are derived from the paraffins a whole series of them exists corre- 

 sponding to the series of paraffins, and known as the fatty acids. Examples of this 

 group are : 



Formic acid Acetic acid Propionic acid Butyric acid 



HCOOH CH 3 CH 3 CH 3 



I I I 



COOH CH 2 CH 2 



I I 



COOH CH 2 



I 



COOH. 



In addition to these fatty acids, there are also unsaturated acids, derived from 

 the unsaturated hydrocarbons. 



DERIVATIVES OF THE FATTY ACIDS 



AMINO- ACIDS are derived from the fatty acids by the replacement of one atom 

 of hydrogen by the group NH 2 . 



Thus from propionic acid we may have: 



CH 2 NH 2 CH 3 



I I 



CH 2 or CH.NH 2 



I I 



COOH COOH. 



13 



The second form, the a-amino acid, is the only one which occurs in the body. 



