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Aryldiazonium Salts to Azo Dyes: Diazo Coupling

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para...

Preparation of 1° Amines: Azide Synthesis

Preparation of 1° Amines: Azide Synthesis

Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...

Basicity of Heterocyclic Aromatic Amines

Basicity 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).

Diazonium Group Substitution: –OH and –H

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.

Structure of Amines

Structure 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...

Nomenclature of Aryl and Heterocyclic Amines

Nomenclature of Aryl and Heterocyclic Amines

The simplest aromatic amine is phenylamine, which contains an –NH2 functionality directly attached to an aromatic ring. The name aniline is designated for this skeleton. As shown in Figure 1, the common names of the functionalized anilines involve prefixes ortho-, meta-, and para- to indicate the substitution position. Different functionalized aniline derivatives also have notable trivial names.

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Pyrazolyl-functionalised Ag(i)-NHC complexes: synthesis, characterisation, antibacterial activity, and computational

Ngonidzashe Ruwizhi¹, Karen Pillay², Janade Moodley²

¹School of Agriculture and Science, Discipline of Chemistry, University of KwaZulu-Natal Westville Campus, Private Bag X54001 Durban 4000 South Africa.

|December 24, 2025

Summary

Five novel pyrazolyl-functionalised azolium salts and their silver(I)-N-heterocyclic carbene complexes were synthesized and tested for antibacterial activity. Compound 2c, featuring a benzyl N-substituent, showed significant potency against bacteria.

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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

Published on: July 30, 2017

Area of Science:

Medicinal Chemistry
Organic Synthesis
Computational Chemistry

Background:

N-heterocyclic carbenes (NHCs) are versatile ligands in coordination chemistry and catalysis.
Pyrazolyl-functionalised azolium salts and their metal complexes are explored for various biological activities.
Developing new antibacterial agents is crucial due to rising antimicrobial resistance.

Purpose of the Study:

To synthesize novel pyrazolyl-functionalised azolium salts and their corresponding silver(I)-NHC complexes.
To evaluate the in vitro antibacterial activity of these synthesized compounds.
To investigate the structure-activity relationship, including the effect of N-substituents and the benzimidazole core.

Main Methods:

Synthesis of five pyrazolyl-functionalised azolium salts (1a-e) and their silver(I)-NHC complexes (2a-e).
Characterization using spectroscopic (e.g., NMR, IR) and analytical techniques.
In vitro antibacterial assays against a broad spectrum of bacterial strains.
Computational studies including DFT calculations and SWISSADME predictions.

Main Results:

All synthesized compounds (salts and complexes) were successfully characterized.
The silver(I)-NHC complexes exhibited in vitro antibacterial activity.
Compound 2c, with a benzyl N-substituent on the benzimidazole core, displayed the highest potency, comparable to the standard drug neomycin.
DFT and SWISSADME analyses suggested enhanced activity for benzimidazole derivatives and highlighted the role of the N-benzyl group.

Conclusions:

Pyrazolyl-functionalised silver(I)-NHC complexes represent a promising class of antibacterial agents.
The N-benzyl substituent and the benzimidazole scaffold significantly contribute to enhanced antibacterial efficacy.
Further research into these compounds could lead to the development of new therapeutic strategies against bacterial infections.