Friedel-Crafts acylation reactions using heterogeneous catalysts stimulated by conventional and microwave heating

The acylation of anisole with decanoic acid over a range of solid-acid catalysts has been studied under conventional heating and microwave stimulation. The microwave-irradiated experiments exhibited increased reaction rates, the extent of which was dependent upon the nature of the catalyst. The origin of this microwave enhancement has been attributed to the selective desorption of water from the surface of the catalyst.Pyridine adsorption has been used to quantify the number of acid sites present on the catalyst. The nature of the acid sites in terms of their Brønsted/Lewis acidity has been determined using infrared analysis of the adsorbed pyridine. The strength of the acid sites has been characterised by differential thermal analysis (DTA) of the pyridine desorption. This indicated that the sulphated zirconia and supported heteropoly acids contained significantly more strong acid sites than the cerium exchanged zeolite.

The use of microwave radiation for the stimulation of the acylation of anisole using decanoic acid results in enhancement of the catalytic activity of a range of solid-acid catalysts. This enhancement of activity cannot easily be explained in terms of selective heating of the catalyst, instead a mechanism whereby the microwaves assist desorption of water from the acid sites is proposed.Figure optionsDownload as PowerPoint slide