Related Experiment Video
Updated: Aug 11, 2026
14:11
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
An azo dye molecule having a pyridine-2,6-dione backbone
1College of Sciences, Nanjing University of Technology, Nanjing 210009, People's Republic of China.
Acta Crystallographica. Section C, Crystal Structure Communications
|February 4, 2006
Summary
This study details the crystallization of a novel azo dye, revealing its hydrazone structure. The azo dye forms aggregates through hydrogen bonding and pi-pi stacking, influencing its solid-state arrangement.
Area of Science:
- Organic Chemistry
- Crystallography
- Materials Science
Background:
- Azo dyes are widely used in various industries due to their versatile chromophoric properties.
- Understanding the solid-state structure of azo dyes is crucial for predicting their physical and chemical behavior.
Purpose of the Study:
- To elucidate the crystal structure of the novel azo dye, 2-(2-methoxyethoxy)ethyl 4-[(5-cyano-1-ethyl-4-methyl-2,6-dioxo-1,2,3,6-tetrahydropyridin-3-ylidene)hydrazino]benzoate.
- To investigate the intermolecular interactions governing the self-assembly of this azo dye in the solid state.
Main Methods:
- Single-crystal X-ray diffraction analysis was employed to determine the molecular and crystal structure.
- Analysis of hydrogen bonding and pi-pi stacking interactions was performed.
Main Results:
- The azo dye crystallizes in the hydrazone tautomeric form.
- Four-molecule aggregates are formed through intermolecular hydrogen bonding.
- These aggregates are further organized into an extended structure via pi-pi stacking interactions between aromatic rings, with a centroid-centroid separation of 3.697 (2) Å.
Conclusions:
- The study reveals the detailed hydrazone crystal structure of the novel azo dye.
- Hydrogen bonding and pi-pi stacking are key interactions driving the self-assembly and extended structure formation.
- The findings provide insights into the structure-property relationships of azo dyes.
Related Concept Videos
01:11Aryldiazonium 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 position.
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).
01:10Nomenclature 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.
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.
01:13Five-Membered Heterocyclic Aromatic Compounds: Overview
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom, respectively.
01:20Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions
Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...