564 CONSIDERATION OF CARBON COMPOUNDS. 



Cymene, C 10 H 14 or CgH^CH^.CgHy (para-methyl-isojjroj^-benzene). 

 This hydrocarbon occurs in the oil of thyme and in the volatile oils 

 of a few other plants ; it has also been made synthetically ; it is a 

 liquid of a pleasant odor, boiling at 175 C. (347 F.). 



Cymene is of special interest, because it is closely related to the 

 terpenes and camphors, from all of which it may be obtained by 

 comparatively simple processes. 



Amino compounds of benzene. 



Aniline, Phenyl-amine, C 6 H 5 NH 2 . The constitution of amines, 

 to which class aniline belongs, has been considered in Chapter 49. 

 Aniline is found in coal tar and in bone-oil; it is manufactured on 

 a large scale by the action of nascent hydrogen upon nitro-benzene, 

 iron and hydrochloric acid being generally used for generating the 

 hydrogen. 



Experiment 69. Dissolve 20 c.c. of nitro-benzene (this may be obtained 

 according to the directions given in Experiment 68, using larger quantities of 

 the material) in alcoholic ammonia and pass through this solution hydrogen 

 sulphide as long as a precipitate of sulphur is produced ; the reaction takes 

 place thus : 



C 6 H 5 NO 2 -f 3H 2 S = C 6 H 5 NH 2 + 2H 2 O + 3S. 



Evaporate on a water-bath to expel ammonium sulphide and alcohol ; add to 

 the residue dilute hydrochloric acid, which dissolves the aniline, but leaves any 

 unchanged nitro-benzene undissolved. Separate the nitro-benzene from the 

 aniline chloride solution, evaporate this to dryness, mix with some lime, in 

 order to liberate the aniline, which may be obtained by distillation from a dry 

 flask. 



Pure aniline is a colorless, slightly alkaline liquid, having a pecu- 

 liar, aromatic odor, a bitter taste, and strongly poisonous properties. 

 It boils at 184.5 C. (364 F.). Like all true amines, it combines 

 with acids to form well-defined salts. 



Aniline dyes. The crude benzene used in the manufacture of aniline 

 dyes is generally a mixture of benzene, C 6 H 6 , and toluene, C 7 H 8 . 

 This mixture is first converted into nitro-benzene, C 6 H 6 NO 2 , and 

 nitro-toluene, C 7 H 7 NO 2 , and then into aniline, C 6 H 5 NH 2 , and tolu- 

 idine, C 7 H 7 NH 2 . When these substances are treated with oxidizing 

 agents, such as arsenic oxide, hypochlorites, chromic or nitric acid, 

 etc., various substances are obtained which are either themselves dis- 

 tinguished by beautiful colors or may be converted into numerous 

 derivatives showing all the various shades of red, blue, violet, green, 

 etc. 



