Highly selective production of propionic acid from lactic acid catalyzed by NaI

Propionic acid (PA), a valuable chemical widely used in the food and feed industry, is currently produced by the petrochemical industry. Selective production of PA from bio-based lactic acid (LA) is difficult due to the high activation energy of the hydroxyl group at the α position of the carboxyl group. Herein, a metal-free catalytic system for the highly selective transformation of bio-based LA to PA, which was used as the solvent to simplify the separation step, is reported using NaI as the catalyst. Under the optimal reaction conditions, a >99% yield of PA can be obtained from LA. A heat-induced radical-activated hydrogen mechanism was proposed based on the kinetic study and intermediate capture. The metal-free system can be reused five times without any loss in activity, and the PA product is easily separated. In addition, a two-step method using cellulose as the raw material to produce PA was conducted. This strategy offers a green and efficient approach to synthesize PA from biomass resources.