Reduction of nitrite

Hydroxylamine can be prepared by a variety of reactions involving the reduction of nitrites, nitric acid or NO, or by the acid hydrolysis of nitroalkanes. In the conventional Raschig synthesis, an aqueous solution of NH4NO2 is reduced with HS04 /S02 at 0° to give the hydroxylamido-A ,A -disulfate anion which is then hydrolysed stepwise to hydroxylammonium sulfate ... 

Abel et studied reduction of nitrite to NO by Fe(ir) obtaining the rate law... 

Indeed, given an improperly designed or understood system, a blocking agent, like ascorbic acid, could be catalytic toward nitrosamine formation. For example, if the source of nitrosatlng agent is nitrite ion and the susceptible amine is in the lipid phase, conceivably ascorbic acid could cause the rapid reduction of nitrite ion to nitric oxide which could migrate to the lipid phase. Subsequent oxidation of NO to NO in the lipid phase could cause nitrosation. 

Liang F, Fan J, Guo Y, Fan M, Wang J, Yang H (2008) Reduction of nitrite by ultrasound-dispersed nanoscale zero-valent iron particles. Ind Eng Chem Res 47(22) 8550-8554... 

According to Summers and Chang from NASA s Ames Research Center, Moffett Field (1993), the oxidation of Fe2+ to Fe3+ provided a possibility for the reduction of nitrites and nitrates to ammonia. This reaction would have been of great importance, as NH3 is required in many syntheses of biogenesis precursors. The authors assume that nitrogen was converted to NO in a non-reducing atmosphere, and thence to nitrous and nitric acids. These substances entered the primeval oceans in the form of acid rain , and here underwent reduction to NH3 with the help of Fe2+, thus raising the pH of the oceans to 7.3. Temperatures above 298 K favoured this reaction, which can be written as ... 

Water soluble iron porphyrins [Fem(TPPS)(H20) ]3-330 and [Fem(TMPy)(H20)2]5+ 331 332 (TPPS = maso-tetrakis(/ -sulfonatophenyl)porphyrin, TMPyP = / /e.vo-tetrakis(7V-methyl-4-pyridi-nium)porphyrin331 or maso-tetrakis (A -methyl-2-pyridinium)porphyrin332 dications) act as effective electrocatalysts for the reduction of nitrite to ammonia in aqueous electrolytes (Equation (64) Ei/2= 0.103 V vs. SCE at pH 7), with NH2OH or N20 also appearing as products depending on the reaction conditions. Nitric oxide then ligates to the iron(III) porphyrin to form a nitrosyl complex [Fen(P)(NO+)] (P = porphyrin) as intermediate. 

Run(Hedta)(NO+)]° and [Fen(Hedta)(NO )] have been shown to be effective electrocatalysts for the reduction of N02 in acidic aqueous media, to yield N20, N2, NH3OH+, or NH4 339,340 An element of selectivity is available by control of pH and applied potential. Steps involved in the typical six-electron reduction of nitrite to ammonia catalyzed by [Run(Hedta)(NO+)]° are summarized in Equations (67)-(69). The mechanisms by which nitrite is reduced appeared to be similar to those identified for Fe-porphyrin331 and Ru or Os-polypyridyl complexes.337... 

The flow injection technique is based on three main principles sample injection, reproducible timing, and controlled dispersion [128]. The dispersion can be described as limited, medium, or large in a colorimetric system based on a reaction between the sample and a suitable reagent, a medium dispersion is preferred. Thus in the flow injection determination of nitrate, the reductor column should not excessively increase the dispersion. In a copperised cadmium reductor, more than 90% of the total nitrate is reduced within 1 - 2 s with minimum risk of further reduction of nitrite [167]. Consequently, the reductor can be made very small, which results in a minimal increase of dispersion. 

In a related observation, reported by Tanaka et al. (81), the copper(II) complex Cu(tpa)2+ (tpa = tris[(2-pyridyl)methyl] amine) was shown to serve as a catalyst for the electrochemical reduction of nitrite to N20 and traces of NO in aqueous solution. NO and/or a copper nitrosyl complex would appear to be the likely intermediates in this process (81a). 

Like assimilatory nitrogen reduction, denitrification proceeds through a series of steps with nitrate first being reduced to nitrite, followed by reduction of nitrite to N2(g). Under some conditions, N20(g) is also produced. 

Nitrite reductases (NiRs)—enzymes found in several strains of denitrifying bacteria— catalyze the one-electron reduction of nitrite anion to nitric oxide (Equation 1). - In addition to the importance of this process in the global nitrogen cycle (Figure 1), further incentive for the study of the denitrification process is provided by its environmental impact, ranging from the production of NO as a pollutant and NjO as a potent greenhouse gas, to lake eutrophication due to farm runoff that contains high concentrations of nitrates and nitrites. 

Report existing knowledge/facts Present-active Nitrite reductases catalyze the one-electron reduction of nitrite. (From Houser, 2001) The Galapagos Islands sit on a large volcanic platform in the Pacific Ocean. (From Harpp, 1998)... 

Since HA is unstable in vivo , and is known to rapidly associate with the heme part of heme proteins , and possibly also with a variety of biological oxidants, such as the superoxide anion that is produced by many mammalian cells, it is difficult to demonstrate its accumulation in vivo. Already in 1932 Lindsey and Rhines discussed some analytical difficulties in the detection of HA, since when added externally, it disappeared rapidly from bacterial cultures this led to the conclusion that even if it is produced as an intermediate, its consumption is too fast to allow the accumulation of sufficient quantities for analytical demonstration. Compelling indirect evidence for the presence of HA as an intermediate in the enzymatically catalyzed reduction of nitrite (N02 ) to NH3 was provided by Einsle and colleagues , who characterized the crystal structure of the complex obtained by soaking cytochrome c-nitrite reductase with NH20H. ... 

Based on crystallographic observations it was suggested that the HA intermediate is bound to the cytochrome reductase via the iron atom, Fe(II)—NH2OH, and undergoes subsequent reduction to produce the NH3 that then dissociates from the protein ". It is of interest that the specific activity of cytochrome c-nitrite reductase from S. deleyianum in the conversion of N02 to NH3 is only 2-fold greater than that recorded for the conversion of HA to ammonia by the same enzyme, an observation that strongly supports the involvement of HA as an intermediate in the catalytic reduction of nitrite to NH3 . 

Blom was the first to demonstrate, in 1928, the formation of HA by an unknown mixture of bacteria which utilized nitrate as their sole nitrogen source to produce ammonia , an observation substantiated by Lindsey and Rhines who generalized this reaction to a diverse set of microorganisms capable of producing NH3 by reduction of both nitrites and nitrates. The mechanism of the 6-electron reduction of nitrite to ammonia (i.e. conversion of the [N + 02] species to by bacterial cytochrome c nitrite reductase... 

Lepidocrocite Reduction of nitrite in the presence of Fe " ions Sorensen and Thorling, 1991... 

Nitric oxide and iron nitrosyl complexes have been observed in the reduction of nitrite by bacterial nitrite reductases, which contain iron chlorin or iron isobac-terichlorin [151]. A specific nitric oxide reductase also exists to convert NO to nitrous oxide [9]. Iron complexes of chlorins, isobacteriochlorins, and porphyrins, as well as ruthenium and osmium polypyridines, and cobalt and nickel... 

The investigation of electrochemical, electrocatalytic, and catalytic reduction of nitrite and nitrate have attracted much... 

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. 

The role of the various crystal faces in the reduction of nitrite, nitrate, and other oxygen-containing nitrogen compounds has been studied recently [231, 232]. 

It is usual that the first reduction wave of commonly studied POMs he monoelec-tronic or, at the utmost, hielectronic [89]. As a consequence, energetically favorable catalytic processes that require larger numbers of electrons can only be accomplished at fairly negative potentials where the necessary number of charges is accumulated and delivered by the POM framework hence the search for strategic parameters that could favor apparently multiple electron uptake on the first wave of POMs. The present case deserves emphasis as a simple illustrative example that proved to be very beneficial in the electrocatalytic reduction of nitrite. 

Cooperative effect of Mn- and Fe-centers within Mn2Fe2P4W3o in the electrocatalytic reduction of nitrite In the preceding sections, it was well established that Fe(III)-substituted POMs catalyze the reduction of NO and/or N02 [1]. The first step in this process is the formation of a complex with the Fe(II) form of the POM and nitrogen oxide. 

Fig. 28 Cyclic voltammetry study of the electrocatalytic reduction of nitrite with a 2 10 M solution of Fe2Mn2P4 in a pH = 1 medium (0.5 M Na2S04 -I- H2SO4). The scan rate was 2 mV s, the working electrode was glassy carbon, and the reference electrode was SCE (taken from Ref 1).

The electrocatalytic behavior of Fe6Ge 2W18 toward the reduction of nitrite... 

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