Nitrous acid solubility

Dissolve 36 g. of p-toluidine in 85 ml. of concentrated hydrochloric acid and 85 ml. of water contained in a 750 ml. conical flask or beaker. Cool the mixture to 0° in an ice-salt bath with vigorous stirring or shaking and the addition of a httle crushed ice. The salt, p-toluidine hydrochloride, will separate as a finely-divided crystalline precipitate. Add during 10-15 minutes a solution of 24 g. of sodium nitrite in 50 ml. of water (1) shake or stir the solution well during the diazotisation, and keep the mixture at a temperature of 0-5° by the addition of a httle crushed ice from time to time. The hydrochloride wUl dissolve as the very soluble diazonium salt is formed when ah the nitrite solution has been introduced, the solution should contain a trace of free nitrous acid. Test with potassium iodide - starch paper (see Section IV,60). 

C NMR, 6, 550 LCAO-MO calculations, 6, 557 melting point, 6, 555 methylation, 6, 565 reactions, 6, 558 with bromine, 6, 560 with 1,3-dicarbonyl compounds, 6, 565 with nitrous acid, 6, 565 ring opening, 6, 561 solubility, 6, 555 5-substituted... 

The mechanism of cyclization of diaminopyrimidines by nitrous acid appears not to have been studied in detail. For the preparative procedure an aqueous solution of alkaline nitrite is treated with the diaminopyrimidine either in the form of a salt or with simultaneous addition of hydrochloric or acetic acid. The first phase of the reaction is usually carried out at 0°C, in some cases the reaction being terminated by heating to 50-60°C. With diaminopyrimidines which are sparingly soluble in water, the reaction was carried out in an organic solvent using amylnitrite. Excess nitrous acid can possibly attack the amino groups present. This was employed in some cases for the preparation of the hydroxy derivatives. ... 

Nitric oxide, 323-326 Nitrogen bonds, 182 hybridization, 188 liquid, 232 reactivity, 555-556 solubility, 267 Nitrogen dioxide, 563 Nitrogen gas, 124 Nitrous acid, 365-366,567 Nitrous oxide, 565... 

With the salts of certain weak acids, such as carbonic, sulphurous, and nitrous acids, an additional factor contributing to the increased solubility is the actual disappearance of the acid from solution either spontaneously, or on gentle warming. An explanation is thus provided for the well-known solubility of the sparingly soluble sulphites, carbonates, oxalates, phosphates(V), arsenites(III), arsenates(V), cyanides (with the exception of silver cyanide, which is actually a salt of the strong acid H[Ag(CN)2]), fluorides, acetates, and salts of other organic acids in strong acids. 

Hydrochloric acid and sulphuric acid are widely employed in the preparation of standard solutions of acids. Both of these are commercially available as concentrated solutions concentrated hydrochloric acid is about 10.5- 12M, and concentrated sulphuric acid is about 18M. By suitable dilution, solutions of any desired approximate concentration may be readily prepared. Hydrochloric acid is generally preferred, since most chlorides are soluble in water. Sulphuric acid forms insoluble salts with calcium and barium hydroxides for titration of hot liquids or for determinations which require boiling for some time with excess of acid, standard sulphuric acid is, however, preferable. Nitric acid is rarely employed, because it almost invariably contains a little nitrous acid, which has a destructive action upon many indicators. 

In most cases diazonium salts are not isolated, but are converted into products by reactions that can be carried out in situ. Moreover, it is actually recommended not to isolate these salts, not even for purification purposes, as many of them have a tendency to explode. In addition, the high solubility of most diazonium salts in water makes precipitation from this medium difficult. Therefore, to obtain solid diazonium salts the recommended method for many decades was to carry out diazotizations in ethanol followed by precipitation with ether. As inorganic salts of nitrous acid are scarely soluble in ethanol, Knoevenagel recommended alkyl nitrites (ethyl or isopentyl nitrite) as diazotization reagents as long ago as 1890. Various other solvents have subsequently been used for diazotizations with alkyl nitrites (see Saunders and Allen, 1985, p. 23 ff.), but as a method for obtaining solid diazonium salts this has been superseded by the isolation of diazonium tetrafluoroborates and, to a lesser degree, of hexafluorophosphates. 

Nitrite is an extremely reactive chemical and is soluble in the aqueous phase of meat. It is usually used for curing in the form of the sodium salt. The nitrite ion is the conjugate base of nitrous acid (a weak acid) and has a PK of 3.36. The usually mild acid conditions found in meat give formation of only a small quantity of nitrous acid when nitrite is added to the meat ( ) ... 

A bacterial phosphatidylinositol specific phospholipase C (PI-PLC) had been available for many years before it was demonstrated to strip a number of membrane-bound proteins from eukaryotic cell surfaces [1], Such proteins are anchored by a PI moiety in which the 6 position of inositol is glycosidically linked to glucosamine, which in turn is bonded to a polymannan backbone (Fig. 3-10). The polysaccharide chain is joined to the carboxyl terminal of the anchored protein via amide linkage to ethanolamine phosphate. The presence of a free NH2 group in the glucosamine residue makes the structure labile to nitrous acid. Bacterial PI-PLC hydrolyzes the bond between DAG and phosphati-dylinositols, releasing the water-soluble protein polysac charide-inositol phosphate moiety. These proteins are tethered by glycosylphosphatidylinositol (GPI) anchors. 

The actual mechanism by which the N=N molecule cleaves is very complicated, and is not fully understood yet. It is nevertheless clear that much nitrogen is oxidized to form nitrous oxide, NO. This NO dissolves in the water that inevitably accompanies lightning and forms water-soluble nitrous acid HNO2, which further oxidizes during the storm to form nitric acid, HNO3. Nitric acid functions as a high-quality fertilizer. It has been estimated that a thunderstorm can yield many tonnes of fertilizer per acre of land. 

Finally, in a method originated by Witt [22], which is occasionally useful for the diazotisation of stable amines of high relative molecular mass that pose solubility problems, the amine is dissolved in nitric acid before the addition of sodium metabisulphite. Nitrous acid is produced in the medium according to Scheme 4-9, enabling diazotisation to proceed. 

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 ... 

B—A (nitrous acid) and D (acetic acid) are weak acids, and E (ammonia) is a weak base. Weak acids and bases are weak electrolytes. C (ethanol) is a nonelectrolyte. Potassium nitrate (B) is a water-soluble ionic compound. 

Becker, K.H., Kleffmann, J., Kurtenbach, R., and Wiesen, P. Solubility of nitrous acid (HONO) in sulfuric acid solutions, J. Phys. Chem., 100(36) 14984-14990, 1996. 

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. 

A volt-equivalent diagram for the water-soluble nitrogen species in acidic solution is shown in Figure 6.4. It shows that the nitrate(V) ion is the least stable species, but also indicates the meta-stability of nitrous acid, which is unstable with respect to disproportionation into oxidation states + 5 and zero ... 

Since the neutralization reaction of an amine with nitrous acid may be presumed to be instantaneous while the nitrosation of an amine proceeds at a slower rate, further investigations would be of interest to elucidate the problem of whether nitrite salt formation is a necessary preliminary step to the formation of iV-nitrosoamines or whether the covalent product forms independently. In the latter case, there would be competitive reactions of significantly different reaction rates and mechanisms. The yield of A-nitrosoamines may be influenced by the extent to which the more water-soluble nitrite salts may be present in the course of a preparation. 

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