Fundamental Studies On The Inclusion Of β-Cyclodextrin With Organic Sulfur Compounds

Along with the increasing enhancement of the environmental protection, the new technology research of desulfurization in light oil is more and more important. In this paper, an innovative idea of removing sulfur compounds by molecular recognition was brought forward; moreover, the systematical studies on the inclusion ofβ-cyclodextrin (β-CD) host with serials of sulfur compounds guest and the influencing factors were carried out for the first time. This work not only enriches the content of supramolecular chemistry in the theoretical research, but also widens the scope of light oil desulfurization technology in the applied research.In our research, with phenolphthalein as a spectral probe, the inclusion ofβ-CD with sulfur compounds without chromophores, such as aliphatic mercaptans, sulfides, and disulfides etc, was investigated by using the competitive spectrophotometric inclusion method. It was found that the inclusion ability ofβ-CD with normal mercaptans was increasing with the increase of the carbon atom number, and the inclusion ability ofβ-CD with isomercaptans was much higher than that ofβ-CD with normal mercaptans. The inclusion ability ofβ-CD with various organic sulfur compounds, which have the same number of carbon atom, decreases from diethyl disulfide to diethyl sulfide and to 1-butylmercaptan. Moreover, the higher temperature was favorable for the inclusion ofβ-CD with mercaptans and sulfides as well, and the inclusion processes were all spontaneously endothermic and controlled by entropy.The direct optical spectrographic method was adopted to study the inclusion ofβ-CD with organic sulfur compounds having chromophores, such as thiophenol, thiophene, benzo[b]thiophene, dibenzothiophene, etc. The inclusion ability ofβ-CD with these sulfur compounds decreased from thiophenol, to thiophene, to dibenzothiophene, to benzo[b]thiophene. It was also found that the higher temperature was unfavorable for the inclusion, and all of the inclusion processes were spontaneously exothermic and controlled by enthalpy.Furthermore, the inclusion mechanism demonstrated that the size match of the host and the guest determined the species of guest molecule entering theβ-CD cavity, while the polarity of the guest had important influence on the stability of the inclusion compounds. Meanwhile, hydrogen bonding, Van der Waals forces, the hydrophobic forces and the electrostatic interactions of dipole-dipole cooperated in the inclusion processes.Whenβ-CD included with the sulfur compound in petroleum ether,β-CD could also include with hydrocarbon components of petroleum ether, which caused the poorer selective recognition and the lower inclusion rate. The inclusion experiments ofβ-CD with sulfur compounds in aqueous solution showed thatβ-CD could recognize and include sulfur compound in aqueous solution, and indicated that inclusion style, inclusion time, the concentration ofβ-CD, and the initial concentration of sulfur compound all had influence on the inclusion processes.