Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

316 HYDROLYSIS OF ^-NITROSODIMBTHYLANILINB
»HON= ^-CH3.
\ci
By addition of methyl iodide there is likewise formed a yellow
quinonoid salt (having the H3CON=group) the constitution of which
can be deduced with some degree of probability from the fact that the
basic group is eliminated by alkalis not as trimethylamine but as
dimethylamine.
DlMETHYLAMINE AND ^-NITROSOPHENOL FROM
^-NlTROSODIMETHYLANILINE
A solution of 25 g. of sodium hydroxide in 500 c.c. of water is
heated to boiling (porous pot!) in a distilling flask (capacity 1 1.)
connected to a downward condenser which is provided with a receiver
containing 60 c.c. of 2 i^-hydrochloric acid. Through the
corked neck of the flask 18-6 g. of nitrosodimethylaniline hydrochloride—preferably
the moist reaction product—are added in
portions. Bach addition is only made after most of the oily drops
of the base from the preceding portion have dissolved, and finally
the liquid is boiled until it has become reddish-brown. The dimethylamine
produced is trapped in the hydrochloric acid in the
receiver : at the conclusion of the distillation the contents of the
receiver must still be acid. They are evaporated to dryness on the
water bath in a small porcelain or glass basin, and finally the completely
anhydrous salt can be recrystallised from a very small
amount of absolute alcohol. Yield 5-6 g.
The nitrosophenol is precipitated from the cooled aqueous solution
by acidification with dilute sulphuric acid and is extracted with
ether in a separating funnel. After brief drying over calcium
chloride the brownish-green solution is concentrated on the water
bath. The sparingly soluble compound crystallises from the ether
on cooling. Melting point 120°-130° (decomp.). Complete purification
of nitrosophenol is difficult.
The nitroso-group in the y-position has a remarkable influence in
making possible the hydrolytic removal of the dimethylamino group
from the benzene ring. The reaction is used technically for the preparation
of secondary amines. (Trimethylamine is obtained by heating
ammonium chloride with formaldehyde.)
The tautomeric quinonoid formula O=\ %=N0H of quinone