Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

366 QUINOLINB
The very remarkable reaction which consists in the introduction
of the NH2-group into an aromatic ring by the action of sodamide is
due to F. Sachs (Ber., 1906, 39, 3006), who studied various examples of
the process in the naphthalene and anthraquinone series.
In the case of pyridine, Tschitschibabin's synthesis proceeds with
special ease. An intermediate addition product of NH2Na to the
—N=C double bond with the grouping —NNa—C(NH2)— is doubtless
formed. The net result is as follows :
C5H5N + NaNH2
> CSH4N.NH2 + Na + H ,
and the a-aminopyridine thus formed behaves, in its reactions, like a
tautomeric compound. Many of its derivatives, especially the cyclic
ones, are derived from a diimino-form which can arise as a result of the
following rearrangement:
2. QUINOLINE
(a) SKRAUP'S QUINOLINE SYNTHESIS 1
Concentrated sulphuric acid (45 c.c.) is poured with shaking into
a flask (capacity 1-5 1.) containing a mixture of 20 g. of nitrobenzene,
31 g. of aniline, and 100 g. of anhydrous 2 glycerol. The flask is then
fitted with a long wide reflux condenser and heated on a wire gauze.
As soon as the sudden escape of bubbles of vapour from the liquid
shows that the reaction has set in, the flame is immediately removed,
and the main reaction, 3 which is sometimes extremely violent, is
allowed to proceed to completion without external heating. When
the reaction has subsided the mixture is kept boiling for three hours
more on a wire gauze or sand bath, then a little water is added and
the unchanged nitrobenzene is completely removed from the acid
liquid by a current of steam. While still warm the liquid in the
flask is made alkaline with concentrated sodium hydroxide, and
1 Monatsh., 1880, 1, 316 ; 1881, 2, 139. M. Wyler, Ber., 1927, 60, 398. Darzens,
Bull. Soc. Mm., 1930, 47, 227.
2 Heat commercial glycerol in a porcelain basin in the fume chamber until a
thermometer hung with the bulb in the liquid registers 180°.
a The main reaction can be moderated by adding only half of the sulphuric acid
at the beginning, heating cautiously to gentle boiling with a small flame, and, after
one hour, adding the remainder of the acid quite slowly drop by drop. The mixture
is then kept boiling as above for three hours more.