Carbonate-promoted C-C bond formation in solvent-free media and its application to polyamide synthesis
Keywords: Chemistry.

The selective formation of carbon-carbon (C-C) bonds has been a longstanding area of study in organic chemistry with broad applications in fine and commodity chemical synthesis. This thesis describes several novel ways that C-C bonds can be made utilizing alkali carbonates in a solvent-free and catalyst-free system. The first chapter provides an introduction to the synthesis of chemicals from lignocellulosic feedstocks. While edible feedstocks have been used industrially to make ethanol and lactic acid via fermentation, the conversion of lignocellulosic feedstocks to value-added chemicals has been limited. One of the few chemicals produced from lignocellulose is furfural, which is made via the acid-catalyzed dehydration of pentoses in hemicellulose. Furfural has limited applications at present. Carbonate-promoted C-H carboxylation, a new C-C bond forming reaction reported by the Kanan group in 2016, is introduced and discussed as a way to convert furfural into more valuable C6 compounds such as 2,5-furandicarboxylic acid. The second chapter investigates an alternative synthesis of benzenetricarboxylates (BTCs), high-value small molecules that are used in the synthesis of metal-organic frameworks, PVC plasticizers, and heat-resistant polyimides. BTCs are currently made from trimethylbenzenes via the Amoco oxidation, an expensive process that produces carbon monoxide and ozone-depleting methyl bromide through undesired side reactions. Here, a non-oxidative route to produce BTCs from alkali phthalates and CO2 via carbonate-promoted C-H carboxylation is studied. While it was discovered that BTCs can be made from phthalates and various alkali carbonates and CO2, competing decarboxylation, over-carboxylation, and isomerization pathways make it difficult to develop a selective synthesis. The third chapter investigates the reactivity of benzylic C-H and C-OH bonds in the presence of alkali carbonates. Using cesium carbonate, the benzylic C-H of alkali m-toluate can be carboxylated; however, an equilibrium between the starting material and desired product resulted in limited yields. The oxidation of the benzylic C-OH bond in alkali 4-(hydroxymethyl)benzoate was also studied. Interestingly, when cesium carbonate was used, the major product was dimerized starting material while the minor products were reduced p-toluate and oxidized terephthalate. In order to explain the formation of the unexpected dimers, a mechanism involving an aldehyde intermediate reacting with a deprotonated p-toluate is proposed. Several follow-up experiments that support this mechanism are also discussed. The fourth chapter studies the synthesis of a tetrahydrofuran-based polyamide monomer from furfurylamine, one of the few chemicals made industrially from inedible lignocellulose. Using carbonate-promoted C-H carboxylation, furfurylamine is converted into a furan-containing amino acid that is purified via anion exchange chromatography. Afterwards, this intermediate is hydrogenated and cyclized to a tetrahydrofuran-containing bicyclic lactam. The synthesis of this bicyclic lactam avoids the use of protecting groups and multiple stoichiometric organic reagents required by previous, longer routes, and is the potential starting point for the design of a scalable process. The fifth and final chapter explores the polymerization of the bicyclic lactam monomer to poly(aminomethyl)tetrahydrofuran (PAT). It was found that PAT can be synthesized under heated neat conditions and in a solvent at room temperature. The mechanism of PAT polymerization is believed to occur via living anionic ring opening polymerization. As such, the number average molecular weight can be controlled by varying the ratio of monomer to imide activator. The values obtained experimentally are consistent with theoretical values. PAT also exhibits an unusually high glass transition temperature, illustrating an advantage over other bio-based polymers