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1.A Molecular Orbital Investigation of the Wacker Process for the Oxidation of Ethylene to Acetaldehyde 2.The oxidation of ethylene to acetaldehyde in the presence of [PdCL]2- has been studied using a CNDO-based method. A new reaction path is postulated involving the intermediate complex [C2H4PdCl]-. The reaction sequence is initiated by the introduction of a water molecule at each of the available coordination sites of the metal perpendicular to the plane of the ethylene palladium trichloride anion. The chloride ligand trans to the coordinat,ed ethylene is displaced by an entering water molecule. The departing halide extracts a proton from the second water and the generated hydroxyl ligand reacts with the ethylene, while remaining in the coordination sphere of the metal. This rate-determining step yields a ,%hydroxyethyl palladium species as an intermediate and this can transform by a series of hydrogen shifts into a weak complex of acetaldehyde and palladium(O). Reasons are presented for the greater catalytic efficiency of [PdClJ+ relative t’o [PtCI$- and for the inability of nickel and titanium complexes to catalyze the reaction. |
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铁杆木虫 (著名写手)
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10楼2009-04-27 16:19:51
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2楼2009-04-26 09:38:35
liubencai
木虫之王 (文坛精英)
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705506(金币+5,VIP+0):专业点啊 4-28 11:02
705506(金币+20,VIP+0):补加，多谢 4-28 11:06
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| 2. 用基于CNDO方法研究了在[PdCl]2-存在下乙烯氧化到乙醛。提出了涉及到[C2H4PdCl]-中间体配合物的一个新的反应途径的假设。该反应的过程是由水分子的引发而开始，该水分子位于与乙烯基三氯化钯阴离子垂直的每一个可配位的金属上。位于配位的乙烯反位的氯离子配体被一个进入的水分子取代。离开的卤离子从第二个水分子得到一个质子，产生的羟基配体同乙烯反应，留在了金属的配位层。这个速率控制步骤产生了作为中间体的羟乙基钯的物种，而这个转换是通过一连串的氢迁移到乙醛和钯的弱配位的配合物完成的。提出了相对于[PtCI$-的[PdClJ+有更高的催化效率的原因以及镍和钛配合物不能催化这个反应的原因。 |
3楼2009-04-26 10:32:09
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| The Wacker process or the Hoechst-Wacker process (named after the chemical companies of the same name) originally referred to the oxidation of ethylene to acetaldehyde by oxygen in water in the presence of a tetrachloropalladate catalyst.[1] The same basic reaction is currently used to produce aldehydes and ketones from a number of alkenes with the Monsanto process for producing acetic acid. This chemical reaction, a German invention, was the first organometallic and organopalladium reaction applied on an industrial scale. The Wacker process is similar to hydroformylation, which is also an industrial process and also leads to aldehyde compounds |
4楼2009-04-26 10:36:26
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