A new route to synthesis of sulphonato-salen-chromium(III) hydrotalcites: Highly selective catalysts for oxidation of benzyl alcohol to benzaldehyde

The Mg–Al layered-double hydroxides (LDHs) intercalated by three kinds of sulphonato-salen-chromium(III) complexes were prepared and characterized by FTIR, UV–vis, XRD and elemental analysis. It was found that the homogeneous complexes were successfully intercalated into the LDH interlayer via the method of anion exchange followed by coordination with chromium(III) chloride. And the resulting LDH hosted chromium complexes were shown to be effective heterogeneous catalysts for the solvent-free oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using 30% H₂O₂ as oxidant. Furthermore, owing to the different local environment of the central metal ion chromium(III), the catalyst with the backbone of o-C₆H₄ displayed the highest catalytic performance followed by the NH(CH₂CH₂)₂ with the (CH₂)₂ showing the lowest BzH yield. In addition, a tentative mechanism was also discussed.