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.
Highlights
Lactic acid (LA) is an important building block for the production of biodegradable polymers, as well as a starting material for the pharmaceutical industry [1]
In the search for catalysts for lactate production that would be suitable on an industrial scale, we propose an inexpensive Brønsted acidic ionic liquid, together with protic ionic liquids based on nitrogen bases and an excess of sulphuric acid
We showed that using protic ionic liquid as the acidic catalyst and solvent enables the esterification of lactic acid with unexpectedly high efficiency
Summary
Lactic acid (LA) is an important building block for the production of biodegradable polymers, as well as a starting material for the pharmaceutical industry [1]. LA is an important feedstock for the production of alkyl lactates, which are used as raw materials for the manufacturing of many products, such as plastics, paints, solvents and detergents. Alkyl lactates are increasingly used in food, cosmetics and pharmaceutical formulations due to their hygroscopic, emulsifying and exfoliating properties. They are known as safe, noncarcinogenic, biodegradable and noncorrosive substances, which are considered green solvents. Their eco-friendly properties have been confirmed by studies in which no toxic or mutagenic effects were observed [1]
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