Nitrite ions

In the formation of dichloroacetylene, chloride ion (from sodium chloride or a quaternary ammonium chloride) adds to an epoxide such as epichlorohydrin and the resulting alkoxide dehydrohalogenates trichloroethylene. The overall process is formulated in equation 9.13. 

Numerous reactions have been investigated which involve alkoxides generated in situ by the reaction of halide with an epoxide. The kinship of this chemistry to the phase transfer method is manifest, but a detailed discussion of this body of work is beyond the scope of this book. In any event, the halide/epoxide technique has recently been reviewed [30]. 

The reactions of halide and azide ions (see above), cyanide ion (see Chap. 7) and thiocyanate ions (see Sect. 13.7) have all been discussed. In the general context of halides and pseudohalides, it should be noted that nitrite ion has been successfully phase-transferred [31, 32]. The yields for the formation of nitroalkanes in either crown [31 ] or quaternary ion catalyzed [32] processes are fair to good for primary alkanes and poor for secondary systems. Bromocyclohexane, for example, afforded only traces of nitrocyclohexane when treated with nitrite ion, the by-products resulting presumably from oxygen attack (nitrite ester formation) or elimination. The conversion of n-octy bromide into the corresponding nitro-compound is formulated in equation 9.14 and several examples of the transformation are recorded in Table 9.6. 

Ellison et propose that the substitution of nitrite ion into chloroam- 

Substitution into ra s-[Pt(en)2Cl2] catalysed by [Pt(en)2] (en = ethylene-diamine) would proceed as follows 

Redox behaviour of this type is considered to influence many substitution reactions of Pt(IV) .  

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Cobalt(II) is also easily oxidised in the presence of the nitrite ion NO2 as ligand. Thus, if excess sodium nitrite is added to a cobalt(II) salt in presence of ethanoic acid (a strong acid would decompose the nitrite, p. 244), the following reaction occurs ... 

Here, effectively, the Co " (aq) is being oxidised by the nitrite ion and the latter (in excess) is simultaneously acting as a ligand to form the hexanitrocobaltate(III) anion. In presence of cyanide ion CN. cobalt(II) salts actually reduce water to hydrogen since... 

The more powerful anticatalysis of nitration which is found with high concentrations of nitrous acid, and with all concentrations when water is present, is attributed to the formation of dinitrogen trioxide. Heterolysis of dinitrogen trioxide could give nitrosonium and nitrite ions 2N2O4 + HjO N2O3 + 2HNO3. 

The anticatalytic action is ascribed to the deprotonation of nitric acidium ions by nitrite ions, which, being more basic than nitrate ions, will be more effective anticatalysts. The effect of nitrite ions should depend upon [HNOaJaioich it does. 

Oxidation. Nitroparaffins are resistant to oxidation. At ordinary temperatures, they are attacked only very slowly by strong oxidi2ing agents such as potassium permanganate, manganese dioxide, or lead peroxide. Nitronate salts, however, are oxidi2ed more easily. The salt of 2-nitropropane is converted to 2,3-dimethyl-2,3-dinitrobutane [3964-18-9], acetone, and nitrite ion by persulfates or electrolytic oxidation. With potassium permanganate, only acetone is recovered. 

Historically, ferrous sulfamate, Fe(NH2S02)2, was added to the HNO scmbbing solution in sufficient excess to ensure the destmction of nitrite ions and the resulting reduction of the Pu to the less extractable Pu . However, the sulfate ion is undesirable because sulfate complexes with the plutonium to compHcate the subsequent plutonium purification step, adds to corrosion problems, and as SO2 is an off-gas pollutant during any subsequent high temperature waste solidification operations. The associated ferric ion contributes significantly to the solidified waste volume. 

During electrolytic reduction of to and the subsequent reduction of Pu to inextractable Pu hydrazine is added as a holding agent to destroy excess nitrite ions and prevent reoxidation of and Pu to their higher valence states. 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Nucleophilic displacement of iodide by the nitrite ion in 1-iodo-17/. l//,2//,2W-perfluoroalkanes affords the 1-nitro analogue (equation 4). Oxidative nitration of the 1-mtro-l//, l//,2//.2//-perfluoroalkane with tetranitromethane yields the ge/n-dinitro compound [4. ... 

Nitrite ion, an ainbident nucleophile in aprotic solvents, favors nitrogen atom attack on the double bond of various fluoro(halo)olefins. 2-Monohydroperfluoro-nitroalkanes can thus be produced [5] (equation 5)... 

The unpaired electron in NO2 appears to be more localized on the N atom than it is in NO and this may explain the ready dimerization. NO2 is also readily ionized either by loss of an electron (9.91 eV) to give the nitryl cation N02 (iso electronic with CO2) or by gain of an electron to give the nitrite ion NO2 (isoeleelronic with O3). These changes are accompanied by a dramatic diminution in bond angle and an increase in N-O distance as the number of valence electrons increases from 16 to 18 (top diagram). 

The nitrite ion, NO2, is a versatile ligand and can coordinate in at least five different ways (i)-(v) ... 

Quite recently, it was reported that heating of tetracyano derivative 268 with potassium nitrite and potassium carbonate in DMF provided 53% of phenoxathiin 270 (Scheme 42) (OOlHl 161). The probable mechanism is, that one activated nitro group in 268 is displaced with a nitrosoxy group by nucleophilic substitution of nitrite ion, followed by hydrolysis to 269, which then undergoes denitrocyclization reaction to the final product. 

Schneider and Busch have showed that tetraazafS 1 8 l paracyclophane catalyzes the nitration of alkyl bromides with sodiiun nitrite In dioxane-water d l at 30 C, the reaction of 2-bromomethylnaphthalene with sodiiun nitrite is accelerated by a factor of 20 in the presence of the catalyst Concomitantly, the product ratio of [R-ONO [RNO-, changes from 0 50 1 to 016 1 Thus, an acciuruiladon of nitrite ions at the positively charged cyclophanes or IRA-900-nitrite form provides a new method for selective nitration of alkyl halides... 

The reacdon pathways for the pyrrole formadon are summarized In Scheme 10.3. The group that is eliminated at the final stage is a nitrite ion (Barton-Zard reacdoni or a tolnenesnlfinate ion (Xensen reacdoni, depending on the reacdon pattern. 

Little work has been carried out on the mechanism of inhibition of the corrosion. of copper in neutral solutions by anions. Inhibition occurs in solutions containing chromate , benzoate or nitrite ions. Chloride ions and sulphide ions act aggressively. There is evidence that chloride ions can be taken up into the cuprous oxide film on copper to replace oxide ions and create cuprous ion vacancies which permit easier diffusion of cuprous ions through the film, thus increasing the corrosion rate. 

The reduction potential of the nitrate ion is lower than the discharge potential of hydrogen, and therefore hydrogen is not liberated. The nitric acid must be free from nitrous acid, as the nitrite ion hinders complete deposition and introduces other complications. The nitrous acid may be removed (a) by boiling the nitric acid before adding it, (b) by the addition of urea to the solution ... 

In this case the nitrite ion, under acidic conditions, causes diazotisation of sulphanilamide (4-aminobenzenesulphonamide) to occur, and the product is coupled with N-( 1 -naphthyl)ethylenediamine dihydrochloride. 

Nitrites are the salts of nitrous acid, discovered by Scheele in 1774. The inorganic nitrites, with die general formula M.N02, where M is a metal, are well known. They are all insol in w with the exception of the alkali nitrites. Nitrites may be prepd either by thermal decompn of alkali nitrates 2KN03 2KNOJ + 02 or by reduction of nitrates by C or Pb 2KN03 + C 2KN02 + C02. The lone pair of electrons in the nitrite ion is sterically significant consequently, the nitrite ion is bent ... 

As described more fully in Sections 3.1-3.3, with increasing pH the reactive forms of the diazotizing agent are converted into ineffective ones, namely free nitrous acid, HN02, and the nitrite ion, N02. From the discussion of the mechanism of diazotization it will also become apparent why the reaction proceeds better, that is faster, in dilute hydrochloric than in dilute sulfuric acid. With very slow diazotizations for instance, because of high dilution as in nitrite titrations, the use... 

In contrast to the acid, sodium nitrite should not in general be added in excess. Firstly, as far as the ratio of amine to nitrite is concerned, diazotization is practically a quantitative reaction. In consequence, it provides the most important method for determining aromatic amines by titration. Secondly, an excess of nitrous acid exerts a very unfavorable influence on the stability of diazo solutions, as was shown by Gies and Pfeil (1952). Mechanistically the reactions between aromatic diazonium and nitrite ions were investigated more recently by Opgenorth and Rtichardt (1974). They showed that the primary and major reaction is the formation of aryl radicals from the intermediate arenediazonitrite (Ar —N2 —NO2). Details will be discussed in the context of homolytic dediazoniations (Secs. 8.6 and 10.6). 

The second nitrite ion which appears in Schmid s equation (Scheme 3-3) was supposed to act as a base in removing a proton from the arylnitrosoamine cation (3.2). This leads to the kinetic equation of Scheme 3-6, which corresponds to that of Schmid except in the distribution of protons. 

The real weakness of Adamson and Kenner s mechanism is the necessity for the proton to be removed from the arylnitrosoamine cation by a nitrite ion. One would expect water to be basic enough to rapidly convert the cation into the uncharged arylnitrosoamine. The splitting off of the proton is only likely to be difficult in highly concentrated sulfuric acid. 

At first sight this seems surprising, as nitrous acid is a fairly weak acid (pKa = 3.15, Tummavuori and Lumme, 1968) and therefore the low equilibrium concentration of nitrite ions in Scheme 3-9 does not appear to favor the formation of dinitrogen trioxide. 

Based on observations by Bamberger, Bucherer, and Wolff at the turn of the century, Matrka et al. (1967) described experiments which show that alkaline solutions (pH 8.5-9.2) of substituted benzenediazonium chlorides form nitrite ions and triazenes. The latter is obviously the reaction product of the amine formed in a retro-diazotization with the diazonium ion that is still present. The yield of nitrite formed was between 0.5% (benzenediazonium ion) and 50.2% (2-nitrobenzenediazonium ion). 

Two inorganic nucleophiles that react easily with arenediazonium ion, namely the nitrite ion and the hydroxide ion, provide good examples of the concept of the nucleophilic homolytic leaving group. By electron transfer to a diazonium ion the... 

The reaction with nitrite proceeds smoothly and with relatively high yields of the corresponding nitroarene (see Sec. 10.6). Obviously a major part of the driving force of this reaction is the formation of a stable, i. e., an energetically favorable, radical, nitrogen dioxide. With the hydroxide ion — a much stronger nucleophile than the nitrite ion — the reaction is expected to produce very unstable radicals, the hydroxy radical OH and the oxygen radical anion O, from the diazohydroxide (Ar - N2 — OH) and the diazoate (Ar-N20 ) respectively. Consequently, dediazoniation in alkaline aqueous solution does not follow the simple Scheme 8-41 with Yn = OH, but instead involves diazoanhydrides (Ar — N2 —O —N2 —Ar) as intermediates (see Sec. 8.8). 

The formation of aryl radicals from benzenediazonium ions, initiated by electron transfer from a nitrite ion, has already been discussed in Section 8.6. It is an excellent example of a dediazoniation assisted by a donor species that is capable of forming a relatively stable species on release of an electron, in this case a nitrogen dioxide radical NO2 (Opgenorth and Rtichardt, 1974). 

In this context two observations reported by Rondestvedt (1960, p. 214) should be mentioned (i) Meerwein reactions proceed faster in the presence of small amounts of nitrite ion. Meerwein reactions in which N2 evolution ceased before completion of the reaction can be reinitiated by addition of some NaN02. (ii) Optimal acidity for Meerwein reactions is usually between pH 3 and 4, but lower (pH — 1) with very active diazonium compounds such as the 4-nitrobenzenediazonium ion or the diphenyl-4,4 -bisdiazonium ion. At higher acidities more chloro-de-diazoniation products are formed (Sandmeyer reaction) and in less acidic solutions (pH 6) more diazo tars are formed. 

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