Nitrous acid properties

Definition Salts of nitrous acid Properties Wh. to paleyel. cryst. sol. in water, liq. ammonia... 

The many industrial uses for sodium nitrite primarily are based on its oxidizing properties or its Hberation of nitrous acid in acidic solutions. 

Indazoles can be considered as either azaindoles or azaisoindoles depending on the reader s prejudice. Benzydamine (54) represents a drug with this heterocyclic nucleus. Alkylation of the amine of anthranilic acid methyl ester with benzyl chloride in the presence of sodium acetate gives 52. Treatment with nitrous acid leads to the nitrosoamine, which cyclizes spontaneously to the 3-ketoindazole system, 53. This intermediate forms an ether of its enol form on heating the sodium salt with 3-dimethylaminopropyl chloride. There is thus obtained benzydamine (54), a fairly potent nonsteroidal antiinflammatory agent with significant antipyretic and analgesic properties. 

Halfpenny, E. and Robinson, P.L. (1952). Pernitrous acid. The reaction between hydrogen peroxide and nitrous acid and the properties of an intermediate product. J. Chem. Soc. 928-938. 

While screening for p-lactam antibiotics stable to p-lactamases, a strain of Streptomyces lactamdurans was found to contain several such agents which have a 6-a-methoxy group whose electronic and steric properties protect the antibiotic from enzymatic attack. Cephamycin C (29a), one of these substances, is not of commercial value, but side chain exchange has led to much more potent materials. Of the various ways of effecting this transformation, one of the more direct is to react cephamycin C with nitrous acid so that the aliphatic diazo product (29b) decomposes by secondary amide participation giving cyclic iminoether 30. The imino ether moiety solvolyzes more readily than the p-lactam to produce 7-aminocephamycinic... 

The esters of nitrous acid are characterised by their high velocities of formation and hydrolysis. They are almost instantaneously decomposed by mineral acids and in the method of preparation given this has been taken into account. The slightest excess of hydrochloric acid must be avoided. Advantage is taken of this property of the alkyl nitrites in all cases where it is desired to liberate nitrous acid in organic solvents (in which metallic nitrites are insoluble). Examples addition of N203 to olefines, preparation of solid diazonium salts (p. 286), production of isonitroso-derivatives from ketones by the action of HN02. This synthesis is often also carried out in the manner of the acetoacetic ester synthesis, with ketone, alkyl nitrite, and sodium ethylate the sodium salt of the isonitrosoketone is formed (cf. in this connexion p. 259) ... 

Nor can there be any question of real tautomerism in the case of phenol. In its chemical properties phenol resembles the aliphatic enols in all respects. We need only recall the agreement in the acid character, the production of colour with ferric chloride, and the reactions with halogens, nitrous acid, and aromatic diazo-compounds (coupling), caused by the activity of the double bond and proceeding in the same way in phenols and aliphatic enols. The enol nature of phenol provides valuable support for the conception of the constitution of benzene as expressed in the Kekule-Thiele formula, since it is an expression of the tendency of the ring to maintain the aromatic state of lowest energy. In this connexion the hypothetical keto-form of phenol (A)—not yet obtained—would be of interest in comparison with... 

The tertiary aromatic bases share with the phenols the property of taking up a nitroso-group in the p-position when treated with nitrous acid in acid solution. As was mentioned elsewhere (p. 307), this reaction may be compared to the coupling of these compounds with diazobenzene. 

An important property of the S-nitroso thiourea derivatives is the ability to effect electrophilic nitrosation of any of the conventional nucleophilic centres. This is manifest kinet-ically by the catalysis of nitrous acid nitrosation effected by added thiourea (equation 29). The situation is completely analogous to the catalysis of the same reactions by added halide ion or thiocyanate ion. The catalytic efficiency of thiourea depends on both the equilibrium constant Xxno for the formation of the intermediate and also its rate constant k with typically a secondary amine65. Since Xxno is known (5000 dm6 mol-2), it is easy to obtain... 

Preparation and Properties. 1. Dissolve a small amount of potassium nitrite in 1-2 ml of water, cool the solution with ice, and add two or three drops of concentrated sulphuric acid to it. What is observed Write the equations of the reactions. How can you explain the difierent strength of nitric and nitrous acids ... 

Fulminic acid can be regarded as the simplest oxime. A number of compounds with an oxime group C=NOH can form salts which possess initiating properties, for example salts of nitroformoxime (methylnitrolic acid) (I) which can be obtained in a known way by the action of nitrous acid on nitromethane. Salts of form-hydroxamic acid (II), particularly the mercuric salt, also possess initiating properties [66]. Formhydroxamic acid can be obtained by the action of hydroxylamine on formic acid esters or by oxidation of methylamine. 

The first of these is obtained by the action of nitrous acid on oxamidohydrazide. It is unstable and decomposes explosively at 115°C. The second is formed by the action of nitrous acid on the trihydrazide of trimesic acid. The explosive properties of neither of these azides have been reported. 

Nitrosophenols are formed very easily by the action of nitrous acid on phenols. Some salts of heavy metals have weak initiating properties. These are lead dini-trosophenate and lead trinitrosophloroglucinate. 

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