Nitrosonium Ion NO

Nitrosonium Ion (NO1). Nitrosonium ion (NO+) 221 is an important species that is generally present in nitrous acid media. It acts as a powerful nitrosating agent of amines (both aromatic and aliphatic) resulting in the diazotization reaction [Eq. (4.148)]. 

The first isolation of nitrosonium ion 221 as a distinct species was in the reaction of dinitrogen trioxide and dinitrogen tetroxide with boron trifluoride531 [Eqs. (4.149) and (4.150)]. 

Since then, a variety of nitrosonium salts have been isolated. The important ones are with the following counterions BF4 , PF6 , FSO , HS04, BCI4, and SbCl6. The ion has been characterized by 15N NMR, IR, and X-ray analysis.245,448,514,531,532 A detailed NMR study by Mason and Christe have showed448 that conditions (solvent, counterion, temperature) have minor effects on observed 14N NMR shifts (814N 372.5-376.8). 

Similar to nitronium ion, attempt was also made to identify protonated nitrosonium ion (protonitrosonium dication, HN02+) by means of 170 NMR spectroscopy.529 The sharp peak at 8170 461.5 observed in HSO3F and identified for NO+ shifted upfield by 5 ppm upon addition of SbF5. This, again, can be attributed to the presence of protonitrosonium dication in small equilibrium concentration. 

The nitrosonium ion does not react toward aromatics except in activated systems. It forms a Jt-complex with aromatics with deep color.533,534 However, it is a powerful hydride-abstracting agent in the case of activated benzylic or allylic positions. Olah and Friedman535 have demonstrated that isopropylbenzenes undergo hydride abstraction to cumyl cations 222 [Eq. (4.151)] which further reacts to give various condensation products. The reaction has been employed to prepare a variety of stable carbocations.536 

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Nitrous acid or nitrite salts may be used to catalyze the nitration of easily nitratable aromatic hydrocarbons, eg, phenol or phenoHc ethers. It has been suggested that a nitrosonium ion (NO + ) attacks the aromatic, resulting initially in the formation of a nitro so aromatic compound (13). Oxidation of the nitro so aromatic then occurs ... 

For nitrosyl chloride (Entry 8) and nitrosyl formate (Entry 9), the electrophile is the nitrosonium ion NO+. The initially formed nitroso compounds can dimerize or isomerize to the more stable oximes. 

The steps in forming a diazonium ion are addition of the nitrosonium ion, +NO, to the amino group, followed by elimination of water. 

It is believed that SCR by hydrocarbons is an important way for elimination of nitrogen oxide emissions from diesel and lean-burn engines. Gerlach etal. [115] studied by infrared in batch condition the mechanism of the reaction between nitrogen dioxide and propene over acidic mordenites. The aim of their work was to elucidate the relevance of adsorbed N-containing species for the F>cNOx reaction to propose a mechanism. Infrared experiments showed that nitrosonium ions (NO+) are formed upon reaction between NO, NOz and the Brpnsted acid sites of H—MOR and that this species is highly reactive towards propene, forming propenal oxime at 120°C. At temperatures above 170°C, the propenal oxime is dehydrated to acrylonitrile. A mechanism is proposed to explain the acrylonitrile formation. The nitrile can further be hydrolysed to yield... 

A further point of preparative significance still requires explanation, however. Highly reactive aromatic compounds, such as phenol, are found to undergo ready nitration even in dilute nitric acid, and at a far more rapid rate than can be explained on the basis of the concentration of N02 that is present in the mixture. This has been shown to be due to the presence of nitrous acid in the system which nitrosates the reactive nucleus via the nitrosonium ion, NO (or other species capable of effecting nitrosation, cf. p. 120) ... 

The subj ect has been treated as part of a general discussion of N O-donors in a number of reviews [1-4]. This chapter will briefly introduce the general properties of these systems and the chief methods to synthesise them, after which it will concentrate on their NO-donor properties and NO-dependent biological activities. The term NO will be used here as a family name, embracing not only nitric oxide (NO ) but also its two redox forms, nitroxyl (HNO) and nitrosonium ion (NO+), which play important roles in the complex signalling system connected with NO [5]. The specific redox form involved in the NO-release will be indicated, if known, when necessary for the discussion. 

Amines react with nitrous acid (formed by the reaction NaN02 + H HNO2) to give a variety of products. The nitrous acid isn t very stable, so generating it in place from sodium nitrite is necessary. (Sodium nitrite is a meat preservative and a color enhancer.) Under acidic conditions, nitrous acid dehydrates to produce the nitrosonium ion, NO. The NO ion is a weak electrophile that s resonance stabilized. (See Chapter 7.) Figure 13-22 illustrates the dehydration of nitrous acid. 

The most broadly useful intermediates for nucleophilic aromatic substitution are the aryl diazonium salts. Aryl diazonium ions are usually prepared by reaction of an aniline with nitrous acid, which is generated in situ from a nitrite salt.75 Unlike aliphatic diazonium ions, which decompose very rapidly to molecular nitrogen and a carbocation (see Section 10.1), aryl diazonium are stable enough to exist in solution at room temperature and below. They can also be isolated as salts with nonnucleophilic anions, such as tetrafluoroborate or trifluoroacetate.76 The steps in forming a dizonium ion are addition of the nitrosonium ion, +NO, to the amino group, followed by elimination of water. 

Nitric oxide readily loses an electron to form nitrosyl or nitrosonium ion, NO , which is known to form salts, such as nitrosyl hydrogen sulfate, (N0) (HS04) or nitrosyl tetrafluoroborate, (N0) (BF4). ... 

Nitric oxide may be oxidized by one electron to give nitrosonium ion (NO ) or reduced by one electron to form nitroxyl anion (NO"), which are important intermediates in the chemistry of nitric oxide (Stamler et al., 1992a). 

The direct reaction of superoxide with nitric oxide is only one of at least four possible pathways that can form peroxynitrite (Fig. 40). For example, superoxide should also efficiently reduce nitrosyldioxyl radical to peroxynitrite. Alternatively, nitric oxide may be reduced to nitroxyl anion, which reacts with oxygen to form peroxynitrite. Superoxide dismutase could even catalyze the formation of peroxynitrite, since reduced (Cu or cuprous) superoxide dismutase can reduce nitric oxide to nitroxyl anion (Murphy and Sies, 1991). Thus, superoxide might first reduce superoxide dismutase to the cuprous form, with nitric oxide reacting with reduced superoxide dismutase to produce nitroxyl anion. A fourth pathway to form peroxynitrite is by the rapid reaction of nitrosonium ion (NO" ) with hydrogen peroxide. This is a convenient synthetic route for experimental studies (Reed et al., 1974), but not likely to be physiologically relevant due to the low concentrations of hydrogen peroxide and the difficulty of oxidizing nitric oxide to nitrosonium ion. 

Laszlo introduced an oxidative cleavage of dithioacetals by their clayfen (4) and claycop reagents under mild conditions with excellent yields [46, 47]. These reagents are convenient sources of the nitrosonium ion NO+, a soft reactive Lewis acid species, well adapted for attack of the soft sulfur atom. 

Nitrosonium ion (NO+) is the electrophilic species formed from nitrous acid media, which is responsible for such reactions as diazotization of amines. Nitrosonium ion has... 

The nitrosonium ion (NO), generated in situ from sodium nitrite in the presence of hydrochloric acid at 0-5 °C, is also a weak electrophile and with tertiary amines, e.g. AyV-dimethylaniline, ring substitution occurs leading to the p-nitroso derivative (Expt 6.62). 

According to more recent views, nitrogen dioxide in sulphuric acid solution gives the nitrosonium ion NO+ Mid a nitric acid molecule. The latter, treated with an excess of sulphuric acid, gives a nitronium ion, which is the actual nitrating agent ... 

The nitrous ion N02" attracts a proton, thus facilitating the nitrosating action of the nitrosonium ion NO+. 

Ingold and his co-workers [152] when investigating the nitration of phenols and their ethers, came to the conclusion that it was the nitrosonium ion, NO+, formed as a result of the hypothetical reactions (a) and (b) ... 

The electron in the 77 orbital is relatively easily lost (A//ion = 891 kJ mol-1), to give the nitrosonium ion (NO+), which has an extensive and important chemistry. Because the electron removed comes out of an antibonding orbital, the bond is stronger in NO+ than in NO the bond length decreases by 0.09 A and the vibration frequency rises from 1840 cm-1 in NO to 2150 to 2400 cm"1 (depending on environment) in NO+. 

Very recently the kinetics of the diazotisation of aniline with N2O4 in acetonitrile, ethyl acetate and in a mixture of these solvents have been established (Aziz et al., 1981). In each solvent, the reaction was first order in N2O4 and zero order in aniline concentration. The rate-limiting step is thought to be the formation of the nitrosonium ion NO (Scheme 18). 

Alternatively, the reaction may proceed through nitrosation by the nitrosonium ion, NO", and subsequent oxidation of the nitroso compound by nitric acid (Scheme 7.3). There is only a small concentration of NO" in dilute nitric acid and so catalytic amounts of sodium nitrite are sometimes added to increase the quantity. This technique is a useful means of effecting smooth, low-temperature nitrations. 

The nitrosonium ion (NO ) is another electrophile which is generated either from the oxides of nitrogen or from nitrosyl chloride. The nitrosochloride may tautomerize to chloro-oxime adducts. 

Phenols are one of the few classes of compounds reactive enough to undergo attack by the weakly electrophilic nitrosonium ion, NO. 

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