Gas-phase pinacol conversion on AlPO4, γ-Al2O3 and SiO2 catalysts

Pinacol (2,3-dimethyl-2,3-butanediol) conversion over AlPO4 (Al/P = 1) and gamma-Al2O3 catalysts proceeded in two parallel reaction pathways with formation of 2,3-dimethyl-1,3-butadiene (by 1,2-elimination) and 3,3-dimethyl-2-butanone (by rearrangement), the latter being the main reaction product. The activity was in accordance with the surface acidity data as measured versus cyclohexene skeletal isomerization reaction. Thus, AlPO4 showed the highest activity (almost total conversion at 523 K). The 1,2-elimination/rearrangement ratio depended on the type of catalyst used and diene formation increased with reaction temperature. Moreover, pinacolone was a reaction intermediate for diene production.