Synthesis of cinnamyl ethyl ether in the hydrogenation of cinnamaldehyde on Au/TiO2 catalysts

In this paper, we report the results of a study on the hydrogenation of hydrocinnamaldehyde (CA) carried out in ethanol under mild conditions (T = 333 K, P-H2 = 1 atm), on the Au/TiO2 reference catalyst, supplied by the World Gold Council. The reaction was carried out on the as received and on the catalyst reduced at 473 K (LTR) and 773 K (HTR). From the hydrogenation of cinnamaldehyde three main products were obtained: cinnamylalcohol (UA) and hydrocinnamaldehyde (HCA), formed from the hydrogenation of the conjugated C=C and C=O bond, respectively, and the asymmetric ether 3-ethoxyprop-1-enylbenzene (C6H5CH=CH - CH2 - O - C2H5) or cinnamyl ethyl ether (CEE). The behavior of Au/TiO2 catalyst in the hydrogenation of cinnamaldehyde is of particular interest because it is the first time, as far as we know, that the formation of the allyl ether is observed during this reaction. The selectivity towards the formation of the CEE, measured at 50% of conversion, increases from 19%, on the as received catalysts, up to 33% on the catalysts reduced at 473 K. A further increase of the reduction temperature does not influence the selectivity to CEE. The mechanism of the formation of the cinnamyl ethyl ether is proposed. (c) 2007 Elsevier B.V. All rights reserved.