Selective hydrogenolysis is a crucial challenge for lignin valorization. A PdCl₂-catalyzed hydrogenolysis of COH bond of various lignin β-O-4 alcohol model compounds was developed for preparation of corresponding phenethoxybenzene in 78–98% isolated yield. Notably, the introduction of low-pressure CO₂ (1 MPa) remarkably improves the reaction efficiency and selectivity of phenethoxybenzene. Neither over-reduction of aromatic ring nor further debenzylation was detected. This is understandable that the in situ methylcarbonic acid generated from CO₂ and methanol acts as an acidic catalyst and enhances the leaving ability of hydroxyl group of β-O-4 alcohols. Besides, the present PdCl₂/CO₂/MeOH catalyst system proved to be effective for reductive cleavage of CO bonds of β-O-4 ketones, producing ethylbenzenes accompanied with phenols in high yields. Furthermore, this protocol could also be extended to selective hydrodeoxygenation of the carbonyl group to methylene in aromatic ketones. As a sound reaction medium, such in situ CO₂/MeOH acidic system could be inherently neutralized by depressurizing CO₂, providing feature advantages for simple post-processing and none waste disposal.

选择性氢解是木质素平衡的关键挑战。开发了一种PdCl ₂催化的各种木质素β-O-4醇模型化合物的C OH键氢解反应，以分离出78-98％的产率制备相应的苯乙氧基苯。值得注意的是，低压CO ₂（1 MPa）的引入显着提高了苯乙氧基苯的反应效率和选择性。既未检测到芳环的过度还原也未检测到进一步的脱苄基作用。可以理解的是，由CO ₂和甲醇产生的原位甲基碳酸充当酸性催化剂，并增强了β-O-4醇的羟基的离去能力。此外，目前的PdCl ₂ / CO₂ / MeOH催化剂体系被证明可有效还原β-O-4酮的C O键，高产率地生产乙苯和苯酚。此外，该方案还可以扩展到芳族酮中羰基选择性加氢脱氢成亚甲基的过程。作为良好的反应介质，这种原位CO ₂ / MeOH酸性系统可通过对CO ₂降压来固有地中和，从而为后处理简单且无废物处置提供了特征优势。