Study Of Green Synthesis Of Substituted Benzoic Acid By Phenol Carboxylation

Carbon dioxide, which can damage the environment and accelerate global warming,is the major type of greenhouse gas. However, it is an important non-toxic, non-flammablecarbon resource. With the increase of CO2emissions and the expansion of conspicuousgreenhouse effect, CO2reduction have caused the attention of the countries all over theworld. Potential solutions include a reduction in emissions through technical advancementand legislation, physical or chemical storage. Particularly, a large amount of CO2can bedirectly consumed via chemical conversion to other useful products, which has played animportant role on reducing the CO2concentration in the atmosphere.Kolbe-Schmitt reaction is an important chemical reaction using CO2as a raw material,and it is also a useful synthetic procedure of3-methyl salicylic acid and4,6-dihydroxy-1,3-benzenedicarboxylic acid. Traditionally, these two important acid are synthesized via theproduction of sodium phenoxides and then carboxylation of sodium phenoxides with CO2.In the process, water must be completely distilled to get dry sodium phenoxides, so highenergy consumption is unavoidable.Moreover, multiple steps are also needed.This research focuses on one-pot direct synthesis of3-methyl salicylic acid and4,6-dihydroxy-1,3-benzenedicarboxylic acid with o-cresol and resorcinol as raw materials,respectively. The activity of anhydrous K2CO3and K3PO4are screened. It is found thatunder the optimum reaction conditions, CO2has not been fully utilized by using K2CO3, but,the utilization rate of CO2will greatly improve by K3PO4. When the reaction conditions iscarried out at the reaction temperature150℃, CO2pressure3.0MPa, reaction time4h, thesubstrate and salt mole ratio of1:2.5, and water content <0.2%by K3PO4, the yield of3-methyl salicylic acid is69.6%, and when the reaction conditions is at the reactiontemperature150℃, pressure1.0MPa, reaction time3h, the substrate and salt molar ratioof1:3, the water content <6%, the yield of4,6-dihydroxy-1,3-benzenedicarboxylic acid is75.4%. Compared to the traditional technology, direct synthesis of3-methyl salicylic acid and4,6-dihydroxy-1,3-benzenedicarboxylic acid have the advantages of simple step, high yield,environmental protection and energy conservation.