•Solvent effect of ionic liquids on the fixation of CO2 is studied by ONIOM and MD.•Critical hydrogen bond and C-Br interaction are analyzed by NCI and AIM.•ONIOM model displays the more reasonable result than PCM model.•Which one is more important, nucleophilic or electrophilic activation?The solvent effect of ionic liquids on CO2 fixation catalyzed by hydroxyl-functionalized quaternary ammonium-based ionic liquids is thoroughly investigated by ONIOM method associated with the molecular dynamics simulation. As compared with the catalytic activity determined in experiment, the catalytic activity estimated by ONIOM model is more credible than previous result calculated by the polarized continuum model. The critical hydrogen bond and C-Br interaction are analyzed by non-covalent interaction and the atoms in molecules methods. The analysis indicates that the electrophilic activation aroused by hydrogen bond provides more contribution than nucleophilic activation aroused by C-Br interaction in reaction catalyzed by trihydroxyethylethyl ammonium bromide. In contrast, the nucleophilic activation is more important in reactions catalyzed by other three ionic liquids. Choice of the suitable model is possible to obtain the reliable catalytic activity, which would be comparable with the experimental result.Download full-size image

•Eight benzyl substituted imidazolium ionic liquids are firstly synthesized.•They are efficient homogeneous catalysts for cycloaddition of CO2 with PO.•The reaction condition is benign with high product yield.•No solvent and co-catalyst are required.•The reaction mechanism is elucidated by DFT calculation.A series of low-cost and easily prepared benzyl substituted imidazolium ionic liquids are firstly synthesized and employed as catalyst for the cycloaddition of carbon dioxide with epoxides without any solvent and co-catalyst. The synthesized imidazolium ionic liquids are characterized by 1H NMR, HRMS, and MS. The influence of different substituted groups in cation and reaction parameters on catalytic activity is investigated. The highest conversion yield of cyclic carbonate (94.89%) could be achieved with slight amount of catalyst (0.25 mol%) under 130 °C and 2.0 MPa during 4 h. Meanwhile, the mechanisms of cycloaddition of carbon dioxide with epoxides catalyzed by four benzyl substituted ionic liquids with different substituted groups are investigated by theoretical calculations. The role of hydrogen bond and other noncovalent interactions played in catalytic process is further uncovered to deeply understand the difference of various catalysts from atomistic level.

•Dialkylpyrazolium ILs are firstly used as catalysts for the fixation of CO2.•Good yields are achieved under a mild condition without solvent or co-catalyst.•The mechanism with a synergistic effect is found to promote the reaction.•They would be reused by five times without decrease of catalytic activity.The efficient fixation of CO2 without co-catalyst and solvent under metal-free condition is still an urgent topic in sustainable chemistry. In this work, a series of dialkylpyrazolium ionic liquids are employed to promote the cycloaddition of CO2 and PO to produce PC. They would be easily synthesized by a simple one-pot reaction. The effect of alkyl chain length in cation and different anion is explored. Diethylpyrazolium iodide presents the excellent catalytic activity with the product yield of 96% and selectivity of 99% in a benign condition. Moreover, the catalyst could be reused for at least five times without significant loss of catalytic activity. An intensive structure-activity research testifies that the cycloaddition of CO2 with PO is activated by a synergistic effect from both cation and anion of ILs. To confirm it, the detailed mechanism is investigated by density functional theory associated with the non-covalent interactions and atoms in molecule analysis. Besides the electrostatic interaction between cation of ionic liquid and PO, the noncovalent interaction, especially for hydrogen bond, plays a vital role in promoting the reaction.Download high-res image (136KB)Download full-size image

A novel pesticide intermediates 3-(6-bromo-2-methyl-3-(methylsulfonyl)phenyl)-4,5-dihydroisoxazole was synthesized with 2,3-dimethylaniline as the starting materials. The final product and intermediates were characterized by mass spectra, 1H NMR, infrared and elemental analysis. The crystal structure of compounds 6 and 8 were determined by single crystal X-ray diffraction. Results shown that two oxazole compounds crystallize in the monoclinic (6) and triclinic (8) with the space group of P 21/c for 6 and P-1 for 8, respectively.

A series of pyrazoline derivatives containing pyrazole group were synthesized and characterized by means of 1H NMR, FT-IR, MS and elemental analysis, and their UV–vis absorption behavior and fluorescent properties were also measured. Moreover, the influence of metal ions on spectral properties of synthetic products was examined with compound A5 as an example. It has been found that all synthetic pyrazoline derivatives show two remarkable absorption peaks at about 260 and 360 nm and the maximum emission peak at 445–467 nm. Especially, the joined of Co2+ can quench the fluorescence of compound A5 obviously.

•A series of quinoline derivatives containing pyrazole group were synthesized and characterized.•The UV–vis spectra and fluorescent spectra of various as-synthesized products were measured.•The effect of acetic acid and triethylamine on the spectroscopic properties of as-synthesized products was examined.Two series of quinoline derivatives containing pyrazole group were synthesized and characterized by means of 1H NMR, FT-IR, MS, elemental analysis and X-ray single crystal diffraction, and their UV–vis absorption behavior and fluorescence properties were also measured. Moreover, the effects of acetic acid and triethylamine on the spectroscopic properties of synthesized products were examined with compounds 3a and 5a as examples. It has been found that all synthesized quinoline derivatives show maximum absorption peak at 303 nm and emission peaks around 445 nm. Besides, both acetic acid and triethylamine can change the acidity of the medium, thereby influencing the UV–vis absorption spectra and fluorescence spectra of synthesized products. Moreover, theoretical investigations indicate that the integration of H+ and N atom of quinoline ring favors the formation of a new product in the presence of acetic acid, and the product obtained in this case shows a new UV–vis absorption peak at 400 nm.

A series of novel Schiff bases containing pyrazole group were synthesized using 1-aryl-3-methyl-4-benzoyl-5-pyrazolone and phenylenediamine as the starting materials. All as-synthesized Schiff bases were characterized by means of NMR, FT-IR, and MS; and the molecular geometries of two Schiff bases as typical examples were determined by means of single crystal X-ray diffraction. In the meantime, the ultraviolet-visible light absorption spectra and fluorescent spectra of various as-synthesized products were also measured. Moreover, the B3LYP/6-1G(d,p) method was used for the optimization of the ground state geometry of the Schiff bases; and the spectroscopic properties of the products were computed and compared with corresponding experimental data based on cc-pVTZ basis set of TD-B3LYP method. It has been found that all as-synthesized Schiff bases show a remarkable absorption peak in a wavelength range of 270–370 nm; and their maximum emission peaks are around 344 nm and 332 nm, respectively.Graphical abstractA series of novel Schiff bases containing pyrazole group were synthesized using 1-aryl-3-methyl-4-benzoyl-5-pyrazolone and phenylenediamine as the starting materials. The ultraviolet-visible light absorption spectra and fluorescent spectra of various as-synthesized products were measured. Moreover, the B3LYP/6-1G(d,p) method was used for the optimization of the ground state geometry of the Schiff bases; and the spectroscopic properties of the products were computed and compared with corresponding experimental data based on cc-pVTZ basis set of TD-B3LYP method.Highlights► A series of novel Schiff bases containing pyrazole group were synthesized and characterized. ► The UV–Vis spectra and fluorescent spectra of various as-synthesized products were measured. ► The B3LYP/6-31G(d,p) method was used for the optimization of the ground state geometry of the Schiff bases. ► The spectroscopic properties of the Schiff bases were computed based on cc-pVTZ basis set of TD-B3LYP method.

A series of novel bis-Schiff base were synthesized from 1-aryl-3-methyl-4-benzoyl-5-pyrazolones and diethylenetriamine (or triethylenetetramine) as the starting materials. All of these bis-Schiff bases were characterized by means of NMR, IR, and MS. The UV–vis absorption spectra and fluorescent spectra of these bis-Schiff bases were also measured. Moreover, the B3LYP/6-31G(d) method was used to optimize the ground state geometry of the bis-Schiff bases; and the UV–vis spectroscopic properties of the products were computed and compared with corresponding experimental data based on cc-pVDZ basis set of TD-B3LYP method. It has been found that all of these bis-Schiff bases show a remarkable absorption peak in a wavelength range of 270–340 nm; and their maximum emission peaks are around 348 nm.Graphical abstractA series of novel bis-Schiff bases containing pyrazole group were synthesized using polyamine and 1-aryl-3-methyl-4-benzoyl-5-pyrazolones as the starting materials. The ultraviolet absorption and fluorescence spectra of these compounds have been studied systematically. Moreover, the B3LYP/6-31G(d) method was used to optimize the ground state geometry of the bis-Schiff bases; and the spectroscopic properties of the products were computed based on cc-pVDZ basis set of TD-B3LYP method.Highlights► A series of novel Schiff bases containing pyrazole group were synthesized and characterized. ► The UV–vis spectra and fluorescent spectra of various as-synthesized products were measured. ► The B3LYP/6-31G(d) method was used for the optimization of the ground state geometry of the Schiff bases. ► The spectroscopic properties of the Schiff bases were computed based on cc-pVDZ basis set of TD-B3LYP method.