Acid-catalysed aromatization of anthranyl derivatives. A kinetic and thermodynamic study
作者:Necmettin Pirinccioglu、Zhi Sheng Jia、Alf Thibblin
DOI:10.1039/b107121a
日期:2001.11.29
The acid-catalysed solvolysis reaction of 9-methoxy-9-methyl-9,10-dihydroanthracene (2-OMe) in 50 vol% acetonitrile in water at 25 °C provides the substitution product 9-hydroxy-9-methyl-9,10-dihydroanthracene (2-OH) and the elimination product 9-methylanthracene (3). The rate-ratio of substitution-to-elimination was measured as kS/kE
= 0.93. The alcohol also undergoes acid-catalysed aromatization to give the thermodynamically favoured product 3. The reaction enthalpy of this dehydration reaction was measured as ΔH
=
−10.2 ± 1.0 kcal mol−1. The corresponding reaction of
the secondary alcohol 9-hydroxy-9,10-dihydroanthracene (1-OH) has a reaction enthalpy of ΔH
=
−12.3 ± 0.8 kcal mol−1. Addition of azide ion (0.25 M) gives rise to a large fraction of azide adduct 2-N33, which rapidly undergoes solvolysis. The “azide-clock” method yields rate constants for reaction of the carbocation to give alcohol and elimination product of kw
= 2.2 × 108 s−1 and ke
= 2.4 × 108 s−1, respectively. The thermodynamic stability of the carbocation was estimated as pKR
=
−9.1. The alkene 9-methylene-9,10-dihydroanthracene (4) undergoes a slow acid-catalysed
aromatization to give 3; no competing formation of 2-OH was observed.
9-甲氧基-9-甲基-9,10-二氢蒽 (2-OMe) 在 50 vol% 乙腈水溶液中于 25 °C 进行酸催化溶剂解反应,得到取代产物 9-羟基-9-甲基-9, 10-二氢蒽(2-OH)和消除产物9-甲基蒽(3)。取代与消除的速率比测量为 kS/kE
= 0.93。醇也会经历酸催化芳构化,得到热力学上有利的产物 3。该脱水反应的反应焓测量为 ΔH
=
−10.2 ± 1.0 kcal mol−1。相应反应为
仲醇 9-羟基-9,10-二氢蒽 (1-OH) 的反应焓为 ΔH
=
−12.3 ± 0.8 kcal mol−1。添加叠氮离子 (0.25 M) 会产生大部分叠氮加合物 2-N33,该加合物会迅速发生溶剂分解。 “叠氮时钟”方法产生碳正离子反应生成醇和消除产物 kw 的速率常数
= 2.2 × 108 s−1 和 ke
分别 = 2.4 × 108 s−1。碳正离子的热力学稳定性估计为 pKR
=
−9.1。烯烃 9-亚甲基-9,10-二氢蒽 (4) 经历缓慢的酸催化反应
芳构化得到3;没有观察到 2-OH 的竞争形成。