Base modified organic mesoporous silicas, their characterization and application in the aldol reaction of n-butanal.

• Synthesis of grafted and co-condensated ordered mesoporous materials. • Quantification of the amount of active base sites by liquid phase NMR. • Variation of the properties of the basic centre by changing the substitution on the nitrogen atom. • Determination of the turn-over number in the aldol condensation of butyraldehyde. • Proposed reaction mechanism for heterogeneously catalysed aldol condensation. Representative ordered mesoporous silica materials MCM-41 and SBA-15 were synthesized and modified with nitrogen-containing groups by grafting and co-condensation. The created catalytic centers strongly differ in basicity depending on the degree of substitution of the nitrogen atom. Furthermore, the introduced amount also depends on the structure of the modifier as shown by quantitative liquid phase 1H NMR. This allowed to calculate the turnover number in the aldol condensation of n -butanal which changed in the sequence: secondary > primary >> tertiary >> pyridinic basic centers. Corresponding reaction mechanisms considering the special structural features of the modifier are proposed. ig. [Display omitted] [ABSTRACT FROM AUTHOR]