ISOMERIC CHANGE 221 



studied by Armstrong, 1 and of benzene compounds by Moody. ? 

 In the former series, isomeric changes were brought about 

 under somewhat drastic conditions and the experimental 

 evidence is of such a character as to lead to the view that, in 

 certain cases at least, the formation of a second series of acids 

 " involves the formation and subsequent partial hydrolysis of a 

 higher sulphonic acid than that which is eventually separated." 

 Some of the naphthalene acids and the majority of the benzene 

 sulphonic acids were found, however, to undergo change under 

 much simpler conditions — for example o-phenetol sulphonic 

 acid was converted completely into the ^-acid by heating during 

 three hours at ioo° in a current of dry air, although no sul- 

 phonating agent was added to bring about isomeric change. 

 Even in this case ; however, the acid, which darkened in colour, 

 was found at the end of the heating to contain a small amount 

 of sulphuric acid ; there can therefore be little doubt that the 

 catalytic action of this acid was an essential factor in the 

 transference of the sulphonic group. 



(c) Transference of a Nitro Group. — It has been seen in 

 the preceding paragraphs that the transference of a halogen 

 atom is effected only in presence of the halogen or halogen-acid 

 and that a sulphonating agent is probably present in all cases 

 in which a sulphonic group is transferred ; in a similar way 

 the transference of a methyl group when methylaniline, 

 C5H5.NH.CH3, is converted into toluidine CH 3 .C 6 H 4 .NH 2 is 

 effected in presence of a methylating agent and may be attri- 

 buted to reversible methylation. The nitro group differs from 

 these radicals in that it can (apparently) be made to wander by 

 means of agents which have no nitrating properties and do not 

 even contain any nitrogen. One of the most striking illustra- 

 tions of this is to be found in the action of bromine on dinitro- 

 /»-bromophenol, whereby the radicals N0 2 and Br are caused 



to interchange. 3 



OH OH 



1 " Isomeric Change in the Naphthalene Series," Proc. Chem. Soc. 1887, 3, 

 143 et seq. 



2 " Studies of Isomeric Change," Proc. Chetn. Soc, 1892, 8, 90 et seq. 



3 Armstrong, Trans. C/iem. Soc. 1875, 5 2 °- 



