urbaf2

182 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

process was one of the tautomeric forms assumed by the nitro compound, so-called

aci- or iso-nitro form (Ia):

I Ia

Experimental evidence of the existence of aci-forms has soon been provided.

In 1895 Holleman [51] found that m- nitrophenylnitromethane yielded a yellow

salt, which under the influence of hydrochloric acid was converted initially into

a yellow substance having a high electrical conductivity. After some time, the

product changed into a colourless substance, showing no electrical conductivity.

The aci-structure was assigned to the yellow substance, and that of a pseudoacid to

the colourless one.

This observation was confirmed by Hantzsch and Schultze [52] in 1896 with

phenylmtromethane. The aci-form of phenylnitromethane is a crystalline product.

Its melting point is 84°C. It charges spontaneously into the normal, liquid form.

Aci-forms differ from the normal ones in that they turn brown-red with ferric

chloride.

Secondary nitroparaffins behave similarly :

II Ha

Thus the anion of the aci-form of nitroparaffins can be written in two ways:

IIIa and IIIb

IIIa IIlb

However, these structures were in doubt for a number of years. Strong evidence

for criticizing them was given in 1927 by Kuhn and Albrecht [53]. They reported

that optically active D- and L-2-nitrobutanes can be converted into their optically

active sodium salts and then regenerated without complete racemization. This

was confirmed by Shriner and Young [54] who found that 2-nitrooctane behaves

similarly. Subsequently the structures Ia and IIa for the aci-forms and IIIa and

IIIb for the aci-anion appeared to be excluded as they cannot correspond to dis-

symmetric configurations. If they were correct, the regenerated nitro compounds
should be racemic.
Shriner and Young tried to explain this behaviour of nitroparaffins by postu-
lating the “normal” structure of anion “stabilized” by combination with the solvent,

e.g. ethanol, through a hydrogen bond (IV):