Catalysis of Organic..

350Heteropoly AcidsTable 3. Acylation of thioanisole with iso-butyric anhydride. Conditions: 90 o C,10wt% catalyst loading.Catalyst a Conv. 2/ %Ketone 3/ %Acid 4/ %Side prods/ %29%STA/SiO 2 100 69.8 26.8 3.325%STA/SiO 2 -Al 2 O 3 -1 92.0 65.0 25.2 6.338%STA/SiO 2 -Al 2 O 3 -2 20.0 trace 98.4 1.629%STA/Al 2 O 3 17.0 18.7 80.4 0.9a analysis of the catalyst supports is given in Table 6.Influence of Reaction TemperatureThe variation in activity and selectivity of 42%STA/SiO 2 at different reactiontemperatures (23°C, 60°C, 90°C, 127°C) is shown in Table 4.Table 4. Variation in product selectivity with reaction temperature in the acylation ofthioanisole with iso-butyric anhydride. Catalyst: 42%STA/silica, 10wt% catalystloading.Temperature Conv. 2 Product selectivity /%/ o C / % p-Ketone 3 o-Ketone Vinyl ester Side prods23 96.0 89.2 1.9 8.9 060 100 97.6 1.4 0.3 0.790 99.0 97.1 1.4 1.5 0127 76.0 95.7 1.3 3.0 0At room temperature (23 o C) incomplete conversion of the anhydride is observed(96%) and the slower reaction leads to reduced selectivity to the desired p-ketone 3.Highest conversions and selectivities are obtained when the reaction is performed inthe range of 60 o C to 90 o C.Catalyst ReuseThe possibility for reuse of the catalyst was investigated by filtration of thecatalyst from the reaction mixture, washing twice with toluene and drying undervacuum. The dry catalyst was then reused for the acylation reaction with freshreactants. Activity of the catalyst in the second cycle (first reuse) was 90% of theoriginal activity. The catalyst displayed very poor activity upon a third cycle (5% oforiginal activity). XRF analysis of the used, washed catalysts confirmed that nosignificant leaching of STA from the catalyst had occurred upon use. Deactivation isbelieved to result from strong adsorption of products onto the catalyst. This is