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QUINALDINB 367
the liberated quinoline, along with unchanged aniline, is likewise
distilled with steam. The distillate is extracted with ether, the ether
is evaporated, and the crude bases are dissolved in a mixture of 50
c.c. of concentrated hydrochloric acid with 200 c.c. of water. After
warming the clear solution so obtained, 30 g. of zinc chloride in 50
c.c. of 2 i^-hydrochloric acid are added. A quinoline-zinc chloride
double salt crystallises as the solution cools, and after the mixture
has been left in ice for some time the crystals are collected at the
pump, washed with cold 2 i\f-hydrochloric acid, and decomposed with
concentrated sodium hydroxide solution. Once more the quinoline
is distilled in steam, extracted from the distillate with ether, dried in
the ethereal solution with solid potassium hydroxide, and ultimately
distilled after the ether has been evaporated. Boiling point 237°.
Yield 24-25 g. The preparation is water-clear.
(6) QUINALDINE SYNTHESIS OF DOEBNER AND MILLER 1
To a mixture of aniline (31 g.) and commercial concentrated
hydrochloric acid (60 c.c.) in a one-litre flask, 45 c.c. of paraldehyde
are added (or 60 c.c. of acetaldehyde carefully dropped in through
a long reflux condenser, while the flask is cooled in ice). The mixture
is left at room temperature ; the condensation takes place gradually
with slight evolution of heat. The liquid is then boiled under reflux
for three hours, made strongly alkaline with sodium hydroxide, and
submitted to steam distillation. From the distillate the crude base
is extracted with ether and the extract is dried with solid potassium
hydroxide. After the ether has been evaporated unchanged aniline
is removed by boiling under reflux for a quarter of an hour with 10 c.c.
of acetic anhydride, cooling, making distinctly alkaline with saturated
sodium carbonate solution, and distilling again with steam.
After working up in the usual way the quinaldine is purified by distillation
in a vacuum. Boiling point 115°-120°/l2 mm. The last portion
of the distillate consists of a small amount of bases of higher boiling
points. Yield 18-20 g.
The quinaldine can also be separated from the crude mixture of
bases by conversion into the zinc chloride double salt in the manner
described in the case of quinoline. This furnishes a somewhat
smaller yield of a purer preparation.
i Ber., 1881, 14, 2816; 1883, 16, 1664 j 1884, 17, 1712.