Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

356 TBTKAPHBNYLHYDRAZINB
fit for use as a solvent for oxidations. 1 ) The solution is kept cool
in ice-water and vigorously shaken while very finely powdered permanganate
is gradually added. Bach portion is added only after
the colour produced by the preceding has disappeared. After about
16 g. of permanganate have been used in the course of an hour and
a half more of the oxidising agent is added without external cooling
of the mixture until the colour persists for half an hour (but in
no case add more than 14 g. additional permanganate). Part of the
diphenylamine is oxidised down to phenylisonitrile (odour, evolution
of carbon dioxide). By means of a few drops of alcohol or of formaldehyde
solution the mixture is now decolorised, and the manganese
dioxide, after being collected at the pump, is pressed down well
and washed twice with a little warm acetone. The acetone is then
distilled under slightly reduced pressure from the water bath at 35° ;
if the receiver is kept cool most of the solvent can be recovered.
The rest of the acetone is removed in a good vacuum at a bath
temperature of 20°.
To the tetraphenylhydrazine which has crystallised 20-30 c.c. of
ether are added with ice cooling. In this way oily material is dissolved.
After some time the compound is filtered dry at the pump
and washed clean with drops of ether. From 20 to 24 g. (60-70 per
cent of the theoretical) of almost colourless crude product are thus
obtained, which is pure enough for the following experiments. By
recrystallisation from a little benzene (about two to three parts)
absolutely pure tetraphenylhydrazine, melting point 144°, is obtained.
The solution should be boiled for a short time only. If
one-third of its volume of boiling alcohol is added with shaking to the
hot solution, more crystallises than from benzene alone. The pure
preparation is collected at the pump, washed, first with benzenealcohol
1:1, then with alcohol alone, and immediately dried in a
vacuum desiccator. The mother liquor may be evaporated in vacuo
and the residue digested with cold ether as before. When pure and
well dried the substance can be preserved unchanged for years if
protected from light and acids.
Experiment,—Dissolve about 0-5 g. of tetraphenylhydrazine in
5 c.c. of xylene and warm the solution slowly over a small flame.
The initially colourless solution becomes intensely olive green, even
before the boiling point of the solvent is reached. The colour is that
of the free radicle which, at this temperature, very rapidly under-
1 Cf. F. Sachs, Ber., 1901, 34, 497.