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

It has been a challenge to synthesize macrolide musk in excellent yields with high purity. KF-La/γ-AlO catalyst was prepared from a highly basic mesoporous framework using a mild method. The prepared KF-La/γ-AlO 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 CO-TPD. The results revealed that the KAlF and LaOF are produced on the surface of KF-La/γ-AlO, and LaO can promote the dispersion of KF on the surface of AlO. Catalysts pore size main distribution ranges between 10 and 30 nm, the maximum CO desorption temperature is 715°C when the La loading is 25%. Because F ion has a higher electronegativity than O ion, the KF-promoted metal oxide (AlO or/and LaO) 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-AlO 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-AlO catalyst has a larger pore size and basic strength, which is more conducive to the macrolactonization of long-chain hydroxy ester.