Abstract
Inexpensive Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid are proposed as both solvents and catalysts in the synthesis of alternative plasticizer bis(2-ethylhexyl) terephthalate, which has a broad spectrum of applications in plasticization processes. The utilization of 50 mol % of Brønsted ionic liquid led to the full conversion of terephthalic acid after 8 h of reaction at 120 °C. Additionally, a 100% selectivity of bis(2-ethylhexyl) terephthalate was obtained. The advantage of the presented reaction system is based on the formation of a biphasic system during the reaction. The bottom phase consists of an ionic liquid and water, and the upper phase is created by the ester and unreacted alcohol. This phenomenon helps overcome the equilibrium of the reaction and drives it towards a high yield of product. The presented new approach is proposed as a safe, cost-effective, and alternative method to conventional processes with organometallic compounds that, in turn, leads to greener and a more economically viable technology.
Highlights
In the recent years, strict regulations on environmental protection has intensified pending restrictions on plasticizers production, limiting the use of some ortho-phthalates esters, due to the concerns about negative effects on human health [1]
The solubility of terephthalic acid in ionic liquids was studied, and the results showed that terephthalic acid is partially soluble in ionic liquids, such as 1-ethyl-3-methylimidazolium diethylphosphate, 1-butyl-3-methylimidazolium acetate, and dialkylimidazolium chlorides up to four times higher than in DMSO (20 g of terephtalic acid per 100 g DMSO at 25 ◦ C) [14]
In order to lower the cost of ionic liquids, inexpensive feedstocks such as sulfuric acid and simple
Summary
Strict regulations on environmental protection has intensified pending restrictions on plasticizers production, limiting the use of some ortho-phthalates esters, due to the concerns about negative effects on human health [1]. Plasticizers are important additives to improve the flexibility, plasticity, and processability of polymers [2]. These additives, which make polyvinylchloride (PVC) flexible, are massively used for the production of medical tubing and bags, toys for children, wires and cables, and many others. Non-phthalate alternative plasticizers include terephthalates, citrates, phosphates, polyesters, halogenated alkanes, and epoxy compounds [3]. Terephthalate esters have been proven to have different toxicological profiles [4] compared to ortho-phthalates, and they may be used as direct replacements, creating an emerging alternative market. The most commercially used terephthalate ester is bis(2-ethylhexyl) terephthalate, which is used as a plasticizer in materials applied as containers for food and drinking water
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