Abstract
ClF, BrF 3 and hexachloromelamine (HCM)/HF system are effective reagents for selective substitution of covalently bonded bromine atoms by fluorine. BrF 3 demonstrates marked amphoteric properties; therefore esters, being weak Lewis bases, lower BrF 3 reactivity in the reactions of substitutive fluorination. For this reason, reaction rate of BrF 3 with bromine containing esters depends not only on the electron properties of substituents at the reaction center, but on ester basicity as well. ClF is far less amphoteric than BrF 3, so its reactivity is not deactivated by the ester function. The HCM/HF system with respect to bromosubstituted esters is effective only with a considerable excess of HF, which protonates the nitrogen atoms in the HCM nucleus, due to the high acidity of the reaction medium. Concrete examples, illustrating the preparative abilities of halogen fluorides in nonpolar media, and of the system HCM/HF will be discussed in the report.
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