Structure of Simpler Organic Compounds. 145 



C 6 H 5 C1, C 6 H 5 C1 2 , C 5 H 5 Br, can be formed. This action is 

 accelerated by the action of the so-called halogen " carriers," 

 such as iodine, aluminium chloride, etc. Benzene is, how- 

 ever, also able to form addition products, the substance 

 C 6 H 6 C1 6 being formed when benzene is treated with 

 chlorine in direct sunlight. The action of halogens on 

 certain benzene derivatives is mentioned later. 



II. The Difference in the Action of Nitric Acid. 

 Nitric acid does not oxidize benzene and its derivatives as it 

 would if it were an unsaturated compound, but forms with 

 it a well-defined series of nitro compounds. The reaction is 

 best carried out with a mixture of nitric and sulphuric acids, 

 the latter acting as a dehydrating agent. At moderate 

 temperatures the mono-nitro derivative is formed 



C 6 H 6 + H 4 N0 3 = C 6 H 5 N0 2 + H 2 O 



At higher temperatures the dinitro-derivatives are formed, 

 of which the mea-derivative preponderates in quantity. 

 The " nitrating " action of nitric acid is a general one. 



III. The action of sulphuric acid on aromatic de- 

 rivatives is a characteristic one. By means of sulphuric 

 acid, a series of substances known as the sulphonic acids 

 is produced, the formation of which is illustrated by the 

 following equation 



C 6 H 6 + H 2 S0 4 = C 6 H 5 -S0 3 H + H 2 



The constitution of these sulphonates may be repre- 

 sented by the general formula S0 2 <^ where R is a 



benzene radicle. They contain, like carboxylic acids, an 

 acid hydroxyl group, which on treatment with phosphorus 



pentachloride yields an acid chloride of the type SO 2 <(^ . 



The sulphonic acids are strongly acid substances, which 

 are generally soluble in water, and yield well-defined salts. 



Cl,W7) 10 



