vogel_practical_ochem_3.pdf

34] AROMATIC COMPOUNDS 563
It is interesting to observe that the hydrochloride is yellow, whereas the free
base is a green crystalline compound.
JV-Nitrosomethylaniline undergoes an interesting molecular rearrangement
in ether-alcoholic solution under the catalytic influence of hydrogen
chloride. The substance rearranges to />-nitroso-JV-methylaniline which
separates as the hydrochloride ; this involves the migration of the nitroso group
from the side chain to the p-position (compare Sulphanilic Acid, Section IV,55):
HC1
- , ON^~^
alcoholic • ether
A'-Nitroso-^V-methylaniline p-Nitroso-A r -methylaniline
It is convenient to include under Aromatic Amines the preparation of mnitroaniline
as an example of the selective reduction of one group in a polynitro
compound. When m-dinitrobenzene is allowed to react with sodium polysulphide
(or ammonium sulphide) solution, only one of the nitro groups is
reduced and m-nitroaniline results. Some sulphur separates, but the main
reaction is represented by :
+ Na2Sa + H20 • [ J + Na2S203
X
N02
X/NNH,
w-Dinitro benzene m-Nitroaniline
IV,34. ANILINE
Method A. Reduction with tin and hydrochloric acid. Into a 500-ml.
round-bottomed flask equipped with a reflux condenser, place 25 g. (21 ml.)
of nitrobenzene and 45 g. of granulated tin. Measure out 100 ml. of
concentrated hydrochloric acid. Pour about 15 ml. of this acid down the
condenser and shake the contents of the flask steadily. The mixture
becomes warm and before long the reaction should be quite vigorous ;
if it boils very vigorously, moderate the reduction somewhat by temporarily
immersing the flask in cold water. When the initial reaction
slackens of its own accord, pour another 15 ml. of hydrochloric acid down
the condenser, shake the flask steadily to ensure thorough mixing, and
cool again if the reduction becomes too violent. Do not cool more than
is necessary to keep the reaction under control; keep the mixture well
shaken. Proceed in this way until all the 100 ml. of acid has been added.
Finally heat the mixture on a boiling water bath for 30-60 minutes, i.e.,
until the odour of nitrobenzene is no longer perceptible and a few drops
of the reaction mixture when diluted with water yield a perfectly clear
solution. During the course of the reduction, particularly during the
cooling, the complex of aniline hydrochloride and stannic chloride may
separate as a white or yellow crystalline solid.
Cool the reaction mixture to room temperature and add gradually a
solution of 75 g. of sodium hydroxide in 125 ml. of water ; if the mixture
boils during the addition of the alkali, cool again. The hydroxide of tin
which is first precipitated should all dissolve and the solution should
be strongly alkaline : the aniline separates as an oil. Equip the flask
for steam distillation as in Fig. II, 40, 1, and pass steam into the warm