Fluorosulfuric acid catalyst

Fluorosulfuric acid [7789-21-17, HSO F, is a colodess-to-light yellow liquid that fumes strongly in moist air and has a sharp odor. It may be regarded as a mixed anhydride of sulfuric and hydrofluoric acids. Fluorosulfuric acid was first identified and characterized in 1892 (1). It is a strong acid and is employed as a catalyst and chemical reagent in a number of chemical processes, such as alkylation (qv), acylation, polymerization, sulfonation, isomerization, and production of organic fluorosulfates (see Friedel-CRAFTSreactions). 

Uses. Fluorosulfuric acid serves as catalyst in the alkylation (qv) of branched-chain paraffins (53—58) and aromatic compounds (59), and in the polymeriza tion of monoolefins (60) and rosin (61). Addition of strong Lewis acids, such as SbF, TaF, and NbF, to fluorosulfuric acid markedly increases... 

Hull and Conant in 1927 showed that weak organic bases (ketones and aldehydes) will form salts with perchloric acid in nonaqueous solvents. This results from the ability of perchlonc aad in nonaqueous systems to protonate these weak bases. These early investigators called such a system a superacid. Some authorities believe that any protic acid that is stronger than sulfunc aad (100%) should be typed as a superaad. Based upon this criterion, fluorosulfuric arid and trifluoro-methanesulfonic acid, among others, are so classified. Acidic oxides (silica and silica-aluminai have been used as solid acid catalysts for many years. Within the last few years, solid acid systems of considerably greater strength have been developed and can he classified as solid superacids. 

The most commonly used catalyst for the commercial polymerization of tetrahydrofuran is fluorosulfuric acid as shown in Eq. (2.60) (Dreyfuss et al., 1989). 

Fluorosulfuric acid is employed as a catalyst and chemical reagent in various chemical processes including... 

It was reported that when oxetane polymerizations are carried out with boron trifluoride catalyst in methylene chloride at temperatures between 0 °C to -27.8 °C, a cocatalyst is not required. The product, however, is a mixture of a linear polymer and a small amount of a cyclic tetramer. This is in agreement with an earlier observation that the polymerizations of oxetane are complicated by formations of small amounts of cyclic tetramers. Other catalysts, protonic acids, capable of generating oxonium ions, will polymerize oxetane. These acids are sulfuric, trifluoracetic, and fluorosulfuric. The initiation reaction can be illustrated as follows ... 

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