Search

The results of a study of tandem reactions - aldol-crotonic condensation and hydrogenation by the mechanism of hydride transfer in acetone-isopropanol mixtures on a МgSnО3 catalyst at 300–400°C and 12.0 MРa are presented. In these conditions the mixture of reactants (acetone and isopropanol) and reaction products is in supercritical state. The temperature dependences of the reactants conversion and the selectivity for condensation and hydrogenation products are considered. It has been established that the hydrogenation of acetone aldol-crotonic condensation products proceeds by the addition of hydrogen from isopropanol molecule to C=O-bonds of isomeric mesityl and phorone oxides and is accompanied by dehydration of alcohols and isomerization of double C=C-bonds. The optimal conditions for the formation of the carbonyl group hydrogenation products are 350°C and the ratio acetone : isopropanol = 7 : 3. At the acetone to isopropanol ratio 1 : 1, methylpentadienes dominate in the products of mesityl oxide conversion. The hydrogenation reaction also proceeds with the participation of isophorones, the condensation products of three acetone molecules. [ABSTRACT FROM AUTHOR]

The aldol condensation of acetone under supercritical conditions at 300–400°C and 11.0 MPa was carried out on BaSnO3-450 and BaSnO3-750 catalysts prepared by calcination of BaSn(OH)6 at 450 and 750°C, respectively. Conducting the reaction under these conditions makes it possible to overcome the problem of catalyst deactivation by coking and to obtain valuable chemicals with high selectivity. At 300°C, both catalysts provide selectivity of 85–87% to isomeric mesityl oxides (C6 products). At 400°C with the BaSnO3-450 catalyst, the selectivity significantly changes from C6 to C9 (phorones). Powder X-ray diffraction and TEM data attest to the multiphase nature of the samples, which contain barium stannates, barium carbonate, and tin oxide. It was found that the catalyst structure rearranges in situ, which greatly affects the catalytic properties and is most pronounced for BaSnO3-450. [ABSTRACT FROM AUTHOR]

The aldol condensation of acetone was carried out under the conditions of the supercritical state of the reagent (350 °C, 8 MPa; 400 °C, 12 MPa) on catalysts prepared by the thermal treatment of CaSn(OH)6 at 450 and 750 °C. The X-ray amorphous phase of CaSnO3 transforms into crystalline calcium stannate as the thermal treatment temperature increases from 450 to 750 °C. At 350 °C and 8.0 MPa, the selectivity of the reaction to mesityl and isomesityl oxides is about 85% (for both samples), but the conversion of acetone is much higher on CaSnO3 after it has been thermally treated at 750 °C. The reuse of the CaSnO3-450 catalyst led to its transformation. The conversion of acetone increases, and the reaction parameters (conversion and selectivity) reach values characteristic of CaSnO3-750. The catalyst structures were studied by XRD and scanning and high-resolution transmission electron microscopies. [ABSTRACT FROM AUTHOR]