Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

FIXATION OF DIPHENYLNITKOGEN 357
goes further alteration, but, as the next experiments show, can be
fixed as diphenylnitrosamine if nitric oxide is present.
Experiment.-—Pour concentrated sulphuric acid on to a few centigrammes
of tetraphenylhydrazine. A beautiful red colour at first
appears ; it changes in a short time to intense blue-violet.
The dye which is formed here is identical with that which is produced
from diphenylamine in the well-known test for nitric acid (and
other oxidising agents), namely, diphenyldiphenoquinone-dhmonium
sulphate) (Kehrmann).
H
OSO3H
When the dye is formed from tetraphenylhydrazine, diphenylhydroxylamine
(pp. 182, 341) is first produced by hydrolysis at the
N—N-linkage.
THE FIXATION OF DIPHENYLNITROGEN BY NITRIC OXIDE 1
An apparatus for producing pure nitric oxide is set up as follows.
As in the apparatus for preparing hydrogen chloride, a filter flask
(capacity 750 c.c.) is fitted with a dropping funnel, from which 4Nsulphuric
acid is dropped into concentrated sodium nitrite solution,
containing 70 g. of NaN02 in 150 c.c. of water. For this amount of
nitrite 250 c.c. of the 4iV-acid are required. The side tube of the
flask leads first to a wash-bottle with concentrated sodium (or
potassium) hydroxide, and then to one with concentrated sulphuric
acid. By means of a short rubber tube a T-tube is attached to the
second wash-bottle. One branch of the tube is connected to a
carbon dioxide Kipp, the other to the reaction vessel. The rubber
tube carries a screw clip so that, at the end of the experiment, the
nitric oxide generator can be removed.
Tetraphenylhydrazine (5 g.) is dissolved in 40 c.c. of toluene in a
small round-bottomed flask fitted with a two-holed cork. A delivery
tube, which is connected to the apparatus just described and
reaches to the bottom of the flask, passes through one hole, a short
glass tube through the other. With the second wash-bottle disconnected
from the rubber tube, and the latter closed by means of
the clip, the dropping in of sulphuric acid is begun, and at the same
1 Annalen, 1911, 381, 211.