The direct transformation of cellulose, which is the main component of lignocellulosic biomass, into building-block chemicals is the key to establishing biomass-based sustainable chemical processes. Only limited successes have been achieved for such transformations under mild conditions. Prof. Ye Wang of Xiamen University and his collegues recently reported the simple and efficient chemocatalytic conversion of cellulose in water in the presence of dilute lead(II) ions, into lactic acid, which is a high-value chemical used for the production of fine chemicals and biodegradable plastics. The lactic acid yield from microcrystalline cellulose and several lignocellulose-based raw biomasses is 460% at 463 K.

They have clarified that the chemistry of the present system for the direct transformation of cellulose into lactic acid involves multistep cascade reactions including 1) the hydrolysis of cellulose into glucose; 2) the isomerization of glucose formed via hydrolysis of cellulose into fructose; 3) the selective cleavage of the C3–C4 bond of fructose to trioses; and 4) the selective conversion of trioses into lactic acid. Their computational results agree well with the experimental findings and provide a basis for understanding the remarkable catalytic role of Pb(II). In particular, the presence of Pb(II) significantly decreases the activation barrier for the retro-aldol fragmentation of fructose changing the main reaction route from the formation of HMF to the formation of lactic acid.

Lactic acid is an important building-block chemical widely used in the food, pharmaceutical, cosmetic and chemical industries. In particular, lactic acid has received much attention as a monomer for the production of biodegradable plastics. At the same time, their results are promising for development of novel chemocatalytic processes of selectively synthesizing chemicals or liquid fuel via multistep cascade catalytic reactions of cellulose.