Abstract:The catalytic performance of solids with basic properties, such as CaO, MgO and hydrotalcites, was evaluated in the aldol condensation of citral and acetone, the first step in the synthesis of ionones from citral. The best results were obtained with CaO and hydrotalcite with high conversions (98%) and selectivities (close to 70% for the main product) observed for both of the catalyst. Such pseudoionone yields were greater than those reported in the literature for the homogeneous reaction
“…In the present work, the citral purchased from Aldrich Co. (with 98 wt.% of citral isomers) substituted the Cuban lemongrass essential oil (91.3 wt.% of citral) used in the former studies [6,7]. The use of this more pure reactant decreased the formation of undesirable products, thus increasing both the citral conversion and the PSI selectivity as compared to those previously reported for the same catalyst on the same reaction conditions [7].…”
Section: Catalytic Testsmentioning
confidence: 87%
“…Noda et al [6] were the first to report the excellent performance of a Mg,Al-mixed oxide (Al/(Al + Mg) = 0.27) derived from hydrotalcite as a catalyst for this reaction under autogenous pressure, at 398 K with an acetone/citral molar ratio equal to 1 and a catalyst content of 10 wt.% (with respect to the total weight of reactants). After 4 h of reaction, a citral conversion of 98% was obtained with selectivity to pseudoionones close to 67%.…”
“…In the present work, the citral purchased from Aldrich Co. (with 98 wt.% of citral isomers) substituted the Cuban lemongrass essential oil (91.3 wt.% of citral) used in the former studies [6,7]. The use of this more pure reactant decreased the formation of undesirable products, thus increasing both the citral conversion and the PSI selectivity as compared to those previously reported for the same catalyst on the same reaction conditions [7].…”
Section: Catalytic Testsmentioning
confidence: 87%
“…Noda et al [6] were the first to report the excellent performance of a Mg,Al-mixed oxide (Al/(Al + Mg) = 0.27) derived from hydrotalcite as a catalyst for this reaction under autogenous pressure, at 398 K with an acetone/citral molar ratio equal to 1 and a catalyst content of 10 wt.% (with respect to the total weight of reactants). After 4 h of reaction, a citral conversion of 98% was obtained with selectivity to pseudoionones close to 67%.…”
“…Due to the wide variety of chemical compositions, they are very efficient catalysts in different reactions. Mg,Al-mixed oxides, for example, are active for base-catalyzed reactions such as aldol condensation of aldehydes and ketones, condensation of the carbonyl group with compounds presenting methylene activated groups (for example, Knoevenagel and Claisen-Schmidt reactions), alkene isomerization, alkylation of diketones and phenols, alkene epoxidation activated by hydrogen peroxide 4,[10][11][12][14][15][16][17][18][19][20][21] . HTLCs containing transition metals such as Ni, Co, Cu or Zn or noble metals such as Rh and Ru [22][23][24][25][26][27] have also been used as precursors for hydrogenation or redox catalysts for methanol synthesis from syngas 28 , removal of SOx and NOx from FCC effluents 29,30 and other redox reactions.…”
The physico-chemical properties of a series of Ni,Mg,Al-HTLC with Al/(Al+Mg+Ni) = 0.25 and low Ni/Mg ratios were studied by means of X-ray diffraction (XRD), thermogravimetric (TGA) and thermodifferential (DTA) analysis, N2 physissorption and temperature programmed reduction (TPR). The as-synthesized materials were well-crystallized, with XRD patterns typical of the HTLCs in carbonate form. Upon calcination and dehydration the dehydroxilation of the layers with concurrent decomposition of carbonate anions produced mixed oxides with high surface area. XRD analysis indicated that the different nickel and aluminum oxides species are well-dispersed in a poor-crystallized MgO periclase-type phase. As observed by TPR, the different Ni species showed distinct interactions with Mg(Al)O phase, which were influenced by both nickel content and calcination temperature. Regardless of the the nickel content, the reduction of nickel species was not complete as indicated by the presence of metallic dispersions
“…Recently, Noda et al [20] studied the production of PS at 330 K using a calcined HT. These authors concluded that at lower temperatures, the condensation of citral with acetone requires stronger basic sites than for the self-condensation of acetone and preferably has to be executed at higher temperatures.…”
A study on the catalytic properties of properly activated hydrotalcite (HT) with special attention to the nature and amount of active sites present in this solid base catalyst has been undertaken. Only a small fraction (5%) of the available basic sites in the rehydrated calcined HT is active in liquid-phase aldol condensations. These sites exhibit high catalytic activity and are most likely localized at the edges of the HT-platelets. Besides a high activity, these modified HTs also show a high selectivity. No further condensation products other than diacetone alcohol (DAA) in the acetone self-condensation could be observed. Initial results with the citral-acetone condensation show that even at 273 K this reaction is catalyzed by modified HTs with a conversion of 65% and a selectivity of 90%, when the citral concentration is not too high (∼1 wt.%). At higher citral concentrations, no reaction is observed indicating a negative order in citral concentration.
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