Issue 8, 2020

Novel insights into biomass delignification with acidic deep eutectic solvents: a mechanistic study of β-O-4 ether bond cleavage and the role of the halide counterion in the catalytic performance

Abstract

Development of innovative technologies for efficient, yet eco-friendly, biomass delignification is required to achieve higher sustainability than traditional processes. In this context, the use of deep eutectic solvents (DESs) for the delignification process could fulfil these requirements and stands today as a promising alternative. This work focuses on understanding the fundamental chemistry behind the cleavage of the β-O-4 ether bond present in 2-phenoxy-1-phenylethanol (PPE), a lignin model compound, with three acidic DESs, including Propionic acid/Urea (PA : U), Lactic acid/Choline Chloride (LA : ChCl) and p-Toluenesulphonic acid/Choline chloride (pTSA : ChCl). The acidic nature of each DES influenced the efficiency of PPE cleavage and determined the extent of further side reactions of cleavage products. Although PA : U (2 : 1) demonstrated the ability to dissolve lignin, it is unable to cleave β-O-4 ether linkage in PPE. On the other hand, LA : ChCl (10 : 1) allowed PPE cleavage, but an esterification between the PPE and lactic acid as well as oligomerization of lactic acid was detected. Among the examined solvents, pTSA : ChCl (1 : 1) demonstrated the highest performance in the PPE cleavage, although the high acidity of this system led to the condensation of cleavage products with prolonged time. The presence of water decreases the ability of DESs for cleavage, but the extension of undesired side reactions was also reduced. Finally, the analysis of intermediates and products of the reactions allowed the identification of a chlorinated species of PPE that precedes the cleavage reaction. A kinetic study using pTSA : ChCl (1 : 1) and pTSA : ChBr (1 : 1) was performed to unveil the role of the halide counterion present in DESs in the cleavage of the β-O-4 ether bond and a new reaction mechanism was herein proposed and supported by density functional theory (DFT) calculations.

Graphical abstract: Novel insights into biomass delignification with acidic deep eutectic solvents: a mechanistic study of β-O-4 ether bond cleavage and the role of the halide counterion in the catalytic performance

Supplementary files

Article information

Article type
Paper
Submitted
24 7 2019
Accepted
26 2 2020
First published
27 2 2020

Green Chem., 2020,22, 2474-2487

Novel insights into biomass delignification with acidic deep eutectic solvents: a mechanistic study of β-O-4 ether bond cleavage and the role of the halide counterion in the catalytic performance

A. M. da Costa Lopes, J. R. B. Gomes, J. A. P. Coutinho and A. J. D. Silvestre, Green Chem., 2020, 22, 2474 DOI: 10.1039/C9GC02569C

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements