Nitrosonium salt

Attempts to prepare 2-aminoazepinium cations by the action of trityl tetrafluoroborate on 3//-azepin-2-amines have failed,64 as have attempts to Ar-methylate 2,5,7-trimethyl-3/f-azepine with an excess of iodomcthanc in a scaled tube at 100°C for seven hours.77 In contrast, the unstable Ar,Ar-dialkyl-6-(methylsulfanyl)-3//-azepin-2-amines, e. g. 1, with trityl tetrafluoroborate, or the corresponding nitrosonium salts, yield their tetrafluoroborate salts, e.g. 2s4 (see also Section 3.1.1.5.4.). 

The NO ligand can be supplied by nitric oxide itself, but there are many other sources such as nitrite, nitrate or nitric acid, nitrosonium salts or N-methyl-7V-nitrosotoluene-p-sulphonamide (MNTS). The introduction of a nitrosyl group into a ruthenium complex is an ever-present possibility. 

Musker29 carried out a systematic study of the oxidation of several cyclic 22 and acyclic 23 bis-sulfides using nitrosonium salts. Several unstable dications were characterized as sulfoxides 24. These oxidations proceed through stepwise transfer of two electrons from a bis-sulfide to the nitrosonium cation and the intermediate formation of the corresponding radical cation. Radical cations of 1,5-dithiacyclooctane 11 and 1,5-dithiacyclononane are sufficiently stable to be isolated as individual compounds (Scheme 8).50... 

Synthetic approaches to selenium, tellurium and mixed dications are similar to the methods used for disulfonium dications. Oxidation of bis-selenides to diselenonium dications 104 with two equivalents of nitrosonium salts -NOBF4, NOPfV,113 occurs more readily than the oxidation of sulfides and affords the corresponding dications in better yields (Scheme 41).96,114... 

One can use the same methods for generation of trithiodications as for synthesis of disulfonium dications, i.e. oxidation of suitable trisulfides with concentrated sulfuric acid or with nitrosonium salts as well as reaction of a... 

The technique of performing halide abstraction via interaction of a metal halo complex with a silverd), thallium(I), or nitrosonium salt (see ref. 142, for discussion) has proved useful in the isolation of many novel sulfoxide complexes. Thus, [Pd(S-Me2S0)2(0-Me2S0)2]-... 

While nitramines are formed from the reaction of secondary amines with nitronium salts the success of the reaction depends on the basicity of the amine (Equation 5.11). Thus, amines of low to moderate basicity are A-nitrated in good yields. The nitration of more basic amines is slow and the nitrosamine is often observed as a significant by-product, a consequence of the partial reduction of the nitronium salt to the nitrosonium salt during the reaction. Increased reaction temperature is also found to increase the amount of nitrosamine formed. The amine substrate is usually used in excess to compensate for the release of the strong mineral acid formed during the reactions. Both nitronium tetrafluoroborate and the more soluble hexafluorophosphate are commonly used for A-nitrations. Solvents like acetonitrile, methylene chloride, nitromethane, dioxane, sulfolane, ethyl acetate and esters of phosphoric acid are commonly used. 

Secondary nitramines are conveniently prepared from the nitrolysis of A, A-dialkylamides with nitronium salts in acetonitrile or ethyl acetate at 20 °C where the acyl group is converted into an acylium tetrafluoroborate (Equation 5.14). Problems can occur if commercial nitronium salts like the tetrafluoroborate are used without purification. The presence of nitrosonium salts can then lead to nitrosamines via nitrosolysis. Yields of secondary nitramine up to 90 % have been reported with solutions of nitronium tetrafluoroborate in acetonitrile di-n-butylnitramine is obtained in 82 % yield from the nitrolysis of corresponding acetamide. ... 

N2O3 is a planar molecule with a long ON-NO2 bond (1.864 A) between the sp nitrogens [19]. It hydrates in water to form HONO in acidic solution or nitrite in basic media. Reaction with H2SO4 or other concentrated acids afford a route to nitrosonium salts, such as NO[HS04] [8]. 

E.K. Kim u. J.K. Kochi, Oxidative Aromatic Nitration with Charge-Transfer Complexes of Arenes and Nitrosonium Salts, J. Org. Chem. 54, 1692 (1989). 

To solution of the nitrosonium salt (5.0 mmol) in dcuteriochloroform (7.0 mL), placed in a 3-necked flask fitted with a dropping funnel, reflux condenser, and gas outlet tube, was added dropwise a solution of the azide (5.0 mmol) in the reaction solvent (3.0 mL). The addition to the rapidly stirred solution was at such a rate (15-20min) as to cause no significant rise in reaction temperature, which was kept at 25 C by means of a water bath. 

In reactions with aliphatic azides gas evolution did not usually begin until approximately 5 min had elapsed from the time of initial addition. In contrast, immediate gas evolution was observed after the initial addition of azido nitriles and phenoxy azides to the nitrosonium salt. Total gas evolution was measured on the closed system by water displacement from a calibrated gas buret. Total gas evolution reflected the total amount of reacted azide and the different pathways for the production of gaseous products (nitrosative decomposition and Curtius rearrangement). The rate of production of gaseous products slowed markedly after the evolution of 40-60 mL (1-2 mmol of reacted azide) with the exception of nitrosative reactions wi th 4-azidobutanonitrilc and 5-azidopentanonitrile, gas evolution terminated when approximately 50 % of the azide had reacted. Gas evolution in the nitrosative reactions of aliphatic azides continued to completion as a result of protonic decomposition. Reactions were usually complete within 2 h. 

The complex with nitrosyl chloride, Th04-2NOC1, is a nitrosonium salt, (NO)2[ThCl6]. 

Nitrosonium salts NO+Y (Y = BF4, PF6 etc.) react with basic precursors which are either coordinatively unsaturated or have displaceable groups. The use of these electrophilic reagents has only recently been developed and their sensitivity to conditions, such as the nature of the solvent, has tended to restrict their application (equation 9). 

Newer methods overcome this difficulty. The corresponding sulfinylamine or isocyanate is first prepared and then reacted with stable nitrosonium salts to give the corresponding carbocations138 [Eqs. (3.24) and (3.25)]. 

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). 

Nitrosonium salts as reagents in inorganic chemistry. (M. T. Mocella, M. S. Okamoto, and E. K. Barefield, Syn. React. Inorg. Metal-org. Chem., 1974,4, 69). 

The nitrosonium cation [NO]+ is isoelectronic with CO and accordingly many mixed nitrosyl-carbonyl complexes are known. For electron counting purposes, the neutral molecule is considered to act as a 3 (or occasionally 1) VE donor. Thus various series of isoelectronic complexes can be envisaged (Table 3.5). The majority of synthetic routes to nitrosyl-carbonyl complexes involve (i) photochemical CO substitution or metal-metal bond cleavage by NO (ii) electrophilic attack by nitrosonium salts, e.g. [NO]BF4 or nitrosyl halides (e.g. C1NO) upon electron-... 

Fluoroalkanes can be obtained by fluoride transfer from complex fluoride anions to carbocat-ions in the nitrosative decomposition of certain aliphatic azides. Several complex nitrosonium salts, such as NO " BF4, NO PF(, , and NO ShF ". " have been used for this purpose. This reaction is similar to the decomposition of arenediazonium tetrafluoroborate salts to form aryl fluorides (the Balz-Schiemann reaction, discussed in Sections 1.1.8.5. and Vol. F 10a, p686ff). in which fluoride is transferred from a very weak nucleophile, such as the complex tetrafluoroborate anion, to an electron-deficient center. 

Small amounts (1-2 mol equiv) of H2O or Lewis acids were added together with the nitrosonium salt. Unreacted azide (40%) was also isolated. 

The addition ofsmall amounts of water (1-2 mol equiv) to the nitrosonium salt, before reaction with the azido nitrile, minimizes telrazolc formation and enhances the amount of fluoro nitrile products obtained (see Table 1, entries 5-7). Water probably results in aquation of the Lewis acids formed during the fluoride transfer, thus minimizing tctrazole production. ... 

---