Zr-containing UiO-66 metal-organic frameworks as efficient heterogeneous catalysts for glycerol valorization: synthesis of hyacinth and other glyceryl acetal fragrances

Zr-containing UiO-66 and UiO-66-NH are good heterogeneous catalysts for the acetalization of phenylacetaldehyde with glycerol, producing the corresponding hyacinth fragrance in high yields after short (2 h) reaction times. Mixtures of 1,3-dioxolanes and 1,3-dioxanes are obtained, whose ratios can be modified between 2.8 and 4.6 depending on the catalyst used, the amount of missing linker defects of the solid, and the reaction time. The catalysts are stable under the reaction conditions used, and they can be reused without loss of activity or selectivity. The scope of UiO-66 materials is demonstrated for the formation of other glyceryl acetals of interest for the flavoring industry, which represents an interesting route for glycerol valorization.