Preparation Of Lactones By Dehydrocyclization Of Diols

Lactone containing an ester function in its molecular structure is an important organic compound and intermediate. It and its derivatives play a role in many fields such as petrochemicals, textiles, spice, pesticide, medicine and so on. Aliphatic polyesters can be obtained by ring-open polymerization of many aliphatic lactones or lactides such asβ-proprolactone(β-PL),δ-valerolactone(δ-VL), lactide(LA), glycolic acid(GA),ε-caprolactone(ε-CL), dioxanone(PDO), 1,5-dioxepan-2-one(DXO), trimethylene carbonate(TMC) and so on. Evenγ- butyro lactone(GBL) with stable structure can polymerize by ring-opening reaction under rigorous conditions. Due to breaking of ester bonds attacked by organism, aliphatic polyesters are apt to degrade easily. With outstanding biodegradability, bioabsorbability and biocompatibility, aliphatic polyethesters have found wide applications in degradable polymeric materials and medical materials. Therefore, the investigation of synthesis of lactone has a vital significance both in the theory and practice.At present, there are several ways to the synthesis of lactone such as dehydrocyclization of diol over catalyst, maleic anhydride hydrogenation, Baeyer-villiger oxidation, direct inner esterification and so on. Due to its brief process, mild reaction conditions and the byproducts easily separated, dehydrocyclization of diol over catalyst provides a way to prepare lactone in industrial application.In this thesis, the CuO/Cr₂O₃/Al₂O₃ catalyst applied to dehydrocyclization reaction was prepared and characterized by XRD,BET, XPS and ICP-AES, which prove the composition of the parent catalyst and reduced catalyst.4-methyl-2-morpholinone (MMO),ε-caprolactone (ε-CL),γ-butyrolactone(GBL)were conveniently prepared in high yield by one-step dehydrocyclization of N-methyldiethanolamine,(MDEA), 1,6-hexanediol(HDO) and 1,4-butanediol(BDO) in a fixed bed in hydrogen flow at 200⁴00°C using CuO/Cr₂O₃/Al₂O₃ as catalyst, respectively. The effects of reaction conditions, including reaction temperature, weight hourly space velocity (WHSV) of diol and H₂/diol molar ratio on the performance of the catalysts have been investigated, and the optimal conditions were as follows: reaction temperature: 300°C, WHSV of MDEA : 0.67 h^-1, H₂/ MDEA molar ratio: 5.2, which gives MDEA conversion of 100% and MMO yield of 99.8%; reaction temperature: 280°C, WHSV of BDO : 0.66 h^-1, H₂/ BDO molar ratio: 4.1, which gives BDO conversion of 100% and GBL yield of 99.%;reaction temperature: 300°C, WHSV of HDO : 0.08h^-1, H₂/ HDO molar ratio: 8.2, which gives HDO conversion of 100% andε-CL yield of 60%. All those lactones will be some potential monomers for the synthesis of the relevant polymers.