Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

DETECTION OF NITKOSO-GKOUPS 317
monoxime is also considered for y-nitrosophenol, although its whole
chemical behaviour is in complete agreement with the phenolic structure.
Like nitrosobenzene, nitrosophenol, when quite pure, is (very
nearly) colourless and the solutions are olive-green. This would not
be expected from the quinonoid formula.
The Liebermann Reaction.—Dissolve a small amount of nitrosophenol
in a little molten phenol and add concentrated sulphuric acid.
A magnificent cherry-red colour is obtained: when the melt is
diluted with water and alkali is added the colour changes to blue.
Since phenol is converted to nitrosophenol by nitrous acid, even
when the latter is combined in the form of the NO-group, labile nitrosogroups
may be detected by the Liebermann reaction.
3. p-AMINODIMETHYLANILINE
In a short-necked, round bottomed flask (capacity 500 c.c.) 100 g.
of stannous chloride are dissolved in 120 c.c. of concentrated hydrochloric
acid, and 38 g. (0'2 mole) of the crude moist nitrosodimethylaniline
hydrochloride are gradually added in small portions with
vigorous stirring or shaking. If the reaction does not set in at once
the flask is warmed on the water bath ; after a short time the salt
which has been added should go completely into solution. The reaction
must be so regulated that it goes on continuously without
becoming altogether too violent.
At the end, the solution, which has become pale yellow, is cooled
externally and internally (drop in some ice) and made alkaline with
a solution of 150 g. of commercial sodium hydroxide in 300 c.c. of
water ; 1 most of the stannic acid which is at first precipitated goes
into solution. The oily base set free is taken up in ether (irrespective
1 The electrolytic separation of the tin is much more elegant. In cases where the
reduction product cannot be extracted as base from the alkaline solution (aminoalcohols,
amino-acids, and the like) this method is much to be preferred to the precipitation
with hydrogen sulphide, and in the present case also it is to be highly
recommended, if only for what it teaches.
The electrolysis is carried out in a medium-sized filter jar; two moderately
thick carbon rods serve as electrodes. The cathode dips into the solution, the
anode into 2i^-sulphuric acid contained in a small porous cell, which also dips into
the liquid. The electrodes are fixed a short distance apart and the current is
obtained from two units, arranged in series, of an accumulator battery of the usual
capacity. At a potential difference of 4 volts 1-5—2 amperes pass through the
solution.
Application of Faraday's Law of Electrochemical Equivalents.—1 equivalent of
1 "I Q Oft Kf\f\
g n + + + + _ o r 29.5 g. requires ? • = 2 6 * 8 a m p e r e h o u r s ; w i t h a current of 2
4 ouOO