title: Carbon dioxide utilization via carbonate-promoted C-H carboxylation.
abstract: Using carbon dioxide (CO2) as a feedstock for commodity synthesis is an attractive means of reducing greenhouse gas emissions and a possible stepping-stone towards renewable synthetic fuels. A major impediment to synthesizing compounds from CO2 is the difficulty of forming carbon-carbon (C-C) bonds efficiently: although CO2 reacts readily with carbon-centred nucleophiles, generating these intermediates requires high-energy reagents (such as highly reducing metals or strong organic bases), carbon-heteroatom bonds or relatively acidic carbon-hydrogen (C-H) bonds. These requirements negate the environmental benefit of using CO2 as a substrate and limit the chemistry to low-volume targets. Here we show that intermediate-temperature (200 to 350 degrees Celsius) molten salts containing caesium or potassium cations enable carbonate ions (CO3(2-)) to deprotonate very weakly acidic C-H bonds (pKa > 40), generating carbon-centred nucleophiles that react with CO2 to form carboxylates. To illustrate a potential application, we use C-H carboxylation followed by protonation to convert 2-furoic acid into furan-2,5-dicarboxylic acid (FDCA)--a highly desirable bio-based feedstock with numerous applications, including the synthesis of polyethylene furandicarboxylate (PEF), which is a potential large-scale substitute for petroleum-derived polyethylene terephthalate (PET). Since 2-furoic acid can readily be made from lignocellulose, CO3(2-)-promoted C-H carboxylation thus reveals a way to transform inedible biomass and CO2 into a valuable feedstock chemical. Our results provide a new strategy for using CO2 in the synthesis of multi-carbon compounds.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, USA.
authors.forename: Aanindeeta
authors.initials: A
authors.lastname: Banerjee
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, USA.
authors.forename: Graham R
authors.initials: GR
authors.lastname: Dick
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, USA.
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Yoshino
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Kanan
mesh_terms: D001554:Benzene / Q000378:metabolism; D001565:Benzoates / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D018533:Biomass; D032701:Biomimetics; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry* / Q000378:metabolism*; D002586:Cesium / Q000302:isolation & purification / Q000378:metabolism; D003998:Dicarboxylic Acids / Q000378:metabolism; D005502:Food; D005663:Furans / Q000378:metabolism; D055772:Green Chemistry Technology; D006860:Hydrogen Bonding; D006865:Hydrogenation; D008031:Lignin / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013696:Temperature
chemical_list: D001565:Benzoates; D001639:Bicarbonates; D003998:Dicarboxylic Acids; D005663:Furans; C036909:lignocellulose; D002245:Carbon Dioxide; D002586:Cesium; C551400:2,5-furandicarboxylic acid; D002244:Carbon; D008031:Lignin; D012273:Ribulose-Bisphosphate Carboxylase; D001554:Benzene; C060089:2-furoic acid; D011188:Potassium