Synthesis of sodium-doped mesoporous alumina and its strong base catalysis for double bond migration of olefins

Sodium-doped mesoporous alumina (Na/mesoAl(2)O(3)) has been successfully synthesized through doping sodium azide and the pyrolysis with the intention to enhance the strength of base sites (O2-) and to weaken that of acid sites (Al3+) on mesoporous alumina (mesoAl(2)O(3)). Powder XRD and pore-size distribution analysis on NalmesoAl(2)O(3) demonstrated that the loaded metallic sodium hardly collapsed the intrinsic mesoporosity and bulk structure of mesoAl(2)O(3). The NalmesoAl(2)O(3) promoted the double bond migration of 2,3-dimethyl-1-butene even at a low reaction temperature of 275 K to afford 2,3-dimethyl-2-butene in a high yield of 81% in 4 h, indicating that NalinesoAl(2)O(3) has very strong base sites including superbase sites on the surface. Na/mesoAl(2)O(3) was also successfully applied to the isomerization of alpha-pinene to yield P-pinene in excellent selectivities of 93-96%, while parent mesoAl(2)O(3) and sodium-doped conventional gamma-Al2O3 gave beta-pinene in lower selectivities of 58% and 89%, respectively. The active strong base sites on Na/lmesoAl(2)O(3) should be a part of surface O2- ions, whose basic character is reinforced by the electron donation from the introduced sodium metals. (c) 2006 Elsevier Inc. All rights reserved.