Halogen azides, reactions

An explosion was experienced dining work up of an epoxide opening reaction involving acidified sodium azide in a dichloromethane/dimethyl sulfoxide solvent. The author ascribes this to diazidomethane formation from dichloromethane [1]. A second report of an analoguous accident, also attributed to diazidomethane, almost certainly involved hydrogen azide for the cold traps of a vacuum pump on a rotary evaporator were involved this implies an explosive more volatile than dichloromethane. It is recommended that halogenated solvents be not used for azide reactions [2]. 

E. D. Binkley and R. W. Binkley, SN2-Type Halogenation and Azidation Reactions with Carbohydrate Triflates, ed. S. Hanessian, Marcel Dekker, New York, 1997. 

SN2-Type Halogenation and Azidation Reactions with Carbohydrate Triflates... 

Halogen azides are compounds with the general formula XN3, where X is one of the halogens. These compounds are extremely reactive and can be spontaneously explosive. Their reactions with water can produce toxic fumes of the elemental halogen, acid (e.g., HC1), and NOx. The compound vapors are irritants. 

In group 16, the intermediate existence of 0(N3)2 as an intermediate in the reaction of OF2 with CSN3 has been proposed. Many sulfur azides are known, for details see (see Sulfur Inorganic Chemistry). Binary selenium and tellurium azides are not known, but several organic derivatives of the azides have been synthesized. For a description of the halogen azides, see Section 8.6. 

The halogen azides are prepared by the reaction of metal azides with halogens or the hypohalogenic acids. 

Reaction of Conjugated Alkenes with Halogen Azides... 

The analogous reactions of alkenes with halogen azides are treated in Section 7.2.2 and those with iodine isocyanate and bromocyanamide are treated in Section 7.2.6. 

The present situation in regard to addition of halogen azide to alkynes is that the synthetic aspects are well established but that mechanistic evidence is sparse and equivocal. Clearly, some rate studies of diese reactions would be of value in elucidating the mechanisms actually involved. 

Mechanistically most of these transformations correspond to 5N2-type substitutions chiral substrates react with inversion. In certain cases, however, azides may also be obtained under 5n1 condi-tions." " " Some di- and tri-arylmethanols for instance (Scheme 32) react with HN3 in the presence of trichloroacetic acid via the corresponding carbenium ions. Sulfuric acid seems to be inferior for these transformations." " Under highly acidic conditions the intermediate (20) obviously tends to decompose with the elimination of nitrogen (c/. Schmidt reaction "). SnI substitution is also highly probable in the reaction of a-halo ethers and sulfides with azide ions." " In some cases even SRNl-type substitution was observed for the halogen/azide exchange." ... 

A halogen-azide replacement easily occurs when the formed, lower boiling chlorosilane (e.g. Me3SiCl) can be removed immediately from the reaction mixture by distillation. 

Aluminum azide is obtained from reacting AICI3 with NaNs in THF, or from the reaction of A1H3-Et20 with HN3 in ether at low temperature. When trimethylamine adducts of alane are employed, solids thought to be azido complexes are produced (equation 7). Aluminium (and gallium) compounds X2M(N3), where X = Br or I, have been prepared by the reaction of MX3 with the halogen azide 7W3 in benzene. They are polymeric solids which show v(M—N3) modes near 490 cm" (M = Al), or 430 cm" (Ga) in the vibrational spectra. 

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