Diazonium Salts: Preparation & Chemical Reactions

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  • 0:04 Azo Dyes
  • 0:47 Diazonium Salt Preparation
  • 1:35 Reactions of Diazonium Salts
  • 2:57 Uses
  • 3:23 Lesson Summary
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Lesson Transcript
Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

In this lesson, we will turn our attention to the synthesis and subsequent reactions of what are called diazonium salts--an important intermediate and building block in the field of organic chemistry.

Azo Dyes

Colors are everywhere. The sky is blue, the grass is green, roses are red, and your shirt is neon yellow! About that shirt. . .have you ever wondered how some of the clothes and fabrics we buy get such vibrant colors? Although there are several answers to that question, a class of organic compounds called azo dyes play in important role in helping to color our world with some pretty spectacular shades.

This lesson is going to focus on one of the vital building blocks used to make azo dyes, an intermediate called a diazonium salt. We'll concentrate on how diazonium salts are prepared and the chemical reactions they can take part in. We then wrap up with some color and briefly mention some of the popular dyes that are made from diazonium salts.

Diazonium Salt Preparation

A diazonium salt is an organic compound that contains a nitrogen-nitrogen triple bond and some other generic side group that could be either alkyl (an alkane derivative) or aryl (benzene ring). The 'salt' portion of the name comes from the fact that the diazo (meaning 'di-nitrogen') portion of the compound is present as its ionic salt, with a chloride ion being a typical counter-ion for the positively charged nitrogen atom.


General form of a diazonium salt
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In terms of how diazonium salts are actually made, the process is quite simple. Taking either an alkyl or aryl primary amine and reacting it with sodium nitrite in the presence of hydrochloric acid will get the job done nicely. Most of the time, the reaction conditions are mild and can be run at room temperature or even below that if the situation calls for it.


General synthesis of diazonium salts
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Reactions of Diazonium Salts

Diazonium salts, once synthesized, can be very versatile building blocks for other organic reactions. Let's take a look at a few of the more common reactions our salts can undergo.

Sandmeyer Reaction

Aromatic diazonium salts can be taken and reacted with copper (I) chloride to form an aryl chloride in a transformation called the Sandmeyer reaction, named after its discoverer Traugott Sandmeyer in the late 1800s. The diazonium salt undergoes the loss of a molecule of nitrogen and ultimately the diazo group on the aromatic ring is replaced by a chlorine atom, supplied by the copper (I) chloride reagent.


The Sandmeyer reaction of a diazonium salt with CuCl to give an aryl chloride
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Phenol Synthesis

If a diazonium salt is taken and heated in water, the diazo portion of the compound is replace by a hydroxyl group (-OH) to give a phenol. Phenols are valuable organic building blocks in the field of pharmaceuticals and drug discovery projects.


Reaction of a diazonium salt to make a phenol
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