Sustainable processes for the chemical upgrading of renewables

The present PhD thesis entitled Sustainable processes for the chemical upgrading of renewables has dealt with the design and implementation of both batch and continuous-flow methods for: i) the upgrading of biobased substrates including glycerol and its derivatives and 5-hydroxymethylfurfural (HMF); ii) the synthesis of cyclic organic carbonates via catalytic insertion of CO2 into terminal epoxides; iii) the preparation of polyesters from Kraft lignin (KL) with poly-anhydrides and polyisopropenyl esters as crosslinking agents. The first and part of the second year have been dedicated to the study of the reactivity of enol esters, particularly the nontoxic isopropenyl acetate (iPAc), with renawable 1,2-diols, glycerol and some of its derivatives. The design of original catalytic tandem protocols was developed, by which the above-mentioned reactants were converted into the corresponding acetates and acetal products with even 100% carbon efficiency. Based on these results, three papers were published on international peer-reviewed journals. Then, a period abroad at the University of Sydney under the supervision of Prof. T. Maschmeyer to start a cotutelle program for the achievement of the joint Italian-Australian PhD title was planned. However, due to the pandemic, the mobility was forbidden, and the related experimental work has been converted in a remote collaboration finalized at the writing of a review paper on the synthesis and reactivity of enol esters. Periodic videocalls have been organized with Prof. Maschmeyer during which the progress of the review article has been discussed. The resulting review paper entitled “Isopropenyl esters in green organic synthesis” and authored by D. Rigo, G. Fiorani, A. Masters, T. Maschmeyer, and M. Selva is currently almost finished, and its submission is expected by the end of this year. Parallelly, two new experimental studies were undertaken aimed to: a) the design of a protocol for the activation of CO2 in the insertion on terminal epoxides in the presence of a binary homogenous mixture of diethylene glycol and NaBr as catalyst/solvent; a) the upgrading of HMF through diversified approaches of transesterification, transcarbonation, reductive amination, aldol condensation, and vinylation reactions using safe reagents and solvents as iPAc, dimethyl carbonate, water, and ad-hoc prepared ionic liquids. Based on these results, two papers were published on international peer-reviewed journals. From March to September 2021 (6.5 months) an exchange research period at Stockholm University under the supervision of Prof. Joseph Samec has been undertaken. The activity was focused on the synthesis of lignin-based thermosetting polyesters. A scalable, ecofriendly, and solvent-free protocol for the preparation of the desired materials using a mixture of polyanhydrides and poly-isopropenyl esters as crosslinking agents of Kraft lignin (KL) has been implemented. Based on these results, a paper entitled “A new family of thermosets: Kraft lignin polyadipates” authored by D. Di Francesco, D. Rigo, K. R. Baddigam, A. Mathew, N. Hedin, M. Selva, J. S. M. Samec has been submitted to an international peer-reviewed journal and is currently on peer reviewing. In addition, the following book chapter M. Selva, G. Fiorani, D. Rigo “Supercritical Solvents” In Sustainable Organic Synthesis: Tools and Strategies, Chapter 10; A. Palmieri, S. Protti, Eds. RSC book, 2021 has been published.