| Alcohols, phenols and esters of natural flavors are important intermediates and raw materials. They are widely used in food industry, pharmaceutical industry and cosmetics industry. However, it is different to extract some organic molecules from natural products owing to their similar physical properties. Thus, it is essential to develop an efficient way for collecting organic molecules with high recovery and selectivity. (3-cyclodextrins (β-CD), which is well-known host among host-guest systems, is a-1,4-linked cyclic oligomer of Severn D-glucopyranose, with an inner hydrophobic and outer hydrophilic characteristics. It can form inclusion complexes with many organic molecules through host-guest interactions. P-CD has been used to separate some mixtures by its molecular recognition. In this paper, β-CD was applied to separate the difficult separation sysetems such as alcohols, phenols and esters of natural flavors, as follows:Firstly, a facile, novel, and cost-effective separation process of the isomeric compounds geraniol and nerol under rather mild conditions has been developed in the presence of β-cyclodextrin (P-CD). P-CD could form inclusion complexes with geraniol and nerol in aqueous solution, so as to selectively separate geraniol and nerol. The complexes have been investigated experimentally and with computational methods. FTIR, TG, DSC, UV-Vis, 1H-NMR, and 2D NOESY, have been utilized to analyze the inclusion complexes. Binding energies between β-cyclodextrin and the two substrates have been calculated with PM3 and ONIOM2(B3LYP/6-31G(d):PM3) methods. The effects of solvent environment, guest/host molar ratio, and binding temperature on the separation of geraniol and nerol were investigated. The results indicated that P-CD showed a higher selectivity for geraniol than nerol under identical experimental conditions, which results from the ability of selective binding and recognition of β-CD towards geraniol. The driving force of the separation between geraniol and nerol was through the different weak interactions with P-CD, i.e., hydrogen bond interaction, which was evidenced by the different binding energies and different inclusion equilibrium constants.Secondly, eugenol and eugenol acetate were selected as guest compounds. β-CD was used as host. The minimum energy structures for the inclusion complexes were calculated with quantum chemical calculations. The results showed that the inclusion complexes of eugenol acetate with p-CD was more stable than that of eugenol. The determination results of the inclusion constant of β-CD with eugenol and eugenol acetate by using UV-vis spectroscopic method. It was found that a more stable inclusion complex of eugenol acetate with P-CD than that of eugenol. Different characterization methods such as NMR, FTIR, TG/DSC, XRD were used to analyze inclusion complexes. Optimization of the solvent content, the molar ratio of guest/β-CD, and temperature for maximizing separation efficiency was performed. Under the condition of 10%ethanol solution,45 °C, a molar ratio of 4/1, the inclusion rate of eugenol acetate increased to 60%with a separation facter of 2.5.Finally, a selective separation method for benzyl alcohol and benzyl acetate has been studied with P-CD. It could form inclusion complexes with benzyl alcohol and benzyl acetate in solid state, so as to selectively separate them. The inclusion equilibrium constants for benzyl alcohol and benzyl acetate over P-CD have been calculated through UV-vis spectroscopic method, and the binding energies between P-CD and the two substrates have been calculated with PM3 and ONIOM2 (B3LYP/6-31G(d):PM3). The driving force of the separation between benzyl alcohol and benzyl acetate was through the different weak interaction with β-CD, i.e., hydrogen bond interaction, which was evidenced by the different binding energies and different inclusion equilibrium constants. Under the condition of 10% ethanol solution,40 °C, a molar ratio of 4/1, the inclusion rate of eugenol acetate increased to 60%with a separation facter of 16.The previous results indicated that a more stable inclusion complex of acetophenone with P-CD could form than that of 1-phenyl ethanol. The optimized conditions were as follows:the molar ratio of guest/β-CD, inclusion temperature, inclusion time and precipitating time were 4/1,40 °C,2 h, and 12 h, respectively. The inclusion rate of acetophenone increased to 90%with a separation facter of 25. Based on the results, some large scale experiment have been carried out. The same results were observed for the separation of acetophenone and 1-phenyl ethanol with P-CD. The Aspen Plus was also used to simulate the distillation process of acetophenone and 1-phenyl ethanol with column separation. The results indicated that theoretical calculations were in accordance with the experimental results.We believe that our current approach will provide a novel convenient method for efficient separation of geraniol and nerol, eugenol and eugenol acetate, and benzyl alcohol and benzyl acetate and is suitable to separate the aromatic aldehydes, alcohols and ethers from the natural products. |
PDF Full Text Request