Difference Between Toluene and Benzene

Main Difference – Toluene vs Benzene

Benzene and toluene are organic compounds. They are called aromatic compounds since they are composed of ring structures containing double bonds. In other words, they are unsaturated ring structures. Benzene and toluene are used as starting material for many synthesis reactions. This article explains the structural similarities as well as the differences between toluene and benzene along with the information about their properties and useful reactions. Toluene is a derivative of benzene. The main difference between toluene and benzene is that toluene has a methyl group attached to a benzene ring whereas benzene has a non-substituted ring structure.

Key Areas Covered

1. What is Toluene
      – Definition, Properties, and Reactions
2. What is Benzene
      – Definition, Properties, and Reactions
3. What are the Similarities Between Toluene and Benzene
      – Outline of Common Features
4. What is the Difference Between Toluene and Benzene
      – Comparison of Key Differences

Key Terms: Benzene, Carcinogenic, Methyl Group, Toluene, Unsaturated Ring

What is Toluene

Toluene is an organic compound having a benzene ring attached to a methyl group. The chemical formula of toluene is C₇H₈. The molar mass of toluene is about 92.14 g/mol. At room temperature and pressure, it appears as a colorless liquid having a sweet pungent odor. The IUPAC name for toluene is methylbenzene.

Figure 1: Chemical Structure of Toluene

The boiling point of toluene is about 111^oC. It is a highly flammable liquid compound. Toluene is considered as a benzene derivative. It can undergo electrophilic aromatic substitution reactions. Toluene is highly reactive due to the presence of methyl group. Methyl groups are good electron releasing groups. Therefore, the methyl group present in the toluene molecule helps to make the benzene ring more electron rich. Hence, it can easily share electrons with electrophiles.

The most common reactions that toluene undergo are as follows.

Reaction between toluene and potassium permanganate gives benzoic acid. Since potassium permanganate is a strong oxidizing agent, it can oxidize the methyl group into a carboxyl group.
Toluene can undergo halogenation. It can be brominated with HBr.
The methyl group of toluene can be deprotonated under very strong conditions.

Toluene is very useful in organic reactions. It can be used as a starting material to produce benzene. It gives a benzene molecule along with a methane (CH₄) molecule as the end products. Toluene is a good solvent that is commonly used in the production of paints. It is also used as a fuel sometimes due to its high flammability. However, toluene is considered as a toxic compound.

What is Benzene

Benzene is an aromatic compound having the chemical formula C₆H₆. The molar mass of benzene is about 78.11 g/mol. It appears as a colorless liquid at room temperature and pressure, and has a gasoline-like odor. The benzene molecule is a planar structure having unsaturation due to double bonds.

The boiling point of benzene is about 80.1^oC. Benzene can be found as a natural constituent of crude oil. Although the structure of benzene should be composed of six sp² hybridized carbon atoms attached in a cyclic manner with three double bonds, the actual benzene structure has no distinguishable double and single bonds between carbon atoms. The actual structure seems like two electron clouds above and below the planar structure of the benzene molecule. This is called the delocalization of electrons. The first to find this was a German chemist named Kekule’.

Figure 2: Different Representations of Chemical Structures of Benzene

Benzene undergoes electrophilic aromatic substitution reactions. That is due to the electron-rich nature of benzene. The electron clouds present in the benzene molecule can share electrons with electrophiles. Therefore, benzene is considered as a nucleophile. There are many derivatives of benzene produced by using benzene as the starting material. The hydrogenation of benzene gives cyclohexane.

However, benzene is considered as a carcinogenic compound. Therefore there are exposure limits for benzene. The routes of exposure to benzene include inhalation, soft drinks (benzoic acid and ascorbic acid in soft drinks may interact with each other to form benzene) and contamination of water supplies with benzene.

Similarities Between Toluene and Benzene

Both are hydrocarbons.
Both are aromatic compounds.
Both compounds are composed of benzene rings.
Both are unsaturated compounds.
Both are composed several sp² hybridized carbon atoms.

Definition

Toluene: Toluene is an organic compound having a benzene ring attached to a methyl group.

Benzene: Benzene is an aromatic compound having the chemical formula C₆H₆.

Molar Mass

Toluene: The molar mass of toluene is about 92.14 g/mol.

Benzene: The molar mass of benzene is about 78.11 g/mol.

Odor

Toluene: Toluene has a sweet, pungent odor.

Benzene: Benzene has a gasoline-like odor.

Boiling Point

Toluene: The boiling point of toluene is about 111^oC.

Benzene: The boiling point of benzene is about 80.1^oC.

Chemical Reactivity

Toluene: Toluene is highly reactive compared to benzene.

Benzene: Benzene is less reactive compared to toluene.

Hybridization of Carbon Atoms

Toluene: Toluene is composed of sp² hybridized carbon atoms and sp³ hybridized carbon atoms.

Benzene: Benzene is composed only of sp² hybridized carbon atoms.

Side Groups

Toluene: Toluene has a methyl group as a side group.

Benzene: Benzene has no side groups.

Conclusion

Toluene and benzene are two related organic compounds. Toluene is a derivative of benzene. The main difference between toluene and benzene is the presence of a methyl group in toluene whereas benzene has no methyl groups attached. Even though it is a slight difference in the chemical structure, this results in the many distinct properties of toluene and benzene.

References:

1. “What is Toluene? – Structure, Uses & Formula.” Study.com, Available here. Accessed 11 Sept. 2017.
2. “Benzene.” Wikipedia, Wikimedia Foundation, 9 Sept. 2017, Available here. Accessed 11 Sept. 2017.
3. “What is Benzene? – Uses, Structure & Formula.” Study.com, Available here . Accessed 11 Sept. 2017.

Image Courtesy:

1. “Toluene acsv” By Calvero – Own work (Public Domain) via Commons Wikimedia
2. “Benzene Representations” By Vladsinger – Own vector drawing based on layout of en:File:Benzol trans.png. (CC BY-SA 3.0) via Commons Wikimedia