Question

In the following reaction, ether linkage is cleaved by $PC{l_5}$
$R - O - R' + PC{l_5} \to RCl + R'Cl + POC{l_3}$
If ${C_5}{H_{12}}O$ (ether) forms 2-chloropropane as one of the products, then ether
A) 1-ethoxypropane
B) 2-ethoxypropane
C) 1-methoxybutane
D) 2-methoxypropane

Answer 1

Hint: Given the molecular formula of the ether in the question is ${C_5}{H_{12}}O$ and when this ether is cleaved by$PC{l_5}$, we get 2-chloropropane as one of the products. You must know the chemical formula of 2-chloropropane and it is $C{H_3} - CH(Cl) - C{H_3}$. Do the chemical reaction of ${C_5}{H_{12}}O$ with $PC{l_5}$ and examine the products.

Complete step by step solution:
In the question, it is given that ether linkage ($R-O-R’$) is cleaved by $PC{l_5}$ as follows:
$R - O - R' + PC{l_5} \to RCl + R'Cl + POC{l_3}$
Now, the molecular formula of the given ether in the question is ${C_5}{H_{12}}O$
When ${C_5}{H_{12}}O$ is cleaved by $PC{l_5}$, we get 2-chloropropane as one of the products.
As you know, the molecular formula of 2-chloropropane is: $C{H_3} - CH(Cl) - C{H_3}$. Thus, it has three carbon atoms and seven hydrogen atoms. Consequently, we are left with ${C_2}{H_5}$ unit from the ether ${C_5}{H_{12}}O$, after getting 2-chloropropane as one of the products. Since ether group is $R - O - R’$, the required R for the given ether will be ${C_2}{H_5}$ and ${R’}$ will be the hydrocarbon unit from 2-chloropropane. Hence, the chemical name of the ether ${C_5}{H_{12}}O$ will be 2-ethoxypropane.
Now, we can write the required chemical equation between given ether, ${C_5}{H_{12}}O$ and $PC{l_5}$ as follows:

Hence, ${C_5}{H_{12}}O$ (ether) is 2-ethoxypropane.

Thus, option B is the correct answer.

Note: Phosphorus pentachloride, $PC{l_5}$ is used as a chlorinating agent. The reaction of cleavage of ethers refers to the chemical substitution reaction. Due to the higher stability of ethers, the cleavage of the C-O linkage is not done easily. Specific reagents are required for cleavage of ethers and $PC{l_5}$ is that one reagent. It should also be noted from the given chemical reaction in question that dialkyl ethers on reacting with phosphorus pentachloride form alkyl chlorides.