Heterogeneous (de)chlorination-enabled control of reactivity in the liquid-phase synthesis of furanic biofuel from cellulosic feedstock†
The utilization of polymeric biorenewables for the synthesis of biofuels and essential chemicals is largely obstructed by their recalcitrant structures and complex product distribution. Here, hydrosilane-mediated hydrodeoxygenation (HDO) of the furanic mixture 5-hydroxymethylfurfural (HMF) and 5-chloromethylfurfural (CMF), directly derived from cellulosic biomass, can be enabled by heterogeneous Pd-catalyzed dechlorination to exclusively give the biofuel 2,5-dimethylfuran (DMF) in a high overall yield of 72%. Kinetic and isotope labeling studies supported by computational calculations explicitly elucidate the reaction pathways. The initial dechlorination of CMF into acidic species promotes the rapid in situ formation of relatively stable acetalized and etherified furanic intermediates, which not only greatly accelerate the reactivity of the entire HDO process (TOF: up to 1200 h−1), but are also able to significantly get rid of unwanted side reactions. Importantly, this catalytic system can also be applied for the upgrade of various chlorinated carboxides to produce ortho-, meta- and para-substituted arenes with satisfactory yields of 82–99% at 25–45 °C, and the used commercial Pd/C catalyst is highly recyclable.