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# Uses of Amines

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Have you ever wondered where the bright red pigment of your favourite woollen socks comes from? It's quite likely that it is derived from amines. This is just one example of the uses of amines.

• We'll start with a recap of what amines actually are before exploring their uses.
• You'll be able to see examples of amines in industryand in real life. This will include looking at quaternary ammonium salts and azo compounds.

## What are amines?

In Amines, we introduced you to a new type of organic molecule: amines. These are ammonia derivatives, characterised by a nitrogen atom bonded to at least one organic hydrocarbon R group. Amines can be further divided into three different types:

• Primary amines contain a nitrogen atom bonded to just one R group and have the general formula NH2R.
• Secondary amines contain a nitrogen atom bonded to two R groups and have the general formula NHR2.
• Tertiary amines contain a nitrogen atom bonded to three R groups and have the general formula NR3.

Primary, secondary, and tertiary amines. Anna Brewer, StudySmarter Original

You can also get quaternary ammonium cations. These consist of a nitrogen atom bonded to four R groups. The nitrogen atom bonds to the fourth R group using a dative covalent bond. Quaternary ammonium ions are an important part of quaternary ammonium salts.

A quaternary ammonium cation. Anna Brewer, StudySmarter

## Properties of amines

Let's now briefly consider some of the characteristic properties of amines:

• Amines are polar molecules.
• Amines form hydrogen bonds, both with other amine molecules and with water. This means that they have high melting and boiling points, and that shorter-chain amines are soluble in aqueous solutions.
• Amines can act as both nucleophiles and bases. Nucleophiles are electron-pair donors whilst bases are hydrogen ion acceptors. This enables many of their reactions.

Check out Amines for a more detailed look into the properties of amines. Head over to Amines Basicity if you want to learn more about their reactions as nucleophiles and bases.

## Uses of amines in daily life

Now that we know what amines are, we can look at some of their day-to-day applications. After that, we'll consider their uses in industry.

• Amines are found in every cell in your body in the form of proteins. Proteins are condensation polymers, made up of repeating units called amino acids. Each amino acid has both a carboxyl functional group and an amine functional group, and they join together to form a long polymer chain. This chain then folds into a specific 3D shape that is unique to each protein.
• Another type of polymer involving amines is polyamides. These include nylon, Kevlar, and a variety of plastics.
• Many common drugs and pharmaceuticals are amines. These include the analgesic morphine, the decongestant ephedrine, and the antidepressant amoxapine.
• Amines play a role in cosmetics, such as shampoos, soaps, and shaving creams. We'll look at how they are made in just a second.
• The common compound tetramethylammonium chloride, used to disinfect water, is also an amine.
• Amines are the precursor to many dyes and tanning agents.

## Uses of amines in industry

Knowing what we use amines for is well and good, but how do we make those products? It is now time to learn about two important industrial applications of amines.

• Quaternary ammonium salts
• Azo compounds

### Quaternary ammonium salts

Earlier, we learned that a quaternary ammonium ion consists of a nitrogen atom bonded to four organic hydrocarbon R groups. It has a permanent positive charge, which means that it can bond ionically to negatively-charged ions, forming a quaternary ammonium salt.

A quaternary ammonium salt. Anna Brewer, StudySmarter Original

#### Uses of quaternary ammonium salts

Quaternary ammonium salts have a few uses: conditioners, detergents, and antimicrobial agents. They're suitable because of their charge. In conditioners and fabric softeners, the positive charge of the ammonium ion is attracted to the negative charge of wet clothes or hair, and the ammonium ions form a layer on the surface. This helps keep the hair or fabric smooth and glossy. In detergents and antimicrobial agents, the positive charge of the ammonium ion is attracted to the negative charge of bacterial cell walls. This disrupts the wall and damages the cell.

### Azo compounds

In industry, we often also use amines to make diazonium salts and azo compounds. Diazonium salts contain an -N+≡N group, while azo compounds contain an N=N azo group. Producing azo compounds involves a multi-step synthesis:

1. Phenylamine (C6H5NH2) is reacted with nitric(III) acid (HNO2) at low temperatures to form a diazonium salt.
2. The diazonium salt reacts with another aromatic organic molecule to form an azo compound.

Let's investigate those steps in more detail.

#### Forming a diazonium salt

First of all, phenylamine reacts with nitric(III) acid at low temperatures to form a diazonium salt containing the -N≡N+ group. Nitric(III) acid is extremely reactive and so must be prepared in situ. To carry out the reaction, we mix phenylamine with a chilled solution of a strong acid, such as hydrochloric acid (HCl), and then add sodium nitrite (NaNO2). The hydrochloric acid and sodium nitrite first react to form nitric(III) acid and sodium chloride:

$\mathrm{HCl}+ {\mathrm{NaNO}}_{2}\to {\mathrm{HNO}}_{2}+\mathrm{NaCl}$

The nitric(III) acid formed then reacts with phenylamine and more hydrochloric acid to form a diazonium salt:

${\mathrm{C}}_{6}{\mathrm{H}}_{5}{\mathrm{NH}}_{2}+ {\mathrm{HNO}}_{2}+ \mathrm{HCl}\stackrel{<10°\mathrm{C}}{\to }{\mathrm{C}}_{6}{\mathrm{H}}_{5}{\mathrm{N}}^{+}\mathrm{N}{\mathrm{Cl}}^{-}+ 2{\mathrm{H}}_{2}\mathrm{O}$

Here's a diagram to help you understand the structure of the molecules involved.

This reaction must be carried out below 10°C. If you heat the mixture, a different reaction takes place. Instead, you produce phenol (C6H5OH), nitrogen gas, and water:

${\mathrm{C}}_{6}{\mathrm{H}}_{5}{\mathrm{NH}}_{2}+ {\mathrm{HNO}}_{2}\stackrel{>10°\mathrm{C}}{\to }{\mathrm{C}}_{6}{\mathrm{H}}_{5}\mathrm{OH}+{\mathrm{N}}_{2}+ {\mathrm{H}}_{2}\mathrm{O}$

#### Forming an azo compound

The second step of the process involves reacting the diazonium salt with another aromatic organic molecule. This is an example of a coupling reaction, forming an azo compound with the N=N azo functional group. In this reaction, the diazonium ion acts as an electrophile and substitutes into the second molecule's benzene ring.

One example is the reaction of a diazonium salt with phenol. This reaction takes place in a basic solution, typically of sodium hydroxide, and produces an azo compound with two benzene rings, one with an -OH group. These benzene rings are joined by an N=N azo bridge. It also produces an acid, which varies depending on the diazonium salt used.

Here's the equation for the reaction between a diazonium chloride salt and phenol. The structural formulae of these molecules can get a little tricky, so we've used displayed formulae to show you the reaction.

A similar reaction takes place between diazonium salts and phenylamine. This produces another type of azo compound, but this time the second benzene has an -NH2 group:

#### Uses of azo compounds

Finally, we'll consider the uses of azo compounds. Thanks to their two benzene rings, which are full of delocalised pi electrons, they are very stable and present with vivid colours. Azo compounds, therefore, form the basis of many dyes, including ones such as methyl orange that are used as pH indicators. They're also used in the textile industry and in tattoo inks.

## Uses of Amines - Key takeaways

• Amines are ammonia derivatives that contain a nitrogen atom bonded to one or more organic hydrocarbon R groups.
• Amines are polar, can form hydrogen bonds, and act as both bases and nucleophiles.
• Amines are found in proteins, plastics, pharmaceuticals, cosmetics, and dyes.
• In industry, amines are turned into quaternary ammonium salts and azo compounds.
• Quaternary ammonium salts contain a nitrogen atom bonded to four R groups and are used in detergents, conditioners, and antimicrobial agents.
• Azo compounds are made from diazonium salts. These in turn are made from phenylamine and nitric(III) acid. Azo compounds are used as dyes.

Examples of amines include methylamine and phenylamine. However, we also find amines in daily life. For example, all proteins are made from amines known as amino acids, whilst many drugs such as morphine are also amines.

Amines are used in cosmetics, dyes, pharmaceuticals, and plastics.

Amines play important roles in many drugs, cosmetics, detergents, plastics, and antimicrobials. They also make up all proteins, which are found in every cell in our body.

Amines aren't acidic, but basic. This means that they act as proton acceptors.

Amines can form hydrogen bonds. This means that they have high melting and boiling points.

Shorter-chain amines are soluble in water.

## Final Uses of Amines Quiz

Question

What is an amine?

An ammonia derivative containing a nitrogen atom bonded to at least one R group.

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Question

Which of the following are true about amines?

Amines are polar molecules.

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Question

True or false? Some proteins are not made of amines.

False

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Question

Compare and contrast a tertiary amine with a quaternary ammonium ion.

• Both are ammonia derivatives.
• Both contain a nitrogen atom bonded to R groups by covalent bonds.
• The tertiary amine contains a nitrogen atom bonded to just three R groups whereas the quaternary ammonium ion contains a nitrogen atom bonded to four R groups.
• The tertiary amine has a neutral charge whereas the quaternary ammonium ion has a positive charge.
• The quaternary ammonium ion features a dative covalent bond.

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Question

Which of the following types of bonding are present in quaternary ammonium salts?

Covalent, dative covalent and ionic

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Question

Which of the following contain amines?

Proteins

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Question

Give three uses of quaternary ammonium salts.

• Conditioners
• Detergents
• Antimicrobial agents

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Question

Explain why quaternary ammonium salts are good antimicrobial agents.

Quaternary ammonium salts contain a quaternary ammonium ion with a positive charge. This is attracted to the negative charge of bacterial cell walls. The ions disrupt the cell wall, damaging the cell.

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Question

Which of the following are made from amines?

Quaternary ammonium salts

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Question

How do you make a diazonium salt from phenylamine?

• Mix phenylamine with a chilled solution of a strong acid such as hydrochloric acid (HCl)
• Add sodium nitrite (NaNO2). This reacts with the hydrochloric acid to form nitric(III) acid.
• The nitric acid reacts with phenylamine and more hydrochloric acid to form a diazonium salt and water.

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Question

How do you make an azo compound from a diazonium salt and phenol?

Mix the diazonium salt with phenol in basic solution, such as in sodium hydroxide. This produces an azo compound and an acid.

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Question

What is the azo group?

N=N

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Question

The reaction between a diazonium salt and phenol is a ____ reaction.

Coupling

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Question

In the reaction between a diazonium salt and phenol, the diazonium salt acts as ____.

An electrophile

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Question

Name the two possible organic products formed in the reaction between phenylamine and nitric acid. Give the conditions needed for the respective reactions.

If the reaction is carried out below 10°C, then it produces a diazonium salt. If the reaction is carried out above 10°C, then it produces phenol.

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