Catalysis of Organic..

356Synthesis of PseudoiononesOOO- H C2O+CH 3 CH 3Oβ-iononaO(1)CitralAcetonePseudoiononeα-iononaboth the synthesis procedure and the activation steps. These previous works showedthat solid bases are potential catalysts for the aldol condensation of citral withacetone but the exact requirements of basic site density and strength to efficientlypromote the selective pseudoionone formation is lacking. In this paper, we havestudied the citral/acetone reaction on Li-doped MgO, taking into account that wehave previously observed that this type of catalysts is highly active for acetonecondensation reactions (8). Our goal was to test new catalytic formulations and alsoto relate the structural properties and the base site density and nature of the solid withtheir ability to promote the pseudoionone formation.ExperimentalTo obtain high-surface area MgO, commercial MgO (Carlo Erba, 99%) was hydratedwith distilled water and the resulting Mg(OH) 2 was decomposed and stabilized at 773K in a N 2 flow for 18 h. Li/MgO-x samples were prepared by incipient wetnessimpregnation from the same mother batch of MgO, using aqueous solutions of LiOHto obtain catalysts with 0.13, 0.3, 0.5, 1.2 and 2.6 wt. % of lithium. Afterincorporation of Li + cation, samples were dried at 353 K and then decomposed andstabilized at 773 K during 18 h in flowing N 2 . The sample composition wasdetermined by Atomic Absorption Spectrometry (AAS). BET surface areas (Sg)were measured by N 2 adsorption at 77 K in a Nova-1000 Quantachrom sorptometer.Structural properties of the samples were determined by X-Ray Diffraction (XRD)using a Shimadzu XD-D1 instrument. Crystallite sizes were evaluated using theScherrer equation.Catalyst base site densities (n b ) were measured by Temperature-ProgrammedDesorption (TPD) of CO 2 pre-adsorbed at room temperature. Samples werepretreated in situ in a N 2 flow at 773 K, cooled down to room temperature and thenexposed to a flowing mixture of 3 % of CO 2 in N 2 until surface saturation. Weaklyadsorbed CO 2 was removed by flushing in N 2 . Finally, temperature was raised up to773 K at 10 K/min. The desorbed CO 2 was converted to CH 4 over a methanationcatalyst (Ni/Kieselghur) and then analyzed with a flame ionization detector.