Synthesis of Salicylic Acid from Phenol Catalyzed by K_2CO_3 in Supercritical CO_2

The process of direct synthesis of salicylic acid from phenol catalyzed by K2CO3 in supercritical CO2 was studied.CO2 could act not only as a reagent but also as a solvent in this process.The conventional two-step synthesizing process of organic phenolic acid by Kolbe Schmitt reaction was improved,and the salicylic acid was synthesized by only one step.The influences of temperature(from 160 to 220℃),pressure(from 4 to 14 MPa),reaction time,amount of catalyst used were investigated.The highest salicylic acid yield could reach 54%,by-product is p-hydroxybenzoic acid of a very small amount,and selectivity is higher than 99%.The obtained optimum conditions of the reaction are as following: reaction temperature 190℃,reaction pressure 8 MPa,reaction time 3~5 h,amount of catalyst 10 mmol(n K2CO3/n phenol=1).