Hajime Kawanami

A rapid and effective synthesis of propylene carbonate using a supercritical CO2–ionic liquid system

The synthesis of propylene carbonate from propylene oxide and carbon dioxide under supercritical conditions in the presence of 1-octyl-3-methylimidazolium tetrafluoroborate was achieved in nearly 100% yield and 100% selectivity within 5 minutes, whose TOF value is 77 times larger than those so far reported.

Hydrogenation of 5-hydroxymethylfurfural in supercritical carbon dioxide–water: a tunable approach to dimethylfuran selectivity

The use of supercritical carbon dioxide–water on the hydrogenation of 5-hydroxymethylfurfural (HMF) was investigated over a Pd/C catalyst. It was possible to achieve a very high yield (100%) of DMF within the reaction time of 2 hours at 80 °C. A significant effect of CO2 pressure was observed on the product distribution. Simply by tuning the CO2 pressure it was possible to achieve various key compound, such as tetrahydro-5-methyl-2-furanmethanol (MTHFM) ( 10 MPa) with very high selectivity. Optimization of other reaction parameters revealed that H2 pressure, temperature, as well as the CO2–water mole ratio, played an important role in the selectivity to the targeted DMF. It is interesting to note that a very high yield of DMF was achieved when a combination of CO2 and water was used. For instance, in the absence of water or CO2, the selectivity of DMF was low; similarly, an excess of water against the fixed pressure of CO2 reduced the selectivity to DMF. Hence, an optimized amount of water was mandatory in the presence of CO2 for the formation of DMF with high selectivity. This method was successfully extended to the hydrogenation of furfural, which could afford 100% selectivity to 2-methylfuran with complete conversion within a very short reaction time of 10 min. The studied catalyst could be recycled successfully without significant loss of catalytic activity.

Regioselectivity and selective enhancement of carbon dioxide fixation of 2-substituted aziridines to 2-oxazolidinones under supercritical conditions

Under supercritical CO2 conditions, regioselectivity in the carbon dioxide fixation of 2-substituted aziridines to 2-oxazolidinones was observed with good yields around 75%. Furthermore, when propylene imine was used in the place of aziridine, the yield was significantly and selectively increased around the critical pressure, and the maximum yield was obtained at 11.8 MPa. The turnover frequency (TOF) at this pressure is 2.1 times greater than that of a hitherto reported TOF which was obtained in ethanol at 6.9 MPa.

Selective hydrogenation of 5-hydroxymethylfurfural to 2,5-bis-(hydroxymethyl)furan using Pt/MCM-41 in an aqueous medium: a simple approach

The hydrogenation of HMF has been conducted in a neutral aqueous medium. Without any additive, HMF was hydrogenated to 2,5-bis-(hydroxymethyl)furan (BHMF) with complete conversion and selectivity (98.9%) using Pt/MCM-41 as catalyst. A very low temperature of 35 °C and 0.8 MPa of hydrogen pressure was used to accomplish the highest selectivity of BHMF within a reaction time of 2 h. Different reaction parameters such as reaction time, hydrogen pressure and the amount of water was optimized to achieve the highest catalytic activity. In particular, the presence or absence of water and the amount of water played an important role to determine the conversion and product distribution of the reaction. For instance, in the absence of water or a large excess of water, the selectivity of BHMF was decreased. In addition, instead of water the influence of three different groups of organic solvent were also explored to obtain BHMF under the studied reaction conditions. It has been observed that the studied organic solvents strongly influenced the catalytic performance, such as solvents with a negative δ value, which followed a clear trend with the substrate conversion, whereas no impact was observed for solvents with a positive δ value. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any significant loss of catalytic activity.

Hydrogenation of nitrile in supercritical carbon dioxide: a tunable approach to amine selectivity

The use of supercritical carbon dioxide (scCO2) on the hydrogenation of benzonitrile was investigated over Pd and other metal catalysts. Without any additive, benzonitrile was hydrogenated to benzylamine with high conversion (90.2%) and selectivity (90.9%) using the Pd/MCM-41 catalyst. A strong influence of CO2 pressure on the conversion and selectivity were observed. As the CO2 pressure increases, the conversion was increased, and after reaching the maximum at around 8–10 MPa, it decreased. Moreover, simply by tuning the CO2 pressure, it is possible to obtain benzylamine or dibenzylamine. For instance, at lower pressure CO2 acts as a protecting agent, leading to the formation of the primary amine, but at higher pressure, the yield of primary amine as well as the solubility of the imine intermediate in CO2 increases, which results high selectivity for dibenzylamine. A plausible mechanism has been proposed to show the role of CO2 on the selectivity toward primary and secondary amines. The results confirm that the presence of CO2 is mandatory for the formation of benzylamine with high selectivity. Furthermore, the other reaction parameters, such as reaction time, H2 pressure, temperature etc., also affect the conversion as well as selectivity of benzylamine. This process has been extended to the hydrogenation of a series of different nitrile compounds.

Green synthesis of titania nanowire composites on natural cellulose fibers

A simple, efficient and environmentally benign approach for the synthesis of titania nanowire is achieved by using natural fibres as templates and ionic liquids as solvent.

Production of linear alkane via hydrogenative ring opening of a furfural-derived compound in supercritical carbon dioxide

A simple method has been described to accomplish the formation of linear alkane with >99% selectivity in supercritical carbon dioxide under very mild conditions using Pd/Al-MCM-41 catalyst. The linear alakne was formed through the hydrogenation and dehydration/hydrogenation of 4-5-(5-(hydroxymethyl)furan-2-yl)but-3-en-2-one, which is an aldol condensation product of 5-hydroxymethyl furfural and acetone.

Reductive amination of furfural to furfurylamine using aqueous ammonia solution and molecular hydrogen: an environmentally friendly approach

A simple and highly efficient method was developed for the transformation of furfural (a biomass derived aldehyde) to furfurylamine by reductive amination using an aqueous solution of ammonia and molecular hydrogen as an amine source and a reducing agent, respectively. By choosing a suitable catalyst, such as Rh/Al2O3, and reaction conditions, a very high selectivity of furfurylamine (∼92%) can be achieved within the reaction time of 2 h at 80 °C. A detailed analysis of the reaction system sheds some light on the reaction pathway and provides an understanding about each elementary step. The reaction was believed to proceed via an imine pathway although no such intermediate was detected because of the highly reactive nature. Optimization of different reaction parameters such as hydrogen pressure, temperature and substrate/ammonia mole ratio is shown to be critical to achieve high selectivity of furfurylamine. Time-dependent reaction profiles suggested that a Schiff base type intermediate was in the detectable range, which offers indirect evidence of the formation of imine. Competitive hydrogenation and amination of an aldehyde group were strongly dictated by the nature of the metal used. The studied protocol represents an environmentally benign process for amine synthesis, which can be effectively extended to the other aldehydes also. The studied catalyst could be recycled successfully without any significant loss of catalytic activity.

Carbon Dioxide to Methanol: The Aqueous Catalytic Way at Room Temperature

Carbon dioxide may constitute a source of chemicals and fuels if efficient and renewable processes are developed that directly utilize it as feedstock. Two of its reduction products are formic acid and methanol, which have also been proposed as liquid organic chemical carriers in sustainable hydrogen storage. Here we report that both the hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized at ambient temperature and in aqueous, acidic solution, with an iridium catalyst. The formic acid yield is maximized in water without additives, while acidification results in complete (98 %) and selective (96 %) formic acid disproportionation into methanol. These promising features in combination with the low reaction temperatures and the absence of organic solvents and additives are relevant for a sustainable hydrogen/methanol economy.

An attempt to achieve the direct hydrogenolysis of tetrahydrofurfuryl alcohol in supercritical carbon dioxide

The use of supercritical carbon dioxide (scCO2) in the hydrogenolysis of tetrahydrofurfuryl alcohol was investigated over a Rh supported MCM-41 catalyst (metal loading ≈ 1%). Without any additive, tetrahydrofurfuryl alcohol was converted to 1,5-pentanediol with high conversion (80.2%) and selectivity (91.2%) under mild reaction conditions (temperature = 80 °C and H2 pressure = 4 MPa). The effects of different variables like CO2 and H2 pressure, temperature and the reaction time were also optimized. A strong influence of CO2 pressure on the conversion was observed. The conversion was increased with pressure due to the enhanced solubility of tetrahydrofurfuryl alcohol in CO2 and reached the maximum at 14 MPa, as the single phase (CO2–H2–substrate) was formed, but the selectivity of 1,5-pentanediol remained unaltered. On the other hand, H2 pressure also changed the conversion as well as the selectivity. Temperature was found to play an important role in enhancing the catalytic efficiency; conversion of the substrate was increased along with the temperature, but the selectivity of 1,5-pentanediol dropped after reaching 120 °C. The Rh catalyst exhibited strikingly different product distribution under the solvent-less conditions compared to scCO2. In addition, instead of CO2, when the reaction was carried out in H2O, the conversion and the selectivity of 1,5-pentanediol decreased substantially. However, addition of only 7 MPa of CO2 modified the conversion and the product selectivity. Under similar reaction conditions, hydrogenolysis of THFA over a Pd catalyst provides a maximum of 50% conversion and the product distribution was different in comparison with Rh catalysts.