Anthraquinone from phthalic acid

The formation of anthraquinone from phthalic anhydride and benzene by the Friedel and Crafts synthesis is conducted in the presence of aluminum chloride.58 Ortho-benzoyl benzoic acid is first formed and then... 

Dichloro-2,2 -dimethyl-1,1 -dianthraquinonyl can be synthesized by Friedel-Crafts reaction from phthalic anhydride and 2,6-dichlorotoluene. Subsequent cyclization of the resulting substituted benzoylbenzoic acid 102 in sulfuric acid affords the corresponding anthraquinone derivative 103, which is dimerized by Ullmann reaction ... 

Since, as the equation shows, this substance is converted by-concentrated sulphuric acid with loss of water into anthraquinone, a very important route to a much-studied group is opened up. Thus /S-methylanthraquinone, which serves as an intermediate for valuable vat dyes, is prepared technically in this way from phthalic anhydride and toluene. 

Exercise 22-19 Anthraquinone can be synthesized from phthalic anhydride and benzene in two steps. The first step is catalyzed by AICI3, the second by fuming sulfuric acid. Write mechanisms for both reactions and suggest why fuming sulfuric is required in the second step but not in the first. 

Methyl anthraquinone has been obtained by the oxidation of /3-methyl anthracene by several investigators 1 and material of the same origin, obtained by the benzene-extraction of crude commercial anthraquinone,2 has been fully described. As regards the synthesis from phthalic anhydride and toluene, both the preparation and properties of />-toluyl-o-benzoic acid 3 and the complete synthesis 4 have been the subject of several papers. This acid has also been prepared from o-carbomethoxy benzoyl chloride and toluene.5 The phthalic anhydride synthesis of anthraquinone derivatives in general has received considerable attention. An account of this work, together with extensive references, is given by Barnett.6... 

The oriAo-benzoyl-benzoic acids readily yield anthraquinone and its derivatives (see p. 82). It may be noted that o-benzoyl-benzoic acid itself, with benzene and aluminium chloride, yields phthalophenone the same compound is made directly from phthalic anhydride by increasing the amount of the latter or by adding acetic anhydride. The same holds for p-toluoylbenzoic acid and ditoluoylphthalide. (Am. Soc., 43, 1965 J. C. S., 122, 539.) (For the use of carbomethoxylbenzoyl chlorides and of homophthalic anhydrides in these reactions, see Am. Soc., 43, 1950.)... 

The condensation of toluene with phthalic anhydride takes place in the presence f aluminum chloride even at room temperature and is complete after about 12 to 15 hours of stirring. The ring closure can be effected with 5 per cent oleum (10 parts for 1 part of toluylbenzoic acid) by heating on a water bath for 2 hours. Usually, however, the preparation is done exactly as described for the preparation of anthra-quinone from phthalic anhydride and benzene. The yield of 2-methyl-anthraquinone, melting at 170-174°C., is about 85 to 88 per cent of the theoretical amount calculated on the phthalic anhydride. 

The development of a normal-phase HPLC method was warranted due to the presence of phthalic anhydride, which is unstable in water. Analysis in organo-aqueous solvent systems that are used in RPLC would lead to an on-column reaction forming the respective carboxylic acid degradation product. Figure 5-5 shows the chromatogram obtained for the separation of 9,10-anthraquinone from the reactants and impurities on a silica column. The method was successfully applied to monitor the reaction conversion and also to determine the stability of 9,10-anthraquinone at the specified storage conditions. 

Figure 5-5. Typical chromatogram of a reaction mixture collected during the course of reaction of phthalic anhydride with benzene in the presence of AICI3, as catalyst. Peaks 1, benzene 2, anthraquinone 3, phthalic anhydride 4, maleic anhydride 5, unknown. Chromatographic conditions Column Spherisob silica, 250 x 4.6mm, 10pm mobile phase, -heptane-ethanol-chloroform-acetic acid (89 5 5 1, v/v/v/v) flow rate, 1 mL/ min detection, UV at 254 nm temperature, 27°C. (Reprinted from reference 29, with permission.)...

In the preceding reactions the benzene nucleii have been numbered I and II in order to follow their course through the various transformations. It may be readily seen, therefore, that the benzene nucleus in brom anthraquinone which remains as a benzene ring in t r//f )-phthalic acid is the nucleus which does not contain bromine. This was derived from the benzene constituent of the s)mthesis and, in anthraquinone, it is linked to the carbonyl groups by ortho positions. Therefore, both benzene nucleii in anthraquinone are linked by ortho positions and both are derived from true benzene ring compounds or may remain as benzene rings on the decomposition of the quinone. 

The remarkable thing is, that while there are ten possible di-brom or di-hydroxy anthraquinones, the particular one necessary was obtained by Graebe and Liebermann. The positions of the two hydroxyl groups were determined by Baeyer and Caro. When alizarin is heated pyro-catechinol, i-2-di-hydroxy benzene, is obtained. Also when pyro-catechinol is heated with ortho- hXhaXic acid and sulphuric acid alizarin results. This last synthesis is analogous to that of anthraquinone from benzene and o //io-phthalic acid (p. 796). 

Alizarin blue was prepared from nitroalizarin, glycerol, and sulphuric acid by M. Prud homme, anthragallol (anthracene brown, i a 3-trihydroxy-anthraquinone) from pyrogallol and phthalic anhydride by C. Seuberlich, di- (or tetra-) azo dyes by Caro and Schraube, rhodamine from ammonium thiocyanate and chloracetic acid by M. Nencki, rocelline or echtrot (naphthalene sulphonic azonaphthol) by Roussin (1877) and Caro and Griess, and methylene blue by Caro (1877). ... 

Anthraquinone itself is traditionally available from the anthracene of coal tar by oxidation, often with chromic acid or nitric acid a more modern alternative method is that of air oxidation using vanadium(V) oxide as catalyst. Anthraquinone is also produced in the reaction of benzene with benzene-1,2-dicarboxylic anhydride (6.4 phthalic anhydride) using a Lewis acid catalyst, typically aluminium chloride. This Friedel-Crafts acylation gives o-benzoylbenzoic acid (6.5) which undergoes cyclodehydration when heated in concentrated sulphuric acid (Scheme 6.2). Phthalic anhydride is readily available from naphthalene or from 1,2-dimethylbenzene (o-xylene) by catalytic air oxidation. 

The aroylation of an aromatic system by reaction with phthalic anhydride under Friedel-Crafts conditions is described in Section 6.11.1, p. 1006. The cyclisation of the derived o-aroylbenzoic acid with polyphosphoric acid is a convenient route to substituted anthraquinones. The reaction is illustrated by the formation of 2-methylanthraquinone from o-(p-toluoyl)benzoic acid (Expt 6.132). 

The common carrier gases are air or nitrogen or steam. Condensate from a carrier usually is finely divided, snowlike in character, which is sometimes undesirable. Substances which are subhmed in the presence of a carrier gas include anthracene, anthraquinone, benzoic acid, phthalic anhydride, and the formerly mentioned sah-cylic acid. 

The hydrogen atom in the ortho position to the carbonyl group unites with the hydroxyl group of the carboxyl to effect the ring closure. The preparation of o-benzoylbenzoic acid from benzene and phthalic anhydride (Experiment 63) and the dehydration of this keto acid to anthraquinone considered in the present experiment illustrate the building up of polynuclear compounds from simpler benzene derivatives. 

The o-benzoyl benzoic acid is prepared by mixing phthalic anhydride with an excess of benzene and adding to an amount of aluminum chloride equimolar to the anhydride used. This mixture is maintained at a temperature of 35° C. in a lead lined kettle, jacketed for steam heating, for about half an hour. The temperature is then slowly raised to the boiling point of benzene and maintained until hydrochloric arid is no longer evolved. Benzene is removed by distillation with steam, the o-benzoyl benzoic arid dried and converted to anthraquinone by treatment with 95 to 98 per cent sulfuric acid at a temperature of from 110° to 150° C. for three-quarters to one hour. The anthraquinone thus fomied is recovered from the concentrated sulfuric acid by careful dilution of the acid with water or treatment with steam to obtain large crystals to facilitate filtration, removal of acid, and washing. 

When mixtures of anthracene and phenanthrene, such as are obtained by removing carbazole from anthracene press cake by caustic fusion, arc oxidized, mixtures of phthalic anhydride and anthraquinone result. A separation of these valuable products is effected by washing out the acids with an alkali solution and recovering as sodium salts or as acids by addification subsequent to removal of anthraquinone by filtration. The products may be distilled or sublimed to separate from any unoxidized material that may be present. Maleic acid may also be present in the products to a small extent and is recovered with the phthalic anhydride from which it must be removed as an impurity.88... 

Chromic acid in hot glacial acetic acid oxidizes anthracene quantitatively to antlmaquinone in a very smooth reaction, but the method is too expensive for coxnmercial application in competition with synthetic anthraquinone made from cheap phthalic anhydride and benzene by means of the Friedel-Crafts reaction Prior to the development of the present methods of phthalic anhydride manufacture, the process was used extensively for anthraquinone production in Europe. The method has been recommended for anthracene analysis. 

Alizarin is reduced to anthracene when heated with zinc-dust—a transformation which was the first step taken in determining the structure of the dye contained in madder-root. The view that alizarin is a dihydroxyl derivative of anthraquinone, follows from the fact that it is formed as the result of the fusion of anthraquinone-sulphonic acid with caustic alkalies, and from the synthesis of the dye by heating phthalic anhydride and pyro-catechol with sulphuric acid at 150° —... 

Liebermann discovered the reaction between nitrous acid and phenols and secondary amines named after him. He prepared amino-naphthols from nitro-naphthols, synthesised the dihydroxyanthraquinones anthrarufin and chrysazin, and studied the reduction of anthraquinone. Another dihydroxy-anthraquinone, quinizarin, was discovered by F. Grimm by heating hydro-quinone with phthalic anhydride. 

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