Abstract
As a result of strict regulations of phthalate plasticizers, alternative non-phthalate forms are desired and increasingly used. This work presents a synthetic method for alternative plasticizers (dialkyl succinates and adipates) via esterification of succinic and adipic acid with alcohols: butan-1-ol and 2-ethylhexan-1-ol. Ionic liquids were synthesized by the reaction of triethylamine with over-equimolar (1:2.7) amounts of sulfuric(VI) acid, which were used as an acidic catalyst and solvent. The two-phase liquid–liquid system was formed during the reaction due to immiscibility of the esters with the ionic liquid. This phenomenon is a driving force of this process, shifting the equilibrium toward the product formation. As a result, dialkyl succinates and adipates were obtained in high yields (99%) and selectivities (>99%), under mild reaction conditions at 70–80 °C and using a 4:1 molar ratio of alcohol to acid and 15 mol% of catalyst. The catalyst was recycled 10 times without any loss of activity. This alternative method is highly competitive: it involves a simple procedure for product isolation as well as a high yield and purity of the resulting esters. These advantages make this method sustainable and promising for industrial applications.
Highlights
Until recently, the most popular and produced plasticizers were phthalates, in particular bis (2-ethylhexyl) phthalate, di-n-butyl phthalate, di(isononyl) phthalate, di(isodecyl) phthalate and di-n-octyl phthalate
Brønsted acidic ionic liquids (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
In the pursuit of an effective method which is sustainable and combines the aspects of green chemistry with economic efficiency, we have studied the esterification of succinic and adipic acid with the alcohols butan-1-ol and 2-ethylhexan-1-ol in the presence of acidic
Summary
The most popular and produced plasticizers were phthalates, in particular bis (2-ethylhexyl) phthalate, di-n-butyl phthalate, di(isononyl) phthalate, di(isodecyl) phthalate and di-n-octyl phthalate. In 2015, the European Union introduced legal regulations that limited the use of phthalates due to their toxicity. Similar regulations limiting the use of phthalates are respected in North America, while in South America, India and. China their use is not currently regulated by legal standards [1]. Dialkyl succinates with longer alkyl chains, e.g., DOS, are the most effective plasticizers with similar or even better plasticizing properties than phthalate esters, having a high compatibility with the polymers that allows a high plasticization efficiency. Succinates with shorter alkyl chains achieve similar plasticizing properties to phthalates but require higher concentrations
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