Production of Benzene from 2‐Hydroxybenzaldehyde by Various Reaction Paths using IRC Calculations within a DFT framework

Abstract

AbstractThe bio‐oil produced from pyrolysis of lignocellulosic biomass comprises of several oxy‐catalogues such as acids, alcohols, aldehydes, furans, phenols, etc. The oxy‐functionals in the bio‐oils vitiate the quality of bio‐oil, therefore, the unprocessed bio‐oils cannot be used directly to transportation vehicles. In this work, 2‐hydroxybenzaldehyde (2‐HB) has been taken as bio‐oil model component and carried out seven reaction pathways to produce benzene and other important intermediate products such as phenol, benzaldehyde, etc. The first reaction pathway is about the cleavage of formyl group of 2‐HB followed by single step hydrogenation reaction to produce phenol which further produces benzene component. The reaction pathway 2 is the hydrogen migration reaction followed by cleavage of formyl group and the reaction pathway 3 is decarbonylation reaction of 2‐hydroxybenzaldehyde to produce phenol component. The reaction pathway 4 is single atom hydrogenation at the aromatic carbon of Caromatic‐CHO sigma bond followed by the removal of formyl group to produce phenol. Similarly, the reaction pathway 5 starts with a single atom hydrogenation at the aromatic carbon of Caromatic‐OH sigma bond followed by hydroxyl group removal to produce benzaldehyde component. The reaction pathway 6 is the dehydrogenation reaction of formyl group followed by CO removal and a single step hydrogenation to produce phenol. The reaction pathway 7 directly cleaves the hydroxyl functional followed by hydrogenation reaction to produce benzaldehyde which further follows two sub‐pathways to produce benzene. The direct cleavages of hydroxyl and formyl functionals are not favourable as they require very high amount of energetics. Instead, the single atom hydrogenation to the aromatic carbon of Caromatic‐X (X=•OH or •CHO) followed by the oxy‐functional removal is found to be favourable reaction pathway.