Hexenes shape-selective epoxidation

A unique titanium(IV)-silica catalyst prepared by impregnating silica with TiCLt or organotitanium compounds exhibits excellent properties with selectivities comparable to the best homogeneous molybdenum catalysts.285 The new zeolite-like catalyst titanium silicalite (TS-1) featuring isomorphous substitution of Si(IV) with Ti(IV) is a very efficient heterogeneous catalyst for selective oxidations with H2C>2.184,185 It exhibits remarkable activities and selectivities in epoxidation of simple olefins.188,304-306 Propylene, for instance, was epoxidized304 with 97% selectivity at 90% conversion at 40°C. Shape-selective epoxidation of 1- and 2-hexenes was observed with this system that failed to catalyze the transformation of cyclohexene.306 Surface peroxotitanate 13 is suggested to be the active spe-... 

The intercalated compounds of hydrotalcite [Mg23.3AlI0(OH)66.6] with M07O24 or W12O4 - catalyze the shape-selective epoxidation of olefins epoxi-dation of 2-hexene was favored over theat of cyclohexene (395). 

An added advantage of the TS-1 catalyst, which could have commercial benefits, is the possibility for accomplishing shape-selective epoxidations. Owing to the limited dimensions (5.6 A X 5.4 A) of its micropores, linear olefins are epox-idized much faster than branched or cyclic olefins, e.g., 1-hexene is smoothly epoxidized while cyclohexene is virtually unreactive [45]. This reactivity is completely the opposite to that observed with the metal catalyst-alkyl hydroperoxide reagents (see earlier). It could be utilized in, for example, the selective epoxidation of linear olefins in mixtures of linear and branched or cyclic olefins. 

Although TS-1 has been investigated for the epoxidation of a range of molecules, e.g. butene, pentene, hexene, allyl chloride and allyl alcohol, little attention has been given to the effect of shape selectivity in the MFI zeotype framework in these reaetions. In this paper we address this aspect and exemplify the shape. selective epoxidation using a range of allylic alcohols. In particular, the shape selective epoxidation of crotyl alcohol is compared and contrasted with the reaction of allyl alcohol in a range of solvents. 

---