Epoxide opening hydrogen bromide

Bromohydrins. As a source of hydrogen bromide, [Ph3PH]Br is useful in opening of epoxides. 

Oxetanes (oxacyclobutanes) react much like oxiranes (epoxides, oxacyclopro-panes),but much more vigorous conditions are required.Thus, oxetane (oxacyclobu-tane) reacts with hydrogen bromide (HBr) under ionic conditions to provide 1,3-dibromopropane. Presumably, the ring-opening reaction occurs first to yield 3-bromo-l-propanol and then, under the more vigorous conditions, protonation and Sn2 displacement of water follows (Equation 8.53) to produce the 1,3-dibromide. 

As an alternative practical method, the opening of epoxides by halide ions has often been used for introducing halogens, especially fluorine, into sugar molecules. Sodium iodide, magnesium bromide, and hydrogen halides (HCl, HF) are frequently used as halogen sources [64,65]. 

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