Aldol Addition Of Acetone Research Articles

Streptavidin-Hosted Organocatalytic Aldol Addition.

In this report, the streptavidin-biotin technology was applied to enable organocatalytic aldol addition. By attaching pyrrolidine to the valeric motif of biotin and introducing it to streptavidin (Sav), a protein-based organocatalytic system was created, and the aldol addition of acetone with p-nitrobenzaldehyde was tested. The conversion of substrate to product can be as high as 93%. Although the observed enantioselectivity was only moderate (33:67 er), further protein engineering efforts can be included to improve the selectivity. These results have proven the concept that Sav can be used to host stereoselective aldol addition.

The mechanism and kinetics of methyl isobutyl ketone synthesis from acetone over ion-exchanged hydroxyapatite

The synthesis of methyl isobutyl ketone (MIBK) can be carried out by the condensation of acetone in the presence of hydrogen over a supported metal catalyst. Previous studies have shown that hydroxyapatite is an excellent catalyst for condensation reactions. The present investigation was undertaken in order to elucidate the reaction mechanism and site requirements for acetone coupling to MIBK over a physical mixture of hydroxyapatite and Pd/SiO2. The reaction is found to proceed by consecutive aldol addition to form diacetone alcohol (DAA), dehydration of DAA to mesityl oxide (MO), and hydrogenation of MO to MIBK. The products formed by feeding DAA and MO reveal that aldol addition of acetone is rapid and reversible, and that the subsequent dehydration of DAA is rate-limiting. Pyridine and CO2 titration show that aldol dehydration occurs over basic sites via an E1cB mechanism. A series of cation-substituted hydroxyapatite samples were prepared by ion-exchange to further investigate the role of acid-base strength on catalyst performance. Characterization of these samples by PXRD, BET, ICP-OES, XPS, CO2-TPD, and Raman spectroscopy demonstrated that the exchange procedure used does not affect the bulk properties of hydroxyapatite. DFT calculations reveal that in addition to affecting the Lewis acidity/basicity of the support, the size of the cation plays a significant role in the chemistry: cations that are too large (Ba2+) or too small (Mg2+) adversely affect reaction rates due to excessive stabilization of intermediate species. Strontium-exchanged hydroxyapatite was found to be the most active catalyst because it promoted α-hydrogen abstraction and CO bond cleavage of DAA efficiently.

ChemInform Abstract: Catalysis by Basic Metal Oxides

Abstract Catalytic properties of basic materials investigated in our laboratories are reviewed. Firstly, the types of metal oxides and the indications of their basic properties are presented. Secondly, the importance of removing H2O, CO2 and O2 from the surfaces to generate basic properties and catalytic activities is demonstrated. Thirdly, the reaction characteristics occuring on solid base catalysts are described for the following reactions. (I) Double bond migration of olefins. (II) Double bond migration of unsaturated compounds containing hetero atoms. (III) Isomerization of alkynes and alienes. (IV) Hydrogenation of olefins, (V) Amination of olefins. (VI) Hydrogenation of CO. (VII) Aldol addition of acetone. Fourthly, structures of active sites are discussed in reference to MgO model structures. Four types of active sites, OH groups and three types of metal-oxygen ion pairs of different coordination numbers, are proposed. Finally, future directions to develop solid base catalysts are suggested.

ChemInform Abstract: Aldol Addition of Acetone, Catalyzed by Solid Base Catalysts: Magnesium Oxide, Calcium Oxide, Strontium Oxide, Barium Oxide, Lanthanum(III) Oxide, and Zirconium Oxide.

Abstract Aldol addition of acetone was studied over alkaline earth oxides, La 2 O 3 , ZrO 2 , SiO 2 Al 2 O 3 and Nb 2 O 5 at 0°C to elucidate the nature of active sites. The activities of catalysts on a unit surface area basis were in the order: BaO > SrO > CaO > MgO > La 2 O 3 > ZrO 2 ≫ SiO 2 Al 2 O 3 > Nb 2 O 5 . The reaction is base-catalyzed, and the oxides of stronger basic sites promote the reaction effectively. The effects of preadsorption of water, ammonia, pyridine and carbon dioxide were investigated with MgO and CaO. For MgO, addition of water and ammonia caused marked increase in activity and selectivity to diacetone alcohol, while pyridine had little effect on the catalytic behavior. Preadsorption of carbon dioxide scarcely inhibited the reaction. For CaO, the effects of preadsorption were small compared with those on MgO. Basic OH − ions, which are either retained on the surfaces or formed by dehydration of diacetone alcohol, are proposed as active sites for aldol addition of acetone.

Aldol Addition of Acetone, Catalyzed by Solid Base Catalysts: Magnesium Oxide, Calcium Oxide, Strontium Oxide, Barium Oxide, Lanthanum (III) Oxide and Zirconium Oxide

Aldol addition of acetone was studied over alkaline earth oxides, La 2O 3, ZrO 2, SiO 2 Al 2O 3 and Nb 2O 5 at 0°C to elucidate the nature of active sites. The activities of catalysts on a unit surface area basis were in the order: BaO > SrO > CaO > MgO > La 2O 3 > ZrO 2 ≫ SiO 2 Al 2O 3 > Nb 2O 5. The reaction is base-catalyzed, and the oxides of stronger basic sites promote the reaction effectively. The effects of preadsorption of water, ammonia, pyridine and carbon dioxide were investigated with MgO and CaO. For MgO, addition of water and ammonia caused marked increase in activity and selectivity to diacetone alcohol, while pyridine had little effect on the catalytic behavior. Preadsorption of carbon dioxide scarcely inhibited the reaction. For CaO, the effects of preadsorption were small compared with those on MgO. Basic OH − ions, which are either retained on the surfaces or formed by dehydration of diacetone alcohol, are proposed as active sites for aldol addition of acetone.

Catalysis by basic metal oxides

Catalytic properties of basic materials investigated in our laboratories are reviewed. Firstly, the types of metal oxides and the indications of their basic properties are presented. Secondly, the importance of removing H 2O, CO 2 and O 2 from the surfaces to generate basic properties and catalytic activities is demonstrated. Thirdly, the reaction characteristics occuring on solid base catalysts are described for the following reactions. (I) Double bond migration of olefins. (II) Double bond migration of unsaturated compounds containing hetero atoms. (III) Isomerization of alkynes and alienes. (IV) Hydrogenation of olefins, (V) Amination of olefins. (VI) Hydrogenation of CO. (VII) Aldol addition of acetone. Fourthly, structures of active sites are discussed in reference to MgO model structures. Four types of active sites, OH groups and three types of metal-oxygen ion pairs of different coordination numbers, are proposed. Finally, future directions to develop solid base catalysts are suggested.