Nitrite ion reactions

Cations react rapidly and indiscriminately with nucleophiles. Thus if a reaction which is suspected to go via a cationic intermediate is carried out in the presence of an added nucleophile, and an adduct containing the new nucleophile is obtained, this provides evidence for a cationic intermediate which is trapped by the added nucleophile. For example, the addition of bromine to alkenes is thought to go via a cationic intermediate 4 (reaction 5.11). If chloride or nitrite ions are added to the reaction mixture, the chloride or nitrite adducts 5 and 6 are obtained, even though the chloride and nitrite ions do not react with ethene (or 1,2-dibromoethane) directly at a rate that would account for the amount of these products in the reaction mixture. This provides strong evidence for the intermediate bromoethyl cation 4, which will be trapped by the added chloride or nitrite ions (reactions 5.12 and 5.13). The structure of bromoalkyl cations is discussed further in the section on electrophilic addition. 

Several preparations of dicarbonyl dinitrosyl iron have been reported including treatment of [Fe3(CO)i2] or [Fe2(CO)9] with nitric oxide, acidification of a mixture of [HFe(CO)4] and nitrite ion, reaction of iron pentacarbonyl with nitrosyl chloride and acidification of a mixture of [Fe(CO)3NO] and nitrite ion as in equations (2) and (3). 

Our experiences with nitrite-ion reactions show that both nitration and oxygen-atom transfer can occur. Thus, 6 " and 10 give 2-nitrodibenzodioxin (12) and 3-nitroperylene (10) respectively according to eq. 6. The cation radical of zinc tetra-phenylporphyrin is similarly nitrated at one of the pyrrolic carbon atoms (44). The perylene reaction is so facile that it... 

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 ... 

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). 

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... 

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). 

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). 

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). 

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. 

It is probable that the test of Wolski88 for sulphoxides depends on the first reaction. He used acetyl chloride or bromide the product from the former gave a red colour with nitrite ion, absorption maximum at 545 nm, and the latter gave a yellowish-orange colour directly. The method was used also by Besyadetskaya and colleagues89 to determine dimethyl sulphoxide in ointments. 

Disproportionation of Pu(IV). There are several needs associated witn the occurrence, detection, and mitigation of the disproportionation of Pu(IV) in applied plutonium recovery/ purification procedures. First, there is a great need for much more detailed information concerning the effect of typical process conditions [e.g., temperature, concentration of plutonium, hydrogen ion, nitrate ion, nitrite ion, fluoride ion, other metal ions (e.g., A13+, Fe3+, etc.), etc.] on the occurrence and extent of the reaction ... 

Nitrite ion is often used in plutonium solvent extraction systems to oxidize Pu(III) to Pu(IV) and to reduce Pu(VI) to Pu(IV). But HONO, produced in HN03 media, is extractable into TBP-diluent systems and can interfere with subsequent reductive stripping of plutonium. There is thus a need to find a reagent comparable to nitrite ion in its reactions with Pu(III) and Pu(VI), but which does not extract into TBP solutions. 

With such a diversity of N-nItrosatlon pathways theoretically possible. It Is comforting to note that only a few combinations of circumstances have been Implicated In environmental nitrosamlne formation thus far. Two of these are so facile and prevalent that, as of 20 years ago, they were the only recognized mechanisms of N-nItrosatlon. They Involve the Interaction of di-or trisubstituted ammonia derivatives with a nitrite Ion, as Illustrated In Figure 1 for the secondary amines, under the catalytic Influence of acid. Note the Important special cases of nucleophilic displacement of water from the nitrous acldlum Ion, H20-N0 , by a second nitrite Ion to yield NoOo (as in the reaction at the top of Figure 1), and by nitrate (bottom of Figure... 

The reaction pathways for the pyrrole formation are summarized in Scheme 10.3. The group that is eliminated at the final stage is a nitrite ion (Barton-Zard reaction) or a toluenesulfinate ion (Leusen reaction), depending on the reaction pattern. 

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