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

• Main Authors: Urszula Dorosz, Natalia Barteczko, Piotr Latos, Karol Erfurt, Ewa Pankalla, Anna Chrobok
• Format: Article
• Language: English
• Published: MDPI AG 2019-12-01
• Series: Catalysts
• Subjects: lactate esters; ionic liquids; acidic catalysis; esterification; plasticisers; solvents
• Online Access: https://www.mdpi.com/2073-4344/10/1/37

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.