A concept for a highly integrated fractionation of lignocellulose in its main components (cellulose-pulp, soluble hemicellulose sugars and lignin) is described, based on the selective catalytic depolymerization of hemicellulose in a biphasic solvent system. This leads to an effective disentanglement of the compact lignocellulose structure, liberating and separating the main components in a single step. At mild temperatures (80–140 °C), oxalic acid catalyzes selectively the depolymerization of hemicellulose to soluble sugars in aqueous solution, whereas the more crystalline cellulose-pulp remains solid and inaccessible to the acid catalysis. In the presence of a second organic phase consisting of bio-based 2-methyltetrahydrofuran (2-MTHF), lignin is directly separated from the pulp and the soluble carbohydrates by in situ extraction. The oxalic acid catalyst can be crystallized from the aqueous solution, recovered and re-used. The delignified cellulose-pulp obtained from this biphasic system can be directly subjected to enzymatic depolymerization, affording soluble oligomers and glucose at rates almost comparable to those observed for the hydrolysis of commercial microcrystalline Avicel^®. Overall, the concept may offer a promising approach for an efficient and selective pre-treatment of lignocellulosic materials under mild and environmentally-friendly conditions

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Dicarboxylic acids have been identified as promising catalysts for the depolymerization of cellulose and other polysaccharides. It has been suggested that they might act in “biomimetic” analogy to the active site of glycosidases, where also two carboxylic groups are present, and it is assumed that one residue acts as proton donor and the other one as proton acceptor. In the present paper, a series of structurally distinct carboxylic acids were experimentally assessed as catalysts in the hydrolysis of cellobiose under fully identical acidic conditions. The results clearly show a pH-dependent activity profile in bulk aqueous solutions without any evidence for a cooperative mechanism. In contrast, the protein environment at the active site in glycosidases was found to be essential for the cooperative action of the two carboxylic acid groups. A detailed computational chemistry study is presented, focusing on the protein electric potential, as well as on a reduced dielectric constant (ε) within the active site, resulting from the limited presence of water. These two aspects alter the pK_a of the carboxylic acid groups dramatically, providing the necessary local environment for a cooperative proton donor–acceptor mechanism, which cannot be mimicked by simple diacids in bulk aqueous phase