Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

SOLID PHENYLDIAZONIUM CHLOKIDE 287
the mixture has stood for five to ten minutes the diazonium salt is
completely precipitated by gradual addition of ether ; it is collected
at the pump and washed, first with alcohol-ether (1:1) and then
with ether alone. The salt is kept moist with ether and only a small
sample is dried on filter paper. The dried material is caused to
explode by a blow or in a flame. Even the material which is moist
with ether must not be touched with a spatula or other hard object.
The diazonium salt on the filter is dissolved in ice-water and is
used for the preparation of phenyldiazonium perbromide and phenyl
azide (see below).
When nitrous gases (from arsenious oxide and nitric acid, d. 1-35)
are passed into a well-cooled suspension of aniline nitrate in water,
and alcohol and ether are then added gradually, crystalline phenyldiazonium
nitrate is obtained. At most only 2 g. of aniline are used,
and of the diazonium salt only as much as covers well the tip of a
knife-blade is dried on porous plate, after collecting at the pump and
washing with alcohol-ether (1 : 1).
The nitrate detonates on heating on a spatula or on being struck
with a hammer. The chloride is less liable to explode, but it too
must not be preserved in the dry state. In general, work with dry
diazonium salts must be carried out cautiously.
On account of their great lability the diazonium salts of the simple
primary amines cannot be isolated from aqueous solution. On the
other hand, they crystallise from alcohol when ether is added. Since
the metallic salts of nitrous acid are insoluble in alcohol, its esters are
used instead for diazotisation in alcohol. These esters are hydrolysed
by acid with extraordinary rapidity and therefore behave almost like
salts (see p. 147).
The diazonium salts are colourless. Their aqueous solutions react
neutral. If the acid is removed from the salts by means of alkali, very
unstable diazonium hydroxides result, which can only be demonstrated
in the solution during quite a short time. These hydroxides change by
addition of alkali and elimination of water into salts of acid diazohydroxides,
the so-called diazotates.
H
CBHK.N=NONa
"Cl
im
Diazonium salt Diazonium
hydroxide
'°, C6H5.N=NONa .
Sodium phenyldiazotate