[359-47-7] · C2F3IO2 · Trifluoroacetyl Hypoiodite · (MW 239.92)
Solubility: sol aromatic solvents, halogenated solvents, ether, acetonitrile, trifluoroacetic acid.
Preparative Methods: is formed in situ from the reaction of equimolar amounts of Iodine and Silver(I) Trifluoroacetate or Mercury(II) Trifluoroacetate in a suitable solvent, typically trifluoroacetic acid (eq 1).1 Trifluoroacetyl hypobromite can be similarly prepared using bromine instead of iodine.
If 2 mol of the silver salt are introduced, then the acyl hypohalite complexes with the additional silver salt to form the complex indicated in eq 2. This preparation is used in addition reactions, whereas the equimolar preparation has been applied in electrophilic substitution reactions.
Trifluoroacetyl hypoiodite may also be formed from equimolar amounts of Phenyliodine(III) Bis(trifluoroacetate) and iodine (eq 3).5 This preparation is purported to allow for milder and faster iodination.6
Handling, Storage, and Precautions: is thermally labile and decomposes to trifluoromethyl iodide and carbon dioxide.2 Concentrated solutions can decompose by as much as 30% per day; negligible decomposition occurs when the concentration of trifluoroacetyl hypoiodite is kept below 20 mM.1
Because of the inductive effect of the trifluoromethyl group, trifluoroacetyl hypoiodite is unusually reactive as a positive iodine source for electrophilic aromatic substitution reactions. The relative reactivity order of hypohalites compared to other electrophilic halogen sources has been reported to be Br2 < ICl &AApprox; CH3CO2I &LLt; CF3CO2I < CH3CO2Br &LLt; CF3CO2Br.1 Product yields from reactions of trifluoroacetyl hypoiodite with aromatics range from 50% to 100% and favor para substitution (eq 4).2,6,7
Acyl hypoiodites, complexed by an additional equivalent of silver salt, e.g. (CF3CO2)2AgI, add across double bonds to form vic-iodocarboxylates. The vic-iodocarboxylates are converted in 60-90% yields to trans- or cis-diols, respectively, under anhydrous and wet conditions3 (iodine and thallium(I) carboxylates also form vic-iodocarboxylates in 60-90% yield).8 The vic-iodotrifluoroacetate derived from the reaction of trifluoroacetyl hypoiodite with an alkene has been used to effect anti-Markovnikov hydration of unsaturated sugars (eq 5).9
When the AgI precipitate is quantitatively removed from the reagent preparation, the trifluoroacetyl hypoiodite, thus prepared, reacts with alcohols to produce alkoxy radicals. The radicals decompose upon irradiation to give aldehydes, ketones, and furans or mixtures thereof in 80-90% yields.4
Ronald G. Brisbois & Randall A. Wanke
Hamline University, St. Paul, MN, USA