Alternate Biobased Route To Produce δ-Decalactone: Elucidating the Role of Solvent and Hydrogen Evolution in Catalytic Transfer Hydrogenation

A widely used food and flavor compound, delta-decalactone (DDL), was produced from catalytic transfer hydrogenation of 6-amyl-alpha-pyrone (6PP), which is a biomass-based platform chemical derived through a fermentation process. The liquid phase reaction may serve as a platform to develop an integrated bio- and chemo-catalytic process for the green synthesis of DDL from lignocellulosic biomass. The catalytic transformation of 6PP to DDL was performed under mild thermal and pressure conditions over a Pd/C catalyst using formic acid as the in situ hydrogen source. The reaction in the presence of formic acid underwent complete conversion (similar to 99% at 433 K in 10 min) of 6PP via progressive hydrogenation of the unsaturation present in the 2-pyrone ring, leading to 79% maximum yield of DDL. On reducing the temperature from 433 to 383 K, DDL yield was observed to reduce from 79% to 2%. An ab initio microkinetic model (MKM) was constructed to understand the decomposition of formic acid with temperature variations. The MKM provided a theoretical insight into the hydrogenation reaction. The reduction in DDL yield and 6PP conversion at the lower temperatures was observed to be in direct correlation to the reduction in HCOOH decomposition rates.