Effective Baeyer–Villiger oxidation of ketones over germanosilicates

Germanosilicates with various topologies (UTL, BEC, UWY, IWR) serve as efficient heterogeneous catalysts for the Baeyer–Villiger oxidation of ketones. The tetrahedrally coordinated Ge ions in germanosilicates exhibited Lewis acidity, and acted as the active sites for converting ketones to corresponding lactones effectively.     

Baeyer–Villiger Oxidation of Cyclohexanone in Aqueous Medium with In Situ Generation of Peracid Catalyzed by Perhydrolase CLEA

A perhydrolase, immobilized as a cross linked enzyme aggregate (CLEA), was employed to catalyze the in situ formation of peracetic acid (PAA) from ethylene glycol diacetate (EGDA) and hydrogen peroxide. The produced PAA was used for the Baeyer–Villiger oxidation of cyclohexanone, which afforded caprolactone in 63 % yield. The effect of type and amount of acyl donor, solvent, pH, temperature and ratio of cyclohexanone to hydrogen peroxide on the production of caprolactone was studied. The highest caprolactone yield was obtained with 100 mM EGDA as the acyl donor at pH 6 and room temperature using a ratio of cyclohexanone to hydrogen peroxide ratio of 1:4. Interestingly, the perhydrolase CLEA exhibited the highest activity in aqueous medium in contrast to the well studied lipase B from Candida antarctica. The perhydrolase CLEA proved to be a very efficient catalyst; the K _m and V_max values were 118 mM and 56.3 μmol min^?1, respectively.     

Selective Catalytic Oxidation (SCO) of Ammonia to Nitrogen over Hydrotalcite Originated Mg–Cu–Fe Mixed Metal Oxides

Abstract  

Mg–Cu–Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia. Copper containing catalysts were active in low-temperature SCO processes; however, their selectivity to nitrogen significantly decreased at higher temperatures. The optimum composition of the catalyst to guarantee high activity and selectivity to N₂ was proposed. Temperature-programmed experiments, SCO catalytic tests performed with various contact times and additional tests on the samples in the selective catalytic reduction of NO with ammonia showed that the SCO process over the studied calcined hydrotalcites proceeds according to the internal SCR mechanism and oxidation of ammonia to NO is a rate-determining step in the low-temperature range.     

Co–Mg–Al Hydrotalcite Precursors for Catalytic Total Oxidation of Volatile Organic Compounds

Co–Mg–Al hydrotalcite type solids were synthesized as precursors of catalysts for the total oxidation of toluene. After calcination at 500 °C, different mesoporous mixed oxides were obtained with high specific surfaces. The comparison of the catalytic activities of the calcined hydrotalcites with those of calcined hydroxides evidenced the superiority of the first oxides explained meanly by higher specific surfaces and more easily reducible particles. DRIFT “operando” allowed to follow the oxidation reaction and the formation of light coke and carbonate species.     

Selective Oxidation of Cyclohexane to Cyclohexanone Catalyzed by Phenanthroline–CuCl2 Complex

A highly efficient oxidation of cyclohexane to cyclohexanone is accomplished over phenanthroline–CuCl₂ catalyst in relatively mild conditions. This study realized nearly 100% selectivity for cyclohexanone at 24.4% conversion of cyclohexane. The reaction has been studied by various parameters like performance of copper(II) salts, effect of solvents, influence of bases, the ratio of o-phenanthroline: CuCl₂, and reaction time. In order to further study this reaction system, the possible mechanism was proposed.     

Clean Baeyer–Villiger Oxidation Using Hydrogen Peroxide as Oxidant Catalyzed by Aluminium Trichloride in Ethanol

Baeyer–Villiger oxidation of ketones was carried out using AlCl₃ as catalyst, H₂O₂ (30%) as oxidant in innocuity and environmentally friendly ethanol conditions. Cyclic ketones and acyclic ketones were transformed into the corresponding lactones or esters in 5–24 h at 40–70 °C with very high conversion and selectivity. A possible reaction mechanism was also given.     

Exploring the Substrate Specificity and Enantioselectivity of a Baeyer–Villiger Monooxygenase from Dietzia sp. D5: Oxidation of Sulfides and Aldehydes

Baeyer–Villiger monooxygenases (BVMOs) are valuable enzymes for specific oxyfunctionalization chemistry. They catalyze the oxidation of ketones to esters, but are also capable of oxidizing other chemical functions, namely aldehydes and heteroatoms such as sulfur, nitrogen, selenium and boron. The oxidation specificity and enantioselectivity of a newly characterized BVMO (BVMO4) from a strain of Dietzia towards sulfide- and aldehyde substrates have been studied. BVMO4 could react with sulfides containing an aromatic group. The presence of a substituent on the aromatic group was tolerated when they were in the meta- and para position and the oxidations yielded predominantly the (R)-sulfoxides. Similarly, BVMO4 displayed a higher activity for aldehydes containing a phenyl group, but long aliphatic aldehydes, namely octanal and decanal, were also accepted as substrate by this enzyme. The major oxidation products of the aldehyde substrates were the respective carboxylic acids in contrast to formate ester that was obtained in most of the previous reports. The Baeyer–Villiger oxidation of the substrate 2-phenylpropionaldehyde was studied in further detail and the corresponding acid product was obtained with good regio- and enantioselectivity. This is a unique feature for BVMO4 and is of great interest for further exploration of an alternative biocatalytic process.     

Fabrication of Ag/WO3 nanobars for Baeyer–Villiger oxidation using hydrogen peroxide

We report the preparation of Ag/WO₃ nanobars, mediated by cationic surfactant CTAB through hydrothermal route. XRD revealed the formation of metallic Ag supported on monoclinic WO₃ phase and TEM diagram showed the formation of bar-like structure, where supported Ag nanoparticles are in the range between 2 and 7 nm. The catalyst exhibited high activity for selective oxidation of cyclohexanone to caprolactone with H₂O₂. A cyclohexanone conversion of 97% with 99% caprolactone selectivity was achieved over this catalyst at 80 °C temperature. Moreover, the catalyst did not show any significant activity loss even after 5 reuses and proved its efficiency in the oxidation of other cycloalkanones also.     

Advances in Infrared Spectroscopy of Catalytic Solid–Liquid Interfaces: The Case of Selective Alcohol Oxidation

Progress in the use of ATR-IR spectroscopy to improve the understanding of liquid-phase heterogeneous catalytic reactions is illustrated using the example of the oxidation of benzyl alcohol over Pd/Al₂O₃ and Bi–Pd/Al₂O₃. The in situ studies performed in both batch and continuous reactor cells provide rich information on the reaction pathway and important facets of the mechanism, such as the nature of active Pd sites and the effect of the Bi-promoter. The combination of CO site blocking prior to reaction and isotopic labeling suggests that alcohol dehydrogenation occurs uniformly over Pd nanoparticles, but only selected sites may allow desorption of the product benzaldehyde thus providing the required selectivity. Promotion of Pd/Al₂O₃ using bismuth produces infrared spectra free of adsorbed CO. This information demonstrates that Bi is deposited on selected adsorption sites (terraces rather than defects) and simultaneously confirms that open terraces favor product decomposition. Experiments performed in the continuous reactor cell using different catalyst film thickness show that reactions can be studied under kinetic or mass transfer limited conditions depending on catalyst film thickness. This allowed to study the alcohol oxidation under conditions of oxygen diffusion limitation, which are preferably applied in praxis in order to prevent catalyst deactivation by over-oxidation.     

Baeyer–Villiger oxidation of ketones with hydrogen peroxide catalyzed by silica supported aluminum chloride

Silica supported AlCl₃ catalyst was prepared by ion-exchange technique. Ketones are oxidized by 30% hydrogen peroxide in ethanol and transformed into the corresponding lactones with very high selectivity catalyzed by silica–AlCl₃. The catalyst was easily prepared in large scale with inexpensive materials and recyclable.     

Highly efficient and reusable Cu-MCM-41 catalyst for the Baeyer–Villiger oxidation of cyclohexanone

A series of Cu-MCM-41 with different Cu contents were successfully synthesized by the direct hydrothermal (DHT) method and evaluated in the Baeyer–Villiger oxidation of cyclohexanone, using only 2 molar equiv of benzaldehyde as sacrificial agents. High conversion (99.0%) of cyclohexanone and ε-caprolactone selectivity (100%) were detected over Cu-MCM-41 (23) within 3 h. Various physical–chemical characterizations, including BET, XRD, UV–vis and H₂-TPR, revealed that isolated Cu^2 + species in the MCM-41 framework were responsible for the catalytic activities. This catalyst could be reused for three times without discernible loss in its activity and selectivity.