4.3 Alcohols and phenols

Phenols

Benzene rings with an alcohol group substituent

Solubility of phenols in water

Phenol is a white solid at room temperature which is sparing soluble in water

The -OH is able to form hydrogen bonds to water

The benzene ring hinders solubility as it can only form weak van der Waals’ forces with water

If you try to dissolve too much you get two phasesof liquid

The top layer is a solution of phenol in water

When dissolved in water, phenol forms…

A weak acidic solution by losing an H+ from the –OH group

Reaction with sodium hydroxide

sodium phenoxide salt formed

Reaction with sodium metal

The sodium metal is seen to effervesce as hydrogen gas is produced.

The salt produced is sodium phenoxide

An aliphatic acid and phenol can be distinguished by adding…

Sodium carbonate or sodium hydrogencarbonate to produce carbon dioxide

If carbon dioxide bubbes form it must be the aliphatic acid

Bromination of phenol by electrophillic substitution

Reagent: phenol, bromine water

Conditions: room temperature

Observation: decolourisation of Br2 (orange to colourless), white precipitate forms

Comparing the bromination of phenol with benzene

Benzene: Requires a catalyst due to the reduced electron density as π electrons are shared across the whole benzene ring.

Phenol: There is an interaction between the delocalised electrons in the benzene ring and one of the lone pairs on the oxygen atom.

Testing for phenols

Add bromine, it will decolourise and form a white precipitate

React it with aqueous iron(III) chloride, generally a purple colour

Primary alcohol

The –OH group is on a carbon atom which is bonded to only one other carbon atom.

Secondary alcohol

The –OH group is on a carbon atom which is bonded to two other carbon atoms.

Tertiary alcohol

The –OH group is on a carbon atom which is bonded to three other carbon atoms

2 ways alcohols can be produced

The nucleophilic substitution of a halogenoalkane

The reduction of aldehydes, ketones or carboxylic acids

Alcohols from halogenoalkanes

Reagent: aqueous sodium (or potassium) hydroxide (an alkali is required)

Conditions: Heat under reflux

Mechanism: nucleophilic substitution

Reduction of Aldehydes and Ketones

Aldehydes and ketones can be reduced to their original alcohols by warming with a reducing agent.

The reducing agent used is an aqueous solution of NaBH4(aq).

The reduction that occurs is a nucleophilic addition reaction