Chunyan Shi

Synthesis of dimethyl carbonate catalyzed by carboxylic functionalized imidazolium salt via transesterification reaction

We investigated the dependence of cations and anions of ionic liquids (ILs) on catalytic activity for the synthesis of dimethyl carbonate (DMC) via the transesterification of ethylene carbonate (EC) with methanol (CH3OH), and demonstrated that an easily prepared carboxylic functionalized imidazolium salt exhibited higher activity, 82% yield of DMC together with 99% selectivity was obtained under the metal-free and halogen-free conditions. The reaction mechanism was also proposed according to experimental and DFT studies. In addition, in order to simplify the catalyst separation and evaluate the catalyst stability, we also covalently anchored the functionalized imidazolium salt onto a highly cross-linked polystyrene resin (PS) as a heterogeneous catalyst for DMC synthesis, and continuously performed the reaction in a fixed bed reactor for 200 h without obvious loss of activity, which would have potential applications in industry. The process thus represented an environmentally friendly pathway for the synthesis of DMC via a transesterification reaction.

Synthesis of dimethyl carbonate from CO2 and ethylene oxide catalyzed by K2CO3-based binary salts in the presence of H2O

We systematically screened binary catalysts for synthesis of dimethyl carbonate (DMC) from CO2, CH3OH and ethylene oxide (EO) in the presence of H2O by two-step transesterification process, and found the commercial quaternary ammonium salts/K2CO3, pyridinium salts/K2CO3 and KI/K2CO3 were effective binary catalysts for two-step synthesis of DMC with no need for separation of ethylene carbonate (EC). Near 100% conversion of EO and 82% yield of DMC were obtained under mild reaction conditions. However, the imidazolium salts were not compatible with inorganic alkaline possibly because of the reactive C(2)–H in the imidazolium ring. Furthermore, the KI/K2CO3 could be easily recovered and reused 12 times without obvious loss of its catalytic activity. The process avoids EC separation, and represents a simple, ecologically safer, cost-effective and energy-saving route for synthesis of DMC with high product quality, as well as easy catalyst recycling.

Base-free preparation of low molecular weight chitin from crab shell

Low molecular weight (LMW) chitin exhibits antimicrobial activity, and its preparation generally employs high molecular weight chitin as raw material. Here we use raw crab shell as material to isolate LMW-chitin. The raw crab shell was treated with hydrochloric acid under different conditions, and the demineralization and deproteinization of acid to the raw and demineralized crab shell were examined. Under conditions of 3-5u202fwt% acid, 110u202f°C, and 180-600u202fmin, the obtained LMW-chitin owns 92% purity and 53-80u202fkDa molecular weight. The method provides feasible one-step base-free strategy to directly obtain LMW-chitin from raw crab shell, and could be potentially extended to other chitin sources.

One-step preparation of an antibacterial chitin/Zn composite from shrimp shells using urea-Zn(OAc)2·2H2O aqueous solution

A one-step method is proposed to prepare a chitin/Zn composite from shrimp shells using urea-Zn(OAc)2·2H2O aqueous solution as a decalcification, deproteinization, and Zn-introduction solvent. The chitin/Zn composite, which contained 34.7 wt% zinc, 1.2 wt% calcium carbonate and 1.6 wt% protein, was obtained under optimal conditions and exhibited an antibacterial effect.

Direct conversion of shrimp shells to O-acylated chitin with antibacterial and anti-tumor effect by natural deep eutectic solvent

To obtain O-acylated chitin from shrimp shells directly, the used solvent should have multiple functions to remove calcium carbonate, protein, and acylated chitin. Herein, we use the acidic natural deep eutectic solvents (NADESs) with the ability to release H+ and various hydrogen bonding sites to achieve the above goal. The involved NADESs with three abilities of decalcification, deproteinization and acylation replaced acids, alkalis, catalysts, and acylation reagents in the conventional method. The experimental results revealed that the components of the NADESs, experiment temperature and time played key roles in the purity and degree of substitution (DS) of O-acylated chitin. Meanwhile, the ratio of shrimp shells to NADESs and a small amount of water had little effect on the preparation of O-acylated chitin. With the optimal NADES (choline chloride/DL-malic acid 1u2006:u20062, ChCl 1–DL Mal 2) treatment under the optimal conditions, the purity of O-malate chitin reached 98.6% with a DS of 0.46, exhibiting antibacterial and anti-tumor effects. The experimental results showed that the removal of calcium carbonate and protein and acylation of chitin were carried out simultaneously. Mechanistic exploration using spectroscopy and experiments confirmed that H+ release from ChCl 1–DL Mal 2 was the main reason for the removal of calcium carbonate and initiation acylation reaction. The protein was degraded to amino acids because of the acidity of ChCl 1–DL Mal 2 and dissolved in the NADES due to hydrogen bonding formation with ChCl 1–DL Mal 2.