Articolo in rivista, 2021, ENG, 10.1021/acssuschemeng.0c08901

New Mechanistic Insights into the Lignin beta-O-4 Linkage Acidolysis with Ethylene Glycol Stabilization Aided by Multilevel Computational Chemistry

De Santi A.; Monti S.; Barcaro G.; Zhang Z.; Barta K.; Deuss P.J.

Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, Groningen, 9747 AG, Netherlands; CNR-ICCOM- Institute of Chemistry of Organometallic Compounds, via Moruzzi 1, Pisa, 56124, Italy; CNR-IPCF-Institute for Chemical and Physical Processes, via Moruzzi 1, Pisa, 56124, Italy; Department of Chemical Engineering (ENTEG), University of Groningen, Nijenborgh 4, Groningen, 9747 AG, Netherlands; Department of Chemistry, Organic and Bioorganic Chemistry, University of Graz, Heinrichstrasse 28/II, Graz, 8010, Austria

Acidolysis in conjunction with stabilization of reactive intermediates has emerged as one of the most powerful methods of lignin depolymerization that leads to high aromatic monomer yields. In particular, stabilization of reactive aldehydes using ethylene glycol results in the selective formation of the corresponding cyclic acetals (1,3-dioxolane derivatives) from model compounds, lignin, and even from softwood lignocellulose. Given the high practical utility of this method for future biorefineries, a deeper understanding of the method is desired. Here, we aim to elucidate key mechanistic questions utilizing a combination of experimental and multilevel computational approaches. The multiscale computational protocol used, based on ReaxFF molecular dynamics, represents a realistic scenario, where a typical experimental setup can be reproduced confidently given the explicit molecules of the solute, catalyst, and reagent. The nudged elastic band (NEB) approach allowed us to characterize the key intermolecular interactions involved in the reaction paths leading to crucial intermediates and products. The high level of detail obtained clearly revealed for the first time the unique role of sulfuric acid as a proton donor and acceptor in lignin ?-O-4 acidolysis as well as the reaction pathways for ethylene glycol stabilization, and the difference in reactivity between compounds with different methoxy substituents.

ACS sustainable chemistry & engineering 9 (5), pp. 2388–2399

Keywords

acidolysis, Lignin, model compounds, NEB profiles, reaction mechanism, ReaxFF Molecular Dynamics

CNR authors

Monti Susanna, Barcaro Giovanni

CNR institutes

ICCOM – Istituto di chimica dei composti organo metallici, IPCF – Istituto per i processi chimico-fisici