The acetosolv extraction, allylation and subsequent cross-linking of wheat straw lignin to thermoset biomaterials is herein described. The extraction temperature proved to be of great importance for the quality of the resulting lignin, with moderate temperature being key for preservation of β-O-4’ linkages. The allylation of the acetosolv lignin was carried out using three different synthetic strategies, resulting in selective installation of either benzylic or phenolic allyl ethers, or unselective allylation of various hydroxyl groups via etherification and carboxyallylation. The different allylation protocols employed either allyl alcohol, allyl chloride, or diallylcarbonate as allyl precursors, with the latter resulting in the highest degree of functionalization. Selected allylated acetosolv lignins were cross-linked using a thiol-ene approach and the lignin with the highest density of allyl groups was found to form a cross-linked thermoset material with properties comparable to kraft lignin-based analogues.

Zirconocene triflate is a powerful moisture-tolerant catalyst for activation of C O bonds in carboxylic acids and alcohols in the absence of water scavenging techniques. Herein, an overview of the use of this robust metal complex for direct amidation, esterification, and etherification is presented, along with a discussion on mechanistic aspects of the transformations and the catalyst class.

The direct etherification of wheat straw lignin and lignin model compounds using alcohols as reagents and zirconocene triflate as moisture-tolerant Lewis acidic catalyst is herein described. Visual kinetic analysis was used to assess the average orders in the reaction components to map similarities between the model substrates and guide the method development. Full selectivity for the formation of benzylic ethers was obtained for models bearing free phenols and/or aliphatic alcohols, demonstrating that the present strategy enables a complementary reactivity to traditional phenolic lignin functionalisation. The reaction proceeds under mild conditions in absence of water-scavenging techniques and furnished a variety of ethers derived from lignin models with side chains bearing synthetic handles of relevance for thermoset applications. Finally, application of the Zr-mediated protocol on wheat straw-derived lignin resulted in the first example of metal-catalysed direct benzylic allylation of lignin using allyl alcohol as reagent, generating water as by-product.

The acetosolv extraction, allylation and subsequent cross-linking of wheat straw lignin to thermoset biomaterials is herein described. The extraction temperature proved to be of great importance for the quality of the resulting lignin, with moderate temperature being key for preservation of β-O-4’ linkages. The allylation of the acetosolv lignin was carried out using three different synthetic strategies, resulting in selective installation of either benzylic or phenolic allyl ethers, or unselective allylation of various hydroxyl groups via etherification and carboxyallylation. The different allylation protocols employed either allyl alcohol, allyl chloride, or diallylcarbonate as allyl precursors where the latter gave the highest degree of functionality. The results also show that it is crucial to choose a functionalization protocol that is adapted to the functional groups present in the specific lignin used. Selected allylated acetosolv lignins were cross-linked using a thiol-ene approach and the lignin with the highest density of allyl groups was found to form a cross-linked thermoset material with properties comparable to kraft lignin-based analogues.