Ruixia Liu

Synthesis of urea derivatives from amines and CO2 in the absence of catalyst and solvent

Urea derivatives are obtained in mild to good yield from the reactions of primary aliphatic amines with CO2 in the absence of any catalysts, organic solvents or other additives. To optimize reaction conditions, experimental variables including temperature, pressure, the concentration of amine, reaction time etc. were studied. Satisfactory yields were obtained at the optimized conditions that are comparable to the presence of catalyst and solvent. The preliminary investigation of the reaction mechanism showed that alkyl ammonium alkyl carbamate was quickly formed as the intermediate, and then the final product was formed by the intramolecular dehydration.

Selective reduction of phenol derivatives to cyclohexanones in water under microwave irradiation

Selective reduction of phenol to cyclohexanone over the Pd/C catalyst in the presence of a hydrogen source of HCOONa/H2O has been studied. Surprisingly, phenol was transformed efficiently to cyclohexanone in an excellent yield of above 98% under microwave irradiation. The influence of some parameters like reaction temperature, time and amount of hydrogen donor, as well as the reaction pathway has been discussed. The combination of microwave irradiation and HCOONa/H2O was certified to be effective for the reduction of phenol as well as its derivatives to their corresponding cyclohexanones.

Radioprotection by fullerenols of Stylonychia mytilus exposed to γ-rays

The aim was to study the protective effects of fullerenols, C60(OH)x, on Stylonychia mytilus cells exposed to 60Co γ-rays and the probable mechanisms of fullerenols protection. Ciliated protozoans Smytilus, kept in solutions of fullerenols at different concentrations, were irradiated with 60Co γ-rays to various dose levels. Surviving cells were counted each day over 5 days after irradiation, and the surviving fraction was calculated. The relations of the surviving fraction to radiation dose and to fullerenols concentration were studied. Superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and lipofusion (LIP) levels in S. mytilus were also measured. The surviving fraction of S. mytilus decreased with increasing γ-ray doses from 100 to 2000u2009Gy. Fullerenols enhanced the surviving fraction, except for the highest γ-ray dose level. The maximum protection by fullernols occurred at a concentration of 0.10u2009mgu2009mlu200a–u200a1. However, fullerenols at concentration of 0.25u2009mgu2009mlu200a–u200a1 yielded a surviving fraction lower than that for the control sample. Fullerenols at a concentration of 0.10u2009mgu2009mlu200a–u200a1 increased the SOD and CAT activities in the γ-ray plus fullerenols (γ + F) group compared with the levels in both the γ-ray (γ) group (pu200a<u200a0.01) and the control group (pu200a<u200a0.01). The MDA and LIP levels in the γ + F groups (pu200a<u200a0.01) were significantly lower than that in both the control group (pu200a<u200a0.05) and the γ group (pu200a<u200a0.01). At a concentration of 0.25u2009mgu2009mlu200a–u200a1, fullerenols reduced the SOD and CAT activities, but increased the MDA and LIP level compared with the control. There was no significant difference in SOD and CAT activities between the γ + F group and γ group. While the MDA and LIP level in the γ + F and γ groups were similar at a dose of 500u2009Gy, the LIP level in the γ + F group was significantly higher than that in the γ group (pu200a<u200a0.01) at a dose of 2000u2009Gy. Fullerenols are good radiation protectors for the protozoan S. mytilus exposed to γ-rays. The effectiveness of radioprotection depends on both fullerenols concentration and γ-ray dose. The protective effect of fullerenols on damage induced by γ-rays seems to be mediated, at least in part, through their anti-oxidative and radical scavenging activities.

Selective hydrogenation of citral catalyzed with palladium nanoparticles in CO2-in-water emulsion

CO2-in-Water (C/W) emulsion was formed by using a nonionic surfactant of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (P123), and palladium nanoparticles were synthesized in situ in the present work. The catalytic performance of Pd nanoparticles in the C/W emulsion has been discussed for a selective hydrogenation of citral. Much higher activity with a turnover frequency (TOF) of 6313 h−1 has been obtained in this unique C/W emulsion compared to that in the W/C microemulsion (TOF, 23 h−1), since the reaction was taking place not only in the surfactant shell but also on the inner surface of the CO2 core in the C/W emulsion. Moreover, citronellal was obtained with a higher selectivity for that it was extracted to a supercritical carbon dioxide (scCO2) phase as formed and thus its further hydrogenation was prohibited. The Pd nanoparticles could be recycled several times and still retain the same selectivity, but it showed a little aggregation leading to a slight decrease in conversion.

Knitting an oxygenated network-coat on carbon nanotubes from biomass and their applications in catalysis

In this work, we presented a new way for the functionalization of carbon nanotubes (CNTs) with the use of biomass as starting materials and introduced a novel concept of knitting process in the chemistry of CNTs for the first time. A mixture of aromatic compounds obtained from the hydrothermal treatment of biomass, rather than the traditional polymer monomers, was used as the nanoscale building blocks to knit an oxygenated network-coat on the CNTs layer-by-layer. It is an effective, mild, green and easily-controlled method for the functionalization of CNTs. The obtained f-CNTs were proved to be a promising catalyst support for metal catalysts, such as Ru/f-CNTs, showed high activity and selectivity for the hydrogenation of citral to unsaturated alcohol. More importantly, we opened a pioneering way for the conversion of low-cost, abundant and renewable biomass into a hydrophilic/chemical reactive network-coat on the inert surface of a wide range of sp2carbon materials, such as prevalent fullerene, carbon nanotubes, carbon nanohorns and hot grapheneetc.

Cyclization of citronellal to p-menthane-3,8-diols in water and carbon dioxide

A clean process has been developed for the synthesis of p-menthane-3,8-diols from cyclization of citronellal in CO2–H2O medium without any additives. With the addition of CO2, the reaction rate could be enhanced about 6 times for the cyclization of citronellal in H2O, because CO2 dissolved into water and formed carbonic acid inducing an increase of the acidity. Although, the reaction conversion in CO2–H2O is slightly lower compared to that obtained with sulfuric acid as catalyst, CO2–H2O could replace the sulfuric acid at a relative higher reaction temperature. The reaction kinetics studies showed that the hydration of isopulegols to p-menthane-3,8-diols is a reversible reaction. The equilibrium constant and the maximum equilibrium yield obtained in CO2–H2O at a range of CO2 pressures are similar to that with sulfuric acid catalyst.

Selective hydrogenation of unsaturated aldehydes in a poly(ethylene glycol)/compressed carbon dioxide biphasic system

Hydrogenation of α,β-unsaturated aldehydes (citral, 3-methyl-2-butenal, cinnamaldehyde) has been studied with tetrakis(triphenylphosphine) ruthenium dihydride (H2Ru(TPP)4) catalyst in a poly(ethylene glycol) (PEG)/compressed carbon dioxide biphasic system. The hydrogenation reaction was slow under PEG/H2 biphasic conditions at H2 4 MPa in the absence of CO2. When the reaction mixture was pressurized by a non-reactant of CO2, however, the reaction was significantly accelerated. As CO2 pressure was raised from 6 MPa to 12 MPa, the conversion of citral increased from 35% to 98%, and a high selectivity to unsaturated alcohols (geraniol and nerol) of 98% was obtained. The products were able to be extracted by high pressure CO2 stream and separated from the PEG phase, dissolving the Ru complex catalyst and the catalyst was recyclable without any post-treatment.

A green and efficient route for preparation of supported metal colloidal nanoparticles in scCO2

An efficient method for dispersing active metal colloidal nanoparticles onto supports uniformly is revealed in this paper. The critical feature of this method is to separate the stabilizer simply with the phase-switch function of scCO2; with it the highly dispersed Pd colloidal catalysts were prepared, and the forming procedure is analyzed and discussed in detail. The present work not only overcame the common difficulties of removing the stabilizers in the preparation of supported colloidal particles, but also provided a facile and green process for preparing supported metal colloidal nanoparticles with using the environmentally benign solvent of scCO2.

The dispersion of TiO2 modified by the accumulation of CO2 molecules in water: An effective medium for photocatalytic H2 production

The photocatalytic H2 production from water with TiO2 can be noticeably enhanced by the presence of both dense phase CO2 and a surfactant of sodium dodecyl sulfate, being larger by more than one order of magnitude than that from water with TiO2 alone. The surface of TiO2 may be modified by the accumulation of CO2 molecules assisted by the TiO2- and CO2-philic surfactant, changing its photocatalytic activity.

Ionic Liquids in Green Carbonate Synthesis

Ionic liquids (ILs), made of relatively large organic cations and inorganic anions, could contribute as solvents and catalysts to green organic synthetic reactions [1-5]. The reaction systems using no organic solvents, dense phase carbon dioxide (supercritical and carbon dioxide-dissolved expanded liquid phases), and/or water are obviously advantageous from environmental viewpoints [1]. ILs would be one of attractive components for environmentfriendly reaction and separation processes because of their physicochemical properties. But we should also note the possibility of negative effects caused by their toxicity on environment and products when we use ILs for practical applications. There are a number of ILs using different cations and anions, and a few typical examples are shown in Fig. 1. It is evidenced that ILs act as good catalysts for several organic synthetic reactions, as noted in recent review articles [1–5], including Friedel-Crafts reactions, Diels-Alder reactions, hydrogenation, polymerization, and other reactions. Haumann and Riisager discuss various aspects (structure of substrates, type of ILs, form of ILs catalysts) in hydroformylation reactions using ILs [4]. Recently Baiker et al. have published a review on multiphase catalytic systems including ILs and carbon dioxide [5]. They point out the significance of the combination of ILs and carbon dioxide for chemical and separation processes. This review deals with physicochemical features of those multiphase reaction systems and catalytic reactions therein including those using carbon dioxide as a reactant. After considering those previous reviews and other chapters of this book, we will concentrate our attention on the application of ILs to the synthesis of carbonate and related compounds using carbon dioxide. Those compounds are of practical importance as solvents, reagents, fuel additives, and intermediates in the production of pharmaceuticals and fine chemicals [6,7]. The authors previously reviewed the potential application of ILs for the synthesis of cyclic carbonates from carbon dioxide [8]. The present chapter will deal with the synthesis of cyclic carbonates, dialkyl carbonates, other related compounds, and polycarbonates using ILs as solvents and catalysts.