Perfluoroalkyl iodides are a class of substances in organic chemistry. They are compounds composed of a perfluoroalkyl chain and an iodine atom (CnF2n+1-I). They therefore belong to the per- and polyfluorinated alkyl compounds (PFAS) and to the alkyl iodides. They are typically constructed from C2 units (pentafluoroethane and tetrafluoroethylene). They are used in the industrial production of fluorotelomers and in a wide range of applications in organic synthesis.
Example compounds
Various perfluoroalkyl iodides containing from two (pentafluoroethane) to more than 10 carbon atoms are known. In the usual manufacturing process, compounds with linear chain lengths are obtained: perfluorobutyliodide, perfluorohexyliodide, perfluorooctyliodide, perfluorodecyl iodide, ...
Production Industrially, perfluoroalkyl iodides are typically produced by fluorotelomerization, starting from pentafluoroethyl iodide and reacting it with tetrafluoroethylene. This process yields a mixture of longer-chain perfluoroalkyl iodides. The complete synthesis begins with the extraction of hydrogen fluoride (HF) from calcium fluoride. The reaction of HF with chloroform produces tetrafluoroethylene via chlorodifluoromethane. The addition of elemental iodine to tetrafluoroethylene and further reaction with iodine pentafluoride then produces pentafluoroethyl iodide via 1,1,2,2-tetrafluoro-1,2-diiodoethane, which, when extended with tetrafluoroethylene, yields various perfluoroalkyl iodides with straight chain lengths.
Reactions Perfluoroalkyl iodides are most commonly employed in radical addition reactions to multiple bonds of alkynes and alkenes, enabling a broad range of synthetic transformations. This also includes the industrially applied reaction with ethene to convert perfluoroalkyl iodides into fluorotelomer iodides. A laboratory method for the addition of perfluoroalkyl iodides to alkenes and alkynes that provides good yields involves reacting an alkene or alkyne with a perfluoroalkyl iodide in the presence of a catalytic amount of triethylborane. Additions to terminal allenes and the introduction of perfluoroalkyl groups into unfunctionalized aromatics (benzene, naphthalene, xylenes, benzofuran) and fullerenes via an addition-elimination mechanism are also known.
Another well-studied class of reactions comprises coupling reactions of perfluoroalkyl iodides with aryl halides (primarily aryl bromides or aryl iodides, including derivatives of heteroaromatics). By reacting aromatic boronic acids with perfluoroalkyl iodides under copper catalysis, the boronic acid group can be replaced by a perfluoroalkyl residue. Upon reaction with an amine in tetrahydrofuran under UV radiation, perfluoroalkyl iodides generate perfluoroalkyl radicals that can be transferred to electron-rich aromatics and heteroaromatics.
Perfluoroalkyl iodides can also be converted into organometallic compounds, with Grignard compounds and organolithium compounds being particularly important. These intermediates can be used in standard reactions, including carboxylation with carbon dioxide and additions to aldehydes, ketones, and carboxylic acid esters. Organic boron organic compounds are obtained by reacting such organometallic compounds with boron trichloride or boron tribromide.
Hypervalent iodine compounds are obtained by reacting perfluoroalkyl iodides, such as perfluorobutyl iodide, with fluorinating agents, primarily chlorotrifluoride.
Use Perfluoroalkyl iodides are important intermediates in the production of fluorotelomer iodides, which in turn serve as precursors for fluorotelomer alcohols and other fluorotelomers.
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