Synthesis, Characterization and Catalytic Activity of Dialdehyde Starch-Schiff Base Co(II) Complex in the Oxidation of C
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Synthesis, Characterization and Catalytic Activity of Dialdehyde Starch-Schiff Base Co(II) Complex in the Oxidation of Cyclohexane Danhong Yang Æ Lin Gao Æ Wenjun Zhao
Received: 10 March 2008 / Accepted: 7 July 2008 / Published online: 25 July 2008 Ó The Author(s) 2008
Abstract Dialdehyde starch-Schiff base Co(II) complex was prepared in a simple way and characterized by FT-IR, UV–vis and XPS. Its ability to catalyze oxidation of cyclohexane with oxygen in the absence of solvents or reducing agents was studied, and its reusability of the catalyst also be investigated. Keywords Dialdehyde starch Schiff base Co(II) complex Cyclohexane Oxidation
1 Introduction The selective oxidation of saturated hydrocarbons is one of the most challenging and promising subjects in oxidation chemistry [1]. Of particular importance is the oxidation of cyclohexane due to the large demand for cyclohexanone and cyclohexanol (KA oil), which are important raw materials for the production of adipic acid and caprolactam [2]. Traditionally, the process for cyclohexane oxidation is carried out at 423–433 K in the presence of a homogeneous catalyst. This process is low in energy efficiency and generates plenty of by-products [3, 4]. So it is necessary to find an environmentally friendly way to improve the catalytic process of oxidizing cyclohexane under mild conditions. Schiff base transition metal complexes are a family of homogeneous oxidation catalysts for a variety of organic D. Yang (&) L. Gao W. Zhao Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Science, Urumqi 830011, People’s Republic of China e-mail: [email protected] D. Yang The Graduate School of Chinese Academy of Science, Beijing 100049, People’s Republic of China
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substrates, and have been widely applied in the area of bioinorganic and bio-organic and catalytic chemistry [5–10]. In the field of biomimetic dioxygen carrier, the ability of Schiff base cobalt complex to bind dioxygen reversibly has been extensively examined since 1938 Tsumaki discovered that Co(Salen) could carry dioxygen reversibly [11], many Schiff base cobalt complexes were synthesized and applied in oxidation reactions. However, difficulty of recovery is one of the major drawbacks of these homogeneous catalysts, so a great deal of efforts has been devoted to the development of heterogeneous catalysts [12–20]. The encapsulation in zeolites [16, 19, 20], the grafting on polymers [12, 18] or silica [13–15, 17] have been used as supporting methods. Application of aluminasupported catalyst also has been received attention in recent years [21]. However, the catalysts based on biopolymers have not received much attention. Dialdehyde starch (DAS), obtained after periodate oxidative cleavage of the C2–C3 bonds in the anhydroglucose units of starch, is an interesting product with several viable industrial applications [22]. The insolubility in the vast majority of solvents makes dialdehyde starch an excellent candidate for a support of catalyst. In this paper, we prepared D
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