Interfacial Catalysis in Biphasic Carboxylic Acid Esterification with a Nickel-Based Metallosurfactant

Abstract

A metallosurfactant catalyst was developed to address the requirements for the utilization of low-molecular-weight carboxylic acids from dilute effluents. The catalyst Ni­(DBSA)2 combines transition-metal catalysis of nickel ions and surfactant catalysis of 4-dodecylbenzenesulfonic acid (4-DBSA). Requirements for the metallosurfactant catalyst are low water solubility, high catalytic activity in biphasic esterification, and self-assembling properties at the interface. Ni­(DBSA)2 was tested for applicability in the interfacial catalysis of esterification of dilute acetic acid with the solvent 1-octanol and resulted in an octyl acetate yield of 31.3%. Under identical reaction conditions, Ni­(DBSA)2 performed better than sulfuric acid with a yield of 1.7%. The limited catalytic performance of sulfuric acid is caused by the presence of sulfuric acid mainly in the aqueous phase. In contrast, Ni­(DBSA)2 is dissolved in the solvent and assembles at the aqueous/solvent interface where the reaction takes place. Additionally, the metallosurfactant lowers the interfacial tension between 1-octanol and deionized water by up to 75%, thus enhancing mass transfer. Compared to catalysis with 4-DBSA in emulsion, the catalytic performance of Ni­(DBSA)2 dropped by 62%, but this drawback is compensated by the complete suppression of emulsification. With Ni­(DBSA)2, the development of a catalyst was achieved, which self-enhances its catalytic performance in the interfacial catalysis through increased mass transfer area due to its surfactant properties.

Reactive Distillation for Solvent Regeneration after Biphasic Carboxylic Acid Esterification

“…To tackle the challenge of carboxylic acid recovery from dilute aqueous streams, a novel process concept based on reactive extraction with esterification and solvent recovery by reactive distillation with transesterification was developed by our group. The esterification‐enhanced reactive extraction step has already been reported by Toth et al 11, 12. The purpose of the present work is to complement the concept by solvent recovery through reactive distillation with transesterification.…”

“…For accelerating the transesterification reaction, the catalysts 4‐dodecylbenzenesulfonic acid (> 95 %, mixture of isomers; Sigma‐Aldrich; 4‐DBSA) and the metallosurfactant Ni(DBSA) 2 were used. The latter catalyst was prepared according to the synthesis instructions reported by Toth et al 12. Characterization of Ni(DBSA) 2 can be found in Toth et al 12.…”

“…The esterification step in an emulsified regime has proven feasible with carboxylic acid conversions far beyond the respective equilibrium conversion in the corresponding aqueous feed 11, 12. In this study, 4‐dodecylbenzenesulfonic acid (4‐DBSA) showed high performance in catalysis and emulsification yet opening the challenge of emulsion splitting.…”

“…However, correction of surfactant properties was exchanged against reduced catalytic activity of Ni(DBSA) 2 . 12…”

Solvent-free synthesis of phytosterol linoleic acid esters at low temperature

“…An early report has shown an interesting "brønsted acid-surfactant-combined catalysis" that 4-dodecylbenzenesulfonic acid (DBSA) could catalyze esterication of lauric acid with 3-phenyl-1-propanol in water. 22 Inspired by the concept of "brønsted acid-surfactant-combined catalyst" in biphasic reaction systems, [22][23][24][25][26] we envisage that DBSA can also promote the esterication of phytosterols with unsaturated fatty acids (e.g., linoleic acid) under solvent-free conditions.…”