Dynamic behavior of chlorofluoroethanes at halogenated surfaces

Abstract

Apparent dismutation and isomerization reactions of chlorofluoroethanes, occurring at 350 - 425°C over a fluorinated chromia surface, can be accounted for by a halogen exchange model consisting of inter-related F-for-Cl and Cl-for-F reactions [1]. Reactions at other halogenated surfaces are now reported. Isomerization of CCl2FCClF2 at aluminum(III) chloride has been demonstrated previously [2]; it is major process at room temperature although retention of CCl2FCClF2 at the surface is also significant (25%). A more active surface is produced by pretreatment of AlCl3 with CH3CCl3. This leads to formation of a purple polymer derived from the dehydrochlorination product CH2 = CCl2 [3]. At this surface, retention of CCl2FCClF2 is less marked (7%) and the major component (93%) of the volatile mixture is CCl3CF3. No detectable 36Cl]-surface activity results when [36Cl]- CCl2FCClF2 is used, suggesting that isomerization may be intramolecular as has been proposed for CCl2FCClF2 at AlCl3 [2]. Treatment of AlCl3 with CCl2FCClF2 followed by CH3CCl3 results not only in dehydrochlorination of the latter, but also in the liberation of CCl3CF3 from the surface. In contrast the almost complete (81%) retention of CCl2FCClF2 by chlorinated γ-alumina blocks any catalytic activity towards dehydrochlorination of CH3CCl3.