Lipase-Catalyzed Transformations for the Synthesis of Butyl Lactate: A Comparison between Esterification and Transesterification

Abstract

The alpha-hydroxy esters are increasingly employed in cosmetic, food, and pharmaceutical formulations as they determine reduced skin-irritant effects in comparison with the respective acids, offering similar hygroscopic, emulsifying, and exfoliating properties. The enzymatic synthesis of lactate esters in nonaqueous systems was studied as regards the influence of the critical process parameters, to enable a comparison between the most commonly used synthetic routes, namely, esterification and transesterification. The experimental results showed that the direct esterification of lactic acid with butanol may be limited by the reduced lipase stability in the presence of the acid (substrate) and of the water (product), in particular when solvent-free media are used. The stability of the enzyme is further reduced as polar solvents are required as a result of the polarity of the lactic acid. Therefore, the use of the lactic acid as substrate is of practical interest only when the acid is significantly cheaper in comparison with its short-chain esters. If this is not the case, the transesterification of the ethyl lactate with butanol is to be preferred for the higher flexibility in the choice of the experimental conditions, the operability of solvent-free systems, and the simplicity of the product removal assembly.

Recent Developments and Optimization of Lipase-Catalyzed Lactone Formation and Ring-Opening Polymerization

“…The esterification reactions still occurred, but the interactions between substrates and lipases were less specific and much slower. Similar results were obtained by Pirozzi et al with CALB, which revealed reduced stability in the presence of acidic reagents and released water, especially in solvent‐free media . They emphasized that 45 and 60 °C are the optimal temperatures for esterification and transesterification, respectively.…”

“…Similar results were obtained by Pirozzi et al with CALB, which revealed reduced stability in the presence of acidic reagents and released water, especially in solvent-free media. [80] They emphasized that 45 and 60 °C are the optimal temperatures for esterification and transesterification, respectively. The impact of released water is more important in solventfree media than under high-dilution conditions where lactones are desired.…”

Dinuclear Zinc–N‐Heterocyclic Carbene Complexes for Either the Controlled Ring‐Opening Polymerization of Lactide or the Controlled Degradation of Polylactide Under Mild Conditions

“…In view of the growing need of PLA, the recycling of PLA through degradation–depolymerization into its starting component (i.e., lactic acid) for reuse and/or for conversion into valuable materials (such as lactate esters, which have applications in cosmetics, fragrances, and food additives) is of current interest 8. Although the enzymatic PLA degradation (through hydrolysis) has been established,9 the chemical depolymerization of PLA typically requires drastic reaction conditions, which are detrimental to product selectivity and impose a high energy input 10. A few representative reports in this area include the following: 1) PLA breakage under harsh acidic or basic conditions (NaOH or HCl),11 2) the use of 4‐dimethylaminopyridine for PLA degradation (135 °C, 24 h) via ester cleavage,12 and 3) PLA depolymerization through transesterification with Sn II octanoate (120 °C, 24 h) 13.…”

Lipase‐catalyzed synthesis of polylactic acid: an overview of the experimental aspects

“…Pirozzi et al have investigated the performance of immobilized CAL‐B as biocatalyst in esterification and transesterification of LA. They observed a severe loss of stability of the enzyme in the presence of LA when operating in a solvent‐free environment 30, 32. Therefore the solution reaction appears to be the most viable route to obtain PLA using this lipase.…”