GENERAL INFORMATION ON NITRO COMPOUNDS^185Again V. Meyer was the first to describe the reaction. As in the formation
of nitrolic acids, here also it is the aci-form of the secondary nitro compound that
takes part in the reaction. It reacts with sodium nitrite to give a compound which.
after acidification, forms pseudonitrole.
According to Veibel [61], the formation of pseudonitrole can be explained by
the following reaction series :
(5)Pseudonitroles are crystalline, colourless products. They exist probably as
dimers. But when molten or in solutions they turn blue, and are probably present
as monomers. The reaction is utilized for the detection of secondary nitro com-
pounds.
Heating the primary nitroparaffins with sulphuric acid of a concentration over
50% results in their isomerization to hydroxamic acids (IX).
From phenylnitromethane, Bamberger [62] obtained benzhydroxamic acid,
and explained the mechanism of the isomerization reaction as:
(6)A blue hydroxynitroso compound (VIII) is formed as an unstable Intermediate
product.
T. Urbanski [63] and T. Urbanski and Gurzydska [64] found that isomerization
also occurs under the influence of acetic anhydride or ketene in the presence of
a basic agent such as sodium acetate or pyridine.
In some cases hydroxamic acid hydrolyses to form hydroxylamine. The reaction
has been utilized by Turski [65] for direct amination of aromatic hydrocarbons.
Primary nitroparaffins were used in place of hydroxylamine, and sulphuric acid
and a catalyst (e.g. V 2 O 5 ) were present.
When a salt of the aci-form of a primary or secondary nitroparaffin is treat-
ed with an acid, it may decompose, evolving nitrous oxide and yielding an al-
dehyde or ketone: