Secondary Amines from Catalytic Amination of Bio-Derived Phenolics over Pd/C and Rh/C: Effect of Operation Parameters

The production of renewable chemicals using lignocellulosic biomass has gained significant attention in green chemistry. Among biomass-derived chemicals, secondary amines have emerged as promising intermediates for synthetic applications. Here, we report a systematic study on the reductive amination of phenolics with cyclohexylamine using Pd/C and Rh/C as catalysts. The catalytic tests were performed in batch reactors under different reaction conditions (various: amine concentration (0.1–0.4 mol/L), hydrogen pressure (0–2.5 bar), temperature (80–160 °C), and substituted phenols (phenol, o-cresol, p-cresol, and methoxyphenol)) and using tert-amyl alcohol as a solvent. The experimental observations were consistent with a multi-step mechanism, where hydrogenation of phenol to cyclohexanone is followed by condensation of the ketone with cyclohexylamine to form an imine, which is finally hydrogenated to produce secondary amines. In addition, there was evidence of parallel self-condensation of the cyclohexylamine. The study also supported a limited dehydrogenation capacity of Rh/C, unlike Pd/C, which increases this capacity at higher temperatures generating a higher yield of cyclohexylaniline (up to 15%). The study of the alkylated phenols demonstrated that the nature and propensity of hydrogenation of the phenolic controls their amination. Kinetic analysis revealed reaction orders between 0.4 and 0.7 for H2, indicating its dissociative adsorption. Meanwhile, phenol’s order (between 1–1.8) suggests a single participation of this compound in the hydrogenation step. The order of 0.4 for cyclohexylamine suggests its participation as a surface-abundant species. The apparent activation energies derived from a power law approximation were of 37 kJ/mol and 10 kJ/mol on Pd/C and Rh/C, respectively.

Tandem process for in situ H2O2 formation coupled with benzyl alcohol oxidation by Pd-Au bimetallic catalysts

Alcohol oxidation is among the most important industrial organic reactions. Traditionally, the best-suited catalysts are Pd, Pt and Au supported nanoparticles. The research community has recently started drawing-up strategies to...

MOF-Mediated Synthesis of Supported Fe-Doped Pd Nanoparticles under Mild Conditions for Magnetically Recoverable Catalysis*

Metal-organic framework (MOF)-driven synthesis is considered as a promising alternative for the development of new catalytic materials with well-designed active sites. This synthetic approach is used here to gradually transform a new bimetallic MOF, with Pd and Fe as the metal components, by the in situ generation of aniline under mild conditions. This methodology results in a compositionally homogeneous nanocomposite formed by Fe-doped Pd nanoparticles that, in turn, are supported on iron oxide-doped carbon. The nanocomposite has been fully characterized by several techniques such as IR and Raman spectroscopy, TEM, XPS, and XAS. The performance of this nanocomposite as an heterogeneous catalyst for hydrogenation of nitroarenes and nitrobenzene coupling with benzaldehyde has been evaluated, proving it to be an efficient and reusable catalyst.

Pd supported on mixed metal oxide as an efficient catalyst for the reductive amination of bio-derived acetol to 2-methylpiperazine

Efficient synthesis of 2-methylpiperazine via reductive cyclo-amination of acetol with ethylenediamine over Pd supported on Ti–Al–O and Ti–Zr–O catalysts.

Tuning product selectivity in the catalytic oxidation of glycerol by employing metal-ZSM-11 materials

Selective oxidation of glycerol towards dihidoxyacetone and lactic acid, employing micro/mesoporous zeolites with copper(ii) and chromium(iii).

Copper and sulphur co-doped titanium oxide nanoparticles with enhanced catalytic and photocatalytic properties

Copper and sulphur co-doped titanium oxide nanoparticles have been prepared by the sol–gel method to develop versatile catalysts exhibiting enhanced catalytic and photocatalytic properties.

W–Nb–O oxides with tunable acid properties as efficient catalysts for the transformation of biomass-derived oxygenates in aqueous systems

The control of Nb incorporation in W–Nb–O system leads to tailored Brönsted/Lewis acid properties for the selective transformation of either glycerol or aqueous mixtures of short chain oxygenates into value added products.

Redox tuning and species distribution in Maya Blue-type materials: a reassessment

Maya Blue-type specimens prepared from indigo (1 wt %) plus kaolinite, montmorillonite, palygorskite, sepiolite, and silicalite are studied. Liquid chromatography with diode array detection, ultra-performance liquid chromatography coupled with mass spectrometry, and pyrolysis-silylation gas chromatography-mass spectrometry analyses of the extracts from these specimens combined with spectral and solid-state voltammetry, electrochemical impedance spectroscopy, and scanning electrochemical microscopy techniques provide evidence for the presence of a significant amount of dehydroindigo and isatin accompanying indigo and other minority organic compounds in all samples. Solid-state electrochemistry data permits the estimatation of indigo loading in archeological Maya Blue, which is in the range of 0.2 to 1.5 wt %. These results support a view of 'genuine' Maya Blue-type materials as complex polyfunctional organic-inorganic hybrids.

Gold supported on a mesoporous CeO2 matrix as an efficient catalyst in the selective aerobic oxidation of aldehydes in the liquid phase

Gold supported on CeO2 catalyses the selective aerobic oxidation of aliphatic and aromatic aldehydes better than other reported catalysts such as Pt/C/Bi materials; the activity is due to the nanometric particle size of Au and CeO2.

Al-free Sn-Beta zeolite as a catalyst for the selective reduction of carbonyl compounds (Meerwein-Ponndorf-Verley reaction)

The catalytic activity of Sn-Beta zeolite in the Meerwein-Ponndorf-Verley (MPV) reduction of carbonyl compounds with secondary alcohols was performed with quantitative yields to the corresponding alcohol. This heterogeneous catalyst exhibits activities and selectivities not observed before with other Me-zeolites.