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首页> 外文期刊>Canadian Journal of Chemistry >Medium effect on the alpha-effect for nucleophilic substitution reactions of p-nitrophenyl acetate with benzohydroxamates and m-chlorophenoxide in DMSO-H2O mixtures as contrasts with MeCN-H2O mixtures: comparing two very different polar aprotic solvent components
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Medium effect on the alpha-effect for nucleophilic substitution reactions of p-nitrophenyl acetate with benzohydroxamates and m-chlorophenoxide in DMSO-H2O mixtures as contrasts with MeCN-H2O mixtures: comparing two very different polar aprotic solvent components

机译：在DMSO-H2O混合物中对苯羟羟基酯和M-氯化苯氧化物与MeCN-H2O混合物的α-硝基苯酯和M-氯化苯氧化物的α-效应的α-效应：比较两个非常不同的极性非质子溶剂组分

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A kinetic study is reported on nucleophilic substitution reactions of p-nitrophenyl acetate (1a) with three alpha-effect nucleophiles, benzohydroxamate (BHA(-)), p-methylbenzohydroxamate (MBHA(-)), and p-methyl-N-methylbenzohydroxamate (M2BHA(-)), and a reference nucleophile, m-chlorophenoxide (m-ClPhO-), in DMSO-H2O mixtures of varying compositions at 25.0 +/- 0.1 degrees C. Second-order rate constants for the reactions with BHA(-) and MBHA(-) decrease upon addition of DMSO to the reaction medium up to 60 mol % DMSO and then increase thereafter only a little. In contrast, M(2)BHA(-) and m-ClPhO- become much more reactive as the DMSO content in the medium increases. Such contrasting medium effects on reactivity are consistent with the report that hydroxamic acids behave as OH acids in H2O but as NH acids in dipolar aprotic solvents (e.g., DMSO and MeCN). It has been concluded that BHA(-) and MBHA(-) form an equilibrium of a reactive form I with less reactive species II in DMSO-H2O mixtures and the position of the equilibrium is dependent on solvent compositions. BHA(-) and MBHA-exhibit the alpha-effect in H2O but not in in 90 mol % DMSO. In contrast, the alpha-effect yielded by M2BHA-increases steeply up to 70 mol % DMSO and then levels off thereafter.
机译：本文报道了对硝基苯乙酸酯（1a）与三种α效应亲核试剂，苯并异羟肟酸（BHA（-）、对甲基苯并异羟肟酸（MBHA（-）和对甲基-N-甲基苯并异羟肟酸（M2BHA（-）以及一种参考亲核试剂间氯酚（m-ClPhO-）的亲核取代反应动力学研究，在25.0+/-0.1摄氏度的不同组成的DMSO-H2O混合物中，当向反应介质中添加高达60 mol%的DMSO时，与BHA（-）和MBHA（-）反应的二级速率常数降低，然后仅略微增加。相比之下，M（2）BHA（-）和M-ClPhO-随着培养基中二甲基亚砜含量的增加变得更加活泼。这种对比介质对反应性的影响与报告一致，即羟肟酸在H2O中表现为OH酸，但在偶极非质子溶剂（如DMSO和MeCN）中表现为NH酸。已经得出结论，在DMSO-H2O混合物中，BHA（-）和MBHA（-）与反应性较小的物种II形成反应性形式I的平衡，且平衡位置取决于溶剂组成。BHA（-）和MBHA在H2O中表现出α效应，但在90 mol%二甲基亚砜中则没有。相比之下，M2BHA产生的α效应急剧增加至70 mol%二甲基亚砜，然后趋于平稳。

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