Benzene vs Phenol
Benzene and phenol are aromatic hydrocarbons. Phenol is a derivative of benzene. Benzene structure was found by Kekule in 1872. Because of the aromaticity, they are different than aliphatic compounds, thus it is a separate field of study in organic chemistry.
Benzene has only carbon and hydrogen atoms arranged to give a planar structure. It has the molecular formula of C6H6. Its structure and some of the 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 colorless liquid with a sweet odor. It is flammable and evaporates quickly when exposed. Benzene is used as a solvent, because it can dissolve a lot of non polar 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 benzene have three sp2 hybridized orbitals. Two sp2 hybridized orbitals of a carbon overlaps with sp2 hybrized orbitals of adjacent carbons in 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 the six carbon atoms and therefore, produces a system of pi bonds, which are spread over the whole carbon ring. Thus,these electrons are said to be delocalized. The delocalization of the electrons means that there aren’t alternating double and single bonds. So all the C-C bond lengths are same, and the length is between single and double bond lengths. Because of the delocalization benzene ring is stable, thus, reluctant to undergo addition reactions unlike other alkenes.
The sources of benzene can be natural products or various synthesized chemicals. Naturally, they are present in petrochemicals like crude oil or gasoline. And as for the synthetic products, benzene is present in some plastics, lubricants, dyes, synthetic rubber, detergents, drugs, cigarette smoke and pesticides. Benzene is released in the burning of above materials, so automobile exhaust, factory emissions contain them. Benzene is said to be carcinogenic, so exposure to high levels of benzene can cause cancer.
Phenol is a white crystalline solid with molecular formula C6H6OH. It is flammable and has a strong odor. 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
Hydrogen atom in the benzene molecule is substituted with a –OH group to give phenol. Therefore, it has the similar aromatic ring structure as in benzene. But its properties are different due to the –OH group. Phenol is mildly acidic (acidic than alcohols). When it loses the hydrogen of the –OH group it forms the phenolate ion, and it is resonance stabilized, which in turn makes phenol a relatively good acid. And it is moderately soluble in water, because it can form hydrogen bonds with water. Phenol evaporates slower than water.
Benzene Vs Phenol
- Phenol has a –OH group in place of a hydrogen atom in benzene.
- Pure phenol is a white crystal, and benzene is a colorless liquid.
- The physical properties (melting point, boiling point, density, etc.) of benzene and phenol widely vary.
- Because of the –OH group, phenol is polar than benzene.
- Compared to benzene, phenol is more soluble in water.
- Benzene evaporates faster than phenol.
- Phenol is acidic and benzene is not.