Aromatic acylations catalysed by metal oxides

Abstract

Dimethylbenzophenones are obtained in high yield from reactions between benzoyl chloride and each of the three isomeric xylenes during 10 h at 150 °C in the presence of small amounts of iron(III) oxide, zinc oxide, ammonium molybdile:tin(II) oxide, molybdenum(VI) oxide, or sodium tungstate. Oxides of titanium, aluminium, chromium, manganese, vanadium, thorium, copper, zirconium, tungsten, and ammonium vanadate are ineffective under these conditions. The benzoylation of 1,4-xylene also occurs in the presence of iron, iron(II) sulphate, iron(III) sulphate, and iron(III) chloride. Iron(III) oxide catalyses the benzoylation of anisole, alkylbenzenes, and halogenobenzenes to give the appropriate 4-substituted benzophenones in high yield. 1,3-Xylene undergoes acylation and sulphcnylation with reagents such as chloroacetyl chloride and benzenesulphonyl chloride, respectively, in the presence of ammonium molybdate to give the appropriate acetophenone or aromatic sulphone. The relative rates of the reaction between benzoyl chloride and 1,4-xylene in the presence of most of the catalysts mentioned have been assessed by estimating the amount of hydrogen chloride evolved.