The key difference between benzene and phenol is that phenol has a –OH group in place of a hydrogen atom in benzene.
Benzene and phenol are aromatic hydrocarbons. Phenol is a derivative of benzene. Benzene structure was found by Kekule in 1872. Because of their aromaticity, they are different than aliphatic compound; thus, benzene and its derivatives are a separate field of study in organic chemistry.
CONTENTS
1. Overview and Key Difference
2. What is Benzene
3. What is Phenol
4. Side by Side Comparison – Benzene vs Phenol in Tabular Form
5. Summary
What is Benzene?
Benzene is an organic compound having the chemical formula C6H6. It has only carbon and hydrogen atoms arranged to give a planar structure. Therefore, we can categorize it as a hydrocarbon. Its structure and some properties are as follows.
- Molecular weight: 78g mole-1
- Boiling point: 80.1 oC
- Melting point: 5.5 oC
- Density: 0.8765 g cm-3
Benzene is a colourless liquid with a sweet odour. It is flammable and evaporates quickly. This compound is useful as a solvent because it can dissolve a lot of nonpolar compounds. However, benzene is slightly soluble in water.
The structure of benzene is unique compared to other aliphatic hydrocarbons; therefore, benzene has unique properties. All the carbons in this compound have three sp2hybridized orbitals. Two sp2 hybridized orbitals of a carbon overlap with sp2 hybridized orbitals of adjacent carbons on either side. Other sp2 hybridized orbital overlaps with the s orbital of hydrogen to form a σ bond. The electrons in p orbitals of a carbon overlap with the p electrons of carbon atoms in both sides forming pi bonds. This overlap of electrons happens in all six carbons, producing a system of pi bonds, which are spread over the whole carbon ring. Thus, we say that these electrons are delocalized.
Figure 01: Benzene
The delocalization of the electrons means that there aren’t alternating double and single bonds. So all the C-C bond lengths are the same, and the length is between single and double bond lengths. Due to delocalization, the benzene ring is stable and reluctant to undergo addition reactions, unlike other alkenes.
Sources of Benzene
Sources of benzene are either natural products or various synthesized chemicals. Naturally, they are present in petrochemicals like crude oil or gasoline. Benzene is also present in some synthetic products like plastics, lubricants, dyes, synthetic rubber, detergents, drugs, cigarette smoke and pesticides. This compound is released during the burning of the above materials, so automobile exhaust, factory emissions contain benzene. Moreover, benzene is said to be carcinogenic, so exposure to high levels of it can cause cancer.
What is Phenol?
Phenol is a white crystalline solid with molecular formula C6H6OH. It is flammable and has a strong odour. Its structure and some of the properties are given below.
- Molecular weight: 94g mole-1
- Boiling point: 181 oC
- Melting point: 40.5 oC
- Density: 1.07 g cm-3
In phenol, the hydrogen atom in the benzene molecule is substituted with a –OH group. Therefore, it has an aromatic ring structure similar to benzene. However, its properties are different due to the –OH group.
Figure 02: Phenol
Phenol is mildly acidic (acidic than alcohols). When it loses the hydrogen of the –OH group, it forms the phenolate ion. Moreover, it is moderately soluble in water, because it can form hydrogen bonds with water. Phenol evaporates slower than water.
What is the Difference Between Benzene and Phenol?
The key difference between benzene and phenol is that phenol has a –OH group in place of a hydrogen atom in benzene. Benzene is an organic compound having the chemical formula C6H6 while Phenol is a white crystalline solid with molecular formula C6H6OH. Furthermore, because of the –OH group, phenol is polar than benzene. Compared to benzene, phenol is more soluble in water. In addition, benzene evaporates faster than phenol. Another difference between benzene and phenol is that phenol is acidic while benzene is not.
Summary – Benzene vs Phenol
Benzene and phenol are aromatic organic compounds. Benzene is an organic compound having the chemical formula C6H6 while Phenol is a white crystalline solid with molecular formula C6H6OH. The key difference between benzene and phenol is that phenol has a –OH group in place of a hydrogen atom in benzene.
Reference:
1. Wade, Leroy G. “Phenol.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available here.
Image Courtesy:
1. “Benzene-aromatic-3D-balls” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
2. “Aryl=Phenyl=Phenol” By Jü – Own work (Public Domain) via Commons Wikimedia