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The heterogeneously catalyzed hydrogenation of biomass‐ or CO2‐derived glycolic acid (GA) is a renewable pathway for obtaining the bulk chemical ethylene glycol (EG). In this study, the reaction network of the aqueous‐phase hydrogenation of GA is investigated over a Ru/C catalyst. Beside this target reaction, both undesired parallel reactions (such as the hydrogenation of GA to acetic acid (AcA)) and unwanted consecutive reactions (such as over‐hydrogenation) can occur. These reactions are experimentally assessed by employing different (possible) reaction intermediates and products (EG, AcA, glycolaldehyde, acetaldehyde, and ethanol) as reactants. The data for all individual reactions as well as the overall GA hydrogenation at different reaction temperatures (120–180 °C) is combined to propose a catalytic reaction pathway network and to develop a corresponding microkinetic model. The kinetic model describes the catalytic data in the range up to 150 °C, where EG is the main reaction product, with high accuracy. It is shown that selectivity for EG is highest at 120 °C (up to ca. 70%) and decreases strongly with increasing temperatures both due to the parallel reaction of GA into acetic acid (AcA), which has a significantly higher activation energy than the overall hydrogenation of GA into EG, and due to degradation of EG into ethanol and other volatile products. Temperatures exceeding 150 °C predominantly yield volatile products, suggesting low yields of EG or AcA at higher temperatures despite enhanced GA conversion. [ABSTRACT FROM AUTHOR]

Combining carboxylation reactions using carbon dioxide (CO2) as a reactant with phenol results in creation of new C-C bonds, and represents one of the most promising routes in sustainable utilization of ubiquitous and readily available resources for production of highly valuable products. This study provides a detailed and well-structured investigation of the effect of various reaction conditions (reactant loading, reaction duration, temperature, CO2 pressure) on the carboxylation of phenol. Sodium phenoxide carboxylation showed well-resolved trends with variation of temperature and time, and resulted in production of salicylic acid (SA) in the range of 11.4 to 47.8%, 4-hydoxybenzoic acid (4HBA) in the range of 2.0 to 8.2%, while the dicarboxylated 4-hydroxyisophthalic acid (4HiPh) was only detected in trace amounts. The effect of the variation of reactant content was shown to be significantly influenced by the reactor size, solid/vessel and gas/solid contact area, as well as the efficiency of the stirring. CO2 pressure was shown to be a crucial element, where reactions carried out below 2 MPa CO2 did not show any activity. While investigating the reaction mechanism, it was shown that the salt analogues of potential products could be acidified in situ by the moisture present, and immediately degraded back to phenol, thus lowering yields of potentially obtained products. The experimental results were successfully used to compose a kinetic model, which very well describes the experimentally obtained results. As such, this study provides a valuable dataset for valorization of lignocellulosic aromatic compounds as well as highly abundant and environmentally detrimental carbon dioxide into industrially valuable mono- and dicarboxylic acids. [ABSTRACT FROM AUTHOR]

Carboxylation reactions using carbon dioxide (CO2) as a reactant to produce new C-C bonds represent one of the most promising routes in carbon capture and utilization practices, which yield higher-atom and energy-efficient products. Kolbe–Schmitt-type reactions represent the carboxylation of aromatic compounds to their carboxylic acid derivatives. This study was the first and only to systematically investigate, thoroughly explain preparation procedures, and minutely describe the analytical methods of Kolbe–Schmitt and Marasse carboxylation of phenol. Most importantly, this study provides guidelines for the utilization of state-of-the-art technology in this century-old yet not sufficiently described reaction system. Kolbe–Schmitt carboxylation of phenol was found to be possible using sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium carbonate (Na2CO3), while the Marasse method was active only with potassium carbonate (K2CO3) as a reactant. The formation of metal phenoxide is the rate-determining step, which, however, could be more efficiently prepared under reflux. A new, simple, and repeatable HPLC method was described to identify and quantify all possible products of mono- and dicarboxylated phenols. It was found that all procedures result in the highest selectivity for salicylic acid (SA), followed by minor amounts of 4-hydroxybenzoic acid (4HBA) and 4-hydroxyisophthalic acid (4HiPh). [ABSTRACT FROM AUTHOR]