Mn(acac)2/Ca(OTf)2-catalyzed short- to middle-length aliphatic aldehyde oxidations to the corresponding acids through dioxygen activation

Short- to middle-length aliphatic acids have significant applications in high quality lubricant synthesis. The present work introduces a Lewis acid (LA) improved aerobic oxidation of short- to middle-length aliphatic aldehydes to the corresponding acids by the Mn(acac)2 catalyst with high efficiency. It was found that adding a modest LA such as Ca(OTf)2 could substantially improve Mn(acac)2-catalyzed aldehyde oxidations to the corresponding acids with yields up to 97%. Quenching experiments with 1,4-benzoquinone indicated that the superoxide radical plays a crucial role in catalysis. The trapping experiments with methyl p-tolyl sulfide disclosed that the content of peroxide and peracid was very limited in the reaction mixtures, and monitoring the temperature and pressure of the oxidation also showed that the reaction proceeded smoothly without obvious temperature and pressure changes, highlighting the promising advantages of this Mn(acac)2/Ca(OTf)2 catalysis in its practical applications for the middle-length aliphatic acid production from the corresponding aldehydes.