1982 Volume 55 Issue 5 Pages 588-599
The thermal properties of surface group of silica gels treated with several alicyclic alcohols (C5, C6, C7, C6-C, C6-C2) were investigated through the analysis of their pyrolysis products in use of Gas Chromatograph-Quadru Pole Mass Spectrometer. These were compared with the pyrolysis of these alcohols in gaseous state or over silica gel. The pyrolysis of these alcohols in gaseous state takes place at 500-6O0°C and both dehydration and dehydrogenation proceed simultaneously. Since the pyrolysis over silica gels takes place at 300°C and water and corresponding alicyclic olefine were detected in the temperature range of 300° to 600°C, the silica gel was found to be catalyst to promote the dehydration of alcohols selectively. In higher temperature range, dehydrogenation takes place simultaneously like the case of gaseous state. Although the water and the corresponding alicyclic olefine were similarly observed for pyrolysis products of the surface-treated silica gels, the amount of water evolved in the temperature range of 300° to 600°C where the alicyclic olefine generates was observed to be small. As the ratio of the amount of water against that of alicyclic olefine were found to be constant against decomposition temperature in the pyrolysis of these alcohols over silica gel, these products could be noticed to be formed by the simple mechanism, i. e., dehydration of alcohol. Whilst these ratios showed to be parabolic in the pyrolysis of surface-treated silica gels. This indicates that the formation of water and alicyclic olefine would proceed by the different mechanism, i. e., dehydration due to condensation of unreacted silanol for water, whilst the mechanism like _??_SiOA→ _??_SiO+A→_??_SiOH+Ol (A, Alicyclic alcoxy group ; Ol, corresponding alicyclic olefine) for alicyclic olefine. Consequently, the surface groups were recognized not to be the species chemisorbed on substrate in the form of AOH, but to be the species bonded chemically with surface silanol like _??_SiOR.
