# A Mechanochemical Kolbe–Schmitt Reaction: Catechol Carboxylation Provides Building Blocks for Renewable Plasticizers

## TL;DR

Researchers developed a new method to create renewable plasticizers from catechol using a low-energy mechanochemical reaction, producing efficient alternatives to commercial plasticizers.

## Contribution

The first mechanochemical Kolbe–Schmitt reaction at low CO2 pressure and room temperature for carboxylating catechol.

## Key findings

- Mono- and dicarboxylated catechol derivatives were synthesized under mild conditions.
- Renewable plasticizers made from these derivatives showed plasticizing efficiency comparable to commercial products.
- Separation of reaction products was unnecessary for optimal performance in plastics.

## Abstract

Catechol, an important aromatic platform molecule which can be derived from biomass, was carboxylated by mechanochemical Kolbe–Schmitt reaction of disodium catecholate with CO2, providing a mixture of mono‐ and dicarboxylated catechol derivatives. While classical protocols require harsh reaction conditions, involving a high temperature and/or CO2 pressure, a mild ball milling method was developed. This represents the first mechanochemical Kolbe–Schmitt reaction featuring a low CO2 pressure and reactivity at room temperature. From the individual catechol‐based mono‐ and dicarboxylic acid reaction products, a library of novel renewable plasticizers was synthesized through esterification of the carboxylic acid functionalities and O‐acylation of the phenolic hydroxy groups. The resulting esters were evaluated in poly(vinylchloride) (PVC) and poly(lactic acid) (PLA), revealing plasticizing efficiencies competitive to benchmark commercial plasticizers. These efficiencies were maintained when the best performing ester substitution pattern was installed on the ball mill‐derived mixture of mono‐ and dicarboxylated catechols, making resource intensive separation (e.g. chromatographic separation) of these ortho‐dihydroxybenzene(di)carboxylic acids redundant.

A mechanochemical Kolbe–Schmitt reaction of disodium catecholate enables the synthesis of mono‐ and dicarboxylated catechols at low temperature and CO2 pressure. Directly derivatizing the resulting carboxylic acid and phenolic moieties in the obtained mixture provides plasticizer blends with efficiencies competitive to commercial benchmarks.