Statistical optimization, mechanistic, and thermodynamics insights into Gallic acid extraction using hydrophobic deep eutectic solvent based on tri‐n‐octyl phosphine oxide and decanoic acid
Saurabh Babu, Neetu Singh, Sushil KumarAbstract
BACKGROUND
Hydrophobic deep eutectic solvents (DESs) have emerged as sustainable alternatives for the extraction of bio‐compounds from aqueous media. In this study, a hydrophobic DES is synthesized using tri‐n‐octylphosphine oxide (TOPO) as hydrogen bond acceptor (HBA) and decanoic acid as hydrogen bond donor (HBD) and employed to extract Gallic acid (GA) from an aqueous solution.
RESULTS
The prepared DES (1:1 of HBA:HBD) exhibited suitable physicochemical properties with density 0.89 gc m −3 , viscosity 22.74 mPa‐s, conductivity 1.03 S m −1 , and pH 4.07. GA extraction is modeled and optimized using response surface methodology (RSM) coupled with central composite design (CCD) by varying initial GA concentration (0.02–0.10 kmol m −3 ), phase ratio (0.2 to 1.8), pH (3–7), and temperature (20–60 °C). The optimized extraction conditions are achieved as 0.04 kmol·m −3 GA, 1:1.4 phase ratio, pH −4, and 30 °C temperature with extraction efficiency of 95.5% (experimental) close to 94.7% (predicted). The Mechanistic analysis based on the law of mass action and differential evolution indicated formation of a 1:1 TOPO:GA complex via hydrogen bonding with equilibrium constant ( K E = 9.1 and m = 0.80), further confirmed by FTIR analysis. Thermodynamic parameters such as enthalpy ( ΔH = −11 382 J mol −1 ), entropy ( ΔS = −19.04 J mol −1 K −1 ), and negative Gibbs free energy (−5822 to −5263 J mol −1 ) confirmed spontaneous and exothermic nature of extraction process.
CONCLUSION
The synthesized hydrophobic DES demonstrates efficient, optimized, and thermodynamically favorable recovery of Gallic acid, offering a sustainable alternative to conventional organic extractants. © 2026 Society of Chemical Industry (SCI).