O-Benzoyl benzoic acid

Unsyimnetiical rhodainines can be piepaied by the condensations of one mole of a yW-aminophenol with phthahc anhydride to give an o-benzoyl benzoic acid (27) which is then further condensed with a different yW-aminophenol to give the requited product, Rhodamine 3GO (28) (2). A general route to asymmetrical acid xanthenes has been patented (39). 

Olah et al. (1999) have been able to realize selective cyclisation of o-benzoyl benzoic acid to anthraquinone using dichlorobenzene as a solvent and Nafion-H as a catalyst. This may lead to avoidance of the Friedel-Crafts reaction using a stoichiometric amount of aluminium chloride and resulting in a lot of wa,ste. Many other examples of similar reactions have been reported. 

Friedel-Crafts). (A., 291, 9 C. r., 119, 139.)—When the dichloride of phthalic anhydride reacts with the hydrocarbon, benzene, in presence of anhydrous aluminium chloride, phthalophenone (diphenylphthalide) is formed (see p. 107). With phthalic anhydride itself the reaction can be made to take the same or a different course. Using an excess of hydrocarbon, condensation and hydrolysis occur, and o-benzoyl-benzoic acid or its homologues are obtained according to the reacting hydrocarbon. Not only can the latter be varied, but derivatives of phthalic anhydride may be used, so that a great number of compounds can be synthesised in this way. 

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.)... 

Sometimes direct combination of two molecules results without any elimination taking- place, as for example, in the union of plithalic anhydride and benzene to form o-benzoyl benzoic acid 5... 

Problem 20.6 When heated with acid (e.g., concentrated H2SO4), o-benzoyl-benzoic acid yields a product of formula C14H8O2. What is the structure of this product What general type of reaction has taken place ... 

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. 

The anthraquinone so obtained is purified by sublimation. Although various modifications of this process ltave been introduced, the basic principles remain the same.1"1 The yield of o-benzoyl benzoic acid is about 95 per cent of theory or 145 per cent of the weight of phthalic anhydride used. The overall yield of sublimed anthraquinone on the phthalic anhydride used is more titan 120 per cent by weight, or 85 per cent of theory. 

Phthalic anhydride and benzene reacts in the presence of finely powdered anhydrous aluminium chloride, acting as a catalyst, to cleave the anhydride and produces o-benzoyl-benzoic acid. The above reaction usually takes place in an absolute anhydrous conditions only. 

An alternate method of synthesizing this compound was reported in 1901 by the reaction of o-benzoyl benzoic acid chloride under similar conditions. ... 

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