Nitryl halides

Nitrogen forms two series of oxohalides — the nitrosyl halides XNO and the nitryl halides XNO2. There are also two halogen nitrates FONO2 (bp -46°) and CIONO2 (bp 22.3°), but these do not contain N-X bonds and can be considered as highly reactive derivatives of nitric acid, from which they can be prepared by direct halogen ation ... 

A number of gaseous oxyhalides of nitrogen are known, including the types XNO (nitrosonium or nitrosyl halides) with X = F, Cl, or Br, and XN02 (nitryl halides) with X = F or Cl. Nitrosonium halides are prepared by the reactions of halogens and NO. 

Nitryl halides effect the nitration of aromatic substrates in the presence of Lewis acids, although competing halogenation is a side-reaction in some cases."" ... 

Nitryl halides have been more popular reagents. Treatment of substituted styrenes with iodine and sodium nitrite leads to Markovnikov addition of NO2I (electropositive NO2) to the double bond. Elimination of HI affords (3-nitrostyrenes149150 as shown in Scheme 73.149 ( )-2-nitro-l-(trimethylsilyl)ethylene has been prepared by addition of nitryl chloride to trimethylsilylethylene, followed by elimination of HI. The author advertises the use of NO2CI and the other reagents involved as more economical than some of the other approaches to the nitroalkene (Scheme 74).151... 

The nitryl halides are FN02 and C1N02 which are colorless gases (bp —72°C and — 15°C, respectively) with planar structures in the gas phase and for C1N02 in the solid state by X-ray diffraction. 

The reaction of NO2 with fluorine or chlorine yields nitryl halides (see Section 9.2). 

Table 40 Properties and bonding parameters of nitryl halides...

Similar to the nitrosyl halides, the nitryl halides are easily ... 

The nitryl halides (C2 symmetry) are planar in analogy to the isoelectronic COs. The gas phase and solid-state structures for CINO2 both show covalently bound molecules (see Table 40). In contrast to the nitrosyl hahdes, the halogen-nitrogen bond distances in the gas phase and in the solid state are similar. The nitryl halides NO2F and NO2CI are the mixed anhydrides of nitric acid and hydrofluoric or hydrochloric acid, respectively. 

The stability of the nitryl halides follows the stabihty of the nitrosyl halides, F > Cl > Br > I. Nitryl bromide BrN02 exists in equilibrium with NO2/N2O4 at room temperature and can be studied spectroscopically. INO2 has a hfetime of only a few seconds at room temperature. 

Reaction of the nitryl halides with strong Lewis acids yields nitryl salts with the linear N02" cation (92) (d(N=0) 115.4pm) (see Figure 16). 

Schweitzer F., Mirabel P., and George C. (1999) Heterogeneous chemistry of nitryl halides in relation to tropospheric halogen activation. J. Atmos. Chem. 34, 101 — 117. 

The existence of two nitryl halides, NO2F and NO2CI, is well established the existence of N02Br is less certain. The fluoride can be conveniently prepared by the action of fluorine on slightly warm dry sodium nitrite NaN02 + F2 -> NO2F + NaF, and is a reactive gas which converts many metals to oxide and fluoride or oxyfluoride, and reacts with many non-metals (Br and Te excepted) to form nitronium salts. Examples of nitronium salts are (N02)BF4, (N02)2SiFe, (N02)PFe, and (N02)IFg. 

Physical Properties of Nitrosyl Halides, HalNO, and Nitryl Halides, HalNQ2... 

The only known nitryl halides, which may be regarded as derivatives of nitric acid where a halogen atom replaces OH, are FN02 and C1N02.47 The former is conveniently prepared by the reaction ... 

Similar to the nitrosyl halides, the nitryl halides are easily hydrolyzed. During the synthesis, water has to be excluded, either by removing it ... 

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