Biobased Aldehydes from Fatty Epoxides through Thermal Cleavage of β-Hydroxy Hydroperoxides

The ring-opening of epoxidized methyl oleate by aqueous H2O2 has been studied using tungsten and molybdenum catalysts to form the corresponding fatty beta-hydroxy hydroperoxides. It was found that tungstic acid and phosphotungstic acid gave the highest selectivities (92-93 %) towards the formation of the desired products, thus limiting the formation of the corresponding fatty 1,2-diols. The optimized conditions were applied to a range of fatty epoxides to give the corresponding fatty beta-hydroxy hydroperoxides with 30-80 % isolated yields (8 examples). These species were fully characterized by H-1 and C-13 NMR spectroscopy and HPLC-HRMS, and their stability was studied by differential scanning calorimetry. The thermal cleavage of the beta-hydroxy hydroperoxide derived from methyl oleate was studied both in batch and flow conditions. It was found that the thermal cleavage in flow conditions gave the highest selectivity towards the formation of aldehydes with limited amounts of byproducts. The aldehydes were both formed with 68 % GC yield, and nonanal and methyl 9-oxononanoate were isolated with 57 and 55 % yield, respectively. Advantageously, the overall process does not require large excess of H2O2 and only generates water as a byproduct.

Automated summary

The ring-opening of epoxidized methyl oleate by aqueous H2O2 using tungsten and molybdenum catalysts resulted in the formation of fatty beta-hydroxy hydroperoxides with high selectivity. The optimized conditions allowed for the synthesis of these compounds with isolated yields of 30-80%. Thermal cleavage of these hydroperoxides in flow conditions showed high selectivity towards aldehyde formation with limited byproducts. Overall, the process is efficient and environmentally friendly, generating water as the only byproduct.