Dados do Trabalho

Título

Sustainable Trends in Sugar Esters Synthesis via Enzymatic Esterification in Supercritical Fluids: Exploring High Pressure and Reaction Efficiency

Introdução

Recently, interest in more sustainable industrial processes in synthesizing sugar esters (SEs) by enzymatic esterification in supercritical fluids (SCFs) has grown due to the environmental and thermodynamic advantages over conventional organic solvents. The flexibility to adjust reaction conditions makes SCFs ideal for producing SEs, enabling faster reaction rates and facilitating product recovery in high purity.

Material e Métodos

In the enzymatic synthesis of sugar esters, glucose was esterified with lauric acid, using CO2 as solvent and 2-methyltetrahydrofuran-3-one (MeTHF-3-one) as cosolvent, catalyzed by the enzyme Novozym435®. Glucose concentrations were adjusted based on solubility in MeTHF-3-one, varying the lauric acid/glucose molar ratio between 1:1 and 6:1 and using 5% of enzyme in relation to the mass of substrate used. High-pressure reactions were carried out in a variable-volume cell with sapphire windows for visual observation, and the pressure was adjusted with a movable piston and a CO2 syringe pump. The operational parameters were set at 69% for the CO2 molar fraction, 100 bar pressure, and 40°C and 60°C. The enzyme kinetics varied from 2 to 10 hours, and at the end of the reaction, the immobilized enzyme was removed by filtration. Samples of 1 mL were taken at each interval and analyzed by gas chromatography. A control without added lipase was used as a blank for the reaction mixtures.

Resultados e Discussão

High-pressure application aims to increase the efficiency of esterification reactions by increasing mass transfer between reactants and improving substrate solubility conditions. However, practical results revealed a consumption of lauric acid above what was theoretically expected, suggesting the esterification of multiple hydroxyls of glucose and the formation of several esters. In addition to glucose, the synthesized products included lauric acid and MeTHF-3-one, all catalyzed by the enzyme, indicating additional complexity in the reaction.

Conclusão

These results point to the beginning of the MeTHF-3-one ring opening by oxygen protonation, followed by the addition of water via the bimolecular nucleophilic substitution (SN2) mechanism and subsequent deprotonation. Thus, the results highlight the complexity of high-pressure reactions and the importance of optimizing process conditions to control secondary reactions and maximize efficiency in synthesizing glucose esters.