Phenol (C6H5OH) has an enough acidity to react with aqueous sodium hydroxide (NaOH). As products, sodium phenoxide (salt) and water are given. This reaction is a weak acid - strong base reaction and also important in explaining acidic behavior of organic compounds.
Because aliphatic alcohols do not react with aqueous NaOH, we can identify phenol from aliphatic alcohols such as ethanol. But, you cannot separate carboxylic acids (such as acetic acid) from phenol because carboxylic acid reacts with aqueous NaOH solution.
Solubility of phenol in water is poor. However phenol solution is acidic. When sodium hydroxide is added slowly, pH value increases. When all phenol amount is finished, formed sodium phenoate is remaining in the solution and solution become basic because sodium phenoate is basic . Then, you add one more several drop of NaOH, solution become more basic and pH value will be more increased.
This reaction is an exothermic one. Also reaction of phenol and NaOH is a neutralization enthalpy. But standard enthalpy of neutralization is lower than strong acid - strong base reaction because phenol absorb energy to break its O-H bond.
When other, different groups are attached to the benzene ring, acidic characteristics of phenol is changed.
Reeaction of phenol and aqueous NaOH can be used to identify alcohols from phenol. Alcohols do not react with aqueous NaOH. You can see, when aqueous NaOH is added to phenol, temperature of the reactant mixture increases and an aqueous solution is formed.
Phenol is not a soluble organic in water and exists as a separate layer. But, when phenol reacts with aqueous NaOH, product sodium phenoate is soluble in water.
Ph- denotes phenyl group.
Questions asked by students
No. Both reactions will give same salt (sodium phenoxide). But, with sodium, hydrogen gas is released. With sodium hydroxide, water is given. Phenol and sodium reaction is a acid - metal reaction.
Product, sodium phenoxide given by the phenol and sodium hydroxide has many uses in chemistry.