Tnflic acid

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

Analogously, tnflic acid isomerizes n-butane into 2 methylpropane [80, 81] Interestingly, perfluorobutanesulfonic acid, which is of similar strength as tnflic acid, does not catalyze the isomerization of n-butane [50]... 

The reaction of tnflic acid with 2-hydroxy-2-adamantanecarboxylic acid results in decarbonylation to adamantanone [84] However, in the presence of carbon monoxide, the same reactants give 4,3 homoadamantanedione as the product of a pinacolone-type rearrangement (equation 35)... 

Carbonylation ot 1-adamantyl triflate in the presence of tnflic acid also gives a derivative of homoadamantane as the result of a similar rearrangement with ring expansion [55] (equation 36)... 

Tnflic acid is a useful reagent for the removal of protecting groups (deblocking) in synthetic proteins [67] At the same time, it is an excellent catalyst for the protection of a variety of phenols in the form of their terf-butyl ethers [5(5] (equation 37)... 

Tnflic acid is an excellent catalyst for the nitration of aromatic compounds [.S7]. In a mixture with nitnc acid, it forms the highly electrophilic nitronium inflate, which can be isolated as a white crystalline solid Nitronium inflate is a powerful nitrating reagent in inert organie solvents and in tnflic acid or sulfuric acid. It nitrates benzene, toluene, chlorobenzene, nitrobenzene, m-xylene, and benzotn-fluoride quantitatively in the temperature range of-110 to 30 °C with exeeptionally high positional selectivity [87],... 

Oxo-bridged diiodonium triflate [Zefirov s reagent), a useful reagent for the synthesis of triflate esters and iodonium salts, can be prepared by the treatment of lodosobenzene with triflic anhydride [92] or by the reaction of lodobenzene diacetate with tnflic acid [93] (equation 44). 

The chloride of triflic acid (trifluoromethanesulfonyl chloride) is an effective sulfonylating agent Like triflic anhydride, it usually reacts with alcohols and other nucleophiles with the formation of the corresponding derivatives of tnflic acid [69] However, in some reactions, it acts as a chlorinating reagent [98] The reactions of tnfluoromethanesulfonyl chloride with 1,3-dicarbonyl compounds or some carboxylic esters in the presence of a base result m the formation of chlonnated products in high yields (equation 49)... 

Fluorinated sulfinates are prepared from sodium dithionite and liquid per-fluoroalkyl halides [74] (equation 67). For the transformation of the gaseous and poorly reactive trifluoromethyl bromide, it is necessary to use moderate pressure [75] (equation 68) These reactions are interpreted by a SET between the intermediate sulfur dioxide radical anion and the halide The sodium tnfluorometh-anesulfinate thus obtained is an intermediate for a chemical synthesis of tnflic acid. 

Oxidation of the tnfluoromethanesulfinate gives tnflic acid [50] (equation 43) Chlonnation of the perfluoroalkylsulfi nates gives the corresponding perfluoroalkyl sulfonyl chlorides [57] (equation 44)... 

Trifluoromethanesulfonic (triflic) anhydride is commercially available or can be prepared easily by the reaction of triflic acid with phosphorus pentoxide [66] This moderately hygroscopic colorless liquid is a useful reagent for the preparation of various organic derivatives of tnflic acid A large variety of organic ionic triflates can be prepared from triflic anhydride A recent example is the preparation of unusual oxo-bndged dicatiomc salts of different types [ S, 89, 90, 91, 92, 93] (equations 38-44) Stabilized dication ether salts of the Huckel aromatic system and some other systems (equations 38 and 39) can be prepared in one step by the... 

Tnflic acid is strong enough to protonate polycyclic saturated hydrocarbons [77, 78, 79], and even -butane [80, 57], and to initiate skeletal rearrangements Acidic treatment of homoadamantane [77] (equation 32), 2-homoprotoadamantane [78] (equation 33), or as 2,3-trimethylenebicyclo[3 3 OJoctane [79] (equation 34) causes their rearrangement to isomenc hydrocarbons... 

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