A Guidebook to Mechanism in Organic Chemistry

Diazo Coupling

products derivable from amines, this latter difference is much less

marked.

The formation of diazoamino compounds by coupling with primary

amines does not constitute a preparative bar to obtaining the products

coupled on the benzene nucleus for the diazoamino compound may

be rearranged to the corresponding amino-azo compound by warming

in acid:

+ N=N'Ph

The rearrangement has been shown undjjr these conditions to be an

//j/ermolecular process, i.e. that the diazonium cation becomes free,

for the latter may be transferred to phenols, aromatic amines or other

suitable species added to the solution. It is indeed found that the

rearrangement proceeds most readily with an a«id catalyst plus an

excess of the amine that initially underwent coupling to yiejd^he

diazoamino compound, it may then be that this amine attacks the

protonated diazoamino compound directly with expulsion of

Ph* NH 2 and loss of a proton:

y^1 -H

J(j N—NH 2 Ph

N

Ar

-*

Ha

£r^^/^N + NH 2 Ph

II

N

Ar

H 8 N-<^^—N=N • Ar+H®

It should perhaps be mentioned that aromatic electrophilic substi­
tution of atoms or groups other than hydrogen is also known. An
example is
Phl+HI - Ph-H + I,