Alkylation trifluoromethanesulfonic acid

Other preparations of trifluoromethanesulfonic acid kiclude oxidation of methyltrifluoromethyl sulfide under a variety of conditions (10,11). Perfluorosulfonyl fluorides have also been prepared by reaction of fluoroolefkis with sulfuryl fluoride (12,13). Chinese chemists have pubflshed numerous papers on the conversion of telomer-based alkyl iodides to sulfonyl fluorides (14,15) (eqs. 8 and 9) ... 

Alkyl esters of trifluoromethanesulfonic acid, commonly called triflates, have been prepared from the silver salt and an alkyl iodide, or by reaction of the anhydride with an alcohol (18,20,21). Triflates of the 1,1-dihydroperfluoroalkanols, CF2S020CH2R can be prepared by the reaction of perfluoromethanesulfonyl fluoride with the dihydroalcohol in the presence of triethylamine (22,23). Triflates are important intermediates in synthetic chemistry. They are among the best leaving groups known, so they are commonly employed in anionic displacement reactions. 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

In order to achieve high yields, the reaction usually is conducted by application of high pressure. For laboratory use, the need for high-pressure equipment, together with the toxicity of carbon monoxide, makes that reaction less practicable. The scope of that reaction is limited to benzene, alkyl substituted and certain other electron-rich aromatic compounds. With mono-substituted benzenes, thepara-for-mylated product is formed preferentially. Super-acidic catalysts have been developed, for example generated from trifluoromethanesulfonic acid, hydrogen fluoride and boron trifluoride the application of elevated pressure is then not necessary. 

Haldor Topspe s fixed-bed alkylation (FBA ) technology is a compromise between liquid and solid acid-based processes. It applies a supported liquid-phase catalyst in which liquid triflic (trifluoromethanesulfonic) acid is supported on a porous material (206,241). The acid in the bed is concentrated in a well-defined catalyst zone, in which all the alkylation chemistry takes place at the upstream... 

Thus, the best compromises for Boc and Fmoc chemistries seem to be cyclohexyl and 2,4-dimethylpent-3-yl (Dmpn), which is of intermediate stability, and the removal of which by trifluoromethanesulfonic acid with the aid of thioanisole (see Section 6.22) leads to minimal imide formation (see Section 6.13). Points to note are that acidolysis of esters by hydrogen fluoride can lead to fission at the oxy-car-bonyl bond instead of the alkyl-oxy bond, thus generating acylium ions that can react with nucleophiles (see Sections 6.16 and 6.22), and that benzyl esters may undergo transesterification if left in methanol. The side reactions of cyclization (see Section 6.16) and acylation of anisole (see Section 6.22) caused by acylium ion formation do not occur at the side chain of aspartic acid.47-51... 

Hydrogen Fluoride-Trifluoromethanesulfonic Acid. The acidity of this binary Brpnsted acid system has not been measured, but the superacidic properties are mentioned in numerous patents concerning fluorination, olefin alkylation, and hydrocarbon conversion. 

Oxetanes have also been used as alkylating agents in the Friedel-Crafts reaction for example, 2-isopropyloxetane was reacted with benzene in superacidic trifluoromethanesulfonic acid (TFSA) to give a mixture of alkylated aromatic products (Equation 9) <2003CAL1>. The main product of the reaction was the tetralin derivative 46 which could be isolated in up to 75% yield. Other notable side products are shown, resulting from monoalkylation or other skeletal rearrangements. 

Activation of a side-chain primary alcohol function with trifluoromethanesulfonic acid anhydride led to exclusive C-alkylation resulting in a cationic ring closure to afford the tetrahydroindoles (A)-584 (Equation 140) <2004T1197>. When R = H the N-Tf-substituted compound (5)-584 was formed as a side product in 18% yield. It was important to conduct the reaction in the presence of 4-methyl-2,6-di-/-butylpyridine as a sterically demanding and effective proton scavenger. 

Protection of phenols by the foregoing methods is complicated by the rapid Friedel-Crafts rearrangement of the nascent rm-butyl ether. By using trifluoro-methanesulfonic add at -78 PC, the rate of /erf-butyl ether formation is fast and the Friedel-Crafts alkylation does not compete [Scheme 4.126].226 Similarly, attempts to deprotect phenol ferf-butyl ethers with trifluoroacetic acid or titanium tetrachloride may give complex mixtures, again as a result of Friedel-Crafts alkylation of the phenol but this side reaction can be suppressed by using a catalytic amount of trifluoromethanesulfonic acid in 2.2,2-trifluoroethanol as solvent at -5 DC. 

Review. This review covers not only trifluoromethanesulfonic acid (triflic acid), but also the anhydride, trimethylsilyl triflate, triflate salts, and alkyl and vinyl triflates (232 references). 

The most important method for the preparation of aryl ketones is known as Friedel-Crafts acylation. The reaction is of wide scope. Reagents other than acyl halides can be used," including carboxylic acids," anhydrides, and ketenes. Oxalyl chloride has been used to give diaryl 1,2-diketones." Carboxylic esters usually give alkylation as the predominant product (see 11-11)." A-Carbamoyl p-lactams reacted with naphthalene in the presence of trifluoromethanesulfonic acid to give the keto-amide." ... 

The trifluoromethanesulfonates have certain advantages over perchlorates (nonexplosive) and tetrafluoroborates (even less reactive toward oxidizing agents) [447]. The tetraalky-lammonium trifluoromethanesulfonates are just as soluble or more soluble in the commonly used organic solvents than the corresponding perchlorates or fluoroborates. They can be prepared either by metathesis or by alkylation of a tertiary amine by an ester of trifluoromethanesulfonic acid. 

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