Classification of Alcohols and Phenols

Classification of Alcohols

• Primary Alcohol: Characterized by the hydroxyl group attached to a primary carbon; example is ethanol.
• Secondary Alcohol: Hydroxyl group is connected to a secondary carbon; 2-propanol (isopropyl alcohol) is a common example.
• Tertiary Alcohol: Hydroxyl group is bonded to a tertiary carbon; an example is 2-methyl-2-propanol (t-butyl alcohol).

Phenols

• Structurally similar to alcohols due to the presence of a hydroxyl (-OH) group.

Properties of Phenols

• More acidic than alcohols.
• Concentrated phenol solutions are toxic and can severely burn skin.
• Generally soluble in water and exhibit polar characteristics.

Properties of Alcohols

• Alcohols mix readily with water.
• Increased number of hydroxyl groups enhances hydrogen bonding with water, increasing solubility in water.
• Also soluble in organic solvents.

Chromic Acid Test

• Used to differentiate primary and secondary alcohols from tertiary alcohols using an acidified dichromate solution.
• Primary alcohols oxidize to carboxylic acids (turning chromic acid from red/brown to blue/green).
• Secondary alcohols oxidize to ketones, showing the same color change.
• Tertiary alcohols do not oxidize, showing no color change.
• Phenols oxidize into a brown tarry mass.

Lucas Test

• Distinguishes among primary, secondary, and tertiary alcohols using Lucas reagent (zinc chloride in concentrated HCl).
• Tertiary alcohols react rapidly, forming an insoluble white layer immediately.
• Secondary alcohols react slowly and may require slight heating, producing a thin white layer within about 10 minutes.
• Primary alcohols do not react, showing no change at all.
• Formation of any heterogeneous phase indicates a positive result.