DIELS-ALDER REACTIONS IN WATER - ENFORCED HYDROPHOBIC INTERACTION AND HYDROGEN-BONDING
DIELS-ALDER REACTIONS IN WATER - ENFORCED HYDROPHOBIC INTERACTION AND HYDROGEN-BONDING
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DOI：
10.1351/pac199567050823
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发表时间：
1995-05-01
影响因子：
1.8
通讯作者：
ENGBERTS, JBFN
中科院分区：
文献类型：
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作者：
ENGBERTS, JBFN
测定了环戊二烯与不同疏水性和氢键受体容量的亲双烯体在水、有机溶剂和醇-水混合物中的Diels-Alder（DA）反应的二级速率常数。在相同的反应介质中，研究了N-糠基-N-烷基丙烯酰胺的分子内DA反应。在水中，通常巨大的速率加速似乎是环加成的活化过程中固有的，而不是源于二烯-亲二烯体缔合。在水中相对于1-丙醇和1-丙醇-水混合物的速率加速的伪热力学分析提供了两个因素的证据，主导在水中的速率增强：极化活化复合物的氢键稳定和在活化过程中的反应物的疏水表面积的减少。
Second-order rate constants have been measured for the Diels-Alder (DA) reactions of cyclopentadiene with dienophiles of varying hydrophobicity and hydrogen-bond acceptor capacity in water, in a series of organic solvents and in alcohol-water mixtures. The intramolecular DA reaction of N-furfuryl-N-alkylacrylamides was also investigated in the same reaction media. The often huge rate accelerations in water appear to be inherent in the activation process of the cycloaddition and do not originate from diene-dienophile association. A pseudothermodynamic analysis of the rate acceleration in water relative to 1-propanol and 1-propanol-water mixtures provides evidence for two factors dominating the rate enhancement in water: hydrogen-bond stabilization of the polarized activated complex and the decrease of the hydrophobic surface area of the reactants during the activation process.