Nitric acid as an oxidant

The possibility of using nitric acid as an oxidizing agent in a leaching operation is often prohibitive because many reagents used in solvent extraction are not stable in an oxidizing solution. By the AX method, however, a nitric acid (nitrate) leach solution can be converted to a weak sulfuric acid (sulfate) solution, well suited for a solvent extraction treatment. 

The reduction potential for the nitrate(V)/nitrate(III) couple in acid solution of +0.94 V indicates from the limited data in Table 6.12 that nitrate(V) ion in acidic solution is a reasonably good oxidizing agent. However, nitric acid as an oxidant usually functions in a different manner, with the production of brown fumes with a metal (e.g. copper) or a metal sulfide (e.g. FeS2). The brown fumes consist of N204 (brown gas) and its monomer N02 (colourless gas). Concentrated nitric acid consists of about 70% of the acid in an aqueous solution. In such a solution there is some dissociation of the nitric acid molecules to give the nitronium ion, N02, which represents the primary oxidizing species ... 

Aliphatic hydrocarbons petrol, paraffin. In the U.S.A. several types of combustibles for liquid propellant jet aircraft are used. One of them, i.e. JP-4, is employed for rocket propulsion, with nitric acid as an oxidizing agent (it can also be used with hydrogen peroxide or liquid oxygen). The specification of JP-4, is as follows ... 

Aliphatic and aromatic primary, secondary and tertiary amines were examined from the point of view of their hypergolicity when used with strong nitric acid as an oxidizer. Various devices for such investigations are discussed) Addnl Refs on Amines a)SODC, liritP 530,... 

See pp. 477-478 for more details on nitric acid as an oxidizing agent.)... 

In one approach cyclohexane is autoxidized to a mixture of cyclohexanol and cyclohexanone in the presence of a Co or Mn naphthenate catalyst. This mixture is subsequently oxidized to adipic acid using nitric acid as the oxidant in the presence of a Cu Vv catalyst. An alternative method using dioxygen in combination with Co or Mn in HOAc gives lower selectivities to adipic acid (70% vs 95%). Alternatively, autoxidation in the presence of stoichiometric amounts of boric acid produces cyclohexanol as the major product, which is subsequently oxidized to adipic acid using HNO3 in the presence of Cu Vv. The latter step produces substantial amounts of N2O as a waste product. 

D-Glucaric acid, directly produced by nitric oxidation of glucose or starch, is usually isolated as its 1,4-lactone. The technical barrier to its large-scale production mainly includes development of an efficient and selective oxidation technology to eliminate the need for nitric acid as the oxidant. Because it represents a tetrahydroxy-adipic acid, D-glucaric acid is of similar utility as adipic acid for the generation of polyesters and polyamides (see later in this chapter). 

L.E.G. Hallstrom N.G. lindner, Preparing Fuel Bodies for Hybrid Rockets with Nitric Acid as the Oxidant by Bringing Together a Fluid Amine Fuel and an Elastomer , SwedP 312293 (1969) CA 78, 74346 (1973)... 

The sulfuric acid promotes the formation of the nitrating agent (the nitronium ion) and prevents the dissociation of nitric acid into an oxidizing NO3 ion by binding water as a hydrate. It also enhances the solubility between the aqueous and organic phases46. 

Aniline also cannot be nitrated because nitric acid is an oxidizing agent and primary amines are easily oxidized. (Nitric acid and aniline can be an explosive combination.) Tertiary aromatic amines, however, can be nitrated. Because the tertiary amino group is a strong activator, nitration is carried out with nitric acid in acetic acid, a milder combination than nitric acid in sulfuric acid. About twice as much para isomer is formed as ortho isomer. 

Lavoisier regarded the acid as an oxide at present it is regarded as (oxide + water), so that the hydrogen really comes from the acid. He says that Laplace, who had assisted in the experiments (avait partagees souvent), in a letter of September 1783 explained the evolution of inflammable air as due to the decomposition of water the metal removes the vital air (oxygen) to form a calx, which then dissolves in the acid to form a salt, and at the same time the inflammable principle [of the water] is evolved in the form of air , which inflammable air on combustion in vital air reproduces water. Lavoisier says that Laplace s letter contained idees simples autant que profondes qu il avoit con9ues d apres les experiences qu il avoit faites en commun avec lui . The metals dissolved in the acid in the form of calces (oxides) (Scheele knew this in 1776, see p. 230), and as this occurred in closed vessels the vital air did not come from the atmosphere. It did not come from the vitriolic acid (sulphur trioxide), as there was no formation of sulphur or sulphurous acid the acid, as Lavoisier had shown, required the same amount of alkali for saturation before and after the dissolution of the metal, and thus only the water could have furnished the vital air to the metal, and its other principle was evolved as inflammable air. The latter could not have come from the metal, as it was not formed with nitric acid. 

Metallic chromium is a white, hard, lustrous, and brittle metal. The metal readily dissolves in acids such as hydrochloric acid and sulfuric acid, but it does not dissolve in concentrated nitric acid (because nitric acid forms an oxide on the surface of the chromium that resists further reaction). The primary use of chromium is in the production of steel alloys called stainless steels. Reducing chromite with carbon produces ferrochrome, an alloy that is added to steel. 

Monosaccharides such as glucose and fmctose are the most suitable as starting materials. When starch is used, it is first hydrolyzed with oxahc acid or sulfuric acid into a monosaccharide, mainly glucose. It is then oxidized with nitric acid in an approximately 50% sulfuric acid solution at 63—85°C in the presence of a mixed catalyst of vanadium pentoxide and iron(III) sulfate. 

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