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A possible mechanism for the formation of Ⅲ from I in ethyl alcohol is that Ⅱ is first formed. Since I1 is soluble in dry ethyl alcohol to the extent of 0.5% at reflux temperature, it could react with the hydrogen sulfide to give the postulated intermediate addition product Ⅳ. Ⅳ would then break down under the reaction conditions to give the observed Ⅲ and ethyl thionoacetate (Ⅴ). This proposed mechanism was tested by treating Ⅱ with hydrogen sulfide in et'hyl alcohol. Ⅲ, and dithiomalonamide[3,4] (Ⅵ) were identified in the product. Ⅴ was identified by gas chroma Ⅱ + H2S + C2H5OH + Ⅲ + Ⅴ + CH2(CSNH2)2 tography and by mass spectrometry. Further evidence for the identity of V was obtained by synthesis of ethyl thionoacetate from ethyl acetimidate and hydrogen sulfide.[5] This authentic sample was found to have the same retention time on the gas chromatographic column as Ⅴ, and the mass spectrum obtqined on this sample was also identical with that of Ⅴ. Other products identified by gas chromatography from the reaction of Ⅱ with hydrogen sulfide in alcohol were hydrogen sulfide, ethyl alcohol, and small quantities of ethyl acetate. The ethyl acetate probably resulted from hydrolysis or from oxidative exchange of the ethyl thionoacetate with air since thiono esters are noted for the ease with which the sulfur atom is removed.6 In some preparations, sulfur was isolated. It was also demonstrated by infrared and gas chromatographic analyses that ethyl thionoacetate is converted in the presence of air to ethyl acetate. |
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一个由I形成III的可能机理是在乙醇中先生成了II.既然II在回流温度下有0.5%能溶于干燥的乙醇，它可能与硫化氢反应生成假定的中间体加成产物IV.IV在该反应条件下分解生成了观测到的III和ethyl thionoacetate（V）。 这个可能的机理用II与硫化氢在乙醇中的反应来检验，发现存在III和dithiomalonamide[3,4](VI).在气相和质谱中发现了V （Ⅱ + H2S + C2H5OH + Ⅲ + Ⅴ + CH2(CSNH2)2 ）。 其它发现V的证据同样在用ethyl acetimidate和硫化氢反应来合成ethyl thionoacetate的反应中被发现【5】。这个可信的样品在气相中和V有着相同的保留时间，另外质谱也验证了确实与V为同一物质。II与硫化氢在乙醇中反应的其他产物在气相中被识别出来，有硫化氢，乙醇，和少量乙酸乙酯。乙酸乙酯可能来源于ethyl thionoacetate的水解或者遇空气氧化置换，因为在硫酯中硫原子很容易被置换【6】。在某些制备中，硫单质被分离出来。红外和气相分析也证明了ethyl thionoacetate在空气存在条件下转化为乙酸乙酯。 |
2楼2009-05-17 21:15:21