Masayoshi Honda

Heterogeneous CeO2 catalyst for the one-pot synthesis of organic carbamates from amines, CO2 and alcohols

Heterogeneous CeO2 catalyst can catalyze the one-pot synthesis of methyl benzylcarbamate from benzylamine, CO2 and methanol. The yield of methyl benzylcarbamate reached 92% at >99% benzylamine conversion and 92% benzylamine-based selectivity even in the absence of the dehydrating agents. The catalyst is reusable after the calcination at 873 K for 3 h. Various carbamates can be synthesized with good yield and high selectivity by the reaction of amines + CO2 + alcohols over CeO2. The main formation route of methyl benzylcarbamate is suggested to be the reaction of dimethyl carbonate or the precursor of dimethyl carbonate formation with benzylamine.

Tandem Carboxylation‐Hydration Reaction System from Methanol, CO2 and Benzonitrile to Dimethyl Carbonate and Benzamide Catalyzed by CeO2

CeO2 is an effective catalyst for a new tandem reaction system; The synthesis of dimethyl carbonate (DMC) from methanol+ CO2 and benzonitrile hydration to benzamide. In combination with benzonitrile hydration, the yield of DMC was drastically promoted even at CO2 pressures as low as 0.1 MPa. The yields of methanol‐ and CO2‐based DMC were as high as 47 % and 70 %, respectively. Calcination of the catalyst at 873 K after the reaction, enables the catalyst to be reused without any structural change, although benzamide, produced by the benzonitrile hydration, poisons of the catalyst. This reaction system can be applied to the synthesis of other dialkylcarbonates from their corresponding alcohols and CO2.

Catalytic CO2 conversion to organic carbonates with alcohols in combination with dehydration system

Recent progress on the direct synthesis of organic carbonate from CO2 and alcohol combined with dehydration systems has been reviewed. Versatile dehydration systems have been developed, which have drastically improved the yields of the target carbonates. In this review, the features and effects of the dehydration systems are discussed by categorizing the dehydration systems into two types, non-reactive dehydration systems and reactive dehydration systems.

Highly efficient synthesis of cyclic ureas from CO2 and diamines by a pure CeO2 catalyst using a 2-propanol solvent

Pure cerium oxide (CeO2) acts as an effective and reusable heterogeneous catalyst for direct synthesis of cyclic ureas from CO2 and diamines even at a low CO2 pressure of 0.3 MPa. 2-Propanol is the most preferable solvent to provide good selectivity. The system composed of a CeO2 catalyst and a 2-propanol solvent is applied to various diamines to provide the corresponding cyclic ureas in high yields (78–98%), including six-membered-ring ureas that are difficult to be synthesized from CO2. Based on the kinetic studies on the effect of CO2 pressure and amine concentration and FTIR studies on adsorption of ethylenediamine and CO2 onto CeO2, the following mechanism for the synthesis of cyclic urea is proposed: (1) formation of carbamic acid and carbamate species on CeO2, (2) decomposition of carbamic acid to a free amino group and CO2, (3) nucleophilic attack of the amino group on the carbamate on CeO2 to produce the cyclic urea and (4) desorption of the product and regeneration of CeO2.

Direct Copolymerization of CO2 and Diols.

Direct polymerization of CO2 and diols is promising as a simple and environmental-benign method in place of conventional processes using high-cost and/or hazardous reagents such as phosgene, carbon monoxide and epoxides, however, there are no reports on the direct method due to the inertness of CO2 and severe equilibrium limitation of the reaction. Herein, we firstly substantiate the direct copolymerization of CO2 and diols using CeO2 catalyst and 2-cyanopyridine promotor, providing the alternating cooligomers in high diol-based yield (up to 99%) and selectivity (up to >99%). This catalyst system is applicable to various diols including linear C4-C10 α,ω-diols to provide high yields of the corresponding cooligomers, which cannot be obtained by well-known methods such as copolymerization of CO2 and cyclic ethers and ring-opening polymerization of cyclic carbonates. This process provides us a facile synthesis method for versatile polycarbonates from various diols and CO2 owing to simplicity of diols modification.

Development of a H3PW12O40/CeO2 catalyst for bulk ring-opening polymerization of a cyclic carbonate

A new reaction system involving a heterogeneous H3PW12O40/CeO2 catalyst and methyl iodide initiator was developed for bulk ring-opening polymerization (ROP) of trimethylene carbonate (TMC). Combination of a Bronsted acid (H3PW12O40) and Lewis base (CeO2) had a synergic effect on a well-controlled ROP without decarboxylation, which gave poly(TMC) of molecular weight (Mn) 30 000 and Polydispersity Index (PDI) of 1.80 at 60 °C and 24 h. Fourier transform infrared (FTIR) spectroscopy elucidated a reaction mechanism in which H3PW12O40 promoted the initiation reaction and CeO2 activated TMC, and the interface of these two components was an active site for ROP. The catalyst was removed readily by filtrating a dimethyl carbonate solution of poly(TMC), which was confirmed by inductively coupled plasma-atomic emission spectroscopy. In addition, various kinds of biomass-derived poly(aliphatic carbonate)s were synthesized and thermal properties were investigated by differential scanning calorimetry and thermogravimetry-differential thermal analysis. In particular, pyrolysis-gas chromatography mass spectrometry of these polymers revealed that the degradation mechanism was highly dependent upon a small amount of ether linkages and a pendant methyl group.

Direct Catalytic Synthesis of N-Arylcarbamates from CO2, Anilines and Alcohols

The direct catalytic synthesis of carbamates from CO2, amines and methanol was achieved by controlling both the reaction equilibrium and the reactivity of the three components. The combination of CeO2 and 2‐cyanopyridine was an effective catalyst, providing various carbamates including N‐arylcarbamates in high selectivities.