Xilong Yan

Preparation of polystyrene fluorescent microspheres based on some fluorescent labels

Five fluorescent labels were synthesized and used in the preparation of polystyrene fluorescent microspheres by the dispersion copolymerization and absorption method. Spectral properties of copolymerization fluorescent microspheres in tetrahydrofuran indicated these individual characteristics of labels should be maintained in the fluorescent microspheres. The differences of the fluorescent spectra between five fluorescent microspheres and their corresponding parent labels in ethanol have been investigated. These fluorescent microspheres were characterized by environmental scanning electron microscopy, laser scanning confocal microscopy and fluorescence spectrophotometry. They exhibited good dispersion and stable and high fluorescence intensity. Furthermore, copolymerization fluorescent microspheres were functionalized with amino groups. This means that a method for the preparation of copolymerization fluorescent microspheres was developed as a platform for the generation of functional fluorescent microspheres for diverse applications.

Spectrofluorimetric determination of trace nitrite with a novel fluorescent probe.

A simple, sensitive and selective fluorimetric determination for trace nitrites was developed using an unsymmetrical rhodamine with a high fluorescence quantum yield and large Stokes shift. The method is based on the reaction of the unsymmetrical rhodamine with nitrite in an acidic medium to form a nitroso product, which has much lower fluorescence because the electron-withdrawing effect of the nitroso group influences the system of p-pi conjugation between N atom and benzene ring. Under optimum conditions, the fluorescence quenching intensity is linear over a nitrite concentration range of 1.0 x 10(-8) to 3.5 x 10(-7)M. The detection limit is 2.0 x 10(-10)M (S/N=3). The method was applied to the determination of nitrite in tap water and lake water with satisfactory results. The mechanism for the reaction is also reported.

Efficient Hydrodeoxygenation of Aliphatic Ketones over an Alkali‐Treated Ni/HZSM‐5 Catalyst

Cyclohexanone was chosen as a model substrate to evaluate certain catalysts for the hydrodeoxygenation of aliphatic ketones in a fixed‐bed reactor. The experimental results indicated that alkali‐treated Ni/HZSM‐5 exhibited excellent performance for this reaction. Two aspects of the catalyst are enhanced by alkaline treatment; the amount of strong acid sites on the catalyst is sharply reduced, and also a large number of mesopores are generated in the catalyst. The decrease of strong acid sites suppresses the formation of low‐boiling products and aldol‐condensation side products, while the mesopores improved hydrogenation and dehydration performances of the catalyst. These two aspects also promoted the catalyst’s excellent time‐on‐stream performance. Additionally, generality of the catalyst is proved; most of the selected carbonyl compounds can be hydrodeoxygenated to the corresponding alkanes with selectivities of more than 97.0 %.

A continuous process for the reductive deoxygenation of aromatic ketones over Cu30Cr10/γ-Al2O3

A continuous process for reduction of aromatic ketones to the corresponding aromatic alkanes over Cu30Cr10/γ-Al2O3 was established in a fixed-bed reactor. A series of aromatic ketones were examined, and all of the corresponding aromatic hydrocarbons were obtained in more than 95% yield. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and H2-temperature programmed reduction. Cu0 is believed to be the active center of the catalyst. Cr was found to have an important effect on catalytic activity and stability.

Continuous asymmetric Michael addition of ketones to β-nitroolefins over (1R,2R)-(+)-1,2-DPEN-modified sulfonic acid resin

A trifunctional catalyst was successfully prepared by bonding (1R,2R)-(+)-1,2-DPEN to sulfonic acid resin. The catalyst was characterized by elemental analysis, thermogravimetric (TG) analysis and infrared (IR) spectroscopy. The results indicated the coexistence of sulfonic, sulfonamido and primary amino groups on the surface of the resin. Based on the IR spectroscopy of the catalyst treated with a solution of acetone and β-nitrostyrene in toluene, the catalytic mechanisms were proposed. It was found that these three groups had a synergistic effect. Subsequently, the continuous Michael addition of acetone to β-nitrostyrene was achieved in a fixed-bed reactor over this catalyst and the reaction parameters were optimized. Under the optimized conditions moderate β-nitrostyrene conversion (65.5%) and excellent enantioselectivity (93.0%) were obtained. Finally, the generality of the catalyst was evaluated with the Michael addition of aldehydes or ketones to β-nitroolefins, and the catalyst exhibited moderate to excellent enantioselectivity (81.6% to 99.0% ee) except for the addition of isobutylaldehyde to β-nitrostyrene.

Hydroarylation of Styrenes with Electron-Rich Arenes Over Acidic Ion-Exchange Resins

Abstract A series of acidic cation-exchange resins were used for the hydroarylation of resorcinol with styrene, in which resin D072 exhibited the excellent catalytic performance in this reaction with 99% conversion of styrene and 90% selectivity of 4-(1-phenylethyl)resorcinol. It was applied to the hydroarylation of various electron-rich arenes with styrenes, and the hydroarylated products were quantitatively obtained. This catalyst could be used for four consecutive runs with slight decrease in activity. The hydroarylation of resorcinol with styrene over resin D072 in a fixed bed was completed effectively with 94% selectivity and 99% conversion, and this green continuous process is potentially applicable to large-scale productions. GRAPHICAL ABSTRACT

A novel near-infrared colorimetric probe for fluoride anions based on a heptamethine dye

A near-infrared heptamethine indocyanine probe was successfully synthesized and demonstrated to be a colorimetric and fluorescent probe for F− with high selectivity and sensitivity. In the presence of F−, the probe shows a new prominent absorption peak at 942 nm, accompanied by a remarkable solution color change from pale red to colorless in a few seconds, which provides a way for the ‘naked-eye’ detection of fluoride anions. These responses were attributed to the deprotonation of the –NH fragment of an indolyl unit, and the 1H NMR study and density functional theory (DFT) calculations are in agreement with them. Moreover, the probe can be employed to detect F− quantitatively within a certain concentration range, and the limit of detection could be as low as 1.3 μM.

Significant effect of alkyl chain length on fluorescent thermochromism of 9,10-bis(p-alkoxystyryl)anthracenes

9,10-Bis(p-alkoxystyryl)anthracenes (DSA-pnn) with different length of alkyl chains (n = 4, 8, 16) were synthesized. It was found that they exhibit aggregation-induced emission (AIE) properties and significant fluorescent thermochromism. Besides, the thermochromic behaviours of DSA-pnn show great dependence on the length of alkyl chains.

Two-Dimensional Imine-Linked Covalent Organic Frameworks as a Platform for Selective Oxidation of Olefins

Two-dimensional imine-linked covalent organic frameworks with hydroxyl groups, TAPT-DHTA-COFHX and TAPT-DHTA-COFDMF, were respectively constructed by the condensation of 1,3,5-tris-(4-aminophenyl)triazine and 2,5-dihydroxyl-terephthalaldehyde under solvothermal and reflux conditions. Both COFs possess excellent thermal stability and a similar eclipsed stacking structure verified by XRD patterns. However, TAPT-DHTA-COFHX presented a larger surface area (2238 m2/g) and higher crystallinity than TAPT-DHTA-COFDMF. Significantly, copper ions are efficiently incorporated into the pores of these two COFs via the coordination interaction with hydroxyl groups and imine linkers. The obtained copper-containing COFs (Cu-COFHX and Cu-COFDMF) were employed in the selective oxidation of styrene to benzaldehyde. Cu-COFHX with superior surface area (1886 m2/g) and pore volume (1.11 cm3/g) exhibited excellent catalytic performance and recyclability. This strategy not only provides a convenient approach to design imine-linked 2D COFs with hydroxyl groups, but also develops their novel application for catalysis.

Reductive cyclization of 2-nitro-2′-hydroxy-5′-methylazobenzene to benzotriazole over K-doped Pd/γ-Al2O3

A series of Pd/γ-Al2O3 catalysts modified by potassium salts were prepared and evaluated in the reductive cyclization of 2-nitro-2′-hydroxy-5′-methylazobenzene without additional base. These solid base-hydrogenation bifunctional catalysts were characterized and the results demonstrated that potassium salts could have an important impact on the properties and catalytic performance of Pd/γ-Al2O3.