Pyrazoline derivatives as valuable five-membered heterocyclic compounds could be readily prepared through the intramolecular cyclization of ketazines. In this paper, transition metals (Zn 2+ , Cu 2+ , Cr 3+ , Mn 2+ , Co 2+ , Ni 2+ , and Fe 3+ ) were applied for the catalytic synthesis of 3,5,5-trimethyl-2-pyrazoline, and FeCl 3 showed the best catalytic performance with 95% conversion and 99% selectivity. Substrate screening exhibited that the steric hindrance of ketazines is a key factor on the conversions of R-substituted pyrazolines, following the order of R as methyl (95%) > ethyl (83%) > propyl (68%) > butyl (55%). Moreover, the mechanism of the cyclization of ketazines catalyzed by FeCl 3 is calculated by density functional theory. The energetic profile shows that the cyclization reaction consists of two steps and FeCl 3 can efficiently reduce their barrier energies. This work provides a feasible method for the preparation of pyrazoline derivatives using inexpensive, less toxic, and environmentally friendly FeCl 3 as a catalyst.

Chemical fixation of CO 2 is an efficient means for decreasing amount of CO 2 in the atmosphere. One of promising technologies is the cycloaddition of CO 2 with epoxides to synthesize cyclic carbonates. In this reaction, ionic liquid (IL) catalysts show versatile and unique advantages. However, the reaction mechanism using ILs is not clear. In this work, a detailed theoretical investigation was performed by DFT calculations. The energetic profile shows that the reaction consists of three steps, with the ring-opening step being the rate-determining step. Based on the results, effects of cations, anions and water were calculated. Cations show strong hydrogen bonding interactions with epoxides, which decreases the energy barrier of the ringopening step, indicating that hydrogen bonds play a positive role in promoting the reaction. The effect of anions was evaluated by nucleophilicity index (N Nu); anions with a larger N Nu (stronger nucleophilicity) value show lower energy barriers. The influence of water was investigated by implicit and explicit models. Compared with the solvent-free case, water as an implicit solvent decreases the energy barriers through polarization with epoxides. In the explicit solvent model, the water molecules form new hydrogen bonds with epoxides and cations, which can efficiently reduce the energy barriers. The result indicates that there is a new synergic catalytic mechanism, in which the water acts not only as solvent but also as a catalyst in the reaction. Supporting experiments further confirm the calculation results.

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Oxygenated fuel has the function of self-supplying oxygen during the combustion process, which can greatly improve emission performance and reduce diesel fuel soot production. In this paper, a novel oxygenated fuel poly­(oxymethylene) dibutyl ether (PODBE n ) is designed and synthesized through experiments in combination with density functional theory (DFT) calculation. The experimental results show that PODBE n has the advantages of high cetane number (73.6), moderate density (868 kg/m3), and low condensation point (−72 °C). According to the DFT calculation results, the molecular (PODBE n ) polarity index of different polymerization degrees is similar to the value of diesel and has good mutual solubility with diesel. Moreover, the mechanism of the entire path of synthesis is calculated at the M06-2X/6-311G­(d,p) level of theory. The energetic profile reveals that the rate-determining step is the nucleophilic addition step with the highest barrier energy (TS1 = 21.59 kcal/mol). This work provides a feasible method to synthesize high-performance oxygenated fuel PODBE n using NKC-9 ion-exchange resins.