urbaf2

GENERAL INFORMATION ON NITRO COMPOUNDS 183

IV

This appeared to be supported by the findings of Ray and Palinchak [55] who

resolved 9-nitro-2-benzoylfluorene with brucine. The brucine salt contained alco-

hol of crystallization and could probably be represented by the formula V:

(H-Brucine)+

V

The theory of “solvated asymmetric anion” therefore appeared to be admissible

[56].

However, in 1947 Kornblum et al. [57] showed that the apparent incompleteness

of racemization is due to incomplete neutralization and also to the presence of

optically active impurities in the nitro compounds used. He found that the complete

neutralization of the pure nitro compounds always leads to complete racemiza-

tion. This was also confirmed by Theilacker and Wendtland [58]. The results of

Komblum and the latter authors evidently supports the formulae Ia and IIa.

Generally speaking it is now admitted that primary and secondary nitroparaf-

fins exist in normal and aci-forms and that there is an equilibrium between them.

The two forms may be distinguished from each other by the fact that aci-form

absorbs bromine and gives characteristic colour reaction with ferric chloride. The

equilibrium constant depends on the solvent used, and mainly on its basicity. Thus

p- nitrophenylnitromethane contains 0.18% of aci-form in ethyl alcohol, 0.79%

and 16% in aqueous methyl alcohol and pyridine respectively [59].

Tertiary nitro compounds, of course, do not undergo tautomeric transformation,

and they might be expected to be resistant to alkalis. Nevertheless aromatic nitro

compounds, and polynitro-ones in particular, are very sensitive to alkalis, and

undergo transformation when treated with them. For example, sym-trinitrobenzene

and also α− trinitrotoluene, when reacted with potassium hydroxide in methyl alcohol

solution, form dark addition products (see also p. 202). Under certain conditions

the nitro group can break off to form high molecular compounds.

Nitro derivatives of benzene, when boiled with sodium hydroxide in methyl

alcohol solution are reduced to azoxy compounds (pp. 31, 237, 251). Nitro

derivatives of toluene under these conditions are oxidized to nitro derivatives of
stilbene (pp. 70, 283, 302).