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NITEOMETHANB 157
to those used to explain the decomposition of malonic acid : the nitroaoetic
acid first formed decomposes into CH3NO2 and CO2. Other
nitroparaffins are usually obtained by the method discovered by
V. Meyer—by the action of silver nitrite on alkyl iodides. The method
of Konovalov—heating in a sealed tube to 120°-l30° with very dilute
nitric acid—is often successful in the case of saturated hydrocarbons,
particularly those of the hydroaromatic series. Phenylnitromethane
is discussed in Chap. VI. 8, pp. 256, 257. Recall the isomerism with the
alkyl nitrites. How do the reactions of the two classes of compounds
differ ?
The primary and secondary nitroparaffins are neutral substances,
but are transformed by alkalis into salts of isomeric aci- forms
(Hantzsch):
R R
\>CHNO2 \
—> >C=N=O.
This change is more fully discussed in the section on tautomerism
on p. 257.
Experiment.—Dissolve 1 c.c. of nitromethane in water and test
the solution with litmus paper. Then add some phenolphthalein
and, drop by drop from a burette, 0-1 2V-sodium hydroxide solution.
Before a permanent pink colour develops about 2 c.c. of the alkali
will be added—a sign that an acid, ad-nitromethane, H2C : NOOH,
has been formed from the neutral nitromethane. A small sample of
this solution gives with ferric chloride a blood-red colour, characteristic
of act-nitro-compounds. The salts of the act-compound undergo
extensive hydrolysis. This is shown by further addition of 0-1 Nalkali
which produces a deep red colour. If 10 c.c. of alkali were
added and 5 c.c. of 0-1 2V-hydrochloric acid are now run in the solution
is decolorised because the liberated act-compound restricts
the hydrolysis of its salt. But the conversion of H2C : N02H into
H3C.NO2 proceeds so rapidly that the red colour reappears in a few
moments.
When the nitroparaffins are reduced with powerful agents, the
corresponding amines are formed in a way similar to that described
in the next section for nitrobenzene. But just as in the case of nitrobenzene,
so also with nitroparaffins, the reaction can be stopped at the
hydroxylamine stage by using zinc dust in a neutral medium.
Experiment.—To a few drops of nitromethane dissolved in a
little water some pieces of granulated zinc and then some concentrated
hydrochloric acid are added. A vigorous reaction takes