Junya Cao,Yi Hui,Yan Cao,Jiaqiang Chen,Zheng Zheng,Liyan Zhao,Peng He,Huiquan Li,Liguo Wang
Methyl diphenylmethane dicarbamate (MDC) was synthesized by condensation of methyl phenylcarbamate (MPC) using trioxane as methylenation reagents over sulfonic acid resin catalyst. The effect of Brønsted's acid amount on the condensation reaction was investigated, and the optimal sulfonic acid resin (NKC-9) with an acid amount of 4.57 was determined. 2-MDC, featuring a methylene-bridged biphenyl structure, achieved 91.6% selectivity and 83.2% yield after response surface methodology optimization. In situ FTIR spectroscopy was employed to monitor the condensation process. The spectroscopic results unequivocally demonstrate that trioxane undergoes catalytic depolymerization to formaldehyde over NKC-9 resin, which subsequently reacts with MPC to form MDC. After sulfuric acid regeneration, NKC-9 maintains its catalytic performance after 4 cycles.
Glycerol caffeates (GC) is one kind of hydrophilic caffeoyl derivatives, which can be synthesized by the reaction of solid caffeic acid (CA) with different caffeoyl acceptors. The poor solubility of solid CA in the reaction resulted in great mass transfer limitation, low yield and time-consuming. In the work, in order to improve reaction efficiency, a novel liquid CA-based deep eutectic solvent (DES) was prepared and firstly used as caffeoyl donor for GC synthesis. Several solid acids were used as catalysts and the maximum GC yield (~55%) was achieved using NKC-9 as catalyst. Compared with solid CA as caffeoyl donor, CA conversion and initial reaction rate can be enhanced using liquid CA-based DES as caffeoyl donor. Especially at low temperature, initial CA conversion rate of liquid CA-based DES at 70 °C was 7 times that of solid CA. And the maximum CA conversion (~91%) was 2 times that of CA (44.6 ± 3.0%). When liquid CA-based DES was used as caffeoyl donor, the effect of external mass transfer limitation can also be neglected, and the activation energies of CA conversion and glyceryl monocaffeate formation (70.66 and 65.38 kJ/mol) were lower than those (83.31 and 80.41 kJ/mol) of solid CA. These indicated that liquid CA-based DES was favorable for hydrophilic GMC and GDC selective formations.
Polyoxymethylene dimethyl ethers (DMM n ) are promising diesel additives. The synthesis of DMM n from methylal (DMM) and paraformaldehyde over the NKC-9 acidic ion-exchange resin catalyst was investigated. Many unrecyclable by-products such as methyl formate, dimethyl ether and formic acid were produced in the reaction. To increase the selectivity of the desired products DMM 3‒6 and reduce the amount of unrecyclable by-products, the effects of reaction temperature, time, pressure and the molar ratio of the raw materials were evaluated through a series of single factor experiments. Experiments revealed that trace amount of water could suppress the formation of unrecyclable by-products, and the optimum initial water content (less than 2 wt%) was investigated. In addition, the synthetic process needs to go through the polyoxymethylene hemiformals intermediate stage, and then the DMM n were obtained when polyoxymethylene hemiformals reacted with methanol. Ultimately, a possible mechanism is proposed to describe the formation of DMM n from polyoxymethylene hemiformals in detail, in which it is revealed that the formation of carbocation intermediates is important in the reaction processes.
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