Explain why is thionyl chloride method preferred for preparing alkyl chlorides from alcohol ?

Explanation

This is because the other products of the reactions are gases and escape during the reaction. As such pure product can easily be obtained. For example,
` underset("ethanol")(C_2 H_5 OH) + underset("Thioryl chloride")(SOCl_2) to underset("Chloroethane ")(C_2 H_5 Cl)+SO_2 uarr + HCI`
Alkyl chloride can also be obtained from corresponding alcohols by using HCl + Anhyd. `ZnCl_2`
` underset("Ethanol")(C_2 H_5 OH ) + HCl (g) overset("Anhyd"ZnCl_2)to underset("Chloroethane ")(C_2 H_5 Cl) +H_2 O`
This method is not preferred because (a) it is difficult to separate the main product (Chloroethane) from the by product (water) (b) The reaction is very slow especially with `1^@` alcohols.