Halogenation epoxide opening

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]. 

Sharghi, H. Niknam, K. Pooyan, M. The halogen-mediated opening of epoxides in the presence of pyridine-containing macrocycles. Tetrahedron 2001, 57, 6057-6064. 

Compounds are prepared by a fairly standard sequence which consists of condensation of an appropriate phenol with epichlorohydrin in the presence of base. Attack of phenoxide can proceed by means of displacement of chlorine to give epoxide (45) directly. Alternatively, opening of the epoxide leads to anion 44 this last, then, displaces halogen on the adjacent carbon to lead to the same epoxide. Reaction of the epoxide with the appropriate amine then completes the synthesis. 

Scheme 5.7 illustrates these and other applications of the hydride donors. Entries 1 and 2 are examples of reduction of alkyl halides, whereas Entry 3 shows removal of an aromatic halogen. Entries 4 to 6 are sulfonate displacements, with the last example using a copper hydride reagent. Entry 7 is an epoxide ring opening. Entries 8 and 9 illustrate the difference in ease of reduction of alkynes with and without hydroxy participation. 

Oxidation is the first step for producing molecules with a very wide range of functional groups because oxygenated compounds are precursors to many other products. For example, alcohols may be converted to ethers, esters, alkenes, and, via nucleophilic substitution, to halogenated or amine products. Ketones and aldehydes may be used in condensation reactions to form new C-C double bonds, epoxides may be ring opened to form diols and polymers, and, finally, carboxylic acids are routinely converted to esters, amides, acid chlorides and acid anhydrides. Oxidation reactions are some of the largest scale industrial processes in synthetic chemistry, and the production of alcohols, ketones, aldehydes, epoxides and carboxylic acids is performed on a mammoth scale. For example, world production of ethylene oxide is estimated at 58 million tonnes, 2 million tonnes of adipic acid are made, mainly as a precursor in the synthesis of nylons, and 8 million tonnes of terephthalic acid are produced each year, mainly for the production of polyethylene terephthalate) [1]. 

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