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Phenols - Organic Chemistry Tutor

Through phenols you understand combinations which contain one or more hydroxyl groups directly connected to the benzoic nucleus. Phenols can be similar to tertiary alcohols through the fact that they also contain the hydroxyl group connected to a carbon atom (which is not bound to a hydrogen atom).

After the number of hydroxyl groups in the molecule, you can distinguish:
- phenols with a single hydroxyl group, meaning mono hydroxyl phenols
- phenols with more than one hydroxyl groups in the molecule, meaning poly hydroxyl phenols

Mono hydroxyl phenols have not isomers because they are produced by de mono substitution of the benzoic nucleus. Containing more than one hydroxyl groups bound in different positions to the aromatic nucleus, the poly hydroxyl phenols exist under the form of isomers. The denomination of phenols is based on the fact that they are considered the results of the substitution of the aromatic hydrocarbons. Properly said, C₆H₅-OH is called hydroxybenzene.

Structure and nomenclature

Hydroxybenzene, C₆H₅-OH, is normally called phenol and is the simplest mono hydroxyl phenol. His homologue is hydroxytoluene, (CH₃)C₆H₄OH, at which you can distinguish 3 isomers, after the relative position of the substitutes at the aromatic nucleus: o-cresol, m-cresol and p-cresol.

o-cresol	p-cresol	m-cresol
Hydroquinine	Hydroxohydroquinine	Fluorine glaucoma
Pirogalol	Pirocatehina	Rezorcina

Physical properties

Phenols are, normally, solid substances (at the usual temperature), with a pervading and unpleasant smell. Phenols are a little soluble in water, but completely soluble in organic solvents.

Obtaining methods

1. Alkaline melting method

Ar-OH + H₂SO₄ Ar-SO₃H (sulfonic acid) Ar-SO₃Na + H₂O Na₂SO₃ + Ar-OH (phenol)

2. The cumin procedure

Benzene + CH2=CH-CH3 Cumin + O₂ Cumin hydro peroxide Ar-OH + acetone

Chemical reactions

1. The reaction with metals and bases

Ar-OH + Na Ar-ONa (sodium phenoxide) + H₂
Ar-OH + NaOH Ar-ONa + H₂O
Ar-ONa + R-X Ar-OR (mix ether) + NaX

2. Substitutions reactions (at the nucleus)(-OH is a first grade substitute)

+ CH3-Cl HCl

+

3. Hydrogenation

Ar-OH + 3H₂ cyclic hexane

4. The identification of phenols (FeCl3)

Ar-OH + FeCl₃ Ar-OFeCl₂ + HCl

- Phenol + FeCl3 violet
- Cresol + FeCl3 blue
- Hydro quinine + FeCl3 blue
- Alfa-naphthol +FeCl3 green
- Beta-naphthol + FeCl3 green

5. Phenols oxidation – at the oxidation, the phenols react different than the alcohols.

Use

» Phenol – plastic masses, medicine industry, coloring industry and perfumes
» Cresols – plastic masses, explosive industry
» Naphthols – coloring industry
» Hydro quinine – photographic technique, coloring industry

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