Isomerization of verbenol oxide to a diol with para-menthane structure exhibiting anti-Parkinson activity
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Isomerization of verbenol oxide to (1R, 2R, 6S)-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol, which exhibits anti-Parkinson activity, has been investigated with large and medium pore zeolites, namely H-USY and H-ZSM-5 types of catalysts with different SiO2 to Al2O3 ratio in dimethylacetamide as a solvent. The catalysts were characterized with nitrogen adsorption, 27Al MAS NMR, pyridine desorption, XRD, SEM and TEM techniques. The main reaction product was the target diol with the highest selectivity of 52 % achieved with H-ZSM-5-23 (the last number corresponds to SiO2/Al2O3 ratio) at 49 % conversion of verbenol oxide. The catalyst deactivation was, however, extensive with medium pore zeolites, compared to large pore zeolites. The second highest selectivities to diol with H-USY-80 and H-ZSM-5-80 were about 47–50 mol% at 100 and 78 % of conversion, respectively, achieved at 140 °C within 3 and 5 h. The other main products were the corresponding cyclopentylhydroxyketone and oxetane. A reaction mechanism was proposed.