Halides nitrogen

Nitrogen trifiuoride is made either by reaction 15.56 which must be carried out in a controlled manner, or by electrolysis of anhydrous NH4F/HF mixtures. 

NF3 is the most stable of the trihalides of nitrogen, being the only one to have a negative value of A[H° (Table 15.5). 

Explain why NH3 is polar. In which direction does the dipole moment act  

NH3 is a trigonal pyramidal molecule with a lone pair of electrons on the N atom  

Account for the fact that the dipole moment of NHF2 (1.92 D) is greater than that of NF3 (0.24 D). 

NF3 is the most stable of the trihalides of nitrogen, being the only one to have a negative value of Af/f (Table 15.5). It is a colourless gas which is resistant to attack by acids and alkalis, but is decomposed by sparking with H2 (eq. 15.60). The resistance towards hydrolysis parallels that observed for the carbon tetrahalides (Section 14.8). 2NF3 + 3H2 N2 + 6HF (15.60) 

The gas-phase structure of NF3 is trigonal pyramidal (15.20), and the molecular dipole moment is very small 

NF3 is the most stable of the nitrogen halides it does not react with water or dilute acid. It is prepared by the direct reaction of ammonia and fluorine  

The trichloride and tribromide are explosively unstable with respect to their constituent elements. Indeed, P. L. Dulong, who first prepared NCI3 in 1811, lost an eye and three fingers whilst studying its chemical properties  

Until recently nitrogen triiodide (which paradoxically is the longest-known nitrogen halide) had only been prepared in combination with coordinated ammonia. Concentrated aqueous ammonia reacts with iodine to form a black crystalline product of composition NI3.NH3. When dry, this explodes with the slightest disturbance, a consequence of the strong tendency to form the dinitrogen molecule (Equation 11.9). 

However, two German chemists, Thomas Klapotke and Inis Tornieporth-Oetting, have now prepared/ree NI3 by treating iodine monofluoride with boron nitride  

Because IF disproportionates rapidly to I2 and IF5 at room temperature, the synthesis was carried out at -30 °C. NI3 was isolated as a deep-red solid, which was highly unstable at room temperature, decomposing with explosive violence. 

Nitrogen is restricted to an octet of valence electrons and does not form pentahalides. The fact that nitrogen pentaha-lides are not known has also been attributed to the steric crowding of five halogen atoms around the small N atom. Important nitrogen halides are NX3 (X = F, Cl), N2F4 and N2F2, selected properties for which are listed in Table 14.5  

NBr3 and NI3 exist but are less well characterized than NF3 and NCI3. 

The gas-phase structure of NF3 is trigonal pyramidal (14.20), and the molecular dipole moment is very small (Table 14.5). In contrast to NH3 and PF3, NF3 shows no donor properties. 

Thiazyl fluoride is a moisture-sensitive, thermally unstable gas. It is conveniently generated by decomposition of compounds which already 

Monomeric thiazyl halides can be stabilized by coordination to transition metals and a large number of such complexes are known (Section 7.5). In addition, NSX monomers undergo several types of reactions that can be classified as follows (a) reactions involving the n-system of the N=S bond (b) reactions at the nitrogen centre (c) nucleophilic substitution reactions (d) halide abstraction, and (e) halide addition. Examples of each type of behaviour are illustrated below. 

Thiazyl trifluoride, a colourless gas with a pungent odour, is prepared by the oxidative decomposition of FC(0)NSF2 with Agp2 (Eq. 8.5).NSF3 is kinetically very stable even in the liquid form. The chemical inertness of NSF3 resembles that of SFe. For example, it does not react with sodium metal below 200°C.  

The reactions of NSF3 have been investigated in considerable detail. They can be classified under the following categories (a) reactions with electrophiles (b) addition to the SN triple bond and (c) reactions with nucleophiles. Some examples of these different types of behaviour are discussed below. 

A different type of behaviour is observed with the chloro Lewis acid BCI3. With this reagent halogen exchange occurs to produce the acyclic cation [N(SC1)2] , as the [BCU] salt, rather than NSCf. Thiazyl trichloride NSCI3 is predicted to be unstable with respect to NSCl -1-Cl2.  

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In spite of the hazardous nature of Sc4N4, this binary selenium nitride has been used for the synthesis of other Se-N compounds, all of which have sulfur analogues (Scheme 5.2). " However, safer alternatives to the use of Sc4N4, e.g., selenium-nitrogen halides and silicon-nitrogen-selenium reagents, are available for the development of Se-N chemistry. ... 

The reaction of Me3SiNSNSiMc3 with TeCU is an especially fruitful source of chalcogen-nitrogen halides that contain both sulfur and tellurium. The initial product of this reaction is the bicyclic compound 8.17, which is obtained when the reaction is carried out in a 1 2 molar... 

Chalcogen-Nitrogen Halides Containing Three-Coordinate Nitrogen... 

The acyclic imidoselenium(II) dihalides ClSe[N( Bu)Se]nCl (8.23, n =1 8.24, n = 2) are obtained from the reaction SeCla with tert-butylamine in a 2 3 molar ratio in THF. There are no sulfur or tellurium analogues of this class of chalcogen-nitrogen halide. 

Sticksto F-gas, n. nitrogen gas. -gehalt, m. nitrogen content, -gleichgewicht, n. nitro gen equilibrium. -halogen, n. nitrogen halide. 

The sulfur-nitrogen halide (NSC1)3 is also a useful reagent in organic chemistry. For example, alkenes or alkynes react readily with (NSC1)3 to produce 1,2,5-thiadiazoles and the reaction with A-alkylpyrroles gives bis-1,2,5-thiadiazoles. 

Selenium- and Tellurium-Nitrogen Halides. The best characterised selenium-nitrogen halide is the cation [863X20 ] (12.26), which forms a... 

Nitrogen halides are destroyed with cold base. Azides and fulminates-may often be destroyed with acid, while heavy metal acetylides are decomposed by ammonium sulfide. The removal of peroxides by reduction has been described above. 

Cyclopropanations are known for several other carbanionic intermediates of the general type (7), in which the substituent G is ultimately lost as an anionic leaving group in the last step of the ring-forming pathway (see Scheme 3 above). The substituent G is most often a functional group based upon sulfur, selenium or nitrogen. Halide-substituted derivatives probably react via the a-elimination pathway in most cases (see Section 4.6.3.1), but in some reactions with electron deficient alkenes as substrates, the normal order of steps may be altered (e.g. Table 10, ref. 162). 

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