562 CONSIDERATION OF CARBON COMPOUNDS. 



are more acid than the fatty alcohols ; aromatic amines are less alkaline than 

 in the fatty series. The phenols do not form esters like the alcohols. 



Fatty amines with nitrous acid yield alcoholic compounds ; aromatic amines 

 behave quite differently, viz., a new series of bodies, known as diazo compounds, 

 is formed. Fatty compounds are easily oxidized, while benzene is very stable 

 in the presence of oxidizing agents. 



Benzene series of hydrocarbons. 



By replacing the hydrogen atoms in benzene by methyl, CH 3 , a 

 series of hydrocarbons is formed having the general composition 

 C n H 2n _ 6 . To this benzene series belong : 



Benzene . . . C 6 H 6 B. P. 80.5 C. 



Toluene . . . C 7 H 8 = C 6 H 5 CH 3 110 



Xylene . . . C 8 H 10 - = C 6 H 4 (CH 3 ) 2 141 



Cumene . . . C 9 H 12 = C 6 H 8 (CH 3 ) 8 169 



Tetra-methyl-benzene C 10 H U = C 6 H 2 (CH 3 ) 4 190 



Penta-methyl-benzene C,,H 16 = C 6 H(CH 3 ) 5 231 



Hexa-methyl-benzene Ci 2 H 18 = = C 6 (CH 3 ) 6 264 



The first four members of this series are found in coal-tar ; the 

 last three have been obtained by synthetical processes. While but 

 one toluene is known, the higher members form quite a number of 

 isomeric compounds. Instead of adding two or more methyl groups 

 it is possible to add an ethyl group, C 2 H 5 , or even higher homologous 

 groups, thus producing a great many isomeric compounds. Thus, 

 cymene, C 10 H 14 , found in the oil of thyme, is not tetra-methyl-ben- 

 zene, but para-methyl-iso-propyl-benzene, C 6 H 4 CH 3 .C 3 H 7 . This com- 

 pound is of interest on account of its close relation to the terpenes 

 and camphors, which will be spoken of later. 



Benzene, C 6 H 6 (Benzol). When coal-tar is distilled, products are 

 obtained which are either lighter or heavier than water, and by col- 

 lecting the distillate in water a separation into so-called light oil 

 (floating on the water) and heavy oil (sinking beneath the water) is 

 accomplished. Benzene is found in the light oil and obtained from 

 it by distillation after phenol has been removed by treatment with 

 caustic soda and some basic substances by means of sulphuric acid. 

 Pure benzene may be obtained by heating benzoic acid with calcium 

 hydroxide : 



C 6 H 5 .CO 2 H -f- Ca(OH) 2 == CaCO 3 + H 2 O + C 6 H fl . 



Experiment 67. Mix 25 grammes of benzoic acid with 40 grammes of slaked 

 lime and distil from a dry flask, connected with a condenser. Add to the dis- 

 tilled fluid a little calcium chloride and redistil from a small flask. The 



