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 CEES 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 ¹⁸O into the isolated hydroxyl groups prior to reaction with CEES. The other reaction product detected at 473 K was HCl. For a more highly dehydroxylated Al₂O₃ surface, the reaction of CEES 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 O^2- Lewis base sites as Al³⁺−Cl^- bonds form on adjacent Lewis acid sites. The adsorption of pyridine onto the Lewis acid sites prior to CEES 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 product1100 cm^-1 mode. This reactivity maximum is expected if both the isolated hydroxyl groups and Lewis acid−base pairs are involved in the reaction.