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

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.

Dialkyl Succinates and Adipates as Alternative Plasticizers—Even More Efficient Synthesis

“…Brønsted acidic ILs for the indicial tests were synthesised as described in the experimental section in the following molar ratios: 1:2.0, 1:2.7 and 1:3.0. Water was added to the reaction mixture to enable heat removal from the exothermic acid–base reaction [ 31 , 32 ]. After drying, the obtained ILs (IL 2.0; 2.7 and 3.0) were colourless liquids.…”

“…Synthesis of these more acidic ILs leads to the formation of a hydrogen-bonded network of H 2 SO 4 molecules and [HSO 4 ] − anions in an anion structure. The resulting ILs were used as both the acidic catalysts and as the solvent for the esterification of levulinic, terephthalic and lactic acids [ 30 , 31 , 32 ], as well as for the synthesis of ε-caprolactam [ 33 ].…”

Organocatalyst Promoted Efficient Synthesis of Carboxylic Acid Esters and its Application as Plasticizer for Polyvinyl Chloride

“…The titanium-based catalysts along with esterification, also lead to isomerization, transesterification, and disproportionation reactions. [6] However, these are not suitable for the current process chemistry because of metal residue in the final product, and hence metal-free catalyst is preferred. [7] Organocatalysis leads to metal-free products for particularly specific applications, for example, active pharma intermediates, microelectronics, biomedical, and cosmetics.…”

“…The commercial availability and low price make titanium base catalysts advantageous. The titanium‐based catalysts along with esterification, also lead to isomerization, transesterification, and disproportionation reactions [6] . However, these are not suitable for the current process chemistry because of metal residue in the final product, and hence metal‐free catalyst is preferred [7] …”

Ionic Liquids in Catalysis

“…Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid were employed as a solvent and catalyst in the synthesis of bis(2-ethylhexyl) terephthalate which is used as a plasticizer in the manufacture of plastics coming into contact with food. This new approach, which is characterized by the replacement of conventional acids and organometallic compounds with ionic liquids, was described by Chrobok's research group [28]. Bouquillon et al presented the synthesis of a series of biobased ionic liquids with natural carboxylates (proline-based ionic liquids) [29].…”