Question

How will you convert ethanol to ethyl fluoride?

Answer 1

In the conversion of ethanol to ethyl fluoride, the substitution of nucleophile takes place in which it follows the ${S_N}2$ mechanism. In the ${S_N}2$ mechanism, the nucleophile attacks from the back-side attack and the product. Since ethanol is primary alcohol so it favours the ${S_N}2$ reaction. If we use tertiary alcohol then the ${S_N}1$ substitution of nucleophile happens when the carbocation intermediate formation takes place.

Complete step-by-step answer:
For the conversion of ethanol to ethyl fluoride it goes with the two-step reaction process;
So, the steps are as follows,
In the first step, the ethanol or ethyl alcohol is reacted with hydrochloric acid in the presence of zinc chloride as a catalyst to form chloroethane and water.
$C{H_3} - C{H_2}OH\, + \,HCl\,\xrightarrow{{ZnC{l_2}}}\,C{H_3} - C{H_2} - Cl\, + \,{H_2}O$

In the second step, the chloroethane is reacted with silver fluoride to form ethyl fluoride as a product.
$C{H_3} - C{H_2} - Cl\, + \,AgF\, \to \,C{H_3} - C{H_2} - F$
There is also another method to convert the ethanol to ethyl alcohol;
So, in the second method instead of using hydrochloric acid and zinc chloride, we are going to use phosphorus pentachloride.

Let’s see the reaction;
For the first step, the ethanol is reacted with phosphorus pentachloride to form chloroethane (ethyl chloride) and the phosphoryl chloride and hydrochloric acid gets removed.
$C{H_3} - C{H_2}OH\, + \,PC{l_5}\,\xrightarrow[{ - POC{l_3}, - HCl}]{}\,C{H_3} - C{H_2} - Cl\,$
Now, in the second step, the chloroethane is reacted with silver fluoride it forms ethyl fluoride.
$C{H_3} - C{H_2} - Cl\, + \,AgF\, \to \,C{H_3} - C{H_2} - F$
So, in both the methods, we can observe that in the first step there is nucleophilic substitution taking place. In which the chloride ion substitutes the hydroxyl ion to form the chloroethane (ethyl chloride).

Note: In the reaction, we can observe that nucleophilic substitution takes place. But what if we use hydrogen fluoride instead of chlorine-containing compounds? The answer is, hydrogen fluoride generally is unreactive towards alcohols. The main reason is because it is less nucleophilic than hydroxyl ion. The nucleophilicity doesn’t only depend upon the lone pair but also depends upon the solvent taken.