There are only a few products manufactured in any considerable tonnage by condensation and addition (Friedel-Crafts) reactions, but those that are find use in several different intermediates and particularly in making high- quality vat dyes. The agent employed in this reaction is usually an acid chloride or anhy- dride, catalyzed with aluminum chloride. Phthalic anhydride reacts with chlorobenzene to give p-chlorobenzoylbenzoic acid and, in a continuing action, the p-chlorobenzoylbenzoic acid forms β-chloroanthraquinone. Since anthraquinone is a relatively rare and expensive component of coal tar and petroleum, this type of reaction has been the basis for making relatively inexpensive anthraquinone derivatives for use in making many fast dyes for cotton. Friedel-Crafts reactions are highly corrosive, and the aluminum-con- taining residues are difficult to dispose.
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