Sustainable CO 2 Fixation onto Bio-Based Aromatics

Carboxylation reactions using carbon dioxide (CO 2 ) 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 (Na 2 CO 3 ), while the Marasse method was active only with potassium carbonate (K 2 CO 3 ) 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).