Selective Partial Oxidation of 2,5-Dimethylhexane with Dioxygen Catalyzed by Manganese Octahedral Molecular Sieves and Promoted by N-Hydroxyphthalimide

Selective oxidation of 2,5-dimethylhexane to 2,5-dimethyl-2,5-hexanediol by molecular oxygen was achieved heterogeneously using manganese octahedral molecular sieves (K-OMS-2) as catalysts and N-hydroxyphthalimide (NHPI) as a promoter. This approach aimed at enhancing catalyst reusability, lowering the expense of replacing catalysts, and minimizing additional contamination caused by typical transition metal salt catalysts. The conversions and yields of the aerobic reaction were optimized by varying the reaction parameters, while the structural, morphological, and electronic properties of the K-OMS-2 catalysts were characterized by X-ray diffraction spectroscopy (XRD), nitrogen sorption analysis, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The promising yield was achieved by applying K-OMS-2 catalyst of higher manganese valence state (υ_Mn = 3.8) under moderate reaction time and catalyst concentration. However, the selectivity of byproducts, vastly acetone, also increased concurrently, indicating the remaining challenge of achieving the balance between product yield and selectivity of this aerobic reaction. Recyclability tests revealed that the K-OMS-2/NHPI catalyst system maintained the diol yield across three successive cycles, highlighting its efficacy as a heterogeneous catalyst for the selective oxidation of 2,5-dimethylhexane.