Prins cyclization of isoprenol and isovaleraldehyde producing 2-isobutyl-4-methyltetrahydro-2H-pyran-4-ol was chosen as a model reaction in iron-modified silica catalysts testing. Two sources of iron were used—iron nitrate and iron chloride. Catalysts were prepared by different procedures and characterized using available methods (XRD, UV/Vis, TPD of pyridine, TGA and XRF). In both types of catalyst, the interaction between the oxygen atoms of silica and the iron atoms of the modifier was confirmed. The iron nitrate-modified catalyst possessed very low acidity enabling only the formation of hemiacetal of isoprenol and isovaleraldehyde or diacetal. The iron chloride modification was performed either by wet impregnation or by impregnation under solvent-free conditions. Both types of such prepared catalysts were active in Prins cyclization, producing the desired substituted tetrahydropyranol. The positive influence of water on the selectivity for the desired compound was confirmed. Siral-type alumosilicates used as support negatively influenced the selectivity. Silica modified by iron chloride may be used as an alternative catalyst in the preparation of substituted tetrahydropyranols; the achieved selectivity was up to 70%.
Research on Chemical Intermediates – Springer Journals
Published: Mar 10, 2017
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