After the initial discovery by Friedel and his American associate, James Mason Crafts, that anhydrous aluminum chloride could be used as a condensing agent in a general synthetic method for furnishing an infinite number of hydrocarbons. They extended their discoveries of the catalytic effect of aluminum chloride in a variety of organic reactions: (1) reactions of alkyl and acyl halides and unsaturated compounds with aromatic and aliphatic hydrocarbons; (2) reactions of acid anhydrides with aromatic hydrocarbons; (3) reactions of oxygen, sulfur, sulfur dioxide, carbon dioxide, and phosgene with aromatic hydrocarbons; (4) cracking of aliphatic and aromatic hydrocarbons; and (5) polymerization of unsaturated hydrocarbons. The diversity of reactions is astounding. Many important industrial processes such as the production of high octane gasoline, ethylbenzene (eventually leading to polystyrene), synthetic rubber, plastics, and detergent alkylates are based on Friedel-Crafts chemistry. Friedel-Crafts-type reactions are generally considered to be any substitution, isomerization, elimination, cracking, polymerization, or addition reaction that takes place under the catalytic effect of Lewis acid-type acidic halides (with or without cocatalysts) or Brønsted acids. Friedel-Crafts reactions can be divided into two general categories: alkylations and acylations. within these two broad areas there is considerable diversity. Friedel-Crafts catalysts are electron acceptors, ie, Lewis acids. Catalysts include acid halides (Lewis acids), metal alkyls and alkoxides, protic acids (Brønsted Acids), acidic oxides and sulfides (acidic chalcogenides), acidic cation-exchange resins, and superacids (Brønsted superacids, super Lewis acids, Brønsted-Lewis superacids, solid superacids, and superacidic zeolites).
G. A. Olah et al., "Friedel-crafts Reactions," Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Dec 2000.
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