Nitric acid ionization

When nitronium salts are used, NOj is of course present to begin with. Esters and acyl halides of nitric acid ionize to form NOj. Nitrocyclohexadienones are converted to NO2 and the corresponding phenol." ... 

Nitric acid ionizes as a base, toward the sulfuric acid, and the maximum rate of nitration occurs at a definite acidity defined by Hammett s Ha function, a logarithmic measure which is equivalent to pH in dilute acids but which acquires a negative value in super-acid solutions. For the nitration of aromatic compounds, on which these rate studies were made, the maximum was reached in sulfuric acid of 90 % concentration. So the simple reaction... 

Nitric acid ionizes in water to produce hydrogen ion, which exists in water as the hydronium ion. This makes it an Arrhenius acid. The equation showing the formation of the hydronium ion, H30+, shows nitric acid as a proton donor, making it an acid in the Bronsted-Lowry concept. 

The nitronium ions produced in this way tend to repress the selfdehydration of the nitric acid and therefore the net concentration of nitronium ions is not proportional to the concentration of the catalyst. When sufficient sulphuric acid has been added to make the self-ioniza-tion of nitric acid relatively unimportant, the nitronium ions will be produced predominantly from the above ionization, and the acceleration will follow a linear law. 

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. ... 

It has already been noted that, as well as alkylbenzenes, a wide range of other aromatic compounds has been nitrated with nitronium salts. In particular the case of nitrobenzene has been examined kinetically. Results are collected in table 4.4. The reaction was kinetically of the first order in the concentration of the aromatic and of the nitronium salt. There is agreement between the results for those cases in which the solvent induces the ionization of nitric acid to nitronium ion, and the corresponding results for solutions of preformed nitronium salts in the same solvent. 

Electron Delocalization in the Conjugate Base With a of —1 4 nitnc acid is almost completely ionized m water If we look at the Lewis structure of nitric acid m light of what we have said about inductive effects we can see why The N atom m nitric acid IS not only electronegative m its own right but bears a formal charge of +1 which enhances its ability to attract electrons away from the —OH group... 

Anhydrous nitric acid has been studied as a nonaqueous ionizing solvent, though salts tend to be rather insoluble unless they produce N02" " or... 

These trends are general ones, observed with other oxoadds of the nonmetals. Recall, for example, that nitric acid, HNO3 (oxid. no. N = +5), is a strong acid, completely ionized in water. In contrast, nitrous add, HN02 (oxid. no. N = +3), is a weak acid (Ka = 6.0 X 10-4). The electronegativity effect shows up with the strengths of the oxoadds of sulfur and selenium ... 

Nitric acid is a strong acid, completely ionized to H+ and N03 ions in dilute water solution HN03(flq)---------------------------- H+(aq) + N03( q)... 

The studies of Bunton et al (Ref 38) using heavy oxygen (18Q) are particularly noteworthy in elucidating the self-ionization process. With moderately dilute nitric acid they found that nitrations required presence of nitrous acid. Ingold and co-workers (Ref 36c) suggest that the action of nitrous acid is as follows ... 

One of the least expensive and popular techniques for the quant detn of bound N in energetic materials is that of titrimetry. There are currently three basic titrimetry systems used aq acid-base, redox and non-aqueous (involving both acid-base and redox systems in which there is association, not ionization of the re-actants). The simple aq acid-base titrimetry system has been shown, earlier in the article, being used in the Kjeldahl, De varda and Ter-Meulen procedures to detn liberated NH3. It is also utilized, for example, to detn nitrosyi-sulfuric acid in mixed acids, total acidity in nitric acid, NG in exp] oils, and the N content of... 

One problem that should be of particular interest for separation processes is the identification and kinetic characterization of the reactive radicals that occur when strong nitric acid solutions are subject to ionizing radiation. The important reducing radical in such solutions is the H atom. There are presently no direct measurements of the rate of reduction of H atoms with any Pu oxidation state. 

Castro and Canselier [114] similarly used reverse phase HPLC with methanol-water containing a low concentration of nitric acid as eluent. Quantification was made possible by using a moving-wire flame ionization detector. 

On addition of nitric acid, the freezing point of sulfuric acid is lowered about four times the amount expected if no ionization has taken place.This means that the addition of one molecule of nitric acid results in the production of four particles, which is strong evidence for the ionization reaction between nitric and sulfuric acids given above. 

In contrast to the equilibrium electrode potential, the mixed potential is given by a non-equilibrium state of two different electrode processes and is accompanied by a spontaneous change in the system. Besides an electrode reaction, the rate-controlling step of one of these processes can be a transport process. For example, in the dissolution of mercury in nitric acid, the cathodic process is the reduction of nitric acid to nitrous acid and the anodic process is the ionization of mercury. The anodic process is controlled by the transport of mercuric ions from the electrode this process is accelerated, for example, by stirring (see Fig. 5.54B), resulting in a shift of the mixed potential to a more negative value, E mix. 

The one-electron oxidation of iV-benzylphenothiazine by nitric acid occurs in the presence of /i-cyclodextrin, which stabilizes the radical cation by incorporation into its cavity. The reaction is inhibited by adamantane, which preferentially occupies the cavity. Novel Pummerer-type rearrangements of / -sulfinylphenyl derivatives, yielding /7-quinones and protected dihydroquinones, and highly enantioselective Pummerer-type rearrangements of chiral, non-racemic sulfoxides have been reviewed. A comprehensive study has demonstrated that the redox potential for 7- and 8-substituted flavins is linearly correlated with Hammett a values. DFT calculations in [3.3.n]pro-pellanes highlight low ionization potentials that favour SET oxidative cleavage of the strained central C-C bond rather than direct C-H or C-C bond attack. Oxidations and reductions in water have been reviewed. ... 

It is generally accepted that nitric acid-acetic anhydride mixtures contain acetyl nitrate (Equation 4.4). Acetyl nitrate is a weak nitrating agent but in the presence of a strong acid, like nitric acid, it can ionize to nitronium and acetate ions. Protonated acetyl nitrate could also be an active nitrating agent under these conditions. 

Nitric acid-trifluoroacetic anhydride mixtures are used extensively for nitrolysis and N-nitration reactions (see Chapters 5 and 6). The same is not true for aromatic nitrations. This reagent contains trifluoroacetyl nitrate, which can ionize to nitronium and trifluoroacetate ions in the presence of strong acid. 

In the solid state, dinitrogen pentoxide is ionic, existing as N02+N03 and sometimes called nitronium nitrate. The same is true of dinitrogen pentoxide in polar solvents like nitric acid where complete ionization to nitronium and nitrate ions is observed. In the vapour phase, and in nonpolar solvents, a covalent structure is observed. This dichotomy of behavior in both physical state and in solution means that no single nitrating agent is as diverse and versatile as nitrogen pentoxide. 

All steps have to be done in glass vessels cleaned with concentrated nitric acid and rinsed thoroughly with de-ionized water. 

The modelling just deseribed of the direct HCl -1- CIONO2 reaction on an ice lattiee to produee molecular chlorine and ionized nitric acid portrayed a relatively faeile eoupled proton transfer/SN2 mechanism, evidently supported in subsequent ealeulations. These results also reinforced the idea of an ionic pathway involving ionized HC1,9-12,21 as opposed to molecular HC1. 

The rate coefficient (k2 enc) for the collision of two species is given by 8RT/3Z (where Z is the viscosity of the medium at the reaction temperature), the Smoluchowski equation. This is the maximum possible rate of reaction, which is controlled by the rate at which the two reacting species diffuse together. For nitration in >90% H2S04, where nitric acid is completely ionized, if exclusively the free base nitrates the rate coefficient (k2 fb) would equal k2 obs KJhx (where Ka is the ionization constant of the base, and hx the acidity function that it follows). Thus, if k2 fb> k2 enc free base nitration is precluded, but if... 

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