Hydrothermal Conversion of Catechol into Four-Carbon Dicarboxylic Acids

Abstract

Conversion of lignin into value-added chemicals is attracting growing attention due to the depletion of fossil fuels and the abundant resource of lignin. In this study, hydrothermal conversion of a model compound of lignin, catechol, into valueadded four-carbon dicarboxylic acids (C4-DCAs), such as tartaric (HOOC−CH(OH)−CH(OH)−COOH), malic (HOOC− CH 2 −CH(OH)−COOH), and fumaric (HOOCCHCHCOOH) acids was investigated. The yield of total C4-DCAs can reach as high as 41.0%, and alkali played a key role in not only promoting the production but also avoiding the decomposition of C4-DCAs. The reaction mechanism of hydrothermal conversion catechol into C4-DCAs showed that catechol is first oxidized to o-quinone, which is then attacked by the hydroxyl radical (OH • ) or the hydroperoxyl anion (HO 2 − ) via conjugate addition to decompose into C4-DCAs. This result is helpful to facilitate studies for developing a new, green, and sustainable process to produce value-added C4-DCAs from lignin.

Catalytic wet peroxide oxidation of vanillic acid as a lignin model compound towards the renewable production of dicarboxylic acids

“…4c). The H 2 O 2 reactivity at alkaline pH is higher than in acidic pH, since, for pH > 9, dissociation to hydroperoxide anions occurs (Yin et al, 2015). This behaviour remains even when the TS-1 catalyst is used, a fact related to the inferior reactivity of H 2 O 2 in acidic pH (Xiang and Lee, 2000).…”

“…Hydrogen peroxide reactivity depends on pH since it can act as a nucleophile or electrophile species (Xiang and hydroperoxyl anions (HOO − ). These compounds can later degrade to molecular oxygen, decreasing their reactivity (Yin et al, 2015). Hydrogen peroxide can decompose during oxidation reactions; it is stable in acidic conditions, but quickly decomposes to H 2 O, O 2 and OH − above pH = 6.0 (maximum decomposition occurs at its pK a ).…”

“…The product selectivity depends on the oxidising agent, catalyst type, process conditions and reactor type (Kang et al, 2013;Ma et al, 2015). In the context of DCA from lignin, several studies have been carried out using wet peroxide oxidation, with and without catalyst (Cronin et al, 2017;Hasegawa et al, 2011;Kang et al, 2019;Ma et al, 2015;Su et al, 2014;Yin et al, 2015;Zeng et al, 2015). However, many of the lignin oxidation processes, including the catalysed ones, are not selective enough to favour the production of a specific DCA, generating a mixture of DCA, introducing the need of additional steps of separation and purification.…”

Research and Mechanism of Two-step Preparation of Acetamide from Microalgae under Hydrothermal Conditions

“…There has been many researches committing to convert various biomass into biofuel and value-added chemicals [1,[8][9][10], and hydrothermal process is one of the most promising methods [11][12][13][14] because of its unique inherent properties when HTW (high-temperature water) behaves as reaction medium. HTW above the critical point undergoes drastic changes in its physical properties such as dielectric constant, density, ionic product, viscosity, and solubility [15].…”

“…HTW above the critical point undergoes drastic changes in its physical properties such as dielectric constant, density, ionic product, viscosity, and solubility [15]. Ionic product (Kw) of HTW, about 1000 times higher than that of ambient liquid water [16], and the low dielectric constant, are both favourable to promote reactions without catalysts and have a good selectivity on the products [12,14]. HTW also haves the good transport property to mix small organic compounds completely and break down hydrocarbons and carbohydrates [17][18][19].…”