Abstract: The synthesis of 3-methyl salicylic acid in supercritical or subcritical carbon dioxide has important meaning for the green synthesis of 3-methyl salicylic acid and resourcization of carbon dioxide. After comparing the catalytic activity of anhydrous potash，anhydrous sodium carbonate and so on，anhydrous potash was chosen as the best catalyst to synthesize 3-methyl salicylic acid directly from o-cresol by one-pot method in supercritical or subcritical carbon dioxide. At the condition of reaction time from 1—6 hours，catalyst′s relative dosage（nK2CO3/ nO-Cresol）from 0.05—1.25，reaction temperature from 130—270 ℃ and reaction pressure from 4—10MPa，o-cresol’s carboxylic reaction was studied in supercritical or subcritical carbon dioxide. The result showed that the conversion of o-cresol and the yield of 3-methyl salicylic acid both increased at first with the increase of time，and then the conversion became stable，but the yield decreased slightly in the end. The conversion and the yield increased rapidly at first and then increased slowly with the increase of catalyst′s relatively dosage. The conversion and the yield increased rapidly at first but then decreased with the increase of reaction pressure or reaction temperature. The conversion is about 19.7% and the yield is about 17.5% under the optimal condition that reaction time was 3 hours，catalyst′s relatively dosage was 0.5，reaction temperature was 190 ℃ and reaction pressure was 8 MPa. In addition，a possible reaction mechanism was proposed.

Key words: supercritical or subcritical carbon dioxide, o-cresol, 3-methyl salicylic acid, one-pot synthesis, anhydrous potash

摘要： 在超/亚临界CO2中合成邻甲基水杨酸，对探索其绿色合成和CO2的资源化利用有重要意义。本实验以邻甲酚为原料，考察了无水K2CO3、无水Na2CO3等催化剂的活性，选取催化效果最好的无水K2CO3在超/亚临界CO2中一步法直接催化合成邻甲基水杨酸。在反应时间1～6 h、催化剂相对投加量nK2CO3/nO-Cresol为0.05～1.25、反应温度130～270 ℃、反应压力4～14 MPa的条件下对邻甲酚在超/亚临界CO2中的羧基化反应进行了研究。结果表明：邻甲酚的转化率与产物收率随反应时间的延长均出现先增加的趋势，不同的是转化率最后趋于稳定，产物收率则略有减少；邻甲酚的转化率与产物收率随催化剂相对投加量的增加先快速增加然后趋缓，随反应温度、反应压力的增加先增加后减少。较佳的实验条件为：反应时间3 h、催化剂相对投加量0.5、反应温度190 ℃、反应压力8 MPa，此时，邻甲酚转化率可达19.7%，邻甲基水杨酸收率可达17.5%。此外，提出了超/亚临界CO2中邻甲酚羧基化反应可能存在的机理。

关键词: 超/亚临界CO2, 邻甲酚, 邻甲基水杨酸, 一步法合成, 无水K2CO3