ORTHO OXIDATION OF 2,6-DIMETHYLPHENOL WITH TRIFLUOROPEROXYACETIC ACID
ORTHO OXIDATION OF 2,6-DIMETHYLPHENOL WITH TRIFLUOROPEROXYACETIC ACID
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DOI：
10.1021/jo01036a013
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发表时间：
1963-01-01
影响因子：
3.6
通讯作者：
MCCLURE, JD
中科院分区：
文献类型：
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作者：
MCCLURE, JD
向2，6-二甲基苯酚和三氟乙酸的二氯甲烷溶液中缓慢加入过氧化氢，主要得到邻位氧化产物，即2，6-二甲基-邻-喹啉（II）的二聚体（III）。然而，当试剂同时混合在一起时，2，6-二甲基苯醌是压倒性的主要产物。有人认为，2，6-二甲基苯酚与过氧化氢和三氟乙酸原位形成的三氟过氧乙酸发生邻位羟基化反应是由环状氢键过渡态引起的。最近，马斯格雷夫及其同事1发现，用三氟过氧乙酸氧化2，6-二甲基苯酚只得到一种可分离的产物2，6-二甲基对苯醌，产率为77%。我们现在要报告的是，在某些条件下，由苯酚的邻位氧化得到不同的主要产物。该产物和2，6-二甲基苯醌形成的相对量强烈地依赖于氧化剂的浓度。当将三摩尔当量的50-85%过氧化氢非常缓慢地加入到2，6-二甲基苯酚（I）和二分之一摩尔当量的三氟乙酸的二氯甲烷溶液中时，主要产物是化合物CielDoCX，以42%的产率分离。2，6-二甲基苯醌（V）的产率为27%。然而，当一次全部加入过氧化氢时，以10%的产率获得CielDoCh，以60%的产率获得2，6-二甲基苯醌。使用任一方法分离2，6-二甲基-3-羟基苯醌（VI）作为次要产物（3-7%产率）。化合物C16 H2O 4（见实验）的物理和光谱性质与最近报道的6-羟基-2，6-二甲基-2，4-环己二烯酮（II）的Diels-Alder二聚体3（III）的物理和光谱性质一致。通过高碘酸钠氧化2 I制备的III真实样品的混合熔点测定证实了该产品的身份。酸性过氧化氢在这些条件下不是有效的氧化剂，这通过在二氯甲烷（非均相）或醚（均相）稀释剂中在对甲苯磺酸存在下2，6-二甲基苯酚与过氧化氢反应的失败来证明。在磷酸氢二钠酸清除剂存在下，将预先形成的三氟过氧乙酸（不存在游离的过氧化氢）缓慢加入到二氯甲烷中的I中，分别以40、20和7%的产率得到产物III、V和VI。因此，三氟过氧乙酸是参与所有三种产物形成的活性氧化剂。
Slow addition of hydrogen peroxide to a solution of 2, 6-dimethylphenol and trifluoroacetic acid in methylene chloride affords primarily a product of ortho oxidation, the dimer (III) of 2, 6-dimethyl-o-quinol (II). When the reagents are mixed together all at once, however, 2, 6-dimethylbenzoquinone is the overwhelmingly predominant product. A cyclic hydrogen-bonded transition state is suggested to accountfor the ortho hydroxylation of 2, 6-dimethylphenol with trifluoroperoxyacetic acid formed in situ from hydrogen peroxide and trifluoroacetic acid.Recently, Musgrave and co-workers1 have found that oxidation of 2, 6-dimethylphenol with trifluoroperoxy-acetic acid affords only one isolable product, 2, 6-dimethylbenzoquinone, in 77% yield. We now wish to report that under certain conditions a different major product, resulting from ortho oxidation of the phenol, is obtained. The relative amounts of this product and 2, 6-dimethylbenzoquinone formed are strongly dependent upon the concentration of oxidant. When three molar equivalents of 50-85% hydrogen peroxide are added very slowly to a solution of 2, 6-dimethylphenol (I) and one half of a molar equivalent of trifluoroacetic acid in methylene chloride solution, the major product is the compound CielDoCX, isolated in 42% yield. 2, 6-Dimethylbenzoquinone (V) is also obtained in 27% yield. When the hydrogen peroxide is added all at once, however, CielDoCh is obtained in 10% yield and 2, 6-dimethylbenzoquinone in 60% yield. 2.6-Dimethyl-3-hydroxybenzoquinone (VI) is isolated as a minor product (3-7% yield) using either procedure. The physical and spectral properties of the com-pound Ci6H2o04 (see Experimental) are in agreement with those reported2 recently for the Diels-Alder dimer3 (III) of 6-hydroxy-2, 6-dimethyl-2, 4-cyclohexadienone (II). Mixed melting point determination with an authentic specimen of III prepared by sodium periodate oxidation2 of I confirms the identity of this product. That acidic hydrogen peroxide is not an effective oxidant under these conditions was shown by the failure of 2, 6-dimethylphenol to react with hydrogen peroxide in the presence of p-toluenesulfonic acid in either methylene chloride (heterogeneous) or ether (homogeneous) diluent. Slow addition of preformed trifluoroperoxyacetic acid (no free hydrogen peroxide present) to I in methylene chloride in the presence of disodium hydrogen phosphate acid scavenger affords products III, V, and VI in 40, 20, and 7% yields, respectively. Accordingly, then, trifluoroperoxyacetic acid is the active oxidizing agent involved in the forma-tion of all three products.