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1 2005

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Catalytic Ketonisation over Oxide Catalysts. Part XI. Cross-Ketonisation of Esters of Aliphatic and Aromatic Acids

Gliński M., Kościk A., Jerzak A., Synoradzki L.

Polish Journal of Chemistry

2005

Vol. 79 / nr 6

995-1001

The cross-ketonisation of a mixture of ethyl acetate and ethyl benzoate under flow conditions has been studied over 20wt%MO2/Al2O3 (M = Mn, Ce or Zr) catalysts, at 673-723 K. High conversions of aromatic ester up to 98% and moderate yields of acetophenone (<45%) have been observed. The main product was accompanied by numerous side-products, among which ethylbenzene, styrene and benzoic acid were identified. CeO2/Al2O3 catalyst was the least selective. In its presence, the yield of styrene (34%) exceeded that of acetophenone (31%). Unexpectedly, pure Al2O3 support exhibited the highest selectivity and moderate activity, at 723 K the yield as high as 51% of acetophenone was noted. The transformations of mixtures of various ethyl alkanoates with ethyl benzoate over alumina have been studied. In the case of straight-chain aliphatic esters, the yields of the corresponding 1-phenyl-1-alkanones were in the range of 41-51%. The presence of a methyl group in the _ position of the ester (isobutyrate) reduced the yield of ketone strongly (11%); two methyl groups (pivalate) completely inhibited the reaction. The reactivity of a series of alkyl acetates was also studied in the cross-ketonisation reaction with ethyl benzoate over alumina. It has been found that secondary and tertiary alkyl acetates were slightly more selective than their primary counterparts due to the absence of products of transesterification. For these esters at 723 K the yields of acetophenone were in the range of 64-67%. The cross-ketonisation of a mixture of ethyl acetate with substituted ethyl benzoates led to the corresponding derivatives of acetophenone. It has been found that the position of the substituent in the benzene ring plays a crucial role in the reactivity of the ester and determines the extent of yield of the product. The highest yield of ketone (62%) was observed at 723 K for 3-methylacetophenone. 2-Methylacetophenone was formed with low yields (<10%) in the whole range of reaction temperatures, probably due to steric effect in the ortho position. At 698 K the maximum yield of 4-methylacetophenone (27%) was attained. The ketonisation of ethyl acetate with ethyl esters of 4-t-butyl- and 4-chlorobenzoic acids led to moderate yields (24-27%) of 4-t-butyl- and 4-chloroacetophenone, respectively.