Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

168 ALKYLATION OF ANILINE
In a quite analogous way ammonia yields hydrocyanic acid.
H.NH2 + C12C< +3K0H = 2
\H
The question of the constitution of hydrocyanic acid has already been
considered (p. 139). Here it need only be remarked that the isonitriles
are converted by hydrolysis into primary amines and formic acid; no
carbon monoxide is produced, although from the formula this might be
expected. The reason for this is to be sought in the fact that the first
stage in the reaction consists in the addition of water to the two free
valencies of the carbon atom. The reaction must therefore be formulated
thus :
z .OH /OH
C6H5.N:C< +H2O = C6H5.N:C< = C6H5.NH2 <
\ \H
tso-form of formanilide
It is consequently no argument against the carbimine structure of
hydrocyanic acid that it likewise does not yield carbon monoxide
but formic acid (in addition to ammonia) on decomposition by mineral
acids.
In a similar way fulminic acid, another derivative of bivalent carbon,
which has been accurately investigated and for which the carboxime
>C:NOH constitution has been established, is decomposed into formic
acid and hydroxylamine (see experiment on p. 159).
5. Hofmann's method for the synthesis of alkylamines can be
applied to the alkylation of aniline. The methylated anilines are
especially important, and in particular the tertiary base dimeihylaniline,
which will be repeatedly used in this practical course as starting material
and is also much used technically. On a large scale aniline (in the form
of its hydrochloride) is methylated in an autoclave with methyl alcohol.
The methyl chloride which is thus produced is the actual alkylating
agent. At very high temperatures the methyl group wanders from the
nitrogen to the yara-position. This is a new example of the rearrangements
which benzene derivatives undergo. Such rearrangements will
be repeatedly mentioned (cf. p. 187).
H Cl H Cl nxT
\ /
NH.CH,
—>
CH3
If the reaction takes place in the presence of an excess of methyl
alcohol mesidine (formula on the right, above) is ultimately produced as