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从Knorr-Paal缩合反应动力学研究得出:(1)速率-pH图有钟罩形曲线;(2)负活化熵大,活化能低;(3)对-取代苯甲酸催化对-乙氧苯胺与β-二酮缩合的Brǒnsted α值为0.25;(4)以ρ~+=-0.881作Hammett图与速率相关比ρ~-或p好;(5)苯胺类分别与β-二酮或乙酰丙酮缩合,两者有很好线性的自由能关系。可见缩合机制应是简单的羰基加成和消除(脱水)过程。结论:(1)在pH1～9范围内降低pH时反应级数从1增加至2,分数级并非一级和二级的混合,而是因控速步骤由消除反应转向加成反应。(2)与甲基酮缩合对照,本缩合似无Schiff碱形成。(3)一级反应有诱导期,是消除控速;二级反应无诱导期,是加成控速;分数级表示两者速率相近。(4)加成控速时,在pH接近胺pK_α值时速率最大;反应物有张力时需用超酸作催化剂或用一般酸则需控制酸量,因这时酸对加成的加速比对消除的加速小,在pH大于胺pK_α值时速率已达最大。(5)否定了诸如二烯醇脱水、羰基碳上的协同置换、电环化机制及Findley提出的逆向反应机制;提出了β-二酮形成五元杂环的通式代替旧的二烯醇式历程。
From the Knorr-Paal condensation kinetics study, we can get: (1) The rate-pH curve has a bell-shaped curve; (2) The negative activation entropy is large and the activation energy is low; (3) Aniline and β-diketone condensation Brǒnsted α value of 0.25; (4) ρ ~ + = - 0.881 for the Hammett and rate-related ratio p ~ - or p good; (5) aniline and β-diketone or Acetylacetone condensation, the two have a very good linear relationship between the free energy. Visible condensation mechanism should be a simple carbonyl addition and elimination (dehydration) process. Conclusions: (1) When the pH is decreased from pH1 to 9, the reaction order increases from 1 to 2, and the fractional order is not a mixture of primary and secondary but a shift from elimination reaction to addition reaction. (2) condensation with the methyl ketone control, the condensation like no Schiff base formation. (3) The first stage reaction has an induction period, which is to eliminate the control rate. The second stage reaction has no induction period and is an addition control speed. The fractional level indicates that the two rates are similar. (4) When the addition rate is controlled, the maximum rate is reached when the pH is close to the pK_α value of the amine. When the reactant has a tension, the super acid needs to be used as a catalyst or the normal acid needs to be controlled. Since the acceleration ratio The acceleration of elimination is small, reaching the maximum at pH greater than amine pK_α. (5) Negatives such as dehydration of dienol, synergistic substitution on carbonyl carbon, electrocyclization mechanism and the reverse reaction mechanism proposed by Findley proposed a general formula of β-diketone to form a five-membered heterocyclic ring instead of the old dienol Style process.