The reaction scheme for the synthesis of tert-butyl chloride from tert-butyl alcohol using CaCl2 can be represented as follows:
(CH3)3COH (tert-butyl alcohol) + HCl (hydrochloric acid) -> (CH3)3CCl (tert-butyl chloride) + H2O (water)
In this reaction, tert-butyl alcohol reacts with hydrochloric acid to form tert-butyl chloride and water. However, the presence of water can reverse the reaction, leading to the formation of tert-butyl alcohol and hydrochloric acid.
This is where anhydrous calcium chloride comes into play. It acts as a desiccant, meaning it absorbs water molecules from the reaction mixture. By removing water, it shifts the equilibrium towards the formation of tert-butyl chloride and prevents the reverse reaction from occurring.
Anhydrous calcium chloride has a strong affinity for water due to its hygroscopic nature. The water molecules in the reaction mixture are attracted to the surface of the calcium chloride particles and become bound to them. This effectively reduces the water content in the reaction mixture, promoting the desired reaction to proceed more efficiently.
Additionally, anhydrous calcium chloride serves as a mild Lewis acid, which can facilitate the protonation of the alcohol oxygen in tert-butyl alcohol. This protonation enhances the reactivity of the alcohol towards the nucleophilic substitution reaction with the chloride ion from hydrochloric acid, ultimately leading to the formation of tert-butyl chloride.
In summary, anhydrous calcium chloride acts as a dehydrating agent in the synthesis of tert-butyl chloride from tert-butyl alcohol. It removes water from the reaction mixture, driving the equilibrium towards the formation of tert-butyl chloride and preventing the reverse reaction. Its hygroscopic nature and mild Lewis acidity contribute to its effectiveness in this synthetic process.
