Etude par spectroscopie infrarouge de la coordination et de l'adsorption de (CD3)2CHOH. II - adsorption sur alumine

Abstract

A preliminary study of aluminium isopropoxyde [(CD₃)₂CHO]₃Al in carbon tetrachloride solutions led to the characterization of the γ(CH), δ(CH) and ν(CH) vibrations in the isopropoxyde groups either free or coordinated in autoassociation complexes. Different species, dissociated or coordinated, formed when isopropanol(D₆) is adsorbed on to site pairs (O,Al) have been shown by the ν(CH) and {δ(CH),δ(OH)} studies of coadsorption of isopropanol(D₆) with pyridine(D₅) (a Lewis base) or aluminium pentachloride (a Lewis acid) or perfluorotertiobutanol, which is dissociatively adsorbed. The isopropanol(D₆) dissociation needs a very basic O site. The coordination takes over both the Lewis base and the H bond donor functions of the hydroxyl groups ; two coordinated species are formed on site pairs (O strong base, Al weak acid) and (O weak base, Al strong acid). The interaction energy is tentatively evaluated to − 40 kcal mol⁻¹. Very acidic hydroxyl groups are created when perfluorotertiobutanol is adsorbed : the energy of the hydrogen bridge which they form with physisorbed isopropanol(D₆) may be of − 12 kcal mol⁻¹.