R. Hutter et al., Control of acidity and selectivity of titania-silica aerogel for the epoxidation of beta-isophorone, J MOL CAT A, 138(2-3), 1999, pp. 241-247
The epoxidation of P-isophorone (3,5,5-trimethyl-3-cyclohexene-1-one) with
an amorphous mesoporous titania-silica aerogel and t-butyl hydroperoxide ha
s been investigated. Dominant side reactions were the acid/base catalyzed i
somerizations of beta-isophorone to alpha-isophorone and of the product epo
xide to 4-hydroxy-isophorone. The acidity of the aerogel was characterized
by the epoxide ring opening reaction (to 4-hydroxy-isophorone). Two methods
were shown to be efficient in tuning the acidity and the hydrophilic-hydro
phobic character of the aerogel, and controlling the product distribution.
A catalyst pretreatment in ethyl benzene afforded 98.5 and 93% epoxide sele
ctivities at 75 and 90% peroxide conversions, respectively, without any inf
luence on the oxidation rate. A simple addition of a weak inorganic base (s
uch as NaHCO3 or Na2HPO4) to the reaction mixture and carrying out the reac
tion in the presence of two solids in an apolar solvent was even more effic
ient: epoxide selectivities up to 95% were achieved at 90% conversion, with
only small changes in reaction time and peroxide selectivity. Moreover, ap
plying other bases the product composition could be varied in a very broad
range. 4-Hydroxy-isophorone was the major product with Na2CO3 (65% selectiv
ity at 90% conversion), while alpha-isophorone was formed almost exclusivel
y in the presence of BaCO3 or NaOH. (C) 1999 Elsevier Science B.V. All righ
ts reserved.