Trifluoromethanesulfonic acid, addition

The first member of the series, CF SO H, has been extensively studied. Trifluoromethanesulfonic acid [1493-13-6] is a stable, hydroscopic Hquid which fumes in air. Addition of an equimolar amount of water to the acid results in a stable, distillable monohydrate, mp 34°C, bp 96°C at 0.13 kPa (1 mm Hg) (18). Measurement of conductivity of strong acids in acetic acid has shown the acid to be one of the strongest protic acids known, similar to fluorosulfonic and perchloric acid (19). 

Trifluoromethanesulfonic acid is miscible in all proportions with water and is soluble in many polar organic solvents such as dimethylformamide, dimethyl sulfoxide, and acetonitrile. In addition, it is soluble in alcohols, ketones, ethers, and esters, but these generally are not suitably inert solvents. The acid reacts with ethyl ether to give a colorless, Hquid oxonium complex, which on further heating gives the ethyl ester and ethylene. Reaction with ethanol gives the ester, but in addition dehydration and ether formation occurs. 

Alkynes react when heated with trifluoroacetic acid to give addition products. Mixtures of syn and anti addition products are obtained. Similar addition reactions occur with trifluoromethanesulfonic acid. These reactions are analogous to acid-catalyzed hydration and proceed through a vinyl cation intermediate. 

Acids that are used in addition to trifluoroacetic acid include trifluoroacetic acid with added sulfuric acid203 or boron trifluoride etherate,210,211 perfluorobu-tyric acid,212 hydrogen chloride/aluminum chloride,136,146,213 perchloric acid in chloroform,214 p-loluenesull onic acid alone134 or with aluminum bromide or aluminum chloride,192 concentrated sulfuric acid in two-phase systems with dichloromethane, alcohol, or ether solvents,209,215 trifluoromethanesulfonic acid,216 chlorodifluoroacetic acid,134 and the monohydrate of boron trifluoride... 

Vinyl trifluoromethanesulfonates (triflates) are a new class of compounds, unknown before 1969, that have been used most extensively in solvolytic studies to generate vinyl cations.2,3,812 Three methods have been used to prepare these sulfonic esters. The first, involving the preparation and decomposition of acyltriazines,4 requires several steps to prepare the acyltriazines and is limited to the preparation of fully substituted vinyl triflates. The second method involves the electrophilic addition of trifluoromethanesulfonic acid to acetylenes5,8,15 and, consequently, is not applicable to the preparation of trisubstituted vinyl triflates and certain cyclic vinyl triflates. However, this second procedure is relatively simple and often gives purer products in higher yield than the subsequently discussed reaction with ketones. Table I lists vinyl triflates that have been prepared by this procedure. ... 

The reaction of dicyclohexylborane and trifluoromethanesulfonic acid is highly exothermic. On one occasion, the checkers cooled the reaction in an ice bath during the addition period, with no effect on product yield. The submitter reports that he once experienced a sudden vigorous reaction under cooling conditions, probably due to accumulation of unreacted triflic acid. It thus appears safer to add the acid at room temperature, slowly, so that it reacts immediately. 

Imines of acyclic and C10- to C15-membered carbocyclic ketones are prepared under the conditions described for cyclohexanone imines using trifluoromethanesulfonic acid or trifluoroacetic acid as additional catalyst. The reaction often takes several days in refluxing benzene or toluene9. 

A. 3-Butyn-l-yl Trifluoromethanesulfonate. A 500-ml., three-necked flask is fitted with a mechanical stirrer, a pressure-equalizing dropping funnel, and a stopper. The system is flushed with nitrogen through a gas-inlet tube attached to the top of the funnel. To 150 ml. of dry methylene chloride (Note 1) in the flask is added 75 g. (0.27 mole) of trifluoromethanesulfonic acid anhydride (Note 2), and the solution is cooled to —40°. After addition of 14.5 g. (0.14mole) of finely powdered anhydrous sodium carbonate (Note 3), 15 g. (0.21 mole) of 3-butyn-l-ol (Note 4) is added dropwise over a 20-minute period to the well-stirred reaction mixture maintained at —40° to —55°. Stirring is continued at —30° for 2 hours and then at 0° for another hour, and finally the... 

Keywords ethyl 2-oxo-cyclohexanecarboxylate, ethyl acrylate, Michael addition, trifluoromethanesulfonic acid... 

Trifluoromethanesulfonic acid FC-24 was obtained directly from the manufacturer, Minnesota Mining and Manufacturing Co. (3M), 15 Henderson Dr., West Caldwell, NJ 07006. Adherence to both the time and temperature during the addition is critical for best results. 

The method is particularly well-suited to the fluorination of dithioketals of aromatic ketones (Table 12). To achieve reasonable yields with dithioketals of aliphatic or alicyclic ketones, the addition of trifluoromethanesulfonic acid or hydrogen fluoride/pyridine is required. In general, dithiane derivatives give better yields than dithiolane derivatives. 

Due to the important role of nitrogen functional groups, the addition reactions of an electrophilic selenium reagent and a nitrogen nucleophile to a carbon-carbon double bond represent a synthetically relevant process with potential practical applications. Among the reactions of this type which have been described already, perhaps the most important contribution is represented by the Ritter-type amide synthesis described by Toshimitsu and Uemura [48a, 48b]. The addition of a phenylselenyl and of an acylamino group to a mono or a 1,2-disubstituted olefin was accomplished by treating the olefin with PhSeCl in acetonitrile and water in the presence of trifluoromethanesulfonic acid. 

Trifluoromethanesulfonic acid (531 pL, 6 mmol) is added to boron tribromide (distilled from A1 powder 190 pL, 2 mmol) at 0 °C. After evolution of HBr has ceased the flask is evacuated for 1 h to give B(OTf)3 as a viscous yellow liquid. In a separate flask, a solution of la is prepared by addition of trifluoromethanesulfonic acid (177 pL, 2 mmol) to a solution of allyltrimethylsilane (320 pL, 2 mmol) in dichloro-... 

TFA at higher temperatures,or TFA/thioanisole where the push-pull mechanism remarkably increases the rate of acidolysis,f l liquid HF/pyridine,t °l BBrj/CHaQa, or BBrj/TFA for longer peptide fragments.By these procedures also the benzyl-type side-chain protection is cleaved as well as Arg(Tos). Additionally, numerous sulfonic acids were shown to efficiently remove the Z group, such as methanesulfonic acid, trifluoromethanesulfonic acid, or fluorosulfonic acid mainly in CH2CI2 or Since the acidolytic removal of the... 

If the solution of iron powder and trifluoromethanesulfonic acid in acetonitrile is to be filtered through a sintered-glass filter, the addition of a small amount of Filter Aid to the reaction mixture will prevent the sinter from becoming clogged with the unreacted iron powder. 

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