Macrolactonization of methyl 15-hydroxypentadecanoate to cyclopentadecanolide using KF-La/γ-Al2O3 catalyst

It has been a challenge to synthesize macrolide musk in excellent yields with high purity. KF-La/γ-Al2O3 catalyst was prepared from a highly basic mesoporous framework using a mild method. The prepared KF-La/γ-Al2O3 catalyst was employed for the synthesis of cyclopentadecanolide from methyl 15-hydroxypentadecanoate. The morphology and structure of prepared catalysts were characterized using XRD, TG-DTG, SEM, EDX, TEM, BET and CO2-TPD. The results revealed that the K3AlF6 and LaOF are produced on the surface of KF-La/γ-Al2O3, and LaO can promote the dispersion of KF on the surface of Al2O3. Catalysts pore size main distribution ranges between 10 and 30 nm, the maximum CO2 desorption temperature is 715°C when the La loading is 25%. Because F− ion has a higher electronegativity than O2− ion, the KF-promoted metal oxide (Al2O3 or/and La2O3) contained more strong basic sites, compared with that of the corresponding metal oxide. The yield of cyclopentadecanolide obtained at 0.5 g KF-25La/γ-Al2O3 catalyst and a reaction temperature of 190°C for 7 h were 58.50%, and the content after reactive distillation is 98.8%. The KF-La/γ-Al2O3 catalyst has a larger pore size and basic strength, which is more conducive to the macrolactonization of long-chain hydroxy ester.