Raman nitric acid

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. ... 

In equimolar mixtures of nitric acid and water a monohydrate is formed whose Raman spectrum has been observed. There is no evidence for the existence of appreciable concentrations of the nitric acidium ion in aqueous nitric acid. 

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 ... 

Raman spectroscopy provides the easiest way of estimating the concentration of nitronium ions in different media ( 2.4.1). The concentration, determined by infra-red spectroscopy, of nitronium ions in nitric acid was increased markedly by the addition of sulphuric acid. ... 

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 relative abilities of nitromethane, sulpholan, and acetic acid to support the ionisation of nitric acid to nitronium ions are closely similar to their efficiencies as solvents in nitration. Raman spectroscopy showed that for a given concentration of mixed acid (i i nitric and sulphuric acids) the concentration of nitronium ions in these three solvents varied in the order nitromethane > sulpholan > acetic acid. The concentration of mixed acid needed to permit the spectroscopic detection of nitronimn ions was 25 %, 50 % and 60 % in the three solvents, respectively (see 4.4.3). 

Solutions of dinitrogen pentoxide in nitric acid or sulphuric acid exhibit absorptions in the Raman spectrum at 1050 and 1400 cm with intensities proportional to the stoichiometric concentration of dinitrogen pentoxide, showing that in these media the ionization of dinitrogen pentoxide is complete. Concentrated solutions in water (mole fraction of NgOg > 0-5) show some ionization to nitrate and nitronium ion. Dinitrogen pentoxide is not ionized in solutions in carbon tetrachloride, chloroform or nitromethane. ... 

Nitration in the presence of strong acids or Lewis acids Solutions of dinitrogen pentoxide in sulphuric acid nitrate 1,3-dimethyl-benzene-4,6-disulphonic acid twice as fast as a solution of the same molar concentration of nitric acid. This is consistent with Raman spectroscopic and cryoscopic data, which establish the following ionisation ... 

In an excess of nitric acid, nitrous acid exists essentially as dinitrogen tetroxide which, in anhydrous nitric acid, is almost completely ionised. This is shown by measurements of electrical conductivity, and Raman and infra-red spectroscopy identify the ionic species... 

When acetic anhydride was in excess over nitric acid, acetyl nitrate and acetic acid were the only products. When the concentration of nitric acid was greater than 90 moles %, dinitrogen pentoxide, present as (N02+)(N0a ), was the major product and there were only small traces of acetyl nitrate. With lower concentrations of nitric acid the products were acetic acid, acetyl nitrate and dinitrogen pentoxide, the latter species being present as covalent molecules in this organic medium. A mixture of z moles of nitric acid and i mole of acetic anhydride has the same Raman spectrum as a solution of i mole of dinitrogen pentoxide in 2 moles of acetic acid. 

Table 1 Hsts some of the physical properties of duoroboric acid. It is a strong acid in water, equal to most mineral acids in strength and has a p p o of —4.9 as compared to —4.3 for nitric acid (9). The duoroborate ion contains a neady tetrahedral boron atom with almost equidistant B—F bonds in the sohd state. Although lattice effects and hydrogen bonding distort the ion, the average B—F distance is 0.138 nm the F—B—F angles are neady the theoretical 109° (10,11). Raman spectra on molten, ie, Hquid NaBF agree with the symmetrical tetrahedral stmcture (12).

At higher concentrations the Raman spectra of aqueous solutions of alkali nitrates and of nitric acid have been investigated. Nitric acid was found to be incompletely dissociated, though for the alkali nitrates no evidence of incomplete dissociation was found. Since accurate measurements on solutions of nitric acid have not been made at concentrations below 4.0 molar, it is not certain how the extrapolation to infinite... 

The Raman spectrum of the monohydrate, HN03.H20, shows it to exist as the hydroxoni-um salt, H30+N03 13. Also, according to analyses of the Raman spectrum, nitric acid exists in aq solns either as a pseudo-acid, N02.0H or as a true acid, N03".H+. In 10 molar aq soln, both acids are present in equal amounts, being caused by the self-dissociation of nitrogen pentoxide (NjOj), while in a 6 molar soln, the pseudo acid is present only to the extent of 2%. and the more dilute the soln, the less pseudo acid is present. In very coned solns, the true acid is present only in small quantities (Refs 32 33)... 

Nitric acid has a peak in the Raman spectrum. When nitric acid is dissolved in concentrated sulfuric acid, the peak disappears and two new peaks appear, one at 1400cm attributable to NOj and one at 1050cm due to... 

The presence of N02, the nitronium ion, both in this solution and in a number of salts (some of which, e.g. NOz C104e, have actually been isolated) has been confirmed spectroscopically there is a line in the Raman spectrum of each of them at 1400 cm"1 which can only originate from a species that is both linear and triatomic. Nitric acid itself is converted in concentrated sulphuric acid virtually entirely into N02, and there can be little doubt left that this is the effective electrophile in nitration under these conditions. If the purpose of the sulphuric acid is merely to function as a highly acid medium in which NOz can be released from HO—N02, it would be expected that other strong acids, e.g. HC104, would also promote nitration. This is indeed found to be the case, and HF plus BF3 are also effective. The poor performance of nitric acid by itself in the nitration of benzene is thus explained for it contains but little N02 the small amount that is present is obtained by the two-stage process... 

Magnesium silicates are characterized by x-ray diffraction and Raman spectroscopy. Magnesium is analyzed in an aqueous acid extract by AA or ICP following digestion of the solid with nitric acid and appropriate dilution. 

Indium nitrate can be prepared from InCl3 and N205 158,159 the dissolution of indium metal in cone, nitric acid yields In(N03) xH20 (x = 3, 4, 5),7 which has been used as the source of cationic and anionic complexes.64 Salts of [In(N03)4] have been reported,64160 and Raman studies161,162 have demonstrated the presence of In/NOj complexes in solution the stability constant results have been reviewed.9... 

When the reagent used is nitric acid, the attacking species is usually the nitronium ion, NOa +. That this ion exists has been abundantly proven. For example, cryoscopic measurements show that each molecule of nitric acid dissolved in sulfuric acid gives rise to four ions. This result is best explained by the equilibria shown in Equations 7.59-7.61.140 Raman spectra also show that in... 

Raman spectroscopic studies in the 1930s on HN03-H2S04 mixtures by Medard513 showed the presence of nitronium ion 219 in the media. A sharp band at 1400 cm-1 was assigned to the symmetric stretching mode of the species. Since then the nitronium ion has been characterized in a variety of Brpnsted and Lewis acid mixtures of nitric acid.514... 

Ingold518 was the first to propose that nitric acid anhydride N205 has an ionic structure N02+N03. This was later confirmed by Wilson and Christe,519 who showed a linear symmetric N02+ with an N—O bond length of about 1.154 A. The structure of reaction products formed between nitrogen oxides and BF3, including N02+BF4 was established by Olah and co-workers520,521 on the basis of Raman, IR, and X-ray diffraction data. 

Raman, S., Ashcraft, R.W., Vial, M., Klasky, M.L. 2005. Oxidation of hydroxylamine by nitrous and nitric acids. Model development from first principle SCRF calculations. J. Phys. Chem. A, Mol. Spectrosc. Kinet. Environ. Gen. Theory 109 (38) 8526-8536. 

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