Question

The order of reactivity of alcohols towards Na or K metal is:
A. Primary > secondary > tertiary
B. Primary < secondary < tertiary
C. Primary < secondary > tertiary
D. Primary > secondary < tertiary

Answer 1

Hint: As we know, sodium and potassium metals are basic in nature while alcohols are acidic in nature. Thus, reactivity of alcohol with these metals decreases with decrease in acidic strength. Primary alcohol has the highest acidic strength.

Complete step-by-step answer:
Alcohols react with active metals such as sodium, potassium, etc. to yield corresponding alkoxides. Alcohol has a hydrogen atom attached to the oxygen atom. Such compounds which contain hydrogen bonded to high electronegative elements like oxygen are acidic in nature. Therefore, alcohols are acids, although their acidic strength is very less. So, alcohol does not take part in reactions in which acid is already present.
Sodium and potassium metals react with alcohol to release hydrogen gas. The order of reactivity depends on the acidic strength of the types of alcohols i.e. primary, secondary and tertiary alcohols. Acids that have higher acidic strength reacts with sodium faster as compared to weaker acids.
In tertiary alcohols, alkyl groups supply the electron density towards the oxygen of alcohol, this reduces the acidic strength of alcohol. Therefore, as the alkyl groups on carbon connected to the alcohol functional group increases, thereby decreasing the acidic strength of an alcohol.
From this we conclude that the reactivity of alcohol with sodium or potassium will be primary > secondary > tertiary.

Hence, the correct option is (A).

Note: Sodium and potassium being highly electropositive metals generally react with acids and release hydrogen gas. Although alcohols are weak acids, yet the strong electropositive character of these metals allow them to react with alcohols and liberate hydrogen.