Dehydration of butan-2-ol using modified zeolite crystals

Modification of zeolite H-Y by dithiane oxides is shown to enhance signific antly the rate of dehydration of butan-2-ol to butenes. Reaction of racemic butan-2-ol over zeolite H-Y modified with (R)-1,3-dithiane-1-oxide indicat es that the high activity catalyst is enantiomerically discriminating, as o ne enantiomer reacts preferentially to the other, although both are present within the micropores under the reaction conditions. The origins of the ra te enhancement have been investigated spectroscopically using FTIR and MAS NMR, The enhanced activity is considered to result from a specific interact ion between the sulfoxide modifier with the Bronsted acid sites associated with framework hydroxyl groups together with a strong interaction with an e xtra-framework aluminium species. This combination results in the formation of a rigid high activity site. Investigations using the amino acid cystine as an alternative to 1,3-dithiane-1-oxide have indicated that in this case the modifier is more weakly bound within the zeolite pores and exhibits co nsiderable molecular motion, leading to the modified catalyst demonstrating no enantioselectivity or rate enhancement. (C) 1999 Elsevier Science B.V. All rights reserved.