Abstract:

2-Heptyl chloroacetate is an important intermediate for synthesizing new pesticides and herbicides. Conventional esterification reactions often use traditional strong acids, which is harmful to equipment and shows low product yield. Using ionic liquids as solvents or catalysts can make the reaction conditions stable, recyclable and environment-friendly, and lead to high product yield. Herein, the transesterification reaction between methyl chloroacetate and 2-heptanol was studied. Four ionic liquid catalysts were synthesized, including 1-methyl-3-（propyl-3-sulfonic acid） imidazole p-toluenesulfonic acid salt [MIM-PS][PTSA], 1-butyl-3-methylimidazole hydrosulfate [BMIM] HSO₄, 1-methyl-3-（propyl-3-sulfonic acid） imidazole hydrosulfate [MIM-PS][HSO₄] and N-methylimidazole phosphoric acid salt [HMIM] H₂PO₄. These four ionic liquid catalysts were used in a transesterification reaction. According to the product yield of the transesterification reaction, the optimal catalyst [MIM-PS] [PTSA] was screened. The effects of ester-alcohol ratio, reaction temperature, reaction time, catalyst dosage and catalyst cycle were investigated in the presence of [MIM-PS][PTSA]. The results showed that, for the reaction between methyl chloroacetate and 2-heptanol, 5% [MIM-PS][PTSA] catalyst was added, the reaction temperature was 100 ℃, and the reaction time was 6 h, indicative of a yield of 76.3%. When the ionic liquid was reused for three times, the yield of 2-heptyl chloroacetate was still greater than the 95% of the initial yield. When the catalyst was more than 5% or the temperature was too high, by-products such as 2-heptene or 2-heptyl ether might be formed. When the reaction time was too long, the product might undergo substitution reaction to form corresponding ether compounds. In this work, ionic liquids were used as solvents or catalysts, and the reaction conditions were stable, recyclable and environment-friendly, and the product yield was high, which could provide reference for the conditions of process amplification.

Key words: ionic liquid, transesterification reaction, 2-heptyl chloroacetate, catalyst