AROMATIC NITRO COMPOUNDS 211(30)IX X
X = H, OH, Cl
Y = H, NO 2This mechanism was suggested by Ishidata and Sagakuchi [68].
The formula X may be considered to correspond with the coloured products
of the Janovsky reaction.
Recently T. Urbanski [70] established that an alcoholic solution of m- dinitro-
benzene is coloured pink with primary nitroparaffins in the presence of sodium
hydroxide. The colour is very intense when nitromethane is used. The spectrum
of the solution shows a maximum of absorption near 550 mμ.
The formation of the coloured products is most likely due to the presence of the
active methylene group in the primary nitroparaffins. Secondary nitroparaffinsdo not give this reaction.
The reaction can be used to detect the presence of nitromethane (T. Urbanski
and Kwiatkowska [70a].
2,4-Dinitrotoluene does not give this reaction. Trinitro compounds (such as sym-
trinitrobenzene and α− trinitrotoluene) also give the colour reaction but this is
less typical, as the trinitro compounds give a similar colour with alcoholic NaOH
alone without primary nitroparaffins.
The reaction of nucleophilic substitution described above admit the ease of
formation of quinoid ring. The problem of quinoid ring formation was recently
examined by Perret and Holleck [47]. On the basis of their spectroscopic ultra-
violet investigations using visible and infra-red techniques and their polarographic
investigations, Perret and Holleck came to the conclusion that differently sub-
stituted derivatives of sym- trinitrobenzene possess different abilities to form a quinoid
structure. Trinitrotoluene belongs to those derivatives which behave in a polaro-
graph in much the same manner as sym- trinitrobenzene because the methyl group
does not take part in the formation of quinoid structure. On the contrary OH
groups promote the formation of quinoid structures.
The ability of higher nitrated aromatic compounds to form dark coloured
products in alkaline medium can be used for the titration of certain weak acids
with bases. For example trinitrobenxene acquires an orange and red colour at
pH 12.2 and 13.6 respectively.
The formation of coloured compounds was used by Brockmann and Meyer
[71] for the quantitative determination of polynitro compounds. The di- or tri-
nitro compound is dissolved in ethylenediamine and titrated potentiometricallv