of the Aromatic Nucleus. 



449 



and meta-laws of substitution (see Armstrong J. C. S. li. 

 p. 259). 



(a) Let us consider the continued action of sulphuric 

 acid upon benzene. The sulphonic group first introduced is 

 itself sulphonizedj and for the moment an unstable body (B) 

 is formed. This compound gives off a molecule of water, the 

 hydroxy! (n) being eliminated with one of the ortho- or meta- 

 hydrogen atoms (o 4 o 6 m ] m 3 ). Simultaneously with this 

 change the two sulphonic groupings (a and b) become dis- 

 united, and (b) takes the place of the eliminated hydrogen 

 atom. As in a large number of such molecules, the hydroxy 1 

 (?i) will be more often in closer proximity to a meta- than to 

 an ortho-hydrogen atom, and always closer to one of these 

 than to the para-hydrogen atom (p), we shall get the forma- 

 tion of meta- and ortho- to the exclusion of para-benzene- 

 disulphonic acid, and of these the meta will be the chief 

 product. These changes may be graphically represented 

 thus : — 



.-<«,» 



oh s:-° ****"£Nw, . 



hVJ 



->J 



(Elevation. 



I// 

 Intermediate Body (B). 



Benzene meta- 

 di-sulplionic acid. 



H- - ■(%) 



"-A 



H--K) 



R--C*) 



(Plan). 

 Benzene sulphonic acid, C 6 H 5 S0 3 H. 



