ALCOHOLS. 479 



43. ALCOHOLS. 



Constitution of alcohols. The old term "alcohol" originally 

 indicated but one substance (ethyl alcohol), but it is now applied to a 

 large group of substances which may be looked upon as being derived 

 from hydrocarbons by replacement of one, two, or more hydrogen 

 atoms by hydroxyl, OH. In other words, alcohols are hydrocar- 

 bon radicals in combination with hydroxyl. 



If hydroxyl replaces but one atom of hydrogen in a hydrocarbon, 

 the alcohol is termed monatomic ; diatomic and triatomic alcohols are 

 formed by replacement of two or three hydrogen atoms respectively. 

 (Diatomic alcohols are also termed glycols.) As an instance of a 

 diatomic alcohol may be mentioned ethylene alcohol, C 2 H 4 (OH) 2 , 

 while glycerin, C 3 H 5 (OH) 3 , is a triatomic alcohol. Tetratomic, 

 pentatomic, and hexatomic alcohols are also known. 



It has been shown before that the higher members of the paraffin series are 

 capable of forming a number of isomeric compounds. Running parallel to the 

 various series of hydrocarbons (and their isomers) we have homologous series 

 of alcohols. The isomeric alcohols also show properties different from one 

 another, and yield different decomposition products. 



Normal alcohols are those with a straight carbon chain derived from normal 

 hydrocarbons. Alcohols are also divided, according to the linkage between tho 

 hydroxyl groups and a carbon atom, into primary, secondary, and tertiary 

 alcohols. 



A primary alcohol is one in which the hydroxyl group is linked to a carbon 

 atom which is united to but one other carbon atom, or, in other words, it is one 

 containing the univalent group, CH 2 OH. For instance, ethyl alcohol, 

 CH 3 CH 2 OH, represents a primary alcohol. Primary alcohols yield by 

 oxidation aldehydes and acids. 



A secondary alcohol is one in which the hydroxyl group is linked to a car- 

 bon atom which is joined to two other carbon atoms-*. ., the hydroxyl forms 

 a side chain and the bivalent group characteristic of secondary alc( 

 is>CH-OH. For instance, iso-propyl alcohol, ggpCH-OH. Secondary 



alcohols yield ketones by oxidation. 



A tertiary alcohol is one in which the hydroxyl group is linked to a carbon 

 atom which is joined to three other carbon atoms, or one containing the tnva- 



CH 3 \ 

 lent group ^C-OH. For instance, tertiary butyl alcohol, CHpC 



tiary alcohols by oxidation yield decomposition products. 



By saturating with hydrogen the three bonds in the above tnatomic radical 

 methyl alcohof, H.O-OH, is obtained. Methyl alcohol ato known as 

 carbinol, and the term carbinoh is used for the hydrocarbon derivative*, 



