A bvamowitz and Larvtchen 2165
Phthalanthranilic Acid, its Structure and Reaction in Friedel-Crafts SynthesesBy (MRs.) E. ABRAMOWITZ and M. LAMCHENThe generally accepted structure (I ; R = C0,H) for phthalaiithraiiilic acid has been shown to be incorrect. Similarly, it has been shown that its chloro-compound, formed on treatment with phosphorus pentachloride, is not an acid chloride as is generally believed and as reactions seemed to indicate. Both from chemical evidence and from X-ray crystallographic studies new structures (XVI) and (XVII) are suggested for phthalanthranilic acid and its chloro-compound, respectively. The structures of the products formed on reaction of the chloro-compound with various substituted benzenes in Friedel-Crafts syntheses, as determined by chemical and X-ray studies, are given and mechanisms to explain the reactions are suggested.GABRIEL considered the fusion product of anthranilic acid and phthalic anhydride to be o-phthalimidobenzoic acid (I ; R = C0,H) ; it is commonly called phthalanthranilic acid.This suggested structure can be justified by analogy with the formation of phthalanil (I; R = H), which is produced by heat on a mixture of aniline and phthalic anhydride.Gabriel has also shown that phosphorus pentachloride replaces an hydroxyl group in phthalanthranilic acid by a chlorine atom, and he assigned the acid-chloride structure (I; R = COCl) to this chloro-compound, since it reacts with the sodium derivative of diethylmalonate to produce the diester [I; R = CO*CH(CO,Et),], which on hydrolysis with boiling hydriodic acid gives phthalic acid and o-aminoacetophenone. These reactions are all in agreement with the structure (I; R = C02H) for phthalanthranilic acid, and the correctness of this structure has never, to our knowledge, been questioned. Since certain N-toluene-$-sulphonylamiiiobenzophenones were extremely difficult to hydrolyse without side-reactions, Engels, Lamchen, and Wicken prepared o-aminobenzophenones from phthalanthranilic acid. The acid was converted into the chloro-compound with phosphorus pentachloride or tliionyl chloride (as was done by Gabriel) and used in typical Friedel-Crafts reactions with benzene, and a variety of substituted benzenes, to produce compounds which, after analysis, were considered to be Z-phthalimidobenzophenones (11). The yields and conditions required for condensation varied according to the substituents on the benzene nucleus : (a) when strongly electron-repelling substituents 1
