Conversion of carbon dioxide to resorcylic acid under ultrasonication by Kolbe-Schmitt reaction

The present work focuses on a new approach for the synthesis of β-resorcylic acid based on Kolbe-Schmitt reaction using carbon dioxide under ultrasonic and mild condition. The Kolbe-Schmitt reaction is a process for the synthesis of β-resorcylic acid (2,4-dihydroxybenzoic acid) from resorcinol in aqueous potassium hydroxide solution with gaseous CO2. The influences of carbonation time, flow rate of CO2 and the molar ratio of resorcinol/potassium hydroxide on the yield percentage of resorcylic acid were investigated. The study was assessed with the conventional thermal method (non ultrasonic method) for Kolbe-Schmitt reaction and it was observed that applying ultrasound to save more than 95% and 38.6% energy as shown by energy consumption calculations in bath type and horn type sonicator respectively. β-Resorcylic acid formed was characterized by 1H NMR, 13C NMR, DEPT NMR and FTIR spectroscopy. The amount of CO2 utilized in the reaction was evaluated from the yield percentage of β-resorcylic acid yield. The maximum yield of resorcylic acid of 30% and 65% was obtained at the resorcinol/potassium hydroxide ratio of 1:3, carbonation time of 150 min and the CO2 flow rate of 2 L/min in bath type and horn type ultrasonicator, respectively. The applicability of the research work was examined in two different positional isomers of resorcinol under optimum conditions.