Reactions of carbonyl compounds in basic solutions. Part 23.1 The mechanism of the base-catalysed ring fission of 2,2-dihydroxyindane-1,3-diones
作者:Keith Bowden、Sanjay Rumpal
DOI:10.1039/a606312h
日期:——
The base-catalysed ring fission of a series of substituted
2,2-dihydroxyindane-1,3-diones and phenalene-1,3-dione has been studied
in 30% (v/v) dioxane–water. The reaction proceeds in two distinct
steps. The first is a relatively fast base-catalysed ring fission to
give substituted o-carboxyphenylglyoxals, and the
second is a rearrangement of the latter resulting in formation of
substituted o-carboxymandelic acids. Rate coefficients
for the ring fission of a limited series of substrates have been
determined at 25.0 °C. The reaction is first order in the
mono-anion of the substrate alone. The Hammett reaction constants,
ρ, have been obtained from both the kinetic and product
studies. The rate- and product-determining step appears to be an
intramolecular nucleophilic attack. The rate coefficients for the
rearrangement have been determined for all substrates at 25.0, 35.0 and
45.0 °C. The activation parameters have been calculated. The
kinetic solvent isotope, solvent and salt effects have been studied. The
effects of the 5-substituted and 5,6-disubstituents on the rates have
been correlated using a modified Hammett equation giving a reaction
constant, ρ, equal to 3.4 at 25 °C.
研究人员在 30% (v/v) 二噁烷-水中对一系列取代的 2,2-二羟基茚-1,3-二酮和苯丙烯-1,3-二酮进行了碱催化环裂变研究。反应分两个不同的步骤进行。第一步是相对较快的碱催化环裂变,生成取代的邻羧基苯基乙二醛;第二步是后者的重排,生成取代的邻羧基扁桃酸。在 25.0 °C条件下测定了一系列有限底物的环裂解速率系数。该反应仅在底物的单阴离子中为一阶反应。从动力学和产物研究中获得了哈米特反应常数 ρ。决定速率和产物的步骤似乎是分子内的亲核攻击。对所有底物在 25.0、35.0 和 45.0 °C 下的重排速率系数进行了测定。计算了活化参数。研究了动力学溶剂同位素、溶剂和盐的影响。使用改进的 Hammett 方程对 5 取代基和 5,6 二取代基对速率的影响进行了相关分析,得出 25 °C 时的反应常数 ρ 等于 3.4。