Nitrous acid decomposition

EXPLOSION and FIRE CONCERNS combustible solid volatile with steam NFPA rating Health 2, Flammability 1, Reactivity 0 sublimes evolves a vapor that is flammable and explosive at elevated temperatures incompatible with nitrous acid decomposition liberates toxic fumes of oxides of nitrogen use carbon dioxide or dry chemical for firefighting purposes. 

More recently, Kirmse and his coworkers found two other deamination reactions where product studies indicated the intermediate formation of radicals, namely the nitrous acid decompositions of 2-aminobutylnitrile (Bunse and Kirmse, 1993) and of the epimeric 2-aminonorbornyl-2-carbonitrile (Kirmse et al., 1993b). Like 2-amino-2-methylpropylnitrile (7.59), these compounds are characterized by a CN group at the same C-atom as the NH2 group. 

MNT cind excess nitric acid, the concentration of nitrous acid reaches a meucimuin and then falls as the rate of nitrous acid decomposition exceeds its formation rate. Detailed results of this work are given elsewhere(14). 

The solution of the aniline hydrochloride should be cooled to 5°C., and this temperature maintained throughout the addition of the sodium nitrite solution. External cooling has to be maintained, otherwise the heat of the reaction would cause the temperature to rise, with the consequent decomposition of the diazonium chloride and the production of phenol. If, on the other hand, the temperature is reduced to about o , diazotisation becomes extremely slow and unchanged nitrous acid may remain in the solution for an impracticably long time. 

Dissolve 15 ml. (15-4 g.) of aniline in a mixture of 40 ml. of concentrated hydrochloric acid and 40 ml. of water contained in a 250 ml. conical flask. Place a thermometer in the solution, immerse the flask in a mixture of ice and water, and cool until the temperature of the stirred solution reaches 5°. Dissolve I2 5 g. of powdered sodium nitrite in 30 ml. of water, and add this solution in small quantities (about 2-3 ml. at a time) to the cold aniline hydrochloride solution, meanwhile keeping the latter well stirred by means of a thermometer. Heat is evolved by the reaction, and therefore a short interval should be allowed between consecutive additions of the sodium nitrite, partly to allow the temperature to fall again to 5°, and partly to ensure that the nitrous acid formed reacts as completely as possible with the aniline. The temperature must not be allowed to rise above 10°, otherwise appreciable decomposition of the diazonium compound to phenol will occur on the other hand, the temperature... 

The evolution of nitrogen is not always entirely satisfactory as a test owing to the possible evolution of gaseous decomposition products of nitrous acid itself. The test may be performed as follows. To i ml. of chilled concentrated sodium nitrite solution add i ml. of dilute acetic acid. Allow any preliminary evolution of gas to subside, and then add the mixed solution to a cold aqueous solution (or suspension) of the amide note the brisk effervescence. 

Action of nitrous acid. To a few ml. of 20% NaNO, solution add a few drops of cold dil. acetic acid. Pour the mixture into a cold aqueous solution of glycine, and note the brisk evolution of nitrogen. NH CH COOH -h HNO2 = HO CH2COOH + N + H O. Owing to the insolubility of cystine in acetic acid use a suspension in dU. acetic acid for this test. In each case care must be taken not to confuse the evolution of nitrogen with any possible thermal decomposition of the nitrous acid cf. footnote, p, 360). 

It is advisable to add the sodium nitrite solution, particularly in preparations on a larger scale, through a separatory or dropping funnel with the tip of the stem extending well below the sui-face of the liquid tliis will prevent loss of nitrous acid by surface decomposition into oxides of nitrogen. 

Figure 22 5 shows what happens when a typical primary alkylamine reacts with nitrous acid Because nitrogen free products result from the formation and decomposition of diazonium ions these reactions are often referred to as deamination reactions Alkyl... 

Sodium nitrite is stable in alkaline solutions. Acidification liberates nitrous acid which is unstable. The decomposition of nitrous acid yields nitric acid [7697-37-2] HNO, according to the following reaction ... 

Sodium azide does not react with carbonyl sulfide to form 5-hydroxy-1,2,3,4-thiatriazole, nor with carboxymethyl xanthates, RO-CS SCH2COOH, to form 5-alkoxy-l,2,3,4-thiatriazoles. The latter, however, could be prepared from xanthogenhydrazides (RO-CS NHNH2) and nitrous acid. They are very unstable and may decompose explosively at room temperature only the ethoxy compound (6) has been examined in detail. This is a solid which decomposes rapidly at room temperature and even at 0°C is transformed after some months into a mixture of sulfur and triethyl isocyanurate. In ethereal solution at 20° C the decomposition takes place according to Eq. (16)... 

At fairly high nitrous acid concentrations (0.1 m) and at moderate acidities (4 m) the blue color of N203 (Amax = 625 nm) is easily detected by eye. The overall equilibrium of Scheme 3-10 has been determined. A relatively recent determination of the equilibrium constant gave the value K = 3.0 x 10"3 m (Markovits et al., 1981). Accurate determinations of this constant are difficult, as N203 decomposes easily into NO and N02. Pure N203 is stable only as a pale blue solid or as an intensely blue liquid just above its freezing point (-100°C). The liquid starts to boil with decomposition above -40°C. 

The reaction conditions necessary to obtain a good yield of the title compound (a difficult isomer), and to avoid hazards during the nitration of resorcinol, are critical and strict adherence to those specified is essential. The necessary 80% white fuming nitric acid must be completely free from oxides of nitrogen and nitrous acid, and procedures for this are detailed. Then the temperature dining addition of the diacetate must be kept between -10 and 0°C by regulating the rate of addition. The alternative use of 80% sulfuric acid as solvent for the 80% nitric acid (5 equiv.) is preferred as more reliable, but both methods have led to violent exothermic decomposition, accompanied by fume-off, after an induction period. In any event, the explosive 2,4,6-trinitroresorcinol ( styphnic acid ) is produced as a by-product. 

See entry thermochemistry and exothermic decomposition (reference 2) Nitrous acid... 

At low temperature, slow decomposition of nitrous acid gives nitric acid and NO,... 

Nitric acid is the only oxyacid of nitrogen which is at all stable in the free condition. The kinetics of its decomposition are discussed below. Nitrous acid exists in the gas phase, although it cannot be isolated. Information on the kinetics of its decomposition is restricted to an estimate103 of the half-life of the forward reaction in the rapid gas-phase equilibrium... 

The reaction of Curtius, which is especially to be preferred in the case of the higher members on account of the favourable solubilities of the intermediate products, involves as its first stage the preparation of the hydrazide from an ester (or acid chloride). The hydrazide is then converted, usually very readily, by the action of nitrous acid into the azide. In many cases it is more convenient to prepare the azide by treating an acid chloride with sodium azide previously activated with hydrazine hydrate.1 Azides easily undergo thermal decomposition, the two azo nitrogen atoms being eliminated as elementary nitrogen. In this way, however, the same radicle is formed as was invoked above to explain the Hofmann reaction ... 

Theory The nitrous acid, generated on the introduction of sodium nitrite solution into the acidic reaction mixture, reacts with the primary amino group of sulphanilamide quantitatively, resulting into the formation of an unstable nitrite that decomposes ultimately with the formation of a diazonium salt. The diazonium salt thus produced is also unstable, and if the reaction mixture is not maintained between 5-10°C, it shall undergo decomposition thereby forming phenol products which may react further with nitrous acid. The reactions involving the formation of the diazonium salt may be expressed in the following manner ... 

A yellow solution is formed when nitrous acid is added to thiosulphate ion in water84. This is believed to be due to the formation of nitrosyl thiosulphate [O3SSNOI, although this has not been isolated and even in solution decomposition is fairly rapid. The equilibrium constant for its formation Wxno is 1.66 x 107 dm6 mol 2 at 25 °C and the UV-visible absorption spectrum is very similar to that of other S -nitroso compounds85. The rate constant for its formation is very large and is believed to represent a diffusion controlled process. Thiosulphate ion does appear to catalyse nitrosation but, over the range studied... 

Park, J.-Y. and Lee, Y.-N. Solubility and decomposition kinetics of nitrous acid in aqueous solution, J. Phys. Chem., 92(22) 6294-6302, 1988. 

Amines are easily identified because they re readily soluble in dilute acid. Sodium fusion converts the cimine to the cyanide ion, which is detectable by a Vciriety of methods. The ready formation and decomposition of diazonium salts (discussed in the earlier section Reactions with nitrous acid ) leads to the identification of primary amines. The Hinsberg test (see the nearby sidebcir) is useful in identifying amines. 

In the presence of adsorbed NH3, nitrous acid produces N2 via decomposition of... 

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