Nitrite ions between

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). 

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. 

The NO reduction of the Cu(II) complex Cu(dmp)2(H20)2+ (dmp = 2,9-dimethyl-l,10-phenanthroline) to give Cu(dmp)2 plus nitrite ion (Eq. (20)) has been studied in aqueous solution and various mixed solvents (42a). The reduction potential for Cu(dmp)2(H20)2+ (0.58 V vs. NHE in water) (48) is substantially more positive than those for most cupric complexes owing to steric repulsion between the 2,9-methyl substituents that provide a bias toward the tetrahedral coordination of Cu(I). The less crowded bis(l,10-phenanthroline) complex Cu(phen)2(H20)2+ is a weaker oxidant (0.18 V) (48). 

Several pathways are known to take place in the reaction between nitrate esters and alkalis. The mechanism that leads to the formation of nitrite ions is an (X-ehmination abstraction of an CC-hydrogen atom, with the conversion of the nitrate ester to nitrite ion and the corresponding carbonyl compound [31] (Eq. (4)) ... 

As stated above, nitrate esters (such as NG or PETN) and nitramines (such as RDX or HMX), form nitrite ions under alkahne conditions and therefore can be detected by the Griess reaction. However, the Griess spot test by itself does not enable to distinguish between individual explosives within these groups. 

Polyetherimides (PEI) are polyimides containing sufficient ether as well as other flexibi-lizing structural units to impart melt processability by conventional techniques, such as injection molding and extrusion. The commercially available PEI (trade name Ultem) is the polymer synthesized by nucleophilic aromatic substitution between 1,3-bis(4-nitrophthalimido) benzene and the disodium salt of bisphenol A (Eq. 2-209) [Clagett, 1986]. This is the same reaction as that used to synthesize polyethersulfones and polyetherketones (Eq. 2-206) except that nitrite ion is displaced instead of halide. Polymerization is carried out at 80-130°C in a polar solvent (NMP, DMAC). It is also possible to synthesize the same polymer by using the diamine-dianhydride reaction. Everything being equal (cost and availability of pure reactants), the nucleophilic substitution reaction is probably the preferred route due to the more moderate reaction conditions. 

I also hope that someone would comment regarding Dr. Yalman s comments about the reaction between the nitrite ion and the azido complex. One finds that the scavenging activity of—I believe it was bromide and thiocyanate—is much more effective in the presence than in the absence of nitrite in the azide system. The... 

The above mentioned authors also established that the nitrate ion (in contrast with the nitrite ion) slowly undergoes reduction in the presence of sodium hydrosulphide. This leads to the conclusion that the nitrite ion formed during the hydrolysis of nitric esters cannot be produced by the reduction of a nitrate ion. Hence if the nitrite ion is formed direct during the hydrolysis of nitric esters, then it could only be produced by breaking the linkage between the oxygen and nitrogen atoms. 

As long ago as 1896 Walther [43] observed that as the result of chemical reaction between ethyl nitrate and phenylhydrazine at an elevated temperature, aniline, ammonium nitrate and nitrogen are formed. If the reaction takes place in the presence of sodium ethoxide then, according to Bamberger and Billeter [44] even at room temperature nitrite ions, nitrogen, benzene, phenyl azide, azobenzene, nitrobenzene, aniline, acetic acid and acetaldehyde are formed. 

Analysing the products of reaction between alkyl nitrates and hydrazine they detected nitrate and nitrite ions, a corresponding alcohol, alkyl hydrazine, nitrogen oxides, ammonia and traces of aldehyde. If the reaction is performed without solvents in an excess of hydrazine, reduction occurs. In an aqueous solution of alcohol the process of substitution predominates particularly when the concentrations of reagents are low. 

Investigating the types of reaction between nitric acid esters and hydrazine Merrow and van Dolah endeavoured first of all to solve the problem of how nitric acid is formed since the answer could in effect make it possible to establish the position of the linkage to be broken off in an ester molecule. They have established experimentally that during the reaction between alkyl nitrates and hydrazine the nitrite ion is produced very quickly. Later it dwindles away as reaction proceeds. The creation of NO in this process can never arise from the removal of a hydrogen atom in the a-posi-tion, since only an insignificant amount of ester can follow the reaction (31) to form an aldehyde ... 

Pi bonding between metal and ligands provides a simple raison d etre lor strong field ligands, an issue that crystal field theory could not resolve. If we examine the strong field end of the spectrochemical series (page 405), we find ligands such as nitrite ion, cyanide ion, carbon monoxide, phosphites, and phosphines. The latter two owe their positions in the series to their ability to serve as rt acceptors, as described above, which increases the value of A, relative to what it would be in u [Pg.756]

As earlier reported for electrochemical sensing, often the active chromo-phore will be dispersed in a polymeric matrix. For example, Mohr and Wolfbeis reported a nitrate sensor [121] where the active chromophore is a rhodamine B dye which had been modified with an octadecyl side chain to render it hydrophobic and prevent leaching. The dye was dispersed in a plasticised PVC membrane containing a hydrophobic anion carrier (tridodecylmethylammo-nium chloride). On exposure to nitrate, the fluorescence of the dye increased. This membrane, however, only displayed Hofmeister-type selectivity and was also affected by pH. Replacing the quaternary ammonium anion carrier with a palladium phospine chloride carrier led to selectivity for nitrite [ 122], probably due to a preferential interaction between Pd and nitrite ion. 

Fig. 4 A linear coordination polymer of silver with 4,4 -bipyridyl and bidentate nitrite anions,13 There is a 3.0 A contact between the silver and the nitrogen of the nitrite ion, shown as a dotted line, if this was a full covalent bond, the system would be two-dimensional. Gray spheres denote carbon, white hydrogen, dark blue nitrogen, red oxygen, and green silver.

The reaction between different types of radical cation and nitrite ion (E° = 0.7 V in acetonitrile) has been extensively studied (Ristagno and Shine, 1971 Johnson and Dolphin, 1976 Shine et al., 1979 Smith et al., 1979 Eberson and Radner, 1980). Generally, one obtains nitration products from this reaction, and in view of its exergonic nature the mechanism most probably consists of an initial, very fast electron-transfer step, followed by a slower nitration reaction, caused by N02 (N204) from the first step. 

In neutral solution, in contrast, phenol nitration and nitrosation are pho-toinduced processes since no thermal reaction has been observed between phenol and nitrite ion. The pH value where the thermal and photoinduced processes have similar importance is around 5.5. Thermal processes prevail at lower pH and photoinduced ones at higher pH [55,62]. 

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