Hydroxyl carboxylate anion catalyzed depolymerization of biopolyesters and transformation to chemicals

TL;DR

A new method uses ionic liquids to break down biopolyesters into useful chemicals without metals and at low temperatures.

Contribution

A novel metal-free protocol using hydroxyl carboxylate anions to depolymerize biopolyesters into chemicals under mild conditions.

Findings

Hydroxyl carboxylate anions activate ester groups via hydrogen bonding to initiate depolymerization.

Ionic liquids like 1-ethyl-3-methylimidazolium glycolate convert PGA into glycolic acid, esters, and amides efficiently.

The process works at low temperatures (e.g., 40 °C) and produces high yields of target chemicals.

Abstract

Upcycling biopolyesters (e.g., polyglycolic acid, PGA) into chemicals is an interesting and challenging topic. Herein, we report a novel protocol to upgrade biopolyesters derived from hydroxyl carboxylic acids over ionic liquids with a hydroxyl carboxylate anion (e.g., glycolate, lactate) into various chemicals under metal-free conditions. It is found that as hydrogen-bond donors and acceptors, hydroxyl carboxylate anions can readily activate the ester group via hydrogen bonding and decompose biopolyesters via autocatalyzed-transesterification to form hydroxyl carboxylate anion-based intermediates. These intermediates can react with various nucleophiles (e.g. H2O, methanol, amines and hydrazine) to access the corresponding acids, esters and amides under mild conditions (e.g., 40 °C). For example, 1-ethyl-3-methylimidazolium glycolate can achieve complete transformation of PGA into various chemicals such as glycolic acid, alkyl glycolates, 2-hydroxy amides, 2-(hydroxymethyl)benzimidazole, and 1,3-benzothiazol-2-ylmethanol in excellent yields via hydrolysis, alcoholysis and aminolysis, respectively. This protocol is simple, green, and highly efficient, which opens a novel way to upcycle biopolyesters to useful chemicals.

Hydroxyl carboxylate-based ionic liquids can achieve degradation of biopolyesters derived from hydroxyl carboxylic acids into various chemicals under mild and metal-free conditions.

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