BENZENE SERIES. AROMATIC COMPOUNDS. 563 



product obtained is pure benzene. Notice that it solidifies when placed in a 

 freezing mixture of ice and common salt. Observe the analogy between Ex- 

 periments 67 and 51. In one case a fatty acid is decomposed by an alkali with 

 liberation of methane, in the other an aromatic acid with liberation of benzene, 

 tin- carbonate of the decomposing hydroxide being formed in both cases. 



Pure benzene is a colorless, highly volatile liquid, having a peculiar, 

 aromatic odor and a specific gravity of 0.884 ; it boils at 80.5 C. 

 (177 F.) and solidifies at C. (32 F.) ; it is an excellent solvent 

 for fats, oils, resins, and many other organic substances. 



Nitro-benzene, C 6 H 3 .NO 2 . When benzene is treated with concen- 

 trated nitric acid, or with a mixture of nitric and sulphuric acids, 

 nitro-benzene is formed . 



C 6 H 6 + HN0 3 == C 6 H 5 N0 2 + H 2 O. 



Experiment 68. Mix 50 c.c. of sulphuric acid with 25 c.c. nitric acid ; allow 

 to cool, place the vessel containing the mixture in water, and add gradually 5 

 c.c. of benzene, waiting after the addition of a few drops each time until the 

 reaction is over. Shake well until all benzene is dissolved and pour the liquid 

 into 300 c.c. of water. The yellow oil which sinks to the bottom is nitro- 

 benzene. It may be purified by washing with water and redistilling, after 

 removal of water and shaking with calcium chloride. 



Nitro-benzene is an almost colorless or yellowish oily liquid, which 

 is insoluble in water, has a specific gravity of 1.2, a boiling-point of 

 205 C. (401 F.), a sweetish taste, highly poisonous properties, even 

 when inhaled, and an odor resembling that of oil of bitter almond, 

 for which it is substituted under the name of essence of mirbane. It 

 is manufactured on a large scale, and is used chiefly in the preparation 

 of aniline. Dinitro benzene is also known. 



Toluene, C 6 H 5 CH 3 (Methyl benzene}. This was first obtained by dry distilla- 

 tion of balsam of tolu, whence its name. It occurs in coal tar, from which it 

 can be separated, but may also be made from benzene by using a reaction gen- 

 erally employed for the introduction of the methyl groups, thus: 



C 6 H 5 Br + CH 3 Br + 2Na = C 6 H 5 CH 3 + 2NaBr. 



Toluene, as well as the other hydrocarbon derivatives of benzene, possesses 

 properties of the fatty hydrocarbons as well as benzene properties. This is 

 quite natural, because of the fatty radicals present in the molecule. Thus, 

 when oxidized, toluene yields benzoic acid, C 6 H 5 CO 2 H, the methyl being 

 oxidized while the benzene ring is unchanged. 



Xylenes, CeH^CHg^ (Dimethyl benzenes}. Three xylenes are found in coal- 

 tar, and are distinguished as ortho-, meta-, and para-xylene. They can be 

 made synthetically from toluene in the same manner as toluene is made from 

 benzene. When oxidized they yield ortho-, meta-, and para-phthalic acids, of 

 the composition C 6 H 4 (C0 2 H) 2 . 



