In general, the common methods of synthesis of ketones can be divided into (1) synthesis from acid halides and organometallic compounds, (2) synthesis from carboxylic acids, (3) Friedel-Crafts reactions, and (4) enolate condensations.
Synthesis from acid halides and organometallic compounds has been extensively used but costs of the organometallic reagents are relatively expensive and care must be used in handling. The use of carboxylic acids and their salts for ketone synthesis suffers from the disadvantage that the method will produce in general only the symmetrical ketones in good yields. The Friedel-Crafts acylation reactions generally give good yields. However, their use is restricted by the orientation of the acyl group introduced and the metal halides are expensive with attendant waste disposal problems. Enolate condensations give a variety of products; however, the overall yields are frequently not so good as those that can be obtained by other methods, and procedures frequently are more involved.
For example, as is well-known, the important methods of formation of benzophenone, i.e., benzophenone and its substituted derivatives, are the following: (1) oxidation of diphenylmethanes or benzohydrols, e.g., by chromic acid or by oxygen in presence of a catalyst, for example, as is taught in U.S. Pat. No. 2,859,274; (2) hydrolysis of ketone chlorides; (3) condensation of benzoyl halides with benzene, its homologues, and substituted derivatives having a reactive position, in presence of AlCl.sub.3 or other catalyst, or under high pressure, as taught in U.S. Pat. No. 2,528,789; (4) reaction of a benzonitrile (or benzoyl halide) with a phenylmagnesium halide; (5) distillation of calcium or other suitable benzoate (Ann 12, 41).
Preparation of anthraquinone specifically has been proposed by several different processes: (1) the DielsAlder reaction of butadiene on 1,4-naphthoquinone, (2) oxidation of anthracene in the presence of catalysts, (3) Friedel-Crafts reaction with benzene and phthalic anhydride, (4) oxidation of suitable precursors such as indane. In the Friedel-Crafts process, since a large amount of aluminum chloride is necessary, disposal of the wastes from the process is difficult. Furthermore, since isomerization reactions, rearrangement reactions, and elimination reactions occur in the process, many by-products derived from these reactions contaminate the product. Oxidation of anthracene is economically accomplished only when relatively pure anthracene is available at moderate costs. The Diels-Alder reaction suffers from the high cost of naphthoquinone. U.S. Pat. Nos. 3,699,134; 3,872,134; 3,872,135; 4,002,653; 4,036,860; 4,036,861; and 4,215,063 teach typical processes for manufacture of anthraquinone by oxidation of diphenylmethane compounds. These processes produce many by-products.
Preparation of fluorenones has been proposed by several different processes also: (1) the heating of salts of diphenyl-o-carboxylic acid or its salts produces fluorenone, (2) the diazonium compound of o-amino-benzophenone gives fluorenone with evolution of nitrogen, (3) the oxidation of phenanthraquinone. Fluorenone-carboxylic acids can be obtained by oxidation of fluoranthene with chromic acid, or by heating isodiphenic acid with concentrated sulfuric acid, or from 2'-aminobenzophenone-2-carboxylic acid by the action of nitrous acid. Fluorenone-1,7-dicarboxylic acid can be obtained by the action of permanganate on retene-quinone. Retene is defined as 1-methyl-7-isopropyl-phenanthrene. These processes produce many by-products.
As a result of these difficulties, considerable investigations have been carried out in efforts to develop syntheses of anthraquinones and fluorenones whereby the desired products in good yield are obtained by simple economic methods. This invention relates to a method for preparation of anthraquinones and fluorenones in good yield. The process can be by batch or by continuous method.