Acid–Base Bifunctional Catalysts for the Preparation of Fine Chemicals: Synthesis of Jasminaldehyde

Jasminaldehyde was prepared by condensation between benzaldehyde and heptanal. Large-pore acid zeolites (HY and Beta), mesoporous aluminosilicate (Al MCM-41), and amorphous aluminophospates (ALPO) were used as catalysts. The results indicated that zeolites showed lower activity and selectivity than mesoporous aluminosilicate (Al MCM-41). These results were attributed to the confinement effects of the reactants and products inside of the voids of the microporous materials, which lead to the preferential formation of the heptanal self-condensation product, as well as to a fast deactivation of the catalyst. However, the amorphous aluminophosphate (ALPO) which possesses weaker acid sites than zeolites and MCM-41, but combines acidic and basic sites, showed the maximum activity and selectivity to jasminaldehyde. This finding was explained on the basis of the acid–base bifunctional character of the ALPO catalyst. The role of the weak acid sites is to activate benzaldehyde by protonation of the carbonyl group, favoring then the attack of the enolate heptanal intermediate generated on the relatively weak basic sites of ALPO.