M.T. Drexler, M.D. Amiridis / Journal of Catalysis 214 (2003) 136–145
145
species. These differences may be responsible for the ob-
served change in the catalytic behavior of MgO during the
synthesis of flavanone in the presence on DMSO.
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Among the different high-boiling-point solvents exam-
ined for the synthesis of flavanone from benzaldehyde and
2-hydroxyacetophenone over a MgO catalyst, the use of
dimethyl sulfoxide (DMSO) was found to significantly pro-
mote the yield of flavanone. The effect of DMSO on the rate
of the second step of the synthesis (i.e., the isomerization
of the 2ꢀ-hydroxychalcone) is more dramatic. In this case,
a 40- to 100-fold increase in the activity of MgO was ob-
served as compared to other solvents. The same promoting
effect was also observed when relatively small amounts of
DMSO were added to other solvents. No apparent corre-
lation was obtained between the polarities of the solvents
and the reactivity of MgO in the presence of these sol-
vents. The results of FTIR studies indicate the formation
of strongly held surface sulfate species following the inter-
action of DMSO with the MgO surface. The presence of
these sulfate species affects the adsorption behavior of ben-
zaldehyde and 2-hydroxyacetophenone on the surface of the
MgO catalyst and leads to the formation of surface benzoate