Acylation of anisole with carboxylic acids catalyzed by tungsten oxide supported on titanium dioxide

Abstract

Friedel-Crafts (F-C) acylation of anisole with octanoic acid was carried out on tungsten oxide (WO3) supported on various types of oxide supports. We have found that the highest activity was obtained when TiO2 was used as the support. WO3/TiO2 was found to be active in the acylation of anisole with carboxylic acids of varying alkyl chain lengths (C6–C10). It was possible to recycle the WO3/TiO2 catalyst for up to 5 times without deactivation. The turnover frequency (TOF) of the catalyst was closely correlated with the electronegativity of the cation of the support used for WO3. When a strong basic oxide such as CeO2 was used as a support, the acid strength of WO3 was diminished, while the strong acidity of WO3 was retained on a weak basic support like TiO2. This explains why the acid strength and consequently, the activity, were found to be the highest for the WO3/TiO2 catalyst. The trend of the catalytic performance was consistent with the order of acid strength of WO3 on different supports measured by temperature-programmed desorption of NH3.