ON DYNAMIC ISOMERISM. 203 
The remarkable manner in which a small amount of o- acid persists in the 
mixture formed on sulphonating toluene affords similar evidence that this 
acid has a definite place in the equilibrium. 
4. The Beckmann Change.—These interactions, in which an alkyl 
group attached to carbon is interchanged with a negative radicle attached 
to nitrogen, belong essentially to the group of isomeric changes now under 
consideration. Such changes are most frequently observed amongst the 
oximes and nitro- compounds, but a somewhat similar rearrangement must 
be assumed to occur in the preparation of amines from amides by Hofmann’s 
reaction and in the decomposition by heat of the acid azides. Although 
the mechanism of the change is only imperfectly known,! the rearrange- 
ment resembles very closely that by which radicles are transferred from 
the side chain to the nucleus in aromatic compounds ; in each case isomeric 
change is usually complete, and is brought about by acid rather than by 
alkaline agents.2_ Thus, whilst alkaline catalysts greatly accelerate the 
conversion of normal into pseudo- nitrocamphor, they do not bring about 
any further change. Acid catalysts, on the other hand, are less powerful 
in producing pseudo-nitrocamphor, but cause a further non reversible 
rearrangement of the Beckmann type whereby the nitro-compound is 
converted into camphory! oxime 
NOH 
ee Se Nae pk 
| <— CeHi< | > C.H,, O 
O \co alts. 9 Lat 
5. Mechanism of Isomeric Changes involving an Interchange of 
fadicles.—These changes appear to be electrolytic in the same sense as 
the chlorination of ethane, in which the main constituents can act only as 
depolarisers and the electrolyte is probably hydrogen chloride 
=e 
C,H, CH Cl C,H;Cl HCl 
| —'+ | gives 
H CIH Cl HCl HCl 
The association of an olefine with HBr may thus take place in a closed 
electrolytic circuit in which HBr is electrolysed 
> > 
R.C.H BrH Br R.CH Br H Br 
| = nia atest 2!) Aap | — + 
0. “EH er" Fo CHAE! “Bret 
< <_ 
whilst the reverse dissociation might be effected by the passage of a 
current in the opposite direction, giving rise either to the original or 
to the isomeric olefine. So also in the aromatic series the conversion 
of phenylchloroacetamide, C,H;.NCl.CO.CH, into p chloroacetanilide, 
Cl.C;H,.NH.CO.CH;, may be regarded as taking place in a circuit 
' See Steiglitz, Amer. Chem. Journ. 1896, 18, 751; 1903, 29, 49; Slossen, 1903, 29, 
289; Steiglitz and Earle, 1903, 29, 399 and 412. 
? The Hofmann reaction takes place in alkaline solution, but is not an isomeric 
change, and can therefore hardly be quoted as an exception. 
