Main Difference – Phenol vs Benzoic Acid
Phenol and benzoic acid are organic compounds. Both are aromatic compounds. An aromatic compound is a substance that is composed of a planar ring system with delocalized pi electron clouds. Phenol is the simplest aromatic alcohol. It is considered as a toxic compound. Benzoic acid is the simplest aromatic carboxylic acid. It is not considered as a toxic compound. Both these compounds are composed of a substituted benzene ring. The main difference between phenol and benzoic acid is that phenol is an alcohol whereas benzoic acid is a carboxylic acid.
Key Areas Covered
1. What is Phenol
– Definition, Structure, Reactions, Uses
2. What is Benzoic Acid
– Definition, Structure, Uses
3. What are the Similarities Between Phenol and Benzoic Acid
– Outline of Common Features
4. What is the Difference Between Phenol and Benzoic Acid
– Comparison of Key Differences
Key Terms: Alcohol, Aromatic Compounds, Benzene Ring, Benzoic Acid, Carboxylic Acid, Phenol
What is Phenol
Phenol is the simplest aromatic alcohol. The molecular formula of phenol is C6H5OH. It indicates that phenol molecules are composed of benzene rings substituted with –OH groups. One phenol molecule contains one –OH group. The molar mass of phenol is about 94.11 g/mol.
Phenol appears as a transparent crystalline solid at room temperature and pressure. It has a sweet odor. The melting point of this solid is about 40.5 °C. The boiling point of phenol is about 181.7 °C. Commercially available phenol can be in solid dry powder form or liquid form. Phenol is miscible with water. This is because -OH groups can form hydrogen bonds with water molecules.
Phenol is a weak acid. It can partially dissociate into phenolate anion, forming a hydronium cation. But it is more acidic when compared to aliphatic alcohols. This increased acidity is a result of the resonance stabilization of phenol. Here, the phenoxide anion that is formed after releasing an H+ ion is stabilized by the delocalization of the negative charge on the oxygen atom.
Figure 1: Resonance Stabilization of Phenoxide Anion
Phenol is considered as a highly toxic compound. Phenol vapors are corrosive to the eyes and the skin. Phenol molecules can undergo electrophilic aromatic substitution since pi electrons of the oxygen atom can be delocalized into the benzene ring, making the ring an electron rich component. Then electrophiles can bind with the ring.
Phenol is used as a precursor for the production of plastics. Apart from that, it is commonly used as an antiseptic and disinfectant. Phenol is also used in the production of cosmetics and drugs (medicine).
What is Benzoic Acid
Benzoic acid is the simplest aromatic carboxylic acid. The molecular formula of benzoic acid is C6H5COOH. The molar mass of benzoic acid is about 122.12 g/mol. One benzoic acid molecule is composed of a benzene ring substituted with a carboxylic acid group (-COOH).
Figure 2: The Chemical Structure of Benzoic Acid
At room temperature and pressure, benzoic acid is a white crystalline solid. It is slightly soluble in water. Benzoic acid has a pleasant odor. The melting point of benzoic acid solid is about 122.41 °C. The boiling point of benzoic acid is given as 249.2 °C. But at 370 °C, it decomposes.
Benzoic acid can undergo electrophilic aromatic substitution due to the electron withdrawing property of the carboxylic group. Carboxylic acid can provide the aromatic ring with pi electrons. Then it becomes rich in electrons. Therefore, electrophiles can react with the aromatic ring.
Benzoic acid is a fungistatic compound that is widely used as a food preservative. This means it can prevent food from fungi growth. Benzoic acid can be naturally found in some fruits such as berries.
Similarities Between Phenol and Benzoic Acid
- Both are organic compounds.
- Both are aromatic substances.
- Both can undergo electrophilic aromatic substitution reactions
- Both are colorless or white crystals at room temperature and pressure.
Difference Between Phenol and Benzoic Acid
Definition
Phenol: Phenol is the simplest aromatic alcohol.
Benzoic Acid: Benzoic acid is the simplest aromatic carboxylic acid.
Molecular Formula
Phenol: The molecular formula of phenol is C6H5OH.
Benzoic Acid: The molecular formula of benzoic acid is C6H5COOH.
Molar Mass
Phenol: The molar mass of phenol is about 94.11 g/mol.
Benzoic Acid: The molar mass of benzoic acid is about 122.12 g/mol.
Substitution
Phenol: Phenol has a –OH substituted benzene ring.
Benzoic Acid: Benzoic acid has a –COOH substituted benzene ring.
Melting Point
Phenol: The melting point of phenol is about 40.5 °C.
Benzoic Acid: The melting point of benzoic acid is about 122.41 °C.
Boiling Point
Phenol: The boiling point of phenol is about 181.7 °C.
Benzoic Acid: The boiling point of benzoic acid is given as 249.2 °C.
Water Solubility
Phenol: Phenol is miscible with water.
Benzoic Acid: Benzoic acid is slightly dissolved in water.
Conclusion
Phenol and benzoic acid are among widely used organic compounds due to their favorable chemical and physical properties. Although phenol is considered as a toxic compound, it is used as an ingredient for some products. Benzoic acid can be found naturally in some fruits. The main difference between phenol and benzoic acid is that phenol is an alcohol whereas benzoic acid is a carboxylic acid.
References:
1. Wade, Leroy G. “Phenol.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 19 Apr. 2016, Available here.
2. “Phenol.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
3. “Benzoic acid.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
Image Courtesy:
1. “Phenol acide” By Yikrazuul – Own work (Public Domain) via Commons Wikimedia
2. “Benzoic acid” (Public Domain) via Commons Wikimedia
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