INTERACTIONS OF PROPIONIC AND ACETIC ACIDS WITH GERMANIA

Infrared spectra were recorded from 4000 to 1000 cm.-1 of acetic and propionic acid sorbed on partially hydrated, dehydroxylated, and deuterated germania surfaces, and also after degassing at temperatures up to 600°. In general, the same results were obtained with both acids. Some HPr was physically adsorbed at high surface coverage, hydrogen bonded to surface Ge-OH groups, and could be desorbed at 100°. Dissociative chemisorption resulted in the formation of surface esters. At least some of the acids reacted with Ge-O-Ge bridges to yield the ester and Ge-OH structures, but the extent of a direct esterification reaction of acids with preexisting Ge-OH groups is uncertain. A small amount of Ge-H and propionate ion may be formed. The surface esters decomposed above 300°. Various data suggest that the surface ester decomposed to form surface carbonate and ketone within the pores of the gel. The ketone then formed a ketene, which became chemisorbed.