Nitrites, as oxidizer

Because NTR links the reduced and oxidized sides of the N cycle, it can be considered a central process that provides substrate to microbes that employ nitrate or nitrite as oxidant (see Chapter 5 by Ward, this volume Fig. 19.1, arrow 4). Like NH4, the products of NTR, N02, and NOs , may experience one of several possible fates, including (1) flux from the sediment, (2) assimilation within the sediment or at the sediment—water interface, or (3) reduction by one of three possible dissimilatory pathways DNF, dissimilatory nitrate reduction to ammonium (DNRA), or ANAM (Fig. 19.1, arrows 5, 6, and 7 Fig. 19.2). Uptake of NO by... 

In addition to CuCfi, some other compounds such as Cu(OAc)2, Cu(N03)2-FeCl.i, dichromate, HNO3, potassium peroxodisulfate, and Mn02 are used as oxidants of Pd(0). Also heteropoly acid salts comtaining P, Mo, V, Si, and Ge are used with PdS04 as the redox system[2]. Organic oxidants such as benzo-quinone (BQ), hydrogen peroxide and some organic peroxides are used for oxidation. Alkyl nitrites are unique oxidants which are used in some industrial... 

As an e.xtension of the oxidative carbonylation with alkyl nitrites, malonate can be prepared by the oxidative carbonylation of ketene (583)[524], Also, the acetonedicarboxylate 585 is prepared by the Pd-catalyzed, alkyl nitrite-mediated oxidative carbonylation of diketene (584)[525],... 

A universal procedure for combined nitrogen is the Dumas method. This gasometric procedure is applicable to any organic compd contg nitrogen in any form, such as amino, nitroso, nitro, azo, cyano, nitrate, nitrite, as well as N in heterocyclic compds. The procedure involves combusting the sample in a closed system in a C02 atm, with subsequent reduction of the oxides... 

Anaerobic lithotrophs that oxidize ammonium using nitrite as electron acceptor (anammox) are noted later in the section on anaerobic bacteria. 

Although they have not been obtained in pure culture, chemolithotrophic anaerobic bacteria (anammox) that oxidize ammonia using nitrite as electron donor and CO2 as a source of carbon have been described. In addition, they can oxidize propionate to CO2 (Giiven et al. 2005) by a pathway that has not yet been resolved. 

Denitrification involves the sequential formation of nitrite, nitric oxide, and nitrous oxide. Two aspects of nitric oxide have attracted attention (a) chemical oxidation of biogenic nitric oxide to Nq, in the context of increased ozone formation (Stohl et al. 1996) and (b) the physiological role in mammalian systems (Feldman et al. 1993 Stuehr et al. 2004), in parasitic infections (James 1995), and in the inhibition of bacterial respiration (Nagata et al. 1998). Nitric oxide may be produced microbiologically in widely different reactions such as... 

There are two mechanisms that could explain the catalytic effects of nitrite an inner-sphere mechanism in which nitrite acts as a nucleophile toward the FeIINO+ moiety (Scheme 3, pathway A) and an outer-sphere path in which nitrite is oxidized to N02 which then reacts with excess NO to form N203 (Scheme 3, pathway B). Although the initial electron transfer step in pathway B is thermodynamically uphill (AE = — 0.3 V) (41,70), one cannot rule out pathway B since N203 is rapidly hydrolyzed, once formed (71). 

Ketene can also be oxidatively carbonylated, using PdC as the catalyst and alkyl nitrites as the oxidant, to give dialkyl malonates (Eq. 26) [125]. Ke-todiesters have been obtained from diketene (Eq. 27) [126]. 

Step 2 represents the chain origin, step 3 is nitrite-ion oxidation, steps 4-6 are the chain propagation, and steps 8 and 10 show the chain termination at the expense of radical dimerization. Steps 4 and 5 can probably be nnited into one stage, as Scheme 4.38 points out. 

Studies on nitrogen cycle enzymology in microorganisms that use ammonia as a major source of energy for growth suggest that HA serves as an intermediate in its oxidation to nitrite , as depicted in equations 1 and 2 ... 

Nitrosyidisulfonic acid, reaction mechanisms, 22 129, 130 Nitrous acid, 33 103 decomposition, rate constants, 22 157 as oxidizing agent, 22 133 reaction mechanisms, 22 143-156 electrophilic nitrosations, 22 144-152 with inorganic species, 22 148, 149 nitrite oxidation by metals, 22 152-154 oxidation by halogens, 22 154, 155 in solution, 22 143, 144 reduction by metals, 22 155, 156 Nitrous oxide reductase, 40 368 Nitroxyl, reaction mechanisms, 22 138 Nitrozation, pentaamminecobalt(III) complexes, 34 181... 

Meyer, J. (1981). Comparison of carbon monoxide, nitric oxide, and nitrite as inhibitors of the nitrogenase from Cbstridium pasteurianum. Arch. Biochem. Biophys. 210, 246-256. 

It is remarkable that this enzyme can accept both O2 and nitrite as its oxidizing substrate, and in fact it was originally isolated as an oxidase rather than a nitrite reductase. Its role in nitrite reduction became clear when it was realized that its synthesis was induced only under anaerobic conditions and its oxidase activity was relatively small compared with the total O2-reducing activity of cells (Lam and Nicholas, 1969 Yamanaka, 1964 Yamanaka and Okunuki, 1963a). 

Cytochrome cd reduces nitrite by one electron to NO as the major product, providing a reducing system was used that does not reduce NO chemically (Kim and Hollocher, 1983, 1984 Mancinelli et al., 1986 ParretaL, 1976 Silvestrini et al., 1979 Timkovich et al., 1982 Yamanaka and Okunuki, 1963a). There is only one rapid kinetic study of cytochrome cd, with nitrite as the oxidant (Sil-vestrini et al., 1990). This work, carried out at pH 8.0, indicated that there was intramolecular electron transfer, c d, as in the O2 reaction, but that the... 

A variation of this procedure is the nitrosation of a phenol such as thymol in an alcohol solution with hydrochloric acid and sodium nitrite. This procedure is said to avoid the evolution of oxides of nitrogen, since it may involve the intermediate formation of ethyl nitrite as the nitrosating agent [31]. However, from the safety standpoint, the oxides of nitrogen and nitrite esters must be considered hazardous. 

If the cation introduced by ion exchange is capable of multiple valence, the clay may serve as a catalyst for oxidation or reduction reactions. For example, montmorillonite treated with iron(III) nitrate is so reactive that it has to be stored under an inert atmosphere the clay catalyzes reactions of the nitrate ion, such as oxidation of secondary alcohols to ketones (via nitrite ester intermediates) and organic hydrazides to azides, and the nitration of phenols. 

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