Catalytic isomerization of α-pinene oxide in the presence of acid-modified clays

Isomerization of α-pinene oxide was studied at 20–50 °C in the presence of commercial montmorillonites K-10 and K-30, acid-treated illite clay as well as synthetic aluminosilicate AS-36 using cyclohexane as a solvent. The catalysts were characterized by XRD, XRF, FTIR, MAS NMR, thermal analysis and N2 low-temperature sorption methods The main reaction products at 99.9% conversion of the substrate are campholenic and iso-campholenic aldehydes, the largest amount of which (68.1 wt.%) is formed on illite clay treated by 10% HCl. The iso-campholenic/campholenic aldehydes ratio decreases from 0.7 to 0.25 with an increase of acidity of the catalyst from 47 to 153 μmol/g. The content of products with p-menthane structure (trans-carveol, trans-sorberol, p-cymene, pinol) reaches a maximum (33.0 wt.%) in the presence of medium-acid (104.0 μmol/g) K-10 clay. The amount of campholenic aldehyde in reaction mixture increases from 34.3 to 48.2 wt.%, and content of iso-campholenic aldehyde decreases from 33.7 to 17.7 wt.% with increasing the drying (calcination) temperature of illite clay from 50 to 600 °C respectively. The scheme for the formation of reaction products on clays was proposed.