Comparison of deep eutectic solvents and solvent-free reaction conditions for aldol production

S. Milker, M. Pätzold, J. Z. Bloh, D. Holtmann

In this work, we investigated the catalytic aldolase activity of the porcine pancreas lipase (PPL) for 4-nitrobenzaldehyde (4-NBA) and acetone in different deep eutectic solvent (DES) compared with bovine serum albumin (BSA)-catalyzed aldol reaction. The PPL catalyzed the aldol addition specifically towards the desired aldol product, especially in hydrophobic DES. In contrast to this result, BSA-catalyzed aldol additions did not exhibit specificity for neither aldol nor olefin formation. For the PPL-catalyzed reactions, the product composition could be directly correlated with the choice of DES, differing in their hydrophobicity. The initial reaction velocity of the aldol addition was higher in the hydrophilic DES ChCl:Gly. However, this DES was limited by the solubility for the 4-NBA substrate. The 4-NBA containing DES exhibited the highest solubility for 4-NBA. However, the fastest reaction with a final yield of 1296.5 mM, which corresponds to 71% yield and 82% conversion after 32 h, was achieved in the co-solvent acetone, making this reaction solvent-less and improving the productivity up to 40.5 mM h−1 compared to reactions performed in DES.

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