Density functional theory study on the initial reactions of d-Xylose and d-Xylulose dehydration to furfural

Xiaowei Fang,Martin P Andersson,Ze Wang,Wenli Song,Songgeng Li

doi:10.1016/j.carres.2021.108463

Xiaowei Fang, Martin P Andersson + Show 3 more

Open Access

https://doi.org/10.1016/j.carres.2021.108463

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Abstract

The mechanism of the initial reactions in the acid-catalytic conversion of d-xylose/d-xylulose to furfural was studied with density functional theory. The reactions included mutual transformations among d-xylose, d-xylulose and the intermediate of 1,2-enediol. The catalytic performances of several acids including H2SO4, HNO3, HCl, HBr and HI, and the solvent effects of water and THF (tetrahydrofuran) were studied. A simplified kinetic model of the d-xylose/d-xylulose-to-furfural conversion in water solvent was built, with the assumption that the conversion from 1,2-enediol to furfural was the rate-limiting step and could be treated as one-step reaction. The simulation can well fit the experimental regulation, which verifies the rationality of the model simplification. The dominant reaction pathways from d-xylose/d-xylulose to furfural were deduced based on the calculated energy barriers and corresponding reaction rate constants, with different acid catalysis and reaction mediums.

Highlights

Furfural is a promising platform chemical that can be employed to produce higher value C4 and C5 chemicals and long-chained biofuel [1,2,3,4]
The dominant reaction pathways from D-xylose/D-xylulose to furfural were deduced based on the calculated energy barriers and corresponding reaction rate constants, with different acid catalysis and reaction mediums
We have proposed a reaction mechanism for the D-xylose-to-furfural conversion under homogenous acid catalysis, which includes formation of D-xylulose by hydride shift as well as enolization of both D-xylose and D-xylulose

Summary

Introduction

Furfural is a promising platform chemical that can be employed to produce higher value C4 and C5 chemicals and long-chained biofuel [1,2,3,4]. As early as 1932, Hurd et al proposed a reaction mechanism via an 2,3-unsaturated aldehyde followed by the intermolecular dehydration to form a 5-membered ring and dehydration to furfural in the acidic solution (Scheme S1) [6] This mechanism conformed to the well-known reaction in organic chemistry that β-elimination reaction took place very readily to lose water molecule on β-hydroxyaldehydes. Blinder et al reported a similar conclusion that the transfer of the deuterium label from C-2 to C-1 was consistent with the hydride shift during the chromium(III)-catalyzed conversion of D-xylose to furfural [16] These observations, the transfer of the labeled carbon on D-xylose1-14C to 2-furaldehyde-α-14C and the absence of solvent hydrogen in furfural, supported all the foregoing mechanisms. To better explain the experimental results, we modelled an acyclic reaction mechanism under homogenous acidic catalysis, including Dxylose-to-D-xylulose isomerization by both hydride shift and enolization, followed by the dehydration of 1,2-enediol intermediate to furfural (Scheme 1). The solvent effect of THF (tetrahydrofuran) was studied, and the dominant reaction pathway for furfural formation was determined with different acid catalysts

Computational approach

Energy barriers for mutual transformations in water

The dominant reaction pathway of furfural formation in different solvents

Conclusion