Nitrolic Acids and Pseudonitroles.
(1). The nitrolic acids may be represented by either of the two following structures: RC(=NOH)NO2 or RCH(-N=O)NO2
Where R represents an alkyl group such as –CH3 or –CH2CH3.
The first of these formulae agrees best with the modes of formation of the nitrolic acids. Furthermore, the compound acts as if it had the formula RC(=O)NHNO2 when it is decomposed by heat or by sulphuric acid.
Nitrolic acids are produced: 1. By the action of nitrous acid, or better of potassium nitrite and sulphuric acid, on the sodium derivatives of primary nitre-paraffins, or ou solutions of these nitro-compounds in caustic potash or soda:
RCH2NO2. + HNO2 --> H2O + RC(=NOH)NO2.
By the action of the dibrominated nitroparaffins on hydroxylamine:
RCBr2NO2 + NH2OH -- > 2HBr + RC(=NOH)NO2
(2). Psendonitroles are formed by the action of potassium nitrite on secondary nitro-paraffins, thus:
CH3CH(NO2)CH3 + KNO2 -- > KOH + CH3C(NO)(NO2)CH3
methyl-nltrolic acid can be represented by H(NO2)C=NOH. This acid is very unstable in aqueous solution, so that its preparation requires special precautions. The following method is given by Tscherniak (Ber. viii. 114): Nitromethane (15 grams) is treated with a quantity of water just sufficient to dissolve it, and the solution is mixed with a moderately dilute solution of potassium nitrite (8 grams) and cooled to 0° by addition of a large quantity of ice. A mixture of sulphuric acid (4 grams) with a large quantity of water is also cooled by ice, and slowly poured into the first liquid, to which, thus diluted, weak aqueous potash is first added till it turns red, and then again dilute sulphuric acid till the colour disappears. To remove any free nitrous acid, the solution is shaken with a little precipitated chalk, after which the nitrolic acid is dissolved out by ether, and the solution evaporated over sulphuric acid.
Methylnitrolic acid thus obtained forms large brittle crystals resembling the ethylcompound; from a dilute ethereal solution it separates in long needles. It decomposes slowly at ordinary temperatures, rapidly at 64°, into formic acid, nitrogen, and nitrogen tetroxide [nitrogen dioxide]:
(2)CH2N2O3 --> HCO2H + NO2 + N2
By boiling with dilute sulphuric acid, it is resolved into formic acid and nitrogen monoxide [nitrous oxide]:
CH2N2O3 --> HCO2H + N2O
Ethylnitrolic Acid, CH3C(NO2)=NOH (V. Meyer a. Locher, Ber. vi. 1494; Meyer, ibid. vii. 425). The preparation of this compound by the action of potassium nitrite and sulphuric acid on an alkaline solution of nitroethane has been already described (vii. 564). It is essential that the nitroethane be first dissolved in the alkali; for if the nitroethane and sulphuric acid be added simultaneously to a solution of potassium nitrite, no ethylnitrolic acid will be produced.
Ethylnitrolic acid crystallises in light yellow, transparent, highly lustrous prisms, very much like saltpetre; by slow evaporation of the aqueous or ethereal solution it is easily obtained in crystals an inch long. According to Kenngott's measurements, they belong to the orthorhombie system, exhibiting the combination ooP.ooPoc.Poo. The angle of the brachydiagonal prismatic edge is approximately 108° 30'; that ot the terminal edge of the transverse dome 47° 30'. The acid has a strong sweet taste and acid reaction. It dissolves readily in all the ordinary solvents, and its difference of solubility in cold and slightly warm water is so great that a solution saturated merely at the heat of the hand deposits an abundant crop of crystals a few minutes after the hand has been removed.
The ethylnitrolates of sodium, potassium, ammonium, and barium dissolve in water, with a deep red colour, but have not been obtained in the pure state. Water is required for their formation, inasmuch as nitroethane dissolves in an ethereal solution of ammonia without coloration, but on adding a trace of water, the liquid assumes a deep red colour. The action of alkalis on ethylnitrolie acid is so sensitive that this acid might be used as an indicator in alkalimetry. The ethylnitrolates of the heavy metals are coloured unstable precipitates, very easily changing into nitrites. The lead salt has a brilliant orange colour, and the silver salt is egg-yellow.
Ethylnitrolic acid, heated to 80°-81°, melts and suffers rapid decomposition, giving off nitrogen tetroxide and free nitrogen, and leaving glacial acetic acid:
(2)C2H4N2O3 -- > C2O2H4 + NO2 + N2
The same decomposition goes on slowly at the common temperature, and quickly on boiling with an alkali. In these decompositions a small quantity of a white solid, containing nitrogen and melting at 61°, is always formed.
Nascent hydrogen obtained from tin and hydrochloric acid or sodium-amalgum,
Strong sulphuric and, when employed in excess in order to moderate the reaction, decomposes it into acetic acid and nitrogen monoxide [nitrous oxide]:
(2)C2H4N2O3 -- > C2O2H4 + N2O
These decompositions are most readily explained on the supposition that ethjl-
CH3C(=O)NHNO2 -- > CH3C(=O)OH + N2O
Propylnltrollc Acld, CH3CH2C(NO2)=NOH, may be prepared either by passing nitrous acid into a solution of nitropropane in potash, and adding sulphuric acid, or by the action of dibromonitropropane on hydroxylamine. Hydroxylamine hydrochloride (7 pts.), dissolved in a small quantity of water, is decomposed
Propylnitrolic acid crystallises in light yellow prisms having a sweet and biting taste, easily soluble in water, alcohol, and ether, coloured deep red by alkalis, melting at 60°, and decomposing at higher temperatures with violent evolution of red vapoure. By sodium-amalgam and water it is resolved into ammonia, nitrous acid, and probably also propionie acid; by strong sulphuric add into propionic acid and nitrogen monoxide. When left to itself in a sealed tube it begins to decompoM »u. in four or five weeks; on subsequently opening the tube, red fumes escape with violence. and the residual liquid is found to consist of propionic acid. The metallic propylnitrolatfs quickly decompose in the same manner as the ethylnitrolates, yielding nitrites (V. Meyer, Lit/rig's Annalen, clxxv. 114).