Hydroxylamine nitrate reductant

It was found that the electrocatalytic activity strongly depends on the nature of the electrode it decreases in the order Rh > Ru > Ir > Pd and Pt for the transition-metal electrodes and in the order Cu > Ag > Au for the coinage metals. It was concluded that the rate-determining step on Ru, Rh, Ir, Pt, Cu, and Ag is the reduction of nitrate to nitrite. It was assumed that chemisorbed nitric oxide is the key surface intermediate in the nitrate reduction. It was suggested that ammonia and hydroxylamine are the main products on transition-metal electrodes. This is in agreement with the known mechanism for NO reduction, which forms N2O or N2 only if NO is present in the solution. On Cu the production of gaseous NO was found, which was explained by the weaker binding of NO to Cu as compared to the transition metals. 

It was found that underpotentially deposited germanium strongly enhances the reduction rate of nitrate. The reduction of nitrite is enhanced to a lesser extent, whereas germanium is inactive for NO and hydroxylamine reduction. It is of interest that the well-known inhibition of the nitrate reduction at low potentials was absent for germanium-modified electrodes. 

Thus, a large excess of U(IV) is required to reduce Pu(IV), diluting the enrichment of the recovered U. Further, the reactions described by Eqs. 7 and 8 will reduce the efficiency of the separation process and may ultimately lead to incomplete separation of U and Pu due to lack of reducing agent, so increasing the cost of the procedure. Alternative methods to reduce Pu include the use of hydroxylamine nitrate with hydrazine as stabiliser or the electroreduction of Pu(III) [66] in situ. Nonetheless, the current use of U(IV) as a reductant for... 

Although the redox potentials for aqueous solution indicate that uranium(IV) should reduce plutonium(IV), anions and other complexing agents can change the potentials sufficiently that uranium(IV) and plutonium(IV) can coexist in solution (25). Since one of the products of photochemical reduction of uranyl by TBP is dibutyl phosphate (DBP), which complexes plutonium(IV) strongly, experiments were done to test the photochemically produced urani-um(IV) solutions as plutonium(IV) reductants (26). Bench-scale stationary tests showed these solutions to be equivalent to hydroxylamine nitrate solutions stabilized with hydrazine (27). 

Hydroxylamine salts were found to be good reductants of plutonium, under certain conditions ( 5). Interest in these reducing agents stemmed from the desire to avoid the introduction of metallic cations in the separated plutonium product. Hydroxylamine sulfate was used on a large scale at the Savannah River Plant (j>). While partitioning was satisfactory, the objectionable presence of sulfate ions led to the adoption of hydroxylamine nitrate (HAN). The reaction mechanism and kinetics of the HAN reduction of plutonium have been studied extensively The... 

At the present time the titanium column shown in figure 4 is installed in a Pu-test cycle at Karlsruhe with a throughput of about 400 g Pu/h, where the electro-reductive Pu backextrac-tion can be tested and compared with the competitive procedure using hydroxylamine nitrate (HAN) as reducing agent. 

The HPO (hydroxylamine phosphate oxime) process, developed byDSMand licensed by Siamicarbon, totally eliminates the production of ammonium sulfate, both in the production of hydroxylamine itself and in die oxime production stage. It consists of the catalytic hydrogenation of the nitrate ions resulting from the oxidation of ammonia to hydroxylamine ions in a solution buffered by phosphates. The nitrate reduction reaction is as follows ... 

Plutonium trifluoride. Plutonium trifluoride can be converted directly to plutonium metal, or it is an intermediate in the formation of PUF4 or PUF4 -PUO2 mixtures for thermochemical reduction, as described in Sec. 4.8. The stabilized Pu(III) solution, produced by cation exchange in one of the Purex process options for fuel reprocessing, is a natural feed for the formation of plutonium trifluoride, as is shown in the flow sheet of Fig. 9.9 [03]. A typical eluent solution from cation exchange consists of 30 to 70 g plutonium/liter, 4 to 5 Af nitric acid, 0.2 Af sulfamic acid, and 03 Af hydroxylamine nitrate. The sulfamic acid reacts rapidly with nitrous acid to reduce the rate of oxidation of Pu(III) to about 4 to 6 percent per day. Addition of ascorbic acid to the plutonium solution just before fluoride precipitation reduces Pu(IV) rapidly and completely to Pu(III). 

Hydroxylamine nitrate (HAN) requires addition of hydrazine as a holding reductant, to prevent destruction of hydroxylamine by the nitrous acid present as a result of radiolysis, in the reaction... 

Reduction with hydroxylamine. No comparable rate data for reduction of Np(V) by hydroxylamine are available. Barney [B2] reported that the initial rate of reduction of Pu(IV) by 0.1 M hydroxylamine nitrate (HAN) was about one-fourth the initial rate of reduction of Pu(lV) by U(IV) at 25°C. If the same ratio applies to reduction of Np(V) by HAN or U(IV), a reaction time of around (4X35) = 140 min might be required. Use of hydroxylamine would have the advantage of not requiring reduction of uranium to U(IV) and its subsequent recycle. 

Me Kibben, J.M. and J.E. Bercaw, 1971. Hydroxylamine nitrate as a plutonium reductant in the PUREX solvent extraction process. Report DP-1248. Aiken, SC Savannah River Laboratory. 

Hydroxylamine is known to be highly toxic to plants so the possibility that it is an obligatory intermediate in nitrate reduction must be considered with caution. Interest in hydroxylamine arises from the lengthy controversy, briefly mentioned here, concerning the rela-j five merits of hydroxylamine or ammonia as the key intermediate in nitrogen fixation. The toxicity of hydroxylamine may well be due to its action as an enzyme inhibitor. However, in spite of its toxicity, there are still some claims that hydroxylamine may be an intermediate in the formation of amino acids by oxime formation with such carbonyl compounds as glyoxilic acid (formed in photosynthesis), I pyruvate, a-ketoglutarate or oxaloacetate (intermediates in carbo-... 

Nitro compounds and their reduction products. Tertiary nitro compounds (these are generally aromatic) are reduced by zinc and ammonium chloride solution to the corresponding hydroxylamines, which may be detected by their reducing action upon an ammoniacal solution of silver nitrate or Tollen s reagent ... 

Nitrous oxide may also be obtained by the controlled reduction of nitrates or nitrites, decomposition of hyponitrites, or thermal decomposition of hydroxylamine. 

Aromatic nitro and nitroso compounds are easily reduced at carbon and mercury electrodes. Other nitro compounds such as nitrate esters, nitramines, and nitrosamines are also typically easily reduced. The complete reduction of a nitro compound consists of three two-electron steps (nitro-nitroso-hydroxylamine-amine). Since most organic oxidations are only two-electron processes, higher sensitivity is typically found for nitro compounds. Several LCEC based determination of nitro compounds have been reported... 

The monovalent Co chemistry of amines is sparse. No structurally characterized example of low-valent Co complexed exclusively to amines is known. At low potentials and in non-aqueous solutions, Co1 amines have been identified electrochemically, but usually in the presence of co-ligands that stabilize the reduced complex. At low potential, the putative monovalent [Co(cyclam)]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) in NaOH solution catalyzes the reduction of both nitrate and nitrite to give mixtures of hydroxylamine and ammonia.100 Mixed N-donor systems bearing 7r-acceptor imine ligands in addition to amines are well known, but these examples are discussed separately in Section 6.1.2.1.3. 

Coin-cyclam322-324 and Nin-cyclam322 catalyze the electroreduction of nitrate in aqueous electrolytes with good current efficiencies and turnover numbers, giving mixtures of ammonia, nitrite, and hydroxylamine at a variety of electrode materials. Mechanistic investigations suggested the adsorption of electroreduced Co1- and Ni1 cyclam onto the electrode surface,322 and the formation of an oxo-metal bond via reduction of coordinated nitrate.323... 

Bajic and Jaselskis [153] described a spectrophotometric method for the determination of nitrate and nitrite in seawater. It included the reduction of nitrate and nitrite to hydroxylamine by the zinc amalgam reactor (Jones reductor) at pH 3.4 and reoxidation of the product with iron (III) in the presence of ferrozine. Interference by high levels of nitrite could be eliminated with azide treatment. Levels of nitrate of 0.1 mg/1 could be detected with a precision of 3% in the presence of large amounts of nitrite and chloride. 

Nitration opens up another pathway to metabolic activation. Nitro-PAHs are wide-spread environmental pollutants that are mutagenic and carcinogenic. Metabolism of nitro-PAHs could occur via nitro-activation (reduction to hydroxylamine, eventually leading to nitrenes that can bind to nucleotides) and/or by ring oxidation and formation of DEs. ... 

Hydroxylamine hydrochloride was first prepared 1 by the reduction of ethyl nitrate by means of tin, with hydrochloric acid hydroxylamine salts have also been prepared by the reduction of nitric acid with metals.2 The. two important... 

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