Yinxi Zhou

Selective Phenol Hydrogenation to Cyclohexanone Over a Dual Supported Pd–Lewis Acid Catalyst

Cooperative Reduction Selective redox transformation remains a general challenge in chemical synthesis. All too often, the most readily available precursor to a compound must be over-reduced (or over-oxidized) and then carefully coaxed back to a desired intermediate state. Such is the case with the synthesis of cyclohexanone, which is mass-produced for use in the preparation of nylon: Access by direct reduction of phenol is plagued by the rapid addition of too many hydrogen atoms to the substrate, producing an alcohol (cyclohexanol) in place of the ketone. Liu et al. (p. 1250) have discovered that the unexpected cooperation of supported palladium and a Lewis acid such as aluminum trichloride—two catalysts widely used alone but rarely in concert—facilitates highly selective conversion of phenol to cyclohexanone near room temperature. The key appears to be inhibition of the undesired ketone-to-alcohol reduction step by the Lewis acid. The cooperation of two common catalysts unexpectedly facilitates selective synthesis of a commodity chemical compound. Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon, but preparing it efficiently through direct hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Here we report that a previously unappreciated combination of two common commercial catalysts―nanoparticulate palladium (supported on carbon, alumina, or NaY zeolite) and a Lewis acid such as AlCl3―synergistically promotes this reaction. Conversion exceeding 99.9% was achieved with >99.9% selectivity within 7 hours at 1.0-megapascal hydrogen pressure and 50°C. The reaction was accelerated at higher temperature or in a compressed CO2 solvent medium. Preliminary kinetic and spectroscopic studies suggest that the Lewis acid sequentially enhances the hydrogenation of phenol to cyclohexanone and then inhibits further hydrogenation of the ketone.

Efficient conversion of glucose into 5-hydroxymethylfurfural catalyzed by a common Lewis acid SnCl4 in an ionic liquid

The common Lewis acid SnCl4 could efficiently convert glucose into 5-hydroxymethylfurfural in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMim]BF4). New evidence indicated that the formation of the five-membered-ring chelate complex of the Sn atom and glucose may play a key role for the formation of HMF, and the mechanism for the reaction was proposed. In addition, the [EMim]BF4/SnCl4 system was also suitable for the conversion of fructose, sucrose, inulin, cellobiose and starch.

Conversion of fructose to 5-hydroxymethylfurfural using ionic liquids prepared from renewable materials

Efficient conversion of fructose to 5-hydroxymethylfurfural is a key step for using carbohydrates to produce liquid fuels and value-added chemicals. Here we show that some ionic liquids synthesized from cheap renewable materials are very efficient for the conversion of fructose to HMF. The yield and selectivity could be higher than 90% as the reaction was conducted in an ethyl acetate/renewable IL biphasic system and the separation process had no cross-contamination. Moreover, the IL can be reused easily.

Direct conversion of inulin to 5-hydroxymethylfurfural in biorenewable ionic liquids

In this work, we found that inulin is soluble in ionic liquids (ILs) choline chloride (ChoCl)/oxalic acid and ChoCl/citric acid, which are prepared entirely from cheap and renewable materials. On the basis of this discovery, we conducted the one pot reaction for the conversion of inulin into 5-hydroxymethylfurfural (HMF), which is a potential substitute for petroleum-based building blocks, using the two ILs as catalysts and solvents. The effects of reaction time, temperature and water added on the reaction were studied. It is demonstrated that the ILs are very efficient for the reaction at relatively lower temperature and could be reused after simple separation.

Solvent-free synthesis of substituted ureas from CO2 and amines with a functional ionic liquid as the catalyst

The synthesis of disubstituted ureas from amines and CO2 were carried out using a basic ionic liquid (IL) 1-n-butyl-3-methyl imidazolium hydroxide ([Bmim]OH) as the catalyst. The effects of reaction time, amount of [Bmim]OH, reaction temperature, pressure, and solvent on yields of the products were investigated. The results indicated that aliphatic amines, cyclohexylamine, and benzylamine could be converted to the corresponding ureas selectively in moderate yields under solvent-free conditions without using any dehydrating regent. The IL could be reused after a simple separation procedure.

Hydrogenolysis of glycerol catalyzed by Ru-Cu bimetallic catalysts supported on clay with the aid of ionic liquids

Glycerol is a well-known renewable chemical, and its effective transformation to valuable chemicals accords well with the principles of green chemistry. In this work, a series of Ru-Cu bimetallic catalysts were prepared using cheap and abundant clay, bentonite, as the support. Bentonite was modified with a functional ionic liquid 1,1,3,3-tetramethylguanidinium lactate (TMGL) in an attempt to develop highly efficient catalysts. Hydrogenolysis of aqueous solution of glycerol was performed with the immobilized Ru-Cu catalyst under temperatures of 190–240 °C and pressures of 2.5–10 MPa. The bimetallic catalysts were very efficient for promoting the hydrogenolysis of glycerol. 100% of glycerol conversion and 85% yield of 1,2-propanediol could be achieved at 230 °C and 8 MPa. The conversion of glycerol and the selectivity to 1,2-propanediol did not decrease after the catalyst was used 5 times. TMGL played a crucial role in fabricating the new catalysts. The catalysts were characterized by FT-IR, XPS, SEM and TEM, and the reasons for the excellent performances of the catalyst were also discussed.

Solvent -free Heck reaction catalyzed by a recyclable Pd catalyst supported on SBA-15 via an ionic liquid

Heck arylation of olefins with aryl halides was carried out in solvent-free conditions with a Pd catalyst supported on 1,1,3,3-tetramethylguanidinium (TMG)-modified molecular sieve SBA-15 (designated as SBA-TMG-Pd). SBA-TMG-Pd was much more active and stable than a Pd catalyst supported on pristine SBA-15 (designated as SBA-Pd). The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), and the reasons for the excellent performance of catalyst SBA-TMG-Pd were also discussed.

The tetramethylguanidine-based ionic liquid-catalyzed synthesis of propylene glycol methyl ether

Tetramethylguanidine-based ionic liquids were used as effective catalysts for the synthesis of propylene glycol methyl ether from methanol and propylene oxide. 1-Methoxy-2-propanol was produced in nearly 90% yield under much milder conditions. The catalyst can be reused at least ten times without any considerable decrease in its activity and selectivity.

Synthesis of Propylene Glycol Methyl Ether Catalyzed by MCM-41

Abstract In this work, we found that MCM-41 prepared using cetyltrimethyl ammonium bromide (CTAB) as the template could be used as a heterogeneous catalyst for the reaction of methanol with propylene oxide to produce propylene glycol methyl ether. 1-Methoxy-2-propanol was the predominant product. The influence of ratio of the reactants, reaction temperature, and time on the yield and selectivity was studied. The as-prepared MCM-41 proved to be an efficient and reusable catalyst, and the separation of the catalyst form the product was very easy.