Highly Efficient Biphasic System for the Synthesis of Alkyl Lactates in the Presence of Acidic Ionic Liquids

Abstract

Alkyl lactates are produced from lactic acid via esterification, and are used in the production of plastics, paints, solvents and detergents. In the pursuit of an inexpensive, industry-suitable catalyst for this reaction, the application of protic ionic liquids based on nitrogen base and sulphuric acid is proposed. The ionic liquid was synthesised via a simple reaction of triethylamine and a threefold molar excess of sulphuric acid. Water was added to remove the heat of the reaction. Next, the reaction conditions for the model esterification of 2-ethylhexanol with lactic acid without additional solvent were optimised. Exceptionally mild conditions, i.e., a twofold molar excess of alcohol to lactic acid with the addition of an ionic liquid in a catalytic amount (15 mol%) at 60 °C, resulted in high yields of ethyl and 2-ethylhexyl lactates (96–97%). The driving force of this reaction is the production of a biphasic system with immiscible ester during the reaction. This phenomenon makes it possible to overcome the reaction equilibrium. Using an inexpensive ionic liquid, which could be recycled up to five times without diminution in conversion or selectivity, leads to both a greener and a more economically-viable process.

Kinetics of Alkyl Lactate Formation from the Alcoholysis of Poly(Lactic Acid)

“…There is therefore a strong potential to use EtOH for industrial chemical recycling of PLA waste to recover the commercially-valuable EtLa. Out of the three product lactates EtLa, PrLa and BuLa, the former is considered the most useful and has the highest demand [9,10]. EtLa is biodegradable so will eventually degrade and assimilate into plants that can be used as carbohydrate feedstocks to generate virgin PLA [10].…”

“…High EtLa selectivities (>95%) from the reaction of dihydroxyacetone and ethanol (EtOH) catalysed by methyl-functionalised tin silicates has been demonstrated [27]. High AL yields (around 96%) were also obtained by using protic ionic liquids formulated from a nitrogen base and sulphuric acid by Dorosz, et al [9].…”

“…The market value of ethyl lactate (EtLa) alone is estimated to reach USD 92 million by 2024 [8]. EtLa is an additive in paints, foods, cosmetics and cleaning items, as well as a solvent in the manufacturing of microelectronics and pharmaceutical products [7,9,10]. Studies have also shown the possibility of using EtLa for the recovery of phenolics and carotenoids (phytonutrients) from fruits and vegetables including palm oil [11][12][13].…”

“…Similarly, propyl lactate (PrLa) is a pesticide and a food additive, whereas n-butyl lactate (BuLa) is an additive and a solvent in food, pharmaceuticals, cosmetics and paint formulations [9,16,17]. The use of BuLa lactate in the recovery of bio-butanol from aqueous mixtures has also been reported [18].…”

Sustainable Method for the Synthesis of Alternative Bis(2-Ethylhexyl) Terephthalate Plasticizer in the Presence of Protic Ionic Liquids

“…Using a new family of Brønsted acidic protic ionic liquids, based on sulfuric acid for esterification processes of acetic [19] and lactic acid [20], we have already achieved competitive advantages over the classical methods. Highly acidic protic ionic liquids were obtained in the simple reaction between amine (e.g., triethylamine or 1-methylimidazole) and sulfuric acid.…”