Nitrite formation, from reaction

Hydroperoxide groups react with NO to give only nitrates as the dominant products, with only traces (< 5%) of nitrite in both oxidized polyolefins and in concentrated solutions of model hydroperoxides (-OOH levels from iodometry -ONO and -ON02 levels by IR). As reported by Shelton and Kopczewski we have confirmed that both nitrate and nitrite result from NO reaction with dilute hydroperoxide solutions (24). Rather than the NO-induced 0-0 scission proposed by these authors, our evidence points to hydrogen abstraction by NO (reaction 4). (A similar scheme may explain nitrite formation from alcohols.) Both e.s.r. and FTIR evidence is... 

Hoffmann and co-workers [178,179] have studied the photolysis of nitrate and nitrite in both water and water ice over broad temperature ranges. In the case of nitrite formation from nitrate photolysis, the photochemical reaction reaches a steady state condition that can be described by the following rate expression ... 

Figure 7. Nitrite formation from hydroxylamine. Reaction mixture contained in 3 mL 50 mM phosphate buffer pH 7.8 1 fjjnol of NH OH chloroplasts with 75 /xg of chlorophyll and where indicated 6.6 /aM paraquat 50 units SOD. Illuminated at 275 Wm at 22°C. Key control, plus paraquat. A plus SOD, and plus paraquat and SOD, A (72).

The presence of nitrate as acelerator has a pronounced effect on the amount and composition of gas evolved from the work being treated (Table 15.8). It will be observed that hydrogen evolution drops to a very low figure with the zinc/nitrate baths. The formation of nitrite arises from decomposition of nitrate by reaction with primary ferrous phosphate to form ferric phosphate ... 

The reaction with nitrite proceeds smoothly and with relatively high yields of the corresponding nitroarene (see Sec. 10.6). Obviously a major part of the driving force of this reaction is the formation of a stable, i. e., an energetically favorable, radical, nitrogen dioxide. With the hydroxide ion — a much stronger nucleophile than the nitrite ion — the reaction is expected to produce very unstable radicals, the hydroxy radical OH and the oxygen radical anion O, from the diazohydroxide (Ar - N2 — OH) and the diazoate (Ar-N20 ) respectively. Consequently, dediazoniation in alkaline aqueous solution does not follow the simple Scheme 8-41 with Yn = OH, but instead involves diazoanhydrides (Ar — N2 —O —N2 —Ar) as intermediates (see Sec. 8.8). 

Recently nitrosamines have attracted attention because of their marked carcinogenic activity in a wide variety of animal species Q, ). Nitrosamines are likely to be carcinogens in man as well human exposure to these compounds is by ingestion, inhalation, dermal contact and vivo formation from nitrite and amines Nitrite and amines react most rapidly at an acidic pH A variety of factors, however, make nitrosation a potentially important reaction above pH 7 these include the presence of microorganisms, and the possibilities of catalysis by thiocyanate, metals and phenols, and of transnitrosation by other nitroso compounds. 

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. 

Assuming that the above rationale for tertiary amine nitrosation was valid, we predicted 3) that the reaction of secondary amines with nitrite at milder pH s should be catalyzed by electrophilic carbonyl compounds, since secondary amines are known to form immonium ions on admixture with appropriate aldehydes and ketones. The prediction turned out to be true. Formaldehyde was shown to promote nitrosamine formation from a... 

F.B. Jensen, Nitric oxide formation from the reaction of nitrite with carp and rabit hemoglobin at intermediate oxygen saturations. FEBS J. 275, 3375-3387 (2008)... 

Although hydrolysis of methyl 3,4,6-tri-O-acetyl-a-D-glucoside 2-nitrate leads to the formation of only 2 % of nitrite ion, the reaction appears to be complex. No pure product was isolated, but the resulting sirup (from its analysis and its resistance to oxidation by periodate) was considered to be essentially a mixture of methyl anhydro-a-D-hexosides. Cautious interpretation of these results gave reason for believing that the nitrate group on C2 had been removed like a similarly situated sulfonate group. 

Essentially the same transformation can be conducted on a more highly substituted steroid. The required nitroso ester can in principle be prepared from reaction of DHEA 3-acetate (6-1) with bromine and nitrous acid (Scheme 3.6). The reaction sequence would start by addition of bromine from the open a-side of the steroid to form bromonium ion 6-2. Attack on that ion by the nitroso anion from the [3 side together with the rule of diaxial opening of a three-membered ring will the lead to formation of the nitrite 6-3. Irradiation of a toluene solution of the nitrite ester with a mercury vapor lamp walks the nitro group across the gap, in effect functionalizing C19. Heating the initially formed nitroso dimer in propan-... 

NO, in tobacco smoke has been quantified by calorimetric analyses (189, 3441, 3720), such as the Saltzman method (19A07), and by the chemical emission method (2122), which has been shown to be a rapid method for quantification (1884). Most of the NO, present in fresh MSS is NO, only a small amount of NO2 is present (189, 816, 2803). The concentration of NO2 in MSS increases (189, 2803, 3691) with the age of the smoke, and can reach levels of 200 ppm after 60 seconds (189). NO2 formation is believed to result from the auto-oxidation of NO. It has also been suggested that some of the NO2 produced by oxidation is converted (2941, 4058) to methyl nitrite through a reaction with methanol in the smoke (1884). Predominate precursors of NO are nitrates (189) and other A-containing compounds in the tobacco. N2O (2941) and HNO3 (4058) have also been reported as components of MSS in addition to the above compounds (1884). The currently preferred method for the determination of NO, is chemiluminescence (1930,19A02). 

Nitrosamines are produced in foodstuffs from reactions of nitrites (added as preservatives to bacon and other processed meat products) with amines in (or derived from) the foodstuff, particularly during cooking, e.g., frying anti-oxidants such as ascorbic acid (vitamin C) are added to such foodstuffs to inhibit formation of nitrosamines. A source of nitrosamines that may be of interest to some analytical chemists is beer, in this case attributed (Sen 1983) to reaction of nitrogen oxides with alkaloids (usually present in germinated malt) during the drying process. NMDA can also be formed inadvertently in a number of industrial processes. 

In the gas phase reaction, CO pressure, the concentration of alkyl nitrite, and the concentration of NO showed different effects on the rates of oxalate and/or carbonate formation from those observed in the liquid phase reaction thus the detail of the reaction mechanism is stUl unclear. 

In both tests, the NO2 outlet trace exhibited first a dead time, then it slowly grew and eventually approached the feed concentration level. Also, immediate evolution of N2 and NO was recorded at both temperatures upon NO2 feed, then the signals of the same species slowly decreased with time, evenmally approaching zero. Figures 9.7a, b clearly point out however that the increase of catalyst temperature from 120 to 200 °C over the Cu-zeolite resulted in an incremented NO formation and a corresponding decreased N2 evolution a higher temperature thus favors the reduction of nitrites by ammonia, reaction (9.7), against the oxidation of nitrites to nitrates, reaction (9.2), in line with what reported for Fe-zeolites. 

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