Nitric acid reduction

Dilute nitric acid oxidises Pu(III) to Pu(IV) slowly and Kraus (9) has shown that water can also bring about the oxidation of Pu(III) to Pu(IV). Ascorbic acid can reduce Pu(IV) to Pu(III) in the presence of sulphuric acid and nitric acid. Reduction of Pu(VI) to Pu(V) and Pu(IV) can be brought about by Fe2+. 

S. Madronich, HN03/N0, Ratio in the Remote Troposphere during MLOPEX 2 Evidence for Nitric Acid Reduction on Carbonaceous Aerosols Geophys. Res. Lett., 23, 2609-2612... 

For the cathodic nitric acid reduction the following mechanism is proposed by Vetter (9) ... 

About 5 billion pounds per year of adipic acid are manufactured worldwide by the nitric acid oxidation of cyclohexanone and/or cyclohexanol (KA). The KA to adipic acid yields are near 94% of theory. Glutaric and succinic acids are the major byproducts and account for most of the yield loss. Monsanto and some other adipic acid producers recover or upgrade these to salable b products resulting in an overall KA utilization efiflciency that approaches 99%. However, the nitric acid efficiency is lower because approximately 1 mole N2O is produced per mole of adipic acid, in addition to the easily recyclable NOx that is generated as a result of nitric acid reduction. 

These facts suggest that the imidazole ring in compounds 86, 330, 334 and 617 is first reversibly covalently hydrated in the acid medium to form 638, and then a hydrolytic ring opening occurs to provide intermediate 639. Then A -nitroso compound 640 forms and ring closes to afford l-methyl-l,2,3-triazolo[4,5-c]pyridine 637 (80KG121). The A -nitrosation occurs with nitrogen oxides formed from nitric acid reduction. 

The isotopically enriched antimony and the aluminum foil in which it was wrapped were dissolved in hydrochloric acid. Iodide carrier was added and oxidized to a mixture of iodate and periodate by means of nitric acid. Reduction of the oxyanions to elemental iodine with hydroxylamine hydrochloride was then... 

Again, nitric acid readily dissolves lead but is unable to oxidise lead beyond the oxidation state -P 2. The reduction products of the nitric acid vary with the concentration of acid used, and a number of nitrogen oxides are usually obtained. Warm dilute nitric acid gives mainly nitrogen oxide, NO. 

Hydroxylamine is derived from ammonia by replacing one hydrogen atom by a hydroxyl group. It is prepared by the electrolytic reduction of nitric acid, using a lead cathode ... 

Under no conditions is hydrogen obtained from nitric acid. With the dilute acid, reduction to ammonia occurs ... 

For this purpose, the usual oxidising agent is nitric acid, which in these circum stances (i.e., in the absence of sulphuric acid) does not nitrate the benzene ring. Owing to the nitrous fumes formed by the reduction of the nitric acid, the experiment should be performed in a fume upboard. 

Control of NO emissions from nitric acid and nitration operations is usually achieved by NO2 reduction to N2 and water using natural gas in a catalytic decomposer (123—126) (see Exhaust control, industrial). NO from nitric acid/nitration operations is also controlled by absorption in water to regenerate nitric acid. Modeling of such absorbers and the complexities of the NO —HNO —H2O system have been discussed (127). Other novel control methods have also been investigated (128—129). Vehicular emission control is treated elsewhere (see Exhaust control, automotive). 

Nitrates. Iron(II) nitrate hexahydrate [14013-86-6], Fe(N03)2 6H20, is a green crystalline material prepared by dissolving iron in cold nitric acid that has a specific gravity of less than 1.034 g/cm. Use of denser, more concentrated acid leads to oxidation to iron(III). An alternative method of preparation is the reaction of iron(II) sulfate and barium or lead nitrate. The compound is very soluble in water. Crystallisation at temperatures below — 12°C affords an nonahydrate. Iron(II) nitrate is a useful reagent for the synthesis of other iron-containing compounds and is used as a catalyst for reduction reactions. 

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

Derivatives. Oxidation of pyrogaHol trimethyl ether with nitric acid, followed by reduction ia acetic anhydride and treatment of the product with aluminum chloride, affords 3,6-dihydroxy-2,4-dimethoxyacetophenone (228). 3,4,5-Trimethoxyphenol (antiarol) has been prepared by treatment of... 

Chromium (II) also forms sulfides and oxides. Chromium (II) oxide [12018-00-7], CrO, has two forms a black pyrophoric powder produced from the action of nitric acid on chromium amalgam, and a hexagonal brown-red crystal made from reduction of Cr202 by hydrogen ia molten sodium fluoride (32). Chromium (II) sulfide [12018-06-3], CrS, can be prepared upon heating equimolar quantities of pure Cr metal and pure S ia a small, evacuated, sealed quartz tube at 1000°C for at least 24 hours. The reaction is not quantitative (33). The sulfide has a coordination number of six and displays a distorted octahedral geometry (34). 

Cyclohexanone shows most of the typical reactions of aUphatic ketones. It reacts with hydroxjiamine, phenyUiydrazine, semicarbazide, Grignard reagents, hydrogen cyanide, sodium bisulfite, etc, to form the usual addition products, and it undergoes the various condensation reactions that are typical of ketones having cx-methylene groups. Reduction converts cyclohexanone to cyclohexanol or cyclohexane, and oxidation with nitric acid converts cyclohexanone almost quantitatively to adipic acid. 

Alloxan forms an oxime (1007) which is the same compound, violuric acid, as that formed by nitrosation of barbituric acid likewise, a hydrazone and semicarbazone. Reduction of alloxan gives first alloxantin, usually formulated as (1008), and then dialuric acid (1004 R = OH) the steps are reversible on oxidation. Vigorous oxidation with nitric acid and alkaline hydrolysis both give imidazole derivatives (parabanic acid and alloxanic acid, respectively) and thence aliphatic products. Alloxan and o-phenylenediamine give the benzopteridine, alloxazine (1009) (61MI21300). 

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