C-13 CP/MAS NMR-STUDY OF ISOBUTYL ALCOHOL DEHYDRATION ON H-ZSM-5 ZEOLITE - EVIDENCE FOR THE FORMATION OF STABLE ISOBUTYL SILYL ETHER INTERMEDIATE

Dehydration of isobutyl alcohol selectively labelled with a C-13 nucleus in the CH2 group (i-BuOH[1-C-13]) has been studied on H-ZSM-5 zeolite within the temperature range 296-448 K using C-13 CP/MAS NMR. The formation of the isobutyl silyl ether intermediate (IBSE) has been detected. It is stable below 398 K. Within the temperature range 398-423 K IBSE decomposes gradually to produce first a butene dimer, probably 2,5-dimethyl-1-hexene and then other butene dimers and oligomers. At T > 423 K scrambling of the selectively labelled carbon of the initial dimeric product over various positions in the carbon skeleton of the final dimers (oligomers) is observed. This is explained in terms of the formation of carbenium ion as the reaction intermediate.