Cations nitrosyl

Nitrosyl cation is also called nitrosonium ion It can be represented by the two reso nance structures... 

Nitrosation of amines is best illustrated by examining what happens when a sec ondary amine reacts with nitrous acid The amine acts as a nucleophile attacking the nitrogen of nitrosyl cation The intermediate that is formed m the first step loses a pro ton to give an N nitroso amine as the isolated product... 

Nitrosyl cation is a relatively weak electrophile and attacks only very strongly activated aromatic rings... 

This principle also applies to polyatomic cations corresponding to radicals with special names ending in -yl (Sec. 3.1.2.10) for example, PO+, phosphoryl cation NO+, nitrosyl cation NOj, nitryl cation O2+, oxygenyl cation. 

When solutions of sodium nitrite (NaN02) aie acidified, a number of species ar e formed that act as nitrosating agents. That is, they react as sources of nitrosyl cation, N=0 . For simplicity, organic chemists group all these species together and speak of the chemistry of one of them, nitrous acid, as a generalized precursor to nitrosyl cation. 

Refer to the molecu-l r model of nitrosyl cation on Learning By Modeling to verify that the region of positive electrostatic potential is concentrated at nitrogen. 

We learned in the preceding section that different reactions are observed when the various classes of alkylamines—primary, secondary, and tertiary—react with nitrosating agents. Although no useful chemistr-y attends the nitrosation of tertiar y alkylamines, electrophilic aromatic substitution by nitrosyl cation ( n Q ) takes place with A,A-dialkyl-arylfflnines. 

The reactive species for the transfer of the nitrosyl cation NO+ is not the nitrous acid 2 but rather N2O3 4 which is formed in weakly acidic solution. Other possible nitrosating agents are NOCl or H2N02 ", or even free NO+ in strong acidic solution. The initially formed N2O3 4 reacts with the free amine 1 ... 

Some gold(I) derivatives have been obtained with other type of /V-donor ligands as acetonitrile the compound [Au(NCMe)2]+ can be obtained by halide-catalyzed electrolysis of gold metal in MeCN.2412 This cation is very moisture sensitive and thermally labile, but the more stable cation [Au(NCPh)2]+ has been obtained by oxidation of gold with the nitrosyl cation in benzonitrile.2413 From EXAFS spectroscopic studies it has been suggested that the solvated gold(I) cations are tetra-coordinate in pyridine or acetonitrile solutions.2414 Other gold(I) complexes have been... 

In the CH3CH=CH2- -NO+ complex, the nitrosyl cation retains the characteristic canted geometry indicative of strong 7tcc-7txo interaction (Fig. 5.46(c)). However, the electrophilic attack shifts toward the terminal C of the pi bond, away from the methyl substituent. Such anti-Markovnikov complexation is, of course, to be expected from the relative polarization of the propylene pi bond toward the terminal C (so that the 7tCc antibond is polarized toward the alkyl pi-donor). 

In analogy to its complexes with nitrosyl cation (as described above), benzene can form donor-acceptor adducts with a variety of metallic and non-metallic Lewis acids. These lead to materials with novel optical and electrical properties that can be tuned through substituents on the aromatic ring. 

Fig. 4. Illustration of limiting cases of NO binding to a metalloporphyrin center as (a) the nitroxyl anion (NO-) with a M-N-0 bond angle of 120° or as (b) the nitrosyl cation (NO+) with a M-N-0 bond angle of 180°.

The reaction of acylsilanes with acid chlorides in the presence of A1C13 leads to furans (Table 9.41) [45]. In these reactions an acyl cation initiates the addition with ensuing silyl migration yielding an intermediate vinyl cation. Attack of the carbonyl oxygen followed by proton loss affords the observed products (Scheme 9.16). An analogous reaction with nitrosyl fluoroborate provides a route to oxazoles (Table 9.42) [65]. The nitrosyl cation serves as the electrophile in this application. 

As a result of their very low reactivity with the HO anion, the organic nitrates show a practically pH-independent (and very slow) hydrolysis at pH 7 and above [27], In contrast, they will react rapidly with alcohols in nonpolar media by nitrosyl exchange (Fig. 9.2,b) [28]. Formally, H+ and NO+ (nitrosyl cation) are exchanged, but the actual reaction mechanism is quite complex. The reaction leads to an equilibrium, which depends on the partners and presumably also on conditions. However, the biological relevance of this reaction remains to be understood. 

Silyl radicals have been produced by one-electron oxidation of silyl metals [11]. This is found to be the method of choice for the generation of persistent silyl radicals and allowed the preparation of the first isolable silyl radical (see later in this chapter). Reactions (1.5) and (1.6) show two sterically hindered silyl anions with Na+ as the counter-cation, and their oxidation by the nitrosyl cation [12] and the complex GeCh/dioxane [13], respectively. 

In reality, nitration of naphthalene with dinitrogen tetroxide in an aprotic medium is a complex process. The leading role belongs to nitrosyl cation. This species is a strong oxidant acting according to the outer-sphere mechanism (compare with Section 1.7.10) ... 

Tautomerism in 277-benzoxazin-2-ones allows carbon substituents at the 3-position to be reactive toward the NO electrophile. Compounds 227 <1963LA83> and 229 <1963LA93> reacted with the nitrosyl cation to give the derivatives 228 and 230 as shown in Scheme 23. 

KLinkenberg and Ketelaar14 have shown that NOC10 , NOBF , and (NO)[Pg.345]

Although the above authors did not advance a detailed mechanism, it appears probable that nitrosyl cation can in effeot function us a proton, forming an oxonium-type intermediate (Eq. 940). Attack hv Cl ion is thereby facilitated and occurs with Walden inversion, us in the cleavage of epoxides with hydrogen chloride itself. 

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