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Radical fluorination is a type of fluorination reaction, complementary to nucleophilic and electrophilic approaches. [1] It involves the reaction of an independently generated carbon-centered radical with an atomic fluorine source and yields an organofluorine compound .
Organofluorine compounds are prepared by numerous routes, depending on the degree and regiochemistry of fluorination sought and the nature of the precursors. The direct fluorination of hydrocarbons with F 2, often diluted with N 2, is useful for highly fluorinated compounds: R 3 CH + F 2 → R 3 CF + HF
Aromatic fluorination: Alkene fluorination: Radical fluorination in radical decarboxylative fluorination reactions, [10] in Hunsdiecker-type reactions where xenon difluoride is used to generate the radical intermediate as well as the fluorine transfer source, [28] and in generating aryl radicals from aryl silanes: [29] XeF
Trifluoromethyl hypofluorite is an organofluorine compound with the chemical formula C F 3 OF.It exists as a colorless gas at room temperature and is highly toxic. [1] It is a rare example of a hypofluorite (compound with an O−F bond).
Radical fluorination with the pure element is difficult to control and highly exothermic; care must be taken to prevent an explosion or a runaway reaction. With chlorine the reaction is moderate to fast; with bromine, slow and requires intense UV irradiation ; and with iodine, it is practically nonexistent and thermodynamically unfavored.
Fluorination of lactones can provide heterocyclic fluorides, although ring opening has been observed for γ-butyrolactone. The six-membered lactide does not experience ring opening. [8] Fluorination opens epoxides to give either geminal or vicinal difluorides in most cases. Monoarylepoxides give geminal products with migration of the aryl group.
The traditional Balz–Schiemann reaction employs HBF 4 and involves isolation of the diazonium salt. Both aspects can be profitably modified. Other counterions have been used in place of tetrafluoroborates, such as hexafluorophosphates (PF 6 −) and hexafluoroantimonates (SbF 6 −) with improved yields for some substrates.
Electrophilic fluorinating reagents could in principle operate by electron transfer pathways or an S N 2 attack at fluorine. This distinction has not been decided. [2] By using a charge-spin separated probe, [3] it was possible to show that the electrophilic fluorination of stilbenes with Selectfluor proceeds through an SET/fluorine atom transfer mechanism.