Nitrous acid in aqueous solution

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. 

Fischer, M., and P. Warneck, Photodecomposition of Nitrite and Undissociated Nitrous Acid in Aqueous Solution, . /. Phys. Chem., 100, 18749-18756(1996). 

The foimation of aromatic diazonium salts from aromatic primary amines is one of the oldest synthetic procedures in organic chemistry. Methods based on nitrosation of amine with nitrous acid in aqueous solution are die best known, but diere are variants which are of particular use widi weakly basic amines and for the isolation of diazonium salts fiom nonaqueous media. General reviews include a book by Saunders and AUen and a survey of preparative methods by Schank. There ate also reviews on the diazotization of heteroaromatic primary amines and on the diazotization of weakly basic amines in strongly acidic media. The diazotization process (Scheme 11) goes by way of a primary nitrosamine. 

HN3 was first obtained as a product of the oxidation of hydrazine by nitrous acid in aqueous solution ... 

The common procedure for diazotization by means of nitrous acid in aqueous solutions is illustrated by the synthesis of benzenediazonium chloride, o-, m-, and p-methylbenzenediazonium sulfates, and/S-naph-thalenediazonium chloride. ... 

Treatment of aminopurine nucleosides with nitrous acid in aqueous solution normally results in replacement of the amino group by a hydroxyl group thus, inosine is prepared from adenosine. Although this process is undoubtedly a diazotization, the intermediate diazonium salt must have... 

The reaction of (5,8-diaza-4,9-dimethyldodeca-3,9-diene-2,l l-dionato)nickel-(ii) with either NO or organic nitrite, or the reaction of acacH, en, Ni ", and nitrous acid in aqueous solution gives the two isomers (162) and (163), which can be separated by chromatography. The complexes (164 = Me, Et,... 

A careful and detailed study of the solubility and decomposition kinetics of nitrous acid in aqueous solution has appeared. This is part of an excellent program of work on atmospheric chemistry, and provides valuable quantitative data, particularly in terms of solubility parameters. Stanbury et have bubbled N0 2 in a stream of N2 into alkaline aqueous solutions of Na N02, and determined the amount of. This is a difficult experiment to do well, and has produced... 

V. S. Koltunov and V. I. Marchenko [Kinet. Ratal., 7, 224 (1966)] studied the reaction between hydrazine (N2H4) and nitrous acid in aqueous solution. The following mechanism has been proposed for this reaction ... 

One of the most versatile classes of intermediates for the synthesis of other aromatic compounds are the aryl diazonium ions formed by diazotization of anilines in acidic solution." Unlike aliphatic diazonium ions, which decompose very rapidly to molecular nitrogen and the aliphatic carbonium ion, aryl diazonium ions have sufficient stability to permit controlled reactions, and in some cases salts of the diazonium ions can be isolated. The usual procedure for nitrosation involves reaction with nitrous acid in aqueous solution ... 

Solutions of nitrous acid in aqueous hydrochloric acid or hydrobromic acid give rise to an equilibrium concentration of the corresponding nitrosyl halides, as indicated in (14). At 25°C, the equilibrium constants for the formation of... 

If the amine is basic enough to form a salt with dilute mineral acids in aqueous solution, the normal diazotization method of adding sodium nitrite in aqueous solution to a solution or suspension of the amine salt is satisfactory. Variations in die order of addition of die reagents are sometimes used, for example, when there is another functional group present which is sensitive to nitrous acid, or if die amine salt is very insoluble. Weakly basic amines can often be diazotized successfully either in concentrated sulfuric acid or in a mixture of sulfuric acid with acetic or phosphoric acid. It is likely that nitrosylsul fiiTic acid is formed on addition of sodium nitrite to concentrated sulfuric acid, and that this is the nitro sating agent when the amine is subsequently added. 

Table 8-9 lists processes leading to the oxidation of N02 to nitrous or nitric acid in aqueous solution. The significance of these reactions in clouds may be assessed by comparing their rates with that for the oxidation of N02 by ozone, which is the major dark reaction in the gas phase. Table 8-9 includes the latter process for comparison. 

Solubility op Nitrous Oxide in Aqueous Solutions of Acids. 

Decomposes below melting point. ° C 288 Relative density (water -1) 1.5 Solubility in water, g/100 ml at 20 ° C 1 Relative molecular mass 191.2 Qrossformula CgH7N03S.H20 COLORLESS CRYSTALS. OISINTEORATING IN UQHT Decomposes when heated above 288 C or on contact with strong acids, giving olf nitrous vapors and sulfur Moxkfe. Slightly acidic in aqueous solution. ... 

This reaction was first reported by Chretien and Longi in 1944. It is a general preparation of nitrite ester by means of the treatment of alcohols with nitrous acid in aqueous acidic solution. In the original protocol, alcohol was mixed with sodium nitrite followed by the addition of aluminum sulfate, which hydrolyzes to lower the pH. This reaction has been modified to occur in acetic acid. ... 

A study of reaction of 3-chloro-pentane-2,4-dione and 3-ethyl pentane-2,4-dione with nitrous acid in aqueous micellar solutions has concluded that nitrosation occurs initially on the enol-oxygen with the release of a proton to form a chelate-nitrosyl complex intermediate in steady state. ... 

In aqueous solutions of sulphuric (< 50%) and perchloric acid (< 45 %) nitrous acid is present predominantly in the molecular form, although some dehydration to dinitrogen trioxide does occur.In solutions contairdng more than 60 % and 65 % of perchloric and sulphuric acid respectively, the stoichiometric concentration of nitrous acid is present entirely as the nitrosonium ion (see the discussion of dinitrogen trioxide 4.1). Evidence for the formation of this ion comes from the occurrence of an absorption band in the Raman spectrum almost identical with the relevant absorption observed in crystalline nitrosonium perchlorate. Under conditions in which molecular nitrous... 

The catalysed nitration of phenol gives chiefly 0- and />-nitrophenol, (< 0-1% of w-nitrophenol is formed), with small quantities of dinitrated compound and condensed products. The ortho para ratio is very dependent on the conditions of reaction and the concentration of nitrous acid. Thus, in aqueous solution containing sulphuric acid (i 75 mol 1 ) and nitric acid (0-5 mol 1 ), the proportion of oriha-substitution decreases from 73 % to 9 % as the concentration of nitrous acid is varied from o-i mol l i. However, when acetic acid is the solvent the proportion of ortAo-substitution changes from 44 % to 74 % on the introduction of dinitrogen tetroxide (4-5 mol 1 ). 

Substitution Reactions. Reaction with nitrous acid in dilute aqueous solutions yields the corresponding hydroxy acid or in solution containing a hydrohahc acid, the corresponding a-halo acid, with inversion in many cases. 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Nitrous acid, HNO2, has not been isolated as a pure compound but it is a well known and important reagent in aqueous solutions and has also been studied as a component in gas-phase equilibria. Solutions of the free acid can readily be obtained by acidification of cooled aqueous nitrite solutions but even at room temperature disproportionation is noticeable ... 

A solution of nitrous acid in sulfuric acid exists as the equilibrium indicated in Scheme 2-15, as was shown by Seel and Winkler (1960), and by Bayliss et al. (1963). These authors determined the equilibrium concentration of [HN02] and [NO+] in various acid concentrations spectrophotometrically. They found that in aqueous sulfuric acid containing more than about 57% w/w H2S04 the equilibrium of Scheme 2-15 is predominantly on the right-hand side. This equilibrium and the problem of the potential intermediate nitrosoacidium ion (H20-N0), which is the proton addition product of HN02, will be discussed in Section 3.2. 

Nitrous acid, the parent acid of the nitrites, has not been isolated in pure form but is widely used in aqueous solution. Nitrites are produced by the reduction of nitrates with hot metal ... 

When thiocyanate ions are added to nitrous acid in water, a pink colouration develops which is believed to be due to the formation of nitrosyl thiocyanate (equation 34), which is too unstable to be isolated but which can be used as a nitrosating agent in aqueous solution. Because the equilibrium constant for ONSCN formation81 is quite large (30 dm6mol 2) at 25 °C, thiocyanate ion is an excellent catalyst for aqueous electrophilic nitrosation. The well established82 series is Cl- < Br < SCN < (NH2)2CS. Thiocyanate ion is also a sufficiently powerful nucleophile to react in acid solution with nitrosamines in a denitrosation process (equation 35), which can only be driven to the right if the nitrosyl thiocyanate is removed by, e.g., reaction with a nitrite trap such as hydrazoic acid. 

Mercaptopyridine (377) reacts rapidly with nitrous acid in mildly acid aqueous solution (via the thione tautomer) to give an unstable 5 -nitroso ion (378) in a reversible... 

According to Tscherniak methylnitrolic acid decomposes in water to give formic acid and N2O, while Wieland found that when methylnitrolic acid 02NCH=NOH is boiled in aqueous solution, with or without the addition of a mineral acid it yields formic acid, nitrous oxide and fuhninic acid, which is precipitated as the silver or mercuric salt if silver or mercuric nitrate is added to the above mixture (equation 9). The yield of fulminate is increased by the presence of mineral acid and by boiling, but it is also formed at ambient temperatures. 

Walden concluded that potassium hydrate and phosphorus penta-chloride acted optically normally, i.e. without alteration of the configuration, but that silver oxide, and therefore also nitrous acid and nitrosyl chloride, acted optically abnormally, but as to which of these reactions was really the normal one he was not able to decide. The conclusion was remarkable, since the action of silver oxide takes place in aqueous. solutions at a low temperature and the effect of potash in producing racemisation is well known. Still more curious is the supposition that nitrous acid and nitrosyl chloride act optically abnormally. 

In aqueous solution, the NO2 formed subsequently disproportionates to nitric and nitrous acids [18] ... 

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