WHAT ARE THE DERIVATIVES OF BENZENE? - CHEMISTRY - 2024

The derivatives of benzene are, according to the system of the International Union of Pure and Applied Chemistry (IUPAC), aromatic hydrocarbons. Figure 1 shows some examples.

Although some compounds are referred to exclusively by IUPAC names, some are more frequently designated by common names (Important Benzene Derivatives and Groups, SF).

Figure 1: some derivatives of benzene.

Historically, benzene-type substances were called aromatic hydrocarbons because they had distinctive aromas. Today, an aromatic compound is any compound that contains a benzene ring or has certain benzene-like properties (but not necessarily a strong aroma).

You can recognize aromatic compounds in this text by the presence of one or more benzene rings in their structure.

In the 1970s, researchers discovered that benzene is carcinogenic. However, this does not mean that compounds that contain a benzene ring as part of their structure are also carcinogenic.

It is a common misconception that if a compound is used to produce a certain chemical, the risks associated with it remain the same.

In fact, when benzene is reacted to produce different derivatives, it is no longer the compound benzene, and the chemical properties of the products can often be completely different.

Therefore, the presence of a benzene ring in the structure of a compound is not an automatic cause for concern, in fact, a large number of compounds found in our food contain a benzene ring somewhere in their structure. (Structure and Nomenclature of Aromatic Compounds, SF).

Nomenclature of benzene derivatives

Benzene derivatives have been isolated and used as industrial reagents for over 100 years and many of the names are rooted in the historical traditions of chemistry.

The compounds mentioned below carry the common historical names and most of the time not by the IUPAC systemic names (Benzene Derivatives, SF).

-Phenol is also known as benzenol.

-Toluene is also known as methyl benzene.

-Aniline is also known as benzenamine.

-Anisole is also known as methoxy benzene.

-The IUPAC name of styrene is vinyl benzene.

-Acetophenone is also known as Methyl Phenyl Ketone.

-The IUPAC name of benzaldehyde is benzenecarbaldehyde.

-Benzoic acid has the IUPAC name of benzene carboxylic acid.

Simple derivatives

When benzene contains only one substituent group they are called simple derivatives. The nomenclature for this case will be the name of the derivative + benzene.

Figure 2: chlorobenzene = chlorine + benzene.

For example, chlorine (Cl) attached to a phenyl group would be called chlorobenzene (chlorine + benzene). Since there is only one substituent on the benzene ring, we do not have to indicate its position on the benzene ring (Lam, 2015).

Disubstituted derivatives

When two of the positions on the ring have been substituted with another atom or group of atoms, the compound is a disubstituted benzene.

You can number the carbon atoms and name the compound in relation to them. However, there is a separate nomenclature to describe the relative positions.

Using toluene as an example, the ortho orientation is the 1.2 ratio; the goal is 1.3 and the para is 1.4. It should be noted that there are two ortho and goal positions.

Substituents are named in alphabetical order unless there is an important or naming one for the molecule, for example phenol.

Figure 3: ortho, meta and para positions relative to the toluene molecule.

The notation for ortho, meta, and para positions can be simplified with the letters o, m and p respectively (in italics).

An example of this type of nomenclature is shown in Figure 4 with the molecules of o-bromoethylbenzene, m-nitrobenzoic acid and p-bromonitrobenzene (Colapret, SF).

Figure 4: structure of o-bromoethylbenzene (left), m-nitrobenzoic acid (cent.) And p-bromonitrobenzene (right).

Polysubstituted derivatives

When there are more than two substituents on the benzyl ring, numbers must be used to distinguish them.

They begin to number at the carbon atom to which one of the groups is attached and count towards the carbon atom that leads to the other substituent group by the shortest path.

The order of the substituents is alphabetical and the substituents are named preceded by the carbon number in which all this is found followed by the word benzene. Figure 5 shows the example of the 1-bromo molecule, 2,4 dinitro benzene.

Figure 5: structure of 1-bromo, 2,3-dinitro benzene.

If a group imparts a special name, the name of the molecule as a derivative of that compound and if no group imparts a special name, list it in alphabetical order, giving them the lowest set of numbers.

Figure 6 shows the TNT molecule, according to this type of nomenclature, this molecule should be called 2, 4, 6 trinitrotoluene.

Figure 6: 2, 4, 6 trinitrotoluene molecule.

Some important derivatives of benzene

A number of the substituted benzene derivatives are well known and commercially important compounds.

One of the most obvious is polystyrene, made by polymerizing styrene. Polymerization involves the reaction of many smaller molecules to form long chains of molecules.

Several billion kilograms of polystyrene are produced per year, and its uses include plastic cutlery, food packaging, foam packaging materials, computer cases, and insulation materials (Net Industries and its Licensors, SF).

Other important derivatives are phenols. These are defined as benzene molecules with OH (hydroxide) groups attached to them.

They are described as colorless or white solids in their purest form. They are used to make epoxies, resins, and films.

Toluene is defined as a benzene molecule with a group of one carbon atom and three hydrogen atoms attached to it. It is "a clear, colorless liquid with a distinctive odor."

Toluene is used as a solvent, although this use gradually ends because toluene can cause headaches, confusion, and memory loss. It is also used in the production of certain types of foam.

Aniline is a benzene molecule with an amino group (-NH ₂) attached to it. Aniline is a colorless oil, but it can darken on exposure to light. It is used to make dyes and pharmaceuticals (Kimmons, SF).

Benzoic acid is a food preservative, it is a starting material for the synthesis of dyes and other organic compounds and it is used for curing tobacco.

The more complex benzene-based molecules have applications in medicine. You may be familiar with Paracetamol, which has the chemical name of acetaminophen, commonly used as an analgesic to relieve pain and headaches.

In fact, a large number of medicinal compounds are likely to have a benzene ring somewhere in their structure, although these compounds are often more complicated than those shown here.

References

1. Andy Brunning / Compound Interest. (2015). Benzene Derivatives in Organic Chemistry. Recovered from compoundchem.com.
2. Benzene Derivatives. (SF). Recovered from chemistry.tutorvista.com.
3. Colapret, J. (SF). Benzene & Its Derivatives. Recovered from colapret.com.utexas.edu.
4. Important Benzene Derivatives and Groups. (SF). Recovered from colby.edu.
5. Kimmons, R. (SF). List of Benzene Derivatives. Recovered from hunker.com.
6. Lam, D. (2015, November 16). Nomenclature of Benzene Derivatives.
7. Net Industries and its Licensors. (SF). Benzene - Benzene Derivatives. Recovered from science.jrank.org.
8. Structure and Nomenclature of Aromatic Compounds. (SF). Recovered from saylordotorg.github.io.