Structure of Simpler Organic Compounds. 147 



droxide solutions, and give fairly stable salts known as the 

 phenates. The phenols, however, are still weak acids, and 

 their salts are decomposed by carbon dioxide. Potassium 

 phenate is C 6 H 5 -OK. These particular properties of 

 phenols are not characteristic of hydroxyl derivatives of 

 benzene, unless the hydroxyl group is directly attached to 

 a carbon atom of the benzene nucleus. Thus, for ex- 

 ample, a hydroxyl group attached to a carbon atom in a 

 substituting group or " side-chain " can behave like an 

 ordinary alcoholic group ; a halogen atom in the same 

 position will also behave like a halogen atom in an ali- 

 phatic compound. As an example, the substances known 

 as benzyl alcohol, C 6 H 5 -CH 2 OH, and benzyl bromide, 

 C 6 H 5 CH 2 Br, may be mentioned. Both these substances 

 behave, in their reactions, in the same way as aliphatic 

 derivatives. 



V. A characteristic series of derivatives known as 

 diazo compounds can be prepared from aromatic amines. 

 When a nitro-derivative is treated with nascent hydrogen, 

 it is reduced to an amino-derivative of which C 6 H 5 -NH 2 , 

 or aniline, is a type. The salts of these compounds, on 

 treatment with nitrous acid, yield unstable compounds, 

 which readily decompose on warming, on a percussion, and 

 are in fact so unstable as to be explosive. To obtain 

 them, therefore, the treatment with nitrous acid must be 

 carried out in cooled solutions. They are known as the 

 diazonium compounds. Their formation is illustrated by 

 the following equation 



The compound thus produced is phenyldiazonium chloride. 

 The process of preparation of diazo compounds is 

 known as " diazotization." A certain number of aliphatic 

 diazo compounds are also known. The aromatic diazo 

 compounds are made by dissolving the salt of the base, 



