Synthesis of methyl lactate from cellulose catalyzed by mixed Lewis acid systems

Lactic acid (LacA) is a potential building block in biomass refinery based on lignocellulose. Herein, we report three-component Lewis acid catalyst systems comprised of metal triflates, In chloride, and Sn chloride for the direct synthesis of methyl lactate (MeLac) from cellulose in methanol. These three catalyst species cooperatively catalyzed this reaction; the metal triflates depolymerized cellulose to sugars, which was converted to trioses by retro-aldol reaction with In chloride, followed by their isomerization with Sn chloride to give MeLac. Among the metal triflates, Sm triflate was the most effective, with which MeLac was formed in 45% yield. Ball-milling pretreatment of cellulose in the presence of methanol increased the yield of MeLac to 64%. [Display omitted] •The mixed Lewis acid catalyst systems - cooperatively catalyze the formation of methyl lactate from cellulose in MeOH.•Among the metal triflates, Sm triflate was the most effective, with which MeLac was formed in 45% yield.•Ball-milling pretreatment of cellulose in the presence of methanol was effective and the yield of MeLac reached 64%.