Selective Catalytic Dehydration of Tetrahydro-2-furanylmethanol Dehydration to 5-Methyl-2,3-dihydrofuran Over Large-pore Zeolites

The first example of selective synthesis 5-methyl-2,3-dihydrofuran (MDHF) via dehydration of tetrahydro-2-furanylmethanol (THFM) is described. This synthesis is accomplished in a single-step reaction and uses readily available catalysts consisting of sodium-exchanged faujasite zeolites (Na-X and Na-USY). The mechanism is hypothesized to involve a hydride shift in reactant THFM, which leads to MDHF. This is fundamentally different from the known ring-expansion pathway for hydrolysis, which synthesizes 3,4-dihydro-2 H -pyran (DHP). The activity and selectivity of the catalysts to MDHF was observed to increase with time on stream, and decrease upon increasing reaction temperature. Upon increasing either the initial water content of the catalyst or water partial pressure during reaction, an increase in the MDHF/DHP ratio was observed. This last observation helps correlate the above-mentioned trends in the catalyst activity and selectivity with increased time on stream, since the dehydration reaction synthesizes water.