Unit 3
Elements of Organic Chemistry


Phenols are hydroxyl derivatives of hydrocarbons formed by replacing a hydrogen on the benzene ring of an aromatic hydrocarbon with the hydroxyl radical. Phenols have the general formula Ar-OH, where Ar represents a substituted or nonsubstituted aromatic hydrocarbon. Thus, phenols are really just a special class of alcohols. However, they have enough unique properties that they deserve to be considered as a separate class of compounds. Below are some examples of typical phenols.

803fig0314.jpg (12916 bytes)

Properties of Phenols. All phenols are white solids with moderately high melting points and are soluble in water. They also have the property of being able to form eutectics with camphor, menthol, or thymol, which are solid alcohols. (A eutectic is a uniform mixture formed from two compounds that melt at a temperature lower than the melting point of either of the two compounds.) Thus, phenol (a solid) and camphor (a solid) form a liquid mixture at room temperature which is called a eutectic.

Reactions of Phenols. Chemically, phenols are weakly acidic compounds. The hydrogen dissociates to a small degree from the hydroxyl radical to act as an acid as shown below.

803fig0315.jpg (5983 bytes)

Since phenols are weak acids, they will form salts with inorganic bases. Phenols with two hydroxyl groups also undergo oxidation reactions.

Uses of Phenols. Medicinally, phenolic compounds have three uses: as keratolytics (compounds that remove hornified or scaling outer layers of skin), antipruritics (relieve itching), and disinfectants. These uses arise from the fact that phenols are very caustic to animal tissues. Precautions must therefore be taken when you are using phenols in preparations. These properties, possessed to different degrees by various phenols, depend on which other functional groups are present and the number of hydroxyl groups.