INFRARED STUDY OF THE SURFACE SPECIES FORMED BY SEQUENTIAL CHEMICAL-VAPOR-DEPOSITION OF DIMETHYL ZINC AND ETHANETHIOL ON HYDROXYLATED ALUMINA SURFACES

The surface species formed by the reaction of gas-phase dimethylzinc w ith self-supported alumina pellets are examined by Fourier transform i nfrared spectroscopy. Dimethylzinc reacts with the surface -OH groups of alumina at room temperature evolving methane and yielding mainly su rface Al-O-Zn-CH3 species. A small amount of CH3 species appears to bi nd to the Lewis acid sites of alumina as well, forming Al-CH3 groups. Temperature-dependence studies reveal that these species are stable at room temperature and gradually decompose upon heating in vacuo. Durin g the annealing process, some of the Zn-bound methyl groups also appea r to migrate to free Lewis acid sites of the alumina surface. The dime thylzinc-treated alumina surface is then exposed to ethanethiol, which reacts with the surface methylzinc species at room temperature, elimi nating methane and producing Zn-bound ethanethiolate surface species. These are stable in air and aqueous environments, and up to about 523 K in vacuo and may provide a possible synthetic strategy for formation of protective layers. The major gas-phase products from their thermal decomposition are found to be diethyl sulfide and ethylene. In additi on, a small amount of methylzinc-thiol coordination intermediate is fo und on the dimethylzinc-treated alumina surface following the room-tem perature reaction with ethanethiol. This intermediate decomposes with methane evolution upon annealing up to 398 K.