Jian-Gang Chen

Insights into the vanadia catalyzed oxidative dehydrogenation of isobutane with CO2

Vanadia-based catalysts were prepared using the sol-gel method and were subjected to the oxidative dehydrogenation of isobutane with CO2. The materials were extensively characterized by using X-ray diffraction, N2 adsorption-desorption, O2-temperature programmed oxidation, temperature programmed surface reaction, and in situ Fourier transform infrared techniques. Catalytic results indicate that a high selectivity toward total C4 olefins over 85% was obtained over all of the catalysts. On the contrary, the highest conversion of isobutane was observed over 12 wt% V2O5/Ce0.6Zr0.4O2(7 wt%)-Al2O3, and a more stable performance was achieved over 6 wt% V2O5-Ce0.6Zr0.4O2(7 wt%)-Al2O3. The catalytic activity for the titled reaction was found to be dependent on the dispersion and crystallinity of the VOx species over the catalyst, and the deposition of the heavier coke over the catalyst was revealed to be the main reason for the catalyst deactivation. Moreover, the benefit of CO2 toward the titled reaction was clearly revealed from TPSR results, and the reaction was confirmed to follow the redox mechanism.

Insight into the role of intermolecular interactions on the enhanced solubility of fluorinated epoxide oligomers in supercritical CO2

A prominent enhancement in solubility of epoxide oligomers in supercritical CO2 (scCO2) was definitively accomplished via fluorination. The fluorinated epoxide oligomers (FEO) exhibited incredibly low transition pressure (PT) as compared with a library of other epoxide oligomers. For determining the nature of the observed special affinity of the FEO to CO2, the detailed solvation behaviors of 14 epoxide oligomers in gaseous and supercritical CO2 were investigated using a high-pressure in situ ATR FTIR system as the pressure increased from 0.1 to 40.0 MPa. The key role of the intermolecular interactions on the enhanced solubility of the FEO in scCO2 was established and the major factors impacting the molecular interplay between the epoxide oligomers and CO2 were systematically evaluated. We attribute the uniquely enhanced solubility of the FEO in scCO2 to the synergistic effects of the increased special attraction between the FEO and CO2, the decreased self-interaction among the FEO and the excellent accessibility of the FEO to CO2. Since the FEO are suggested to be the most soluble species in scCO2, we optimistically believe that the FEO may act as the ideal solubilizing chain after being transplanted or grafted into other targeted molecules and thus can be employed in developing a series of novel fluorinated monomers, ligands/complexes/catalysts and surfactants in a scCO2 system.

2-Nitrobenzyl Borate Based Photolabile Linker for Breakable Polymer Vesicles.

Fluorescent photolabile groups undergoing convenient synthesis and fast cleavage are being explored because of their increasing utility in both synthetic and biological chemistry. Herein, a model photosensitive poly(ethylene glycol)-lipid of NP-B-PEG with a 2-nitrobenzyl 2-pyridinylmethyl borate hydrophobic tail is synthesized. The (1) H-NMR and absorption spectra analysis of NP-B-PEG upon 365 nm irradiation in water supports a rapid photocleavage of nitrobenzyl borate with the concomitant hydrolysis of 2-pyridinylmethyl borate. It is also shown that the borate tail hydrolyzes slowly in water. Fortunately, when the polymer aqueous solution is loaded with the hydrophobic doxorubicin (DOX), the borate hydrolysis can be much retarded. The phototriggered experiment shows a two-stage DOX release: first, the slow leakage as a result of the photocleavage of 2-nitrobenzyl borate before the vesicle disintegration; second, the quick DOX precipitation from the disintegrated vesicles induced by the speeding up hydrolysis of 2-pyridinylmethyl borate.

Density functional theory study on the reaction of triazol-3-one with nitronium: direct nitration versus acidic group-induced nitration

The nitration mechanism as well as the kinetics of triazol-3-one (TO) with nitronium (NO2+) in both a concentrated nitric acid and a nitric–sulfuric acid system was theoretically studied. Firstly, the density functional theory (DFT) with a B3LYP functional was employed to investigate the mechanism of the mentioned reactants towards the targeted product, 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (NTO). An unexpected induction effect, which derived from the coexisting acid group (NO3− and/or HSO4−), was proclaimed. The impact of the induction effect on the nitration of TO was systematically demonstrated. It is found that unlike the nitration of most aromatics, the nitration of TO with NO2+ to form NTO does not follow the typical electrophilic substitution mechanism. Based on the results calculated in each acid system, the nitration mechanisms, including the NO2+ direct nitration (path A), NO3−-induced nitration (paths Bn–Dn) and HSO4−-induced nitration (paths Bs–Ds), were proposed. It is indicated that path A is unlikely or unfavorable due to the high activation barrier in the rate-determining step, whereas paths Bn–Dn and Bs–Ds are favorable, mainly attributed to the significant decrease of the activation energy induced by NO3− and HSO4− during the nitration process, especially for the NTO-oriented path Bn and Bs. Secondly, the canonical variational transition (CVT) state theory with small curvature tunneling (SCT) correction was used and the rate constants of the rate-determining steps for all paths at different temperatures were calculated. It is shown that the nitration rate in either path Bn or path Bs outdistances that in path A, indicating that NO3− and HSO4− accelerate the nitration of TO with NO2+, and ultimately favour the formation of NTO due to the proposed induction effect of each acid group. An enhanced catalytic effect of the nitric acid or/and sulfuric acid is thought to be embodied in not only the acceleration to the formation of NO2+, but also the induction effects of NO3− and HSO4− during the nitration processes. Meanwhile, it is suggested that the concentration of nitric acid and sulfuric acid in each nitration system should be well controlled since the favourable condition to produce NO2+ and NO3−/HSO4− differs in the concentrations of the corresponding acids.

Fabricating Triple-Sensitive Polymer Nano-Aggregates via an Aqueous Iminoboronate Multicomponent Reaction

A triple-sensitive polymer of poly(ethylene glycol)-iminoboronate nitrobenzyl ethanediol chelate (PEG-INEC) is efficiently fabricated via the convenient aqueous iminoboronate multi-component reaction (MCR) of methoxypolyethylene glycol amine (mPEG-NH2 ), 2-formylphenylboronic acid (FPBA), and bis(2-nitrophenyl) ethanediol (BNPE, a photo-cleavable nitrobenzyl alcohol derivate). The aqueous MCR synthetic procedure is followed using 1 H NMR and turbidity analysis. It is shown that polymer nano-aggregates of PEG-INEC in aqueous solution can be dissociated through the stimuli responsive reactions of the hydrophobic iminoboronate nitrobenzyl ethanediol chelates (INECs) when exposed to UV light, acid, and H2 O2 , respectively. Furthermore, upon the stimulation of combined triggers, the dissociation of polymer nano-aggregates can be accelerated to different extents, resulting in the synergistic release of encapsulated hydrophobic molecules in water. The proposed facile and general method is quite desirable and of great importance in practical applications like drug and gene delivery.

A superhydrophobic hyper-cross-linked polymer synthesized at room temperature used as an efficient adsorbent for volatile organic compounds

Cost-effective adsorbents for volatile organic compounds elimination were synthesized at room temperature. New kinds of external cross-linkers were developed and used in the one-step Friedel–Crafts reaction. The synthesized polymers exhibit a high surface area (BET surface area up to 1345 m2 g−1), large pore volume, superhydrophobic nature and excellent adsorption capacity for benzene, which is one of the highest to date among the reported adsorbents. It also possesses super preferential selectivity towards benzene in a high humid gas stream. Therefore, this kind of material is a promising adsorbent for air purification and environmental protection.

Perfectly Alternating Copolymerization of Propylene Oxide and CO2 over SalenCo/SalenCr Complexes

Schiff-cobalt (salenCo) and Schiff-chromate (salenCr) were synthesized and used as catalysts for copolymerizing of propylene oxide (PO) and CO2. The alternating copolymer of polycarbonate was successfully obtained under mild conditions in the presence of 4-(dimethylamino)-pyridine (DMAP) cocatalyst. The influences of DMAP amount, polymerization time, temperature, and CO2 pressure on the copolymerization efficiency and selectivity to polycarbonate were investigated in the presence of catalysts. Under the optimized conditions, salenCo/DMAP exhibited an excellent catalytic efficiency with perfectly alternating copolymerization products (99% carbonate and more than 99% polycarbonate with head-to-tail linkage) and high selectivity to polycarbonate over cyclic carbonate (more than 99% polymeric product) without byproduct (polyether). While only 76% selectivity to polymer, 95% carbonate linkage, and 80% head-to-tail connection unit were obtained over salenCr/DMAP catalyst. Furthermore, the catalytic activity of salenCo was superior to that of salenCr, resulting in higher molecular weight, more regular microstructure, and higher stability of copolymer.

Carbon Fibers/Poly(trifluoroethyl methacrylate) Composites Synthesized under Supercritical CO2

Carbon fibers(CFs)/poly(trifluoroethyl methacrylate) (CFs/PTFEMA) composites were prepared by the in-situ radical polymerization of trifluoroethyl methacrylate with CFs under the supercritical carbon dioxide (scCO2) medium. The structure of composites was characterized by SEM, FT-IR, BET, 1H-NMR, GPC, TGA-DSC and RT-109, respectively. SEM illustrated that the diameter of CFs was about 200–500 nm and CFs was well dispersed in composites. Results showed that CFs strongly influences the properties of composite, especially the electrical properties and resistivity-temperature behaviors. A low percolation threshold was obtained at CFs content of 12 wt% for CFs/PTFEMA composites. The conductive network of the CFs/PTFEMA composites was formed by the contact of the CFs particles. CFs was distributed in PTFEMA and the conductive network constructed by CFs, especially the distribution of conductive filler significantly affects the properties of the CFs/PTFEMA composites. CFs was well dispersed in PTFEMA under the environmental friendly scCO2 medium and CFs/PTFEMA can be a functional and structural material.

Insight into the acidic group-induced nitration mechanism of 2-methyl-4,6-dihydroxypyrimidine (MDP) with nitronium

The strong desire for developing promising candidates of insensitive nitro energetic materials has spurred numerous attempts to discern the nitration details. The nitration mechanism of 2-methyl-4,6-dihydroxypyrimidine (MDP) with nitronium (NO2+) to form 2-dinitromethylene-5,5-dinitropyrimidine-4,6-dione is studied via DFT-B3LYP/6-311G(d,p) method. The possible nitration pathways are excavated and illustrated. Herein, a unique/incredible induction/enhancement of the co-existing acidic group of HSO4− to the targeted nitration is definitively proposed. The impact of the introduction order of four nitro groups (–NO2) on the title nitration is systematically demonstrated. It is suggested that the proposed induction of HSO4− may effectively promote/catalyze not only the NO2+ attack, but the H-transfer and H-abstraction as well, and thus dramatically decreases the activation free energy of the nitration system. Moreover, the NO2+ attack may be dynamically affected by the pre-introduced –NO2 and the resulted fluctuation of charge distribution in the pre-intermediates, which has been primarily supported via the calculated atomic charge, Coulomb attraction and Fukui function. It is indicated that the preferential dinitration on –CH3 with the induction of HSO4− (path A) is the most likely pathway. It is optimistically expected that the present study may provide a theoretical basis to the research and engineering tests of the title nitration, and promote the exploration of related insensitive energetic materials.

Highly enantioselective catalytic domino reaction: Synthesis of (R)-2-phenyl-2H-thiochromene-3-carbaldehyde in supercritical carbon dioxide

With the development of green chemistry, supercritical carbon dioxide (scCO2) was used as a replacement medium for conventional organic solvents because it is inexpensive, nontoxic, non-flammable, and has moderate critical conditions (Tc 31.1°C, Pc 7.38 MPa) [1]. It also has advantages for chemical reactions, such as adjusting the solvent properties of scCO2 and separating products from scCO2 by controlling the pressure and temperature [2]. Herein, several research groups have independently reported some catalytic asymmetric reactions in scCO2 [3–8]. Recently, domino or cascade reactions have been the subject of intense research from the number of reviews that have appeared [9–12]. Domino reactions enable rapid construction of complex molecular scaffolds in an efficient way, and are even more appealing due to their high atom economy, operational simplicity, and environmental friendliness [13]. Most highly enantioselective catalytic asymmetric domino reactions reported by Wang [14] and Córdova [15] were carried out in organic solvents, but the majority of solvents are volatile, toxic, and flammable. In this paper we describe organocatalytic asymmetric domino reaction between 2-sulfanylbenzaldehyde and 3-phenylprop-2-enal, which affords a high enantioselectivity in scCO2 in the presence of L-proline as catalyst (Scheme 1). First, we carried out the reaction at 40°C and 20 MPa for different times. The effects of reaction time on the yield and ee of the product, (R)-2-phenyl-2Hthiochromene-3-carbaldehyde (I), are shown in Fig. 1. After 16 h, the ee decreased with time, presumably due to transformation of the R isomer into the S isomer under high pressure. In order to prove this assumption, the product with 96% ee was kept for 16 h in scCO2 at 40°C and 20 MPa. In fact, the ee decreased from 96 to 20%. The effect of pressure on the domino reaction in scCO2 was investigated (Fig. 2). The ee decreased from 92% to 28% when the pressure changed from ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 12, pp. 1854–1856.