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AROMATIC NITRO COMPOUNDS^207

In the case of nitro derivatives of benzene at least two nitro groups should be

present on the ring. Here are the most typical reactions, as suggested by Meisen-

heimer :

(28a)

Here the ammo group enters the ortho or para position in relation to the

nitro groups.

The reaction of sulphitation of polynitro compounds is also a nucleophilic

substitution reaction. It is dealt with more fully on pp. 237, 308 and 332.

The so-called Janovsky reaction [53] is a very characteristic one for many higher

nitrated benzene derivatives. It is probably also of nucleophilic character. It con-

sists in treating a diluted di- or tri-nitro compound solution in acetone with a con-

centrated solution of potassium or sodium hydroxide (generally of 30% concentra-

tion). The acetone solution turns bright coloured. Red to violet colours may

appear according to the nitro compound present.

Thus, as Janovsky [53] reports, m- dinitrobenzene produces a reddish violet

colour, 2,4-dinitrotoluene a blue one, 1,3-dinitronaphthalene a bluish-red.

Bitt6 [54] stated that di- and tri-nitro compounds give colour reactions with

a number of aliphatic and aromatic aldehydes and ketones in the presence of al-

kalis.

Thus, m- dinitrobenzene produces the following colours:

with pulegone hyacinth red

with carvone blue pink

with camphor (in nitrobenzene solution) brown red

with propionic aldehyde dark brown

No colour appears with some aldehydes, for example, furfural and cinnamic

aldehyde. Bittó has suggested this reaction may be used for the identification of

aldehydes and ketones (see also p. 239).

The Janovsky reaction and its Bittó modification were investigated by Rei-

tzenstein and Stamm [55]. Both these as well as other authors (Bost and Nicholson

[56], Nisida [57], Canäck [58]) stated a number of irregularities.