Perfluoroalkanesulfonic Acid Catalyzed Acylations of Alkylbenzenes: Synthesis of Alkylanthraquinones

Franz Effenberger; Frank Buckel; Andreas H. Maier; Judith Schmider

doi:10.1055/s-2000-7102

Synthesis 2000; 2000(10): 1427-1430
DOI: 10.1055/s-2000-7102

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Perfluoroalkanesulfonic Acid Catalyzed Acylations of Alkylbenzenes: Synthesis of Alkylanthraquinones

Franz Effenberger^* , Frank Buckel, Andreas H. Maier, Judith Schmider

^*Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany; Fax + 49(711)6 85 42 69; E-mail: franz.effenberger@po.uni-stuttgart.de

Abstract

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The acylation of alkylbenzenes 1 with benzoyl chloride 2 and catalytic amounts of perfluorobutanesulfonic acid affords the corresponding 2-, 3-, and 4-alkylbenzophenones 3 with unusually high amounts of ortho products. Surprisingly, even tert-butylbenzene reacts under these reaction conditions without any acid catalyzed dealkylation. The yield of benzoylation of p-xylene 4 with benzoic acid in the presence of 5 mol% C₄F₉SO₃H to give 2,5-dimethylbenzophenone 5 could significantly be improved from 14% to 90% by continuous removal of water formed during the acylation. Also in the preparation of alkylanthraquinones 7 by reaction of alkylbenzenes with phthalic anhydride, water removal is the decisive factor to obtain satisfactory yields for the second acylation, allowing to cyclize 6 with catalytic amounts (10 mol%) of CF₃SO₃H in organic solvents to the corresponding alkylanthraquinones 7.

acylation - alkylbenzophenones - alkylanthraquinones - perfluoroalkanesulfonic acid catalysis

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