B. U. W. Maes

Confined hot-pressurized water in Brønsted-acidic beta zeolite speeds up the O demethylation of guaiacol

M. Bocus, E. Van den Broeck, X. Wu, M. Bal, J. Bomon, L. Vanduyfhuys, B. F. Sels, B. U. W. Maes, V. Van Speybroeck

Nature Catalysis

2025

A1

Abstract

Biorefinery technologies that convert lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In these technologies, a key process is the acid-catalysed O demethylation of guaiacol derivatives in hot-pressurized water using Brønsted mineral acids or microporous zeolites. The fundamental understanding of how hydronium ions behave in a confined environment versus bulk is still limited. Here we investigate the O demethylation of guaiacol in hot-pressurized water with HCl or H-BEA zeolite catalysts to elucidate the impact of zeolite microporosity on reaction mechanisms and rates. Operando molecular simulations combined with experimental kinetic studies reveal that, regardless of the catalyst type, O demethylation follows a concerted O-activated S_N2 mechanism. The reaction rate is higher in the zeolite due to more active, under-coordinated hydronium ions. Additionally, the molecular organization of solvent and reactants around the confined active site plays a crucial role in modulating the association of the reacting species and the reaction kinetics.

DOI

https://doi.org/10.1038/s41929-024-01282-6

Access to bio-renewable and CO2-based polycarbonates from exovinylene cyclic carbonates

F. Siragusa, E. Van den Broeck, C. Ocando, A. Müller, G. De Smet, B. U. W. Maes, J. De Winter, V. Van Speybroeck, B. Grignard, C. Detrembleur

ACS Sustainable Chemistry & Engineering

9 (4), 1714–1728

2021

A1

Abstract

We investigate the scope of the organocatalyzed step-growth copolymerization of CO2-sourced exovinylene bicyclic carbonates with bio-based diols into polycarbonates. A series of regioregular poly(oxo-carbonate)s were prepared from sugar- (1,4-butanediol and isosorbide) or lignin-derived (1,4-benzenedimethanol and 1,4-cyclohexanediol) diols at 25 °C with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst, and their defect-free structure was confirmed by nuclear magnetic resonance spectroscopy studies. Their characterization by differential scanning calorimetry and wide-angle X-ray scattering showed that most of them were able to crystallize. When the polymerizations were carried out at 80 °C, some structural defects were introduced within the polycarbonate chains, which limited the polymer molar mass. Model reactions were carried out to understand the influence of the structure of alcohols, the temperature (25 or 80 °C), and the use of DBU on the rate of alcoholysis of the carbonate and on the product/linkage selectivity. A full mechanistic understanding was given by means of static- and dynamic-based density functional theory (DFT) calculations showing the determining role of DBU in the stability of intermediates, and its important role in the rate-determining steps is revealed. Furthermore, the origin of side reactions observed at 80 °C was discussed and rationalized by DFT modeling. As impressive diversified bio-based diols are accessible on a large scale and at low cost, this process of valorization of carbon dioxide gives new perspectives on the sustainable production of bioplastics under mild conditions.

DOI

http://dx.doi.org/10.1021/acssuschemeng.0c07683

Brønsted Acid Catalyzed Tandem Defunctionalization of Biorenewable Ferulic acid and Derivates into Bio-catechol

J. Bomon, E. Van den Broeck, M. Bal, Y. H. Liao, S. Sergeyev, V. Van Speybroeck, B. F. Sels, B. U. W. Maes

Angewandte Chemie int. Ed.

59 (8), 3063-3068

2020

A1

Abstract

An efficient conversion of biorenewable ferulic acid into bio‐catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C−O (demethylation) and C−C (de‐2‐carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H2SO4) as catalyst in pressurized hot water (250 °C, 50 bar N2). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84 % di‐ (catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work‐up.