Fluoroantimonic acid

Fluondes of boron, phosphorus, and antimony react with hydrogen fluoride, producing complex fluoroboric, fluorophosphoric, and fluoroantimonic acid,... 

KGS632). In general this approach has only produced moderate yields, and the requirement for the use of 97% sulfuric acid renders workup difficult. Fluoroantimonic acid seems to be an improvement. Yields of up to 57% of 6-bromo products have been reported free of the traces of the 5-isomers still formed in 97% sulfuric acid (83JHC349). 

Fluoroantimonic acid, 3 65 Fluoroaromatics, preparation of, 77 862 Fluorobenzene, 3 602 Fluoroborates, 4 149-159 properties of metal, 4 152t... 

In discussing superacids as catalysts for chemical reactions, we will review both liquid (Magic Acid, fluoroantimonic acid, etc.) and solid (Nafion-H, etc.) acid-catalyzed reactions, but not those of conventional Friedel-Crafts-type catalysts. The latter reactions have been extensively reviewed elsewhere (see G. A. Olah, Friedel-Crafts Chemistry, Wiley, New York, 1972 G. A. Olah, ed., Friedel-Crafts and Related Reactions, Vols. I-IV, Wiley-Interscience, New York, 1963-1965). 

This stable alkoxycarbenium salt can be prepared in about 90 % yield by the reaction of either methoxyacetyl chloride or chloromethyl methyl ether with anhydrous hexa-fluoroantimonic acid in sulfur dioxide or dichloromethane ... 

Trityl hexafluoroantimonate, (CeHsljC SbF ", and trityl hexafluorophosphate, (C5ll5)3C Pf4", can be prepared in the same way using anhydrous fluoroantimonic acid and the ether complex of hexalluorophosphoric acid, respectively. 

The electrophilic formylation of arenes with CO in the presence of acids (Gatterman-Koch conditions) is an efficient method for preparing aromatic aldehydes. HF-SbFs-SO2CIF is the most active system for this reaction [82]. It has been demonstrated that even diformylation can be achieved on polymeric aromatics such as biphenyl with the use of fluoroantimonic acid (Eq. 36) [83]. 

Trimethylcarbenium fluoroantimonate, (Cf )jCSbFj. This relatively stable salt can be prepared as light-colored crystals by the reaction at -70° of (CH3)3CC1 with fluoroantimonic acid (HF SbFs) or with antimony penta-fluoride in sulfuryl chloride fluoride, CISO2F. It is stable at 20°, but decomposes at room temperature. 

Fluoroanthracene, 670 Fluoroantimonic acid, 24 Tr-(Fluorobenzene) chiomium tiicarbonyl,... 

CYCLIZATION n-Butyllithium. Diisobutylaluminum hydride. Fluoroantimonic acid. Phosphoric acid-Boron trifluoride complex. ThaDium(IlI) perchlorate. Trifluoroacetic acid. 

Hydrogen Fluoride-Antimony Pentafluoride (Fluoroantimonic Acid)... 

Superacids such as Magic Acid and fluoroantimonic acid have made it possible to prepare stable, long-lived carbocations, which are too reactive to exist as stable species in more basic solvents. Stable superacidic solutions of a large variety of carbocations, including trivalent cations (also called carbenium ions) such as t-butyl cation 1 (trimethyl-carbenium ion) and isopropyl cation 2 (dimethylcarbe-nium ion), have been obtained. Some of the carbocations, as well as related acyl cations and acidic carboxonium ions and other heteroatom stabilized carbocations, that have been prepared in superacidic solutions or even isolated from them as stable salts are shown in Fig. 1. 

Far stronger than magic acid is fluoroantimonic acid, which is a mixture of HF and SbF5 in various ratios. The 1 1 mixture is the strongest superacid known, some 2 x 10 (20 quin-tillion) times stronger than 100% sulfuric acid. Its molecular structure maybe represented as follows ... 

The F-H bond in HSbFg is clearly exceedingly weak, and the proton as a result is as close to naked as is possible in the liquid phase. As might be expected, fluoroantimonic acid is exceedingly corrosive and moisture-sensitive it can, however, be kept in Teflon containers. Compatible solvents include SO2CIF, SO2, and chlorofluorocarbons. 

Observe that this reaction employs fluoroantimonic acid, one of the most potent superacids. The perchlorate anion is thus readily protonated, even though perchloric acid is one of the strongest common acids. 

The highest acidity level measured according to the Ho acidity scale is around -27 for 90% SbFs in HSO3F. However, based on rate measurements in superacidic reactions the fluoroantimonic acid system is predicted to be even stronger [Fig 2.3], Similar to BF3 in HF, SbFs also ionises in dilute solutions to produce the H2F cation. The lower Hammett acidity of the HF/BF3 system compared to SbFs and TaFs, can be attributed to the lower concentration of the H2F " cation produced in the HF/BF3 system. The HF/BF3... 

---