Friedel-Crafts catalysts, hydrogen sulfuric acid

The alkylation of paraSins with olefins to yield higher molecular weight branched-chain paraffins may be carried out thermally or catalyt-ically. The catalysts for the reaction fall into two principal classes, both of which may be referred to as acid-acting catalysts (1) anhydrous halides of the Friedel-Crafts type and (2) acids. Representatives of the first type are aluminum chloride, aluminum bromide, zirconium chloride, and boron fluoride gaseous hydrogen halides serve as promoters for these catalysts. The chief acid catalysts are concentrated sulfuric acid and liquid hydrogen fluoride. Catalytic alkylations are carried out under sufficient pressure to keep at least part of the reactants in the liquid phase. 

Since the Friedel-Crafts catalysts are usually thought of as halides of a few metals, a natural question to raise might be If these halides are really acids differing in no fundamental manner from H-acids in their behavior, why do not H-acids catalyze reactions of the Friedel-Crafts type also The answer is that they do. Hydrogen fluoride,phosphoric acid, and sulfuric acid have... 

Bronsted Acids. Sulfuric acid (H2SO4) is an inexpensive, easy to handle protic acid used widely as catalyst in hydrolysis, hydration and dehydration, elimination, substitution, and rearrangements. It also catalyzes aromatic electrophilic substitutions mostly Friedel-Crafts acylations and alkylations (22). A very important application of sulfuric acid is its use in commercial isoalkane-alkene alkylation technologies. These commercial processes are still based on the use of sulfuric acid (and hydrogen fluoride) catalysts (23). 

Alkylation of Aromatics. Aromatic hydrocarbons containing a replaceable hydrogen can be alkylated unless steric effects prevent introduction of the alkyl group (61,78-82). The reaction is called the Friedel-Crafts alkylation, first realized in the presence of aluminum chloride, which is the catalyst still the most frequently used and studied in Friedel-Crafts reactions. In addition, many other acid catalysts are effective (80,82-84). These include other Lewis acids (other aluminum halides, gallium chloride, boron trifluoride, ferric chloride, zinc chloride, stannous and stannic chloride, antimony chloride) and protic acids (hydrogen fluoride, concentrated sulfuric acid, phosphoric acid, polyphosphoric acid, trifluo-romethanesulfonic acid, and alkane- and arenesulfonic acids). 

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