Titanium IV -on-silica

More recently. Mayoral and coworkers [34] prepared Ti(IV)/Si02 catalysts by impregnating silica with Ti(0-i-Pr)4 then heating at 140 °C in vacuo. Under these conditions the catalyst retained (presumably one per titanium) isopropoxy groups. It was shown to be an excellent catalyst for epoxidations with TBHP, giving smooth conversions with a variety of olefins at room temperature (Table 1). 

The same group subsequently showed that the activity of the catalyst could be tuned by exchanging the surface isopropoxy groups with vie diols such as ethylene glycol [35]. The best catalyst was obtained by treating the original Si-Ti(O-i-Pr) with tartaric acid. This catalyst was active in epoxidations with 30% H2O2 at 

Olefin Olefin/TBHP Time (h) TBHP conv. % Selectivity (%) TBHP Olefin 

Conditions 1 g catalyst (ca 1 mmol Ti g ) with 36 or 96 mmol olefin and 12 mmol TBHP (TBHP/ Ti = 12 1) in CH2CI2 at room temperature. 

80 °C albeit with reactive olefins (cyclooctene and cyclohexene). Cyclohexene afforded mixtures of epoxide, cyclohexane-1,2-diol, and ally lie oxidation products. 

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