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1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism

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.

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.

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 position.

Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions

Diazonium 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...

Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1

Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic S_N1

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...

1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Overview

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...

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Solution effect on diazonium-modified Au(111): reactions and structures.

Bo Cui¹, Jing-Ying Gu, Ting Chen

¹CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.

Langmuir : the ACS Journal of Surfaces and Colloids

|February 16, 2013

Summary

This summary is machine-generated.

Surface modification of gold electrodes using 4-bromobenzenediazonium tetrafluoroborate (BBD) yielded different results in acetonitrile versus aqueous solutions. Acetonitrile produced disordered organic films, while aqueous solutions formed a 4,4-dibromobiphenyl monolayer via radical coupling.

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Area of Science:

Electrochemistry
Surface Science
Organic Chemistry

Background:

Surface modification of electrodes is crucial for tuning their properties.
Diazonium salts are versatile reagents for surface functionalization.
Understanding reaction mechanisms is key to controlling surface chemistry.

Purpose of the Study:

To investigate the surface modification of Au(111) electrodes using 4-bromobenzenediazonium tetrafluoroborate (BBD).
To compare the outcome of surface modification in acetonitrile (ACN) and aqueous acidic media.
To elucidate the reaction pathways involved in the surface functionalization process.

Main Methods:

Scanning tunneling microscopy (STM) for high-resolution surface imaging.
Electrochemical grafting experiments using BBD.
Use of radical scavengers to probe reaction mechanisms.

Main Results:

In acetonitrile, disordered thin organic films were formed on Au(111).
Radical scavengers inhibited film formation, indicating radical intermediates.
In 0.1 M HClO4, a well-ordered 4,4'-dibromobiphenyl monolayer was formed.
The biphenyl formation is attributed to a radical-radical coupling reaction.

Conclusions:

Solvent choice significantly influences the outcome of diazonium salt-mediated surface modification.
Radical intermediates play a key role in film formation in acetonitrile.
Aqueous conditions favor coupling reactions, leading to ordered monolayers.