一种弱酸性丁芳醇与胺的相互作用:避免迈森海默陷
Eric J Olson1, Teng T Xiong, Christopher J Cramer
1Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
Journal of the American Chemical Society
|July 9, 2011
概括
2,4-丁托 (DNT) 和氨基溶液中的蓝色不是由于梅森海默复合物,而是DNT的脱质. 这种deprotonation,虽然是一个小的物种,是负责观察到的颜色.
科学领域:
- 有机化学 有机化学
- 物理化学 物理化学
- 频谱学是一种光谱学.
背景情况:
- 众所周知,像2,4-丁二 (DNT) 这样的多酸芳化合物会形成阳离子 σ-复合体 (Meisenheimer复合体).
- 之前的假设将迈森海默复合体的形成与在DNT和氨酸溶液中观察到的蓝色联系起来.
研究的目的:
- 为了调查DNT-胺溶液中蓝色的原因.
- 要确定梅森海默复合体是否是导致观察到颜色的主要物种.
- 准确地描述DNT与各种氨基之间的相互作用.
主要方法:
- 质子核磁共振 ((1) H NMR) 光谱法用于评估DNT质子转移.
- 密度函数计算以建模DNT-乙烯胺复合体.
- 紫外可见 (UV/vis) 光谱和主要成分分析以确定吸收物种.
- 乔布斯的情节分析来量化复杂的形成和平衡.
- 定位实验以确定pK (a) 值.
主要成果:
- 核磁共振光谱显示了最小的变化,表明DNT在很大程度上保留了芳香度.
- 密度函数计算表明梅森海默复合体的自由能量很高,并且存在于非常小的度.
- 紫外线/紫外线光谱分析揭示了一个主要的吸收物种,但 1:1 关联无法完全解释光谱.
- 约伯的情节分析最好通过DNT去质子化来解释,氨基酸作为基.
- 在二甲基硫氧化物中DNT的一致的pK (a) 确定为15.3 ± 0.2.2.
结论:
- 在DNT-氨基溶液中的蓝色来自去质子化的DNT,而不是Meisenheimer复合物.
- 脱质平衡远远偏向未反应的DNT,使得有色物种成为一个小的,NMR无法检测到的组件.
- 这项研究澄清了颜色的化学基础,并为DMSO中的DNT提供了可靠的pK ().
相关概念视频
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism
Nitrous acid is a relatively weak and unstable acid prepared in situ by the reaction of sodium nitrite and cold, dilute hydrochloric acid. In an acidic solution, the nitrous acid undergoes protonation when it loses water to form a nitrosonium ion—an electrophile. Nitrous acid reacts with primary amines to give diazonium salts. The reaction is called diazotization of primary amines.
Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1
Treating arylamines with nitrous acid gives aryldiazonium salts that are effective substrates in nucleophilic aromatic substitution reactions. The diazonio group in these salts can be easily displaced by different nucleophiles, yielding a wide variety of substituted benzenes. The leaving group departs as nitrogen gas, and this easy elimination is the driving force for the substitution reaction.
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
2° Amines to N-Nitrosamines: Reaction with NaNO2
Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.
Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)
Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between the...
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between the...
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Overview
Nitrous acid and nitric acids are two types of acids containing nitrogen, among which nitrous acid is weaker than nitric acid. Nitrous acid with a pKa value of 3.37 ionizes in water to give a nitrite ion and the hydronium ion.
The nitrous acid is unstable. Hence, it is formed in situ from a solution of sodium nitrite and cold aqueous acids such as hydrochloric or sulfuric acid. In an acidic solution, the –OH group of nitrous acid undergoes protonation to give oxonium ion, followed by water loss...
The nitrous acid is unstable. Hence, it is formed in situ from a solution of sodium nitrite and cold aqueous acids such as hydrochloric or sulfuric acid. In an acidic solution, the –OH group of nitrous acid undergoes protonation to give oxonium ion, followed by water loss...
Diazonium Group Substitution: –OH and –H
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.


