Macrolactonization of methyl 15-hydroxypentadecanoate to cyclopentadecanolide using KF-La/γ-Al ₂ O ₃ catalyst

Abstract

It has been a challenge to synthesize macrolide musk in excellent yields with high purity. KF-La/γ-Al 2 O 3 catalyst was prepared from a highly basic mesoporous framework using a mild method. The prepared KF-La/γ-Al 2 O 3 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 2 -TPD. The results revealed that the K 3 AlF 6 and LaOF are produced on the surface of KF-La/γ-Al 2 O 3 , and LaO can promote the dispersion of KF on the surface of Al 2 O 3 . Catalysts pore size main distribution ranges between 10 and 30 nm, the maximum CO 2 desorption temperature is 715°C when the La loading is 25%. Because F − ion has a higher electronegativity than O 2− ion, the KF-promoted metal oxide (Al 2 O 3 or/and La 2 O 3 ) 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-Al 2 O 3 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-Al 2 O 3 catalyst has a larger pore size and basic strength, which is more conducive to the macrolactonization of long-chain hydroxy ester.