Pushing the Limits in Alcoholysis of Waste Polycarbonate with DBU-Based Ionic Liquids under Metal- and Solvent-Free Conditions

Abstract

The development of efficient and green protocol for recycling of waste plastics is of great significance in terms of “sustainable society” and “green chemistry” concepts. Several ionic liquids (ILs) with different acidity–basicity and structures were one-step synthesized and characterized. They were applied to alcoholysis of polycarbonate (PC) without metal and solvent. The IL structures and reaction conditions were optimized. Moreover, the alcohol scopes and catalyst reusability were evaluated. The results showed that 100% PC conversion and 99% bisphenol A (BPA) yield were obtained by using [HDBU]­[LAc] catalyst, and the [HDBU]­[LAc] could keep high-activity after using for six times under the optimized conditions. Finally, the possible reaction mechanism was proposed via the FT-IR and NMR analysis technique.

Selective Degradation of End‐of‐Life Poly(lactide) via Alkali‐Metal‐Halide Catalysis

“…With respect to the degradation process, a number of organocatalysts have been proven to be active, but often long reaction times and “costly” organocatalysts are required; hence, improvements are needed. For example, ionic liquids (ILs) have been established as catalysts . It was supposed that the alcohol is activated by the anion and the carbonyl function by the cation.…”

“…[12] An attractive alternative to petrochemical-based plastics are plastics originated from renewables (biopolymers and bio-based polymers), but so far the rate of production is significantly lower. [56,[71][72][73][74][75] It was supposed that the alcohol is activated by the anion and the carbonyl function by the cation. Lactic acid methyl lactate (2) can be transformed to compound 3 (lactide), which is a fundamental compound in the industrial production chain of PLA (Scheme 1).…”

“…Afterward, the degradation was carried out at a temperature of 180 °C for 20 min. [56,[71][72][73][74][75] The potassium cation can function as Lewis acid and coordinates the oxygen of the carbonyl function and by doing so the carbonyl carbon is activated and methanol can attack (oxygen atom of the methanol) the group as nucleophile. Nevertheless, a reuse/recycling of potassium fluoride is possible, which is in contrast to our earlier reported DMAP system.…”

“…For example, ionic liquids (ILs) have been established as catalysts. [56,[71][72][73][74][75] It was supposed that the alcohol is activated by the anion and the carbonyl function by the cation. In this context, we wondered if straightforward alkali metal halides can mimic the action of ILs.…”

“…With respect to the underlying degradation mechanism we assume that the alkali metal halide can act as dual catalyst in accordance to ionic liquid catalysts applied in the methanolysis of polycarbonate (Scheme 3). [56,[71][72][73][74][75] The potassium cation can function as Lewis acid and coordinates the oxygen of the carbonyl function and by doing so the carbonyl carbon is activated and methanol can attack (oxygen atom of the methanol) the group as nucleophile. The nucleophilicity of the methanol can be increased by the interaction of the fluoride anion with the proton of methanol via hydrogen bonding.…”