CONTINUOUS FLOW: A NEW APPROACH TO THE ETHERIFICATION OF BIO-BASED FURANIC COMPOUNDS

The ultimate goal of biorefinery is to move away from a fossil-based industry aiming to a more sustainable one centered on the use of renewable feedstocks; on this way, in chemistry, Bio-based platform chemicals play an important role. Bio-based platform chemicals derived from hemicellulosic materials are extensively investigated to synthesize several value-added molecules, useful for different applications in the polymer sector[1] such as composites, thermosets [2] and coatings.[3] Among them, biomass-derived C6 carbohydrates are of particular interest since they lead to furanic building blocks such as 5-hydoxymethyl furfural (HMF), 2,5-furandicarboxylic acid (FDCA) and 2,5-bis(hydroxymethyl)furan (BHMF) [3]. In the last years, a family of HMF and BHMF derivatives - 5-(alkoxymethyl)furfurals (AMFs) and 2,5-bis(alkoxymethyl) furans (BAMFs), respectively - has attracted increasing attention due to their potential applications as bio-diesel additives.[4] In addition, HMF, when subjected to self-etherification, leads to 5,5′-[oxybis(methylene)]bis-2-furfural (OBMF), another bio-based monomer of growing interest due to its exploitation in the synthesis of macrocycles (16-crown-6) [5] and as a precursor of polyurethanes, polyamides, and polyamines.[6] In this work, a comprehensive investigation on the etherification of Bio-Based furanic compounds promoted by a commercially available ion exchange resin - Purolite CT275DR - is conducted using a continuous flow apparatus. The reaction conditions are initially optimized for the etherification of BHMF with ethanol and then extended to achieve a library of BAMFs. The long-term stability of Purolite CT275DR was investigated using the optimized reaction conditions for BEMF synthesis and with other two alcohols, i.e., 2-propanol - a more sterically hindered alcohol - and allyl alcohol, too. In addition, HMF etherification and self-etherification are studied. HMF self-etherification to form OBMF is conducted using dimethyl carbonate as green solvent in the presence of both heterogeneous and homogeneous acid catalysts, with the latter being the most effective. Finally green metrics are calculated for the optimized etherification of BHMF with ethanol and the values are compared to previously published procedures [7].