Related Experiment Video
Updated: Jun 21, 2026
06:35
Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
Published on: February 15, 2016
Structural analyses of N-acetylated 4-(dimethylamino)pyridine (DMAP) salts
Volker Lutz1, Jörg Glatthaar1, Christian Würtele2
1Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany), Fax: (+49) 641-99-34309.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|July 29, 2009
Summary
N-acetyl-4-(dimethylamino)pyridine (DMAP) salts form tight ion pairs stabilized by hydrogen bonds. In nonpolar solvents, their low concentration suggests alcohols are key to stabilizing subsequent acetylations.
Area of Science:
- Organic Chemistry
- Physical Chemistry
- Computational Chemistry
Background:
- 4-(dimethylamino)pyridine (DMAP) is a widely used acylation catalyst.
- The catalytically active species in DMAP-catalyzed reactions are believed to be N-acetyl-DMAP salts.
- Understanding the formation and stability of these salts is crucial for optimizing catalytic efficiency.
Purpose of the Study:
- To investigate the formation and structural dynamics of N-acetyl-DMAP salts with various counterions (Cl-, CH3COO-, CF3COO-).
- To elucidate the role of hydrogen bonding in the stabilization of these active species.
- To understand the factors influencing the concentration and reactivity of N-acetyl-DMAP salts in nonpolar solvents.
Main Methods:
- Crystal structure analysis.
- Variable temperature matrix infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy.
- Computational chemistry methods (UAHF-PCM-B3LYP/6-311+G(d,p)//B3LYP/6-31G(d)).
Main Results:
- Clear evidence for the formation of tight ion pairs in N-acetyl-DMAP salts.
- Dynamic hydrogen-bonding interactions were identified as key stabilizing factors.
- In nonpolar solvents, the steady-state concentration of the acetate anion in its N-acetyl-DMAP salt is less than 1% at room temperature.
Conclusions:
- N-acetyl-DMAP salts exist as tight ion pairs stabilized by dynamic hydrogen bonds.
- The low concentration of N-acetyl-DMAP acetate in nonpolar solvents indicates limited intrinsic nucleophilicity.
- Additional hydrogen-bonding interactions with alcohol substrates are proposed as the critical stabilization mechanism for subsequent acetylation steps.
Related Concept Videos
01:19Structure of Amines
The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are illustrated in Figure...
01:28Structures of Carboxylic Acid Derivatives
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
01:19Amines to Amides: Acylation of Amines
Various carboxylic acid derivatives (such as acid chlorides, esters, and anhydrides) can be used for the acylation of amines to yield amides. The reaction requires two equivalents of amines. The first amine molecule functions as a nucleophile and attacks the carbonyl carbon to produce a tetrahedral intermediate. This is followed by the loss of the leaving group and restoration of the C=O bond.
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...
01:17Nomenclature of Primary Amines
Primary, secondary, and tertiary amines are compounds consisting of one, two, and three alkyl groups connected to the amino group (–NH2), respectively. As depicted in Figure 1, the common name of the primary amines is obtained by adding the suffix -amine to the alkyl substituent attached to the amino group as the corresponding alkylamine.
01:19Diazonium 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.
01:25Basicity of Heterocyclic Aromatic Amines
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).