50 PHYSIOLOGY 



The unsaturated hydrocarbons have the general formulae C n H 2n , C H 2n . 2 , 

 CH 2n _ 4 , &c. 



Examples of the first two groups are ethylene CH 2 



II 

 CH 2 



and acetylene CH 



III 

 CH 



Derivatives of all these groups occur in the body. 



THE ALCOHOLS. The first product of the oxidation of hydrocarbons 

 is the series of bodies known as the alcohols. Examples of these are : 



and so on, 



the general formula for the group being 

 C n H 2n + 1 OH. 



In all these alcohols the OH group is, so to speak, more mobile than the other 

 atoms connected with the carbons, and can therefore be replaced by other 

 substances or groups with comparative ease. In this respect therefore an 

 alcohol can be compared to water HOH or to an alkaline hydroxide NaOH or 

 KOH. The best-known example of the group is ethyl alcohol, the ordinary 

 product of fermentation of sugar. In these alcohols the OH group can be 

 replaced by Na. Thus, water with metallic sodium gives sodium hydroxide 

 and hydrogen as follows : 



2HOH + 2Na - 2NaOH + H 2 . 



In the same way alcohol treated with metallic sodium gives off hydrogen, and 

 the remaining fluid contains sodium ethylate, thus : 



2C 2 H 5 OH + 2Na = 2C 2 H 5 ONa + H 2 



(sodium ethylate) 



On the other hand, the OH group may be replaced by acid radicals. Thus, if 

 ethyl alcohol be treated with phosphorus pentachloride, ethyl chloride is formed 

 together with phosphorus oxychloride and hydrochloric acid. Thus : 



Et.OH + PC1 5 - POC1 3 + HC1 + Et.Cl 



(ethyl chloride) 



With concentrated sulphuric acid the reaction is similar to that which obtains 

 between sodium hydrate and this acid, and we have formed ethyl sulphate and 

 water. Thus : 



Et.OH + H 2 S0 4 *= Et.HS0 4 + HOH 



If alcohol be warmed with acetic acid and strong sulphuric acid, among the 

 products of the reaction is ethyl acetate, which is volatile, and therefore passes 

 off. Thus : 



Et.OH + HC 2 H 3 O 2 = Et.C 2 H 3 2 + HOH. 



These compounds of the hydrocarbon group of the alcohol, such as methyl, 

 ethyl, propyl, &c., with an acid, in which the ethyl takes the part of a base, 

 are known as esters. 



