Solvent-free Alcohol Oxidation Research Articles

Solvent-free oxidation of alcohols by a heterogeneous Fe3O4@SiO2-DTPA-Ru nanocatalyst

A novel magnetic heterogeneous ruthenium catalyst (Fe3O4@SiO2-DTPA-Ru) was prepared by using magnetic silicon spheres as support, ethylenediaminepentaacetic acid (DTPA) as functional ligands, ruthenium chloride as catalyst precursor. The results obtained after a series of characterizations showed that the catalyst Fe3O4@SiO2-DTPA-Ru was 5–15 nm in size with a 0.205 nm lattice and contained 0.31 mmol Ru/g catalyst. It also had a good thermal stability under 232°C which was verified by thermal filtration method. Besides, the saturation magnetic intensity was as high as 20.54 emu/g. The catalyst Fe3O4@SiO2-DTPA-Ru was applied for the first time into thirteen oxidation reactions of aromatic alcohols and showed good catalytic activity even the yields of eleven aromatic alcohols were all over 90%. In catalyzing 1-phenylethanol to acetophenone, its TOF and TON were 9677 h−1 and 6991, respectively. The Fe3O4@SiO2-DTPA-Ru catalyst could still maintain good reusability and catalytic performance after 15 cycles of 1-phenylethanol oxidation, which was superior to many reported catalysts and had great potential in future industrial production.

New Polymer Colloidal and Carbon Nanospheres: Stabilizing Ultrasmall Metal Nanoparticles for Solvent-Free Catalysis

Herein, we report the synthesis of new colloidal polydiaminopyridine (PDAP) nanospheres with uniform particle size tuned from 76 to 331 nm. The polymer colloidal nanospheres and thin films assembled by the nanospheres exhibit amphiphilic or superhydrophilic properties, originated from the different polymer surfactants. In addition, the polymer nanospheres can be easily carbonized into microporous carbon nanospheres with high N content up to 24 wt %, thus enabling a preferred basicity for CO2 adsorption. As-synthesized PDAP show good compatibility that can not only encapsulate typical nanoparticles to form core–shell composite nanospheres but also stabilize noble metal ions to obtain ultrasmall metal nanoparticles (e.g., Pd and Au) during the thermal reduction process by the nitrogen sites from sphere frameworks. The nanocomplex Pd/PDAP-500 shows exceptional activity and high selectivity in the solvent-free oxidation of alcohols with O2.

Synthesis and Application of Hyperbranched Polyester-Grafted Polyethylene (HBPE-g-PE) Containing Palladium Nanoparticles as Efficient Nanocatalyst

In nowadays, palladium-catalyzed reactions are of utmost importance in synthetic organic chemistry. Due to advantages of heterogeneous catalysts such as the easy handling and good recyclability, usually these types of catalysts are first choice in constructing a new catalytic system. Here we report a facile approach to prepare hyperbranched polyester-grafted-polyethylene supported palladium nanoparticles as an efficient catalyst in Suzuki reaction and solvent-free aerobic oxidation of alcohols. The reactions were carried out in different conditions with various reagents and the efficiency was determined. Because of the amplification effect of hyperbranched polyester, high loading capacities (around 0.276 mmol g−1 for Pd) was achieved. The catalyst was characterized with X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. This metal nanocatalyst has a very low leaching loss, high activity and selectivity, excellent thermal stability and can be reused at least five times without deactivation of catalytic activity. In this work, a hyperbranched polyester based on 2,2-bis (methylol) propionic acid (bis-MPA) was synthesized and grafted onto carboxylic acid functionalized polyethylene powder. The final nanocatalyst was prepared via solution loading of PdCl2 and reduction to palladium nanoparticles on the HBPE-g-PE. The activity and stability of prepared polymer-supported heterogeneous catalyst was carefully examined for Suzuki reaction and solvent-free oxidation of alcohols.

Solvent-free alcohol oxidation using paper-structured catalysts: Flow dynamics and reaction kinetics

Paper-structured fibrous composites with micrometer-sized pores were prepared using a papermaking technique, followed by in situ synthesis of Pd nanoparticles in the paper matrix using a facile impregnation method. The Pd-containing paper-structured catalysts showed high catalytic activities in solvent-free benzyl alcohol oxidation in a flow reaction system. Highly selective oxidation was achieved using the porous paper-structured catalysts set inside a gas–liquid–solid multiphase reactor. Kinetic and mechanistic studies of various reactions showed that the catalytic activity and selectivity were associated with microfluidic behavior in the fiber-network pores. A uniform distribution of the liquid-phase substrate, i.e., benzyl alcohol, provided high catalytic activity. High selectivity for the oxidation pathways can be attributed to efficient gas–liquid–solid mass transfer toward the thin liquid layer formed at the interface between the alcohol and Pd catalyst inside the porous fiber networks.

Pd on boron-doped hollow carbon spheres – PdO particle size and support effects

Boron-doped hollow carbon spheres (B-HCSs) were synthesized using a CVD injection method (BCl3 in toluene; Ar; 900°C; 4h) using Stöber silica spheres as template. A Pd complex was loaded onto the B-HCSs using deposition and impregnation methods, and the materials were studied by XRD, SEM, TEM, Raman spectroscopy, TGA, ICP-OES, XPS, and 11B solid-state NMR spectroscopy. The boron-doped carbon-supported Pd catalysts (Pd/B-HCS) were compared with a Pd-loaded boron-doped carbon nanotube (Pd/B-CNT) catalyst (both have a hollow interior) in the solvent-free oxidation of alcohols using oxygen as an oxidant at 125°C under base-free conditions. The Pd particle size was varied (2.5–12nm) by changing the Pd/B-HCS calcination temperature (200–550°C), and this affected the activity but not the selectivity of the benzyl alcohol to benzaldehyde reaction. The data revealed the key role of the Pd particle size on the reaction that was influenced by the B–Pd–C interaction. The reaction rate depended on the mean size of Pd particles and showed a maximum when catalysts were calcined at 300°C, revealing that the aerobic oxidation of benzyl alcohol catalyzed by the supported PdO (dPd>2.5nm) nanoparticles was not a structure sensitive reaction.

Solvent free clean selective oxidation of alcohols catalyzed by mono transition metal (Co, Mn, Ni)-substituted Keggin-phosphomolybdates using hydrogen peroxide

Traditional procedures for synthesis of carbonyl compounds suffer from a lack of selectivity, use of organic solvents, toxicity of the reagents, and waste production. As a cleaner alternative, an environmentally benign solvent free oxidation of alcohols catalyzed by mono transition metal-substituted Keggin-phosphomolybdates, PMo11M (M=Co, Mn, Ni) using hydrogen peroxide was carried out under mild conditions. The influence of different parameters such as mole ratio of benzyl alcohol to H2O2, amount of the catalyst, reaction time and reaction temperature on oxidation of benzyl alcohol was investigated. Further, oxidation of various alcohols such as cyclopentanol, 1-hexanol and 1-octanol with PMo11M was carried out under optimized conditions. The catalytic activity of recycled catalysts was also evaluated and it was found that catalysts are stable under present reaction conditions. All the catalysts are very much efficient, especially in terms of % selectivity of the desire product.

Phosphotungstic acid loaded on hydrophilic ionic liquid modified SBA-15 for selective oxidation of alcohols with aqueous H2O2

Phosphotungstic acid (H3PW12O40) has been successfully loaded onto amino-functionalized ionic liquid modified mesoporous silica SBA-15 by totally anion-exchange and partly protonating in the channel of SBA-15 with Keggin-type H3PW12O40. XRD patterns, N2 adsorption–desorption isotherms and TEM images confirm the intact mesostructures of the samples. Thermal analysis, 29Si MAS NMR and 31P MAS NMR indicate the presence of the [PW12O40]3− (PW) in the mesopores. FT-IR spectra suggest that a portion of free amino groups in the amino-functionalized IL moiety are remained in the channel of the catalysts, although there are ionic interactions between PW anions and protonated amino groups, as well as between PW anions and imidazolium cations. Hydrophilic amino-functionalized IL moiety in the mesostructures, especially, the remained free amino groups flexibly anchored on the imidazolium, plays a crucial role in enhancing the accessibility of H2O2, which in turns significantly improves the catalytic performance. The resultant PW loaded on amino-functionalized IL modified SBA-15 (PW-NH2-IL-SBA-15) catalysts are proven to be versatile in the solvent-free oxidation of alcohols with aqueous 30% H2O2, presenting high efficiency, convenient recovery and steady reuse.

Solvent-free oxidation of alcohols by hydrogen peroxide over chromium Schiff base complexes immobilized on MCM-41

A series of chromium(III) Schiff base complexes immobilized on MCM-41 were prepared and characterized by various physicochemical and spectroscopic methods. The complexes were used for the selective oxidation of alcohols by 30% hydrogen peroxide without any organic solvent, phase transfer catalyst or additive. The immobilized complexes proved to be effective catalysts and generally exhibited much higher catalytic performance than their corresponding homogeneous analogs. The catalytic performance of the immobilized complexes was also found to be closely related to the Schiff base ligands used. Under the optimal reaction conditions, secondary alcohols, cyclic alcohols and benzyl alcohol were prevailingly oxidized to their corresponding ketones or aldehydes.

Selective alcohol oxidation to aldehydes and ketones over base-promoted gold–palladium clusters as recyclable quasihomogeneous and heterogeneous metal catalysts

Bimetallic gold–palladium clusters, with an average size of 1.9 nm and composed of 80 mol% gold, proved to be highly active and selective metal catalysts for the organic phase oxidation with O 2 of aliphatic, allylic and benzylic alcohols to the corresponding carbonyl products. Polyvinylpyrrolidone stabilized gold–palladium clusters dispersed in N, N-dimethylformamide emerged as promising quasihomogeneous metal catalysts for the oxidation of benzyl alcohol to benzaldehyde with full selectivity; they could be efficiently recycled with unaffected catalytic performance by solvent-resistant nanofiltration. Highly active and durable heterogeneous catalysts for the amide phase or solvent-free alcohol oxidation were prepared by the quantitative immobilization of the optimized gold–palladium clusters on the high surface area basic BaAl 2O 4 spinel support with preservation of the bimetallic clusters’ nanodispersion.

Solvent-Free Oxidation of Alcohols with Potassium Persulphate in the Presence of Brönsted Acidic Ionic Liquids

An efficient conversion of alcohols to aldehydes was achieved using potassium persulphate and 3-methylimidazolinium methane sulfonate.

Ce(NO3)3] 3×H2IO6: Efficient Oxidation Reactions under Solvent‐Free Conditions.

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Ce(No3)3]3.H2IO6: Efficient Oxidation Reactions Under Solvent-Free Conditions

Efficient solvent-free oxidation of alcohols, deprotection and oxidative deprotection of trimethylsilyl ethers and oxidative deprotection of oximes using tris [trinitratocerium (IV)] paraperiodate (TTCPP) is reported.

Solvent-Free Aerobic Oxidation of Alcohols Catalyzed by an Efficient and Recyclable Palladium Heterogeneous Catalyst

A simple alumina-supported palladium catalyst prepared by an adsorption method is highly efficient and recyclable in the solvent-free oxidation of alcohols with molecular oxygen. The adsorption method results in high dispersion of palladium probably as mononuclear or oligonuclear species on alumina surface. These palladium species are transformed to small Pd nanoparticles (ca. 5 nm), which are probably the true active species, during the course of alcohol oxidation.

Cautionary Comments (author response)

Reply to concerns about a safety factor in the paper, “A Solvent-Free Oxidation of Alcohols in an Organic Laboratory.

Solvent-free oxidation of alcohols by t-butyl hydroperoxide catalyzed by water-soluble copper complex

The catalytic system composed of CuCl 2 and 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC), was found to be highly efficient for the selective oxidation of secondary benzylic, allylic and propargylic alcohols to the corresponding ketones, with aqueous t-butyl hydroperoxide under phase-transfer catalysis conditions. The catalytic system is stable and can be recycled and reused several times without loss of activity.

Solvent free oxidation of alcohols catalyzed by KMnO 4 adsorbed on Kieselguhr

Efficient and selective oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones catalyzed by potassium permanganate supported on Kieselguhr reagent under solvent free conditions are reported.

A Solvent-Free Oxidation of Alcohols in an Organic Laboratory

An oxidation experiment for a first-year organic chemistry class is presented. This oxidation utilizes a solid mixture of CuSO4•5H2O and KMnO4 prepared by mortar and pestle. The oxidations take place under solvent-free conditions and near quantitative yields are obtained for the reactions. Thin-layer chromatography is used to monitor the progress of the reaction. This experiment provides for the simple oxidation of a secondary alcohol to a ketone using a relatively nontoxic oxidizing agent under solvent-free conditions.See Letter re: this article.

Solvent free oxidation of alcohols with manganese dioxide

The oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones by manganese dioxide under solvent free conditions are described. This new oxidation procedure is very simple and affords good yields.