Adsorption and reaction of 2-chloroethylethyl sulfide with Al2O3 surfaces

The reaction of 2-chloroethylethyl sulfide (CEES) with a high-area Al2O3 surface was investigated, Two different reactive sites were created by thermally pretreating the Al2O3 powder: isolated hydroxyl sites and Lewis acid-base pair sites. The reaction of GEES with the isolated hydroxyl groups at 303 and 473 K produced a surface-bound species, which is characterized by a carbon-oxygen stretching mode near 1100 cm(-1). This assignment was confirmed by isotopic substitution of O-18 into the isolated hydroxyl groups prior to reaction with GEES. The other reaction product detected at 473 K was HCl. For a more highly dehydroxylated Al2O3 surface, the reaction of GEES with the Lewis acid-base pairs produced a surface-bound species also exhibiting a carbon-oxygen stretching mode near 1100 cm(-1). This species is postulated to form at O2- Lewis base sites as Al3+-Cl- bonds form on adjacent Lewis acid sites. The adsorption of pyridine onto the Lewis acid sites prior to GEES exposure effectively closes this reaction pathway. A maximum Al2O3 reactivity was achieved by pretreatment of the Al2O3 in the temperature range 673 - 773 K, judging by the integrated absorbance intensity of the product-1100 cm(-1) mode. This reactivity maximum is expected if both the isolated hydroxyl groups and Lewis acid-base pairs are involved in the reaction.