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Isomerization of 3-carene over MgO and CaO

1977; Elsevier BV; Volume: 48; Issue: 1-3 Linguagem: Inglês

10.1016/0021-9517(77)90103-8

1090-2694

Keiko Shimazu,

Asymmetric Hydrogenation and Catalysis

The isomerization of 3-carene was studied over MgO, and CaO. The main product was 2-carene which resulted from a double bond migration within a six-membered ring. The catalytic activity and selectivity varied with starting materials and pretreatment temperature of the catalysts. Two kinds of magnesium oxides were prepared. From magnesium hydroxide, MgO(I) was prepared and MgO(II) from magnesium carbonate hydroxide. Both MgO(I) and MgO(II) became active when pretreated at 400 °C, and attained their maximum activities when pretreated at 900 and 500 °C, respectively. Active sites on both kinds of MgO were strongly poisoned by carbon dioxide and butylamine but were only slightly poisoned by triethylamine. The activities of CaO(I), which was prepared from calcium hydroxide, and CaO(II), prepared from calcium carbonate, appeared when pretreated at 300 and 600 °C, respectively, and reached their maximum activities when pretreated at 600 and 1000 °C, respectively. Over MgO(I) and MgO(II) pretreated at 500 °C, 3-carene and 2-carene exchanged their allylic hydrogen atoms in the six-membered ring more easily than the allylic hydrogen atoms in the methyl group. Dehydrogenation of 3-carene to m- and p-cymenes occurred over CaO(II) pretreated at 600–800 °C but it hardly took place over CaO(I), MgO(I), and MgO(II) pretreated at any temperatures.