Gas and liquid-phase FTIR study of the acylation capacity of supported phosphotungstic Wells-Dawson heteropolyacid

S.E. COLLINS, S.R. MATKOVIC, A.L. BONIVARDI, L.E. BRIAND

Washington, EE.UU

Congreso; 238th American Chemical Society National Meeting; 2009

American Chemical Society

Undoubtedly, the catalytic processes based on heteropoly-acids are an outstandingcontribution in the development of environmental benign technologies. Along with thisworldwide trend, our group explores the catalytic activity of phosphotungstic Wells-DawsonHPA in the Friedel-Crafts acylation of p-isobutylbenzene with acetic anhydride toward pisobutylacetophenone,which is an intermediate in ibuprofen synthesis.Infrared spectra collected during the interaction of acetic anhydride with the HPA catalystbetween 20-70 ºC, showed the production of IR bands characteristic of molecularly adsorbedacetic acid and adsorbed acetate species. Blank experiments flowing HAc corroborated thislast interpretation. Additionally, a weaker band was registered at 1650 cm-1, along side withthe production of HAc. This signal could be ascribed to the acetyl [CH3C(O)+] intermediatedbonded to the heteropoly-anion, as was reported previously on HZSM5 (1705 cm-1) andKeggin type HPA (1654 cm-1). In order to corroborate this assignment, an additionalexperiment was performed adsorbing acetyl chloride (CH3COCl).The intermediate-reactive acetyl species partially reacts/desorbs by flowing AA/CCl4 underheating up to 70 ºC. The typical acetyl IR band is also clearly observed during the reactionbetween p-isobutylbenzene/acetic anhydride (10/1) in the temperature range of 20-70 ºC.