162 Nitrate ion

Strong oxidising agents such as acidified potassium manganate(VII) oxidise NOj to the nitrate ion ... 

Tin(ll) chloride, in presence of hydrochloric acid, is oxidised to tin(IV) chloride, the nitrate ion in this case being reduced to hydroxylamine and ammonia. 

The Raman spectrum of nitric acid shows two weak bands at 1050 and 1400 cm. By comparison with the spectra of isolated nitronium salts ( 2.3.1), these bonds were attributed to the nitrate and nitronium ion respectively. Solutions of dinitrogen pentoxide in nitric acid show these bands , but not those characteristic of the covalent anhydride , indicating that the self-dehydration of nitric acid does not lead to molecular dinitrogen pentoxide. Later work on the Raman spectrum indicates that at —15 °C the concentrations of nitrate and nitronium ion are 0-37 mol 1 and 0 34 mol 1 , respectively. The infra-red spectrum of nitric acid shows absorption bands characteristic of the nitronium ion. The equivalence of the concentrations of nitronium and nitrate ions argues against the importance of the following equilibrium ... 

The state of aqueous solutions of nitric acid In strongly acidic solutions water is a weaker base than its behaviour in dilute solutions would predict, for it is almost unprotonated in concentrated nitric acid, and only partially protonated in concentrated sulphuric acid. The addition of water to nitric acid affects the equilibrium leading to the formation of the nitronium and nitrate ions ( 2.2.1). The intensity of the peak in the Raman spectrum associated with the nitronium ion decreases with the progressive addition of water, and the peak is absent from the spectrum of solutions containing more than about 5% of water a similar effect has been observed in the infra-red spectrum. ... 

The infra-red absorption bands of molecular nitric acid do not change as the medium is varied beween 100% and 70% of acid on further dilution the nitrate ion becomes the dominant species. ... 

The effect of potassium nitrate on the rate arises in a similar way. The concentration of nitrate ions in concentrated nitric acid is appreciable, and addition of small quantities of nitrate will have relatively little effect. Only when the concentration of added nitrate exceeds that of the nitrate present in pure nitric acid will the anticatalysis become proportional to the concentration of added salt. 

The two absorption bands, at 1050 and 1400 cm , which appear in the Raman spectra of solutions of nitric acid in concentrated sulphuric acid are not attributable to either of the acid molecules. In oleum the lower band appears at 1075-1095 cm. That these bands seemed to correspond to those in the spectra of anhydrous nitric acid and solid dinitrogen pentoxide caused some confusion in the assignment of the spectrum. The situation was resolved by examining the Raman spectra of solutions of nitric acid in perchloric or selenic acids , in which the strong absorption at 1400 cm is not accompanied by absorption at about 1050 cm . Thus, the band at 1400 cm arises from the nitronium ion, and the band at about 1050 cm can be attributed in the cases of nitric acid and solid dinitrogen pentoxide to the nitrate ion formed according to the following schemes ... 

THE STATE OF NITRIC ACID IN INERT ORGANIC SOLVENTS The absence of ions in mixtures of acetic acid and nitric acid is shown by their poor electrical conductivity and the Raman spectra of solutions in acetic acid, nitromethane, and chloroform show only the absorptions of the solvent and molecular nitric acid the bands corresponding to the nitronium and nitrate ions cannot be detected. -... 

The influence of added species upon the rates and kinetic forms of nitration in organic solvents were of the greatest importance in elucidating details of the processes involved, particularly of the steps leading to the nitronium ion. These influences will first be described, and then in the following section explained. The species to be considered are sulphuric acid, nitrate ions, urea and water. The effect of nitrous acid is considered later ( 4.3). 

In experiments on the nitration of benzene in acetic acid, to which urea was added to remove nitrous acid (which anticatalyses nitration 4.3.1), the rate was found to be further depressed. The effect was ascribed to nitrate ions arising from the formation of urea nitrate. In the same way, urea depressed the rate of the zeroth-order nitration of mesitylene in sulpholan. ... 

The addition of water depresses zeroth-order rates of nitration, although the effect is very weak compared with that of nitrate ions concentrations of 6x io mol 1 of water, and 4X io mol 1 of potassium nitrate halve the rates of reaction under similar conditions. In moderate concentrations water anticatalyses nitration under zeroth-order conditions without changing the kinetic form. This effect is shown below (table 3.5) for the nitration of toluene in nitromethane. More strikingly, the addition of larger proportions of water modifies the kinetic... 

The most crucial observation concerning the effects of added species is that nitrate ion anticatalyses nitration without changing the kinetic form of the reaction. This shows that nitrate does not exert its effect by consuming a proportion of the nitronium ion, for, as outlined above, this would tend to bring about a kinetically first-order reaction. Nitrate ions must be affecting the concentration of a precursor of the nitronium... 

The catalysed reaction was considered to arise from the heterolysis of dinitrogen pentoxide induced by aggregates of molecules of nitric acid, to yield nitronium ions and nitrate ions. The reaction is autocatalytic because water produced in the nitration reacts with the pentoxide to form nitric acid. This explanation of the mechanism is supported by the fact that carbon tetrachloride is not a polar solvent, and in it molecules of nitric acid may form clusters rather than be solvated by the solvent ( 2.2). The observation that increasing the temperature, which will tend to break up the clusters, diminishes the importance of the catalysed reaction relative to that of the uncatalysed one is also consistent with this explanation. The effect of temperature is reminiscent of the corresponding effect on nitration in solutions of nitric acid in carbon tetrachloride ( 3.2) in which, for the same reason, an increase in the temperature decreases the rate. 

If we consider the effect of nitrous acid upon zeroth-order nitration in organic solvents we must bear in mind that in these circumstances dinitrogen tetroxide is not much ionised, so the measured concentration of nitrous acid gives to a close approximation the concentration of dinitrogen tetroxide. Further, the negligible self-ionisation of nitric acid ensures that the total concentration of nitrate ions is effectively that formed from dinitrogen tetroxide. Consequently as we can see from the equation for the ionisation of dinitrogen tetroxide ( 4.3.1),... 

NO3-] oc [N20J and so [NOai oc Now nitrate ions reduce the rate of formation of nitronium ion by de-protonating nitric acidium ions, and this effect must also depend upon [HN02]"toich> as was observed. 

The weak effect of nitrous acid upon nitration in nitric acid is a consequence of the already considerable concentration of nitrate ions supplied in this case by the medium. 

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. 

Added nitrate ions, and to a smaller extent water, depress the rate of the catalysed reaction, therefore excluding the operation of HNO2 and H2NO2+. The depression of the rate by nitrate obeys the following... 

The effect of acetate ions cannot be distinguished from that of nitrate ions, which... 

Ridd - has reinterpreted the results concerning the anticatalysis of the first-order nitration of nitrobenzene in pure and in partly aqueous nitric acid brought about by the addition of dinitrogen tetroxide. In these media this solute is almost fully ionised to nitrosonium ion and nitrate ion. The latter is responsible for the anticatalysis, because it reduces the concentration of nitronium ion formed in the following equilibrium ... 

Considering first pure nitric acid as the solvent, if the concentrations of nitronium ion in the absence and presence of a stoichiometric concentration x of dinitrogen tetroxide are yo and y respectively, these will also represent the concentrations of water in the two solutions, and the concentrations of nitrate ion will be y and x- y respectively. The equilibrium law, assuming that the variation of activity coefficients is negligible, then requires that ... 

Three equally stable Lewis structures are possible for nitrate ion The negative charge in nitrate is shared equally by all three oxygens... 

But inductive effects are only part of the story When nitric acid transfers its proton to water nitrate ion is produced... 

Nitrate ion is stabilized by electron delocalization which we can represent m terms of resonance between three equivalent Lewis structures... 

The negative charge is shared equally by all three oxygens Stabilization of nitrate ion by electron delocalization increases the equilibrium constant for its formation... 

What IS the average formal charge on each oxygen in nitrate ion 3... 

Many stabilizer systems have been tailored to a particular industry need or for particular areas where dilution water quaUty is poor. These grades are heavily stabilized and may contain organic sequestering agents, ie, staimate, phosphates, and nitrate ions, so that the weak solutions produced by dilution from hard water retain acceptable stabihty. The nitrate is not a stabilizer, but it inhibits corrosion of aluminum storage tanks by chloride ion. 

Ammonium nitrate fertilizer incorporates nitrogen in both of the forms taken up by crops ammonia and nitrate ion. Fertilizers (qv) containing only ammoniacal nitrogen are often less effective, as many important crops tend to take up nitrogen mainly in the nitrate form and the ammonium ions must be transformed into nitrate by soil organisms before the nitrogen is readily available. This transformation is slow in cool, temperate zone soils. Thus, ammonium nitrate is a preferred source of fertilizer nitrogen in some countries. 

In reahty the chemistry of breakpoint chlorination is much more complex and has been modeled by computer (21). Conversion of NH/ to monochloramine is rapid and causes an essentially linear increase in CAC with chlorine dosage. Further addition of chlorine results in formation of unstable dichloramine which decomposes to N2 thereby causing a reduction in CAC (22). At breakpoint, the process is essentially complete, and further addition of chlorine causes an equivalent linear increase in free available chlorine. Small concentrations of combined chlorine remaining beyond breakpoint are due primarily to organic chloramines. Breakpoint occurs slightly above the theoretical C1 N ratio (1.75 vs 1.5) because of competitive oxidation of NH/ to nitrate ion. Organic matter consumes chlorine and its oxidation also increases the breakpoint chlorine demand. Cyanuric acid does not interfere with breakpoint chlorination (23). 

Potassium peroxymonosulfate, introduced in the late 1980s, is finding increasing use as an auxiUary oxidant for shock treatment and oxidation of chloramines. Sodium peroxydisulfate is also being sold for shock treatment, however, it is less reactive than peroxymonosulfate. Mixtures of sodium peroxydisulfate and calcium hypochlorite can be used for shock treatment (28). Disadvantages of peroxymonosulfate and peroxydisulfate are they do not provide a disinfectant residual and peroxymonosulfate oxidizes urea and chloramines to nitrate ion, which is a nutrient for algae. 

Zirconium is completely resistant to sulfuric acid up to Foiling temperatures, at concentrations up to 70 wt %, except that the heat-affected zones at welds have lower resistance in >55 wt % concentration acid (Fig. 1). Fluoride ions must be excluded from the sulfuric acid. Cupric, ferric, or nitrate ions significantly increase the corrosion rate of zirconium in 65—75 wt % sulfuric acid. 

The iacreased chemical stabiUty of the 6-deoxytetracyclines allows chemical modification with retention of biological activity electrophilic substitutions have been carried out at C-7 and C-9 under strongly acidic conditions (46—53). Reactions of 6-deoxy-6-demethyltetracycline [808-26-4] (16), C21H22N2O7, with electrophiles, such as nitrate ion (49), bromomium ion (46,47) (from N-bromosuccinimide), or N-hydroxymethylphthalimide (53), yielded 7-substituted tetracyclines. In the case of the nitration reaction, both the 7- and 9-nitro isomers (17, X = NO2, Y = H) and (17, X = H, Y = NO2) were obtained. 

Bismuth subnitrate [1304-85-4] (basic bismuth nitrate) can be prepared by the partial hydrolysis of the normal nitrate with boiling water. It has been used as an antacid and in combination with iodoform as a wound dressing (183). Taken internally, the subnitrate may cause fatal nitrite poisoning because of the reduction of the nitrate ion by intestinal bacteria. 

A large proportion (30-90% in tropical waters) is absorbed by bacteria and oxidized to FfjS in order to allow the sulfur to be used by these organisms. Once in the atmosphere, DMS is oxidized by various free radicals such as hydroxyl and nitrate ions. In the presence of low concentrations of NO the hydroxyl reaction... 

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