Explain the preparation of ethers by dehydration of alcohols and its mechanism with a suitable example.

(N/A) The preparation of ethers by the dehydration of alcohols depends on the reaction conditions,specifically temperature and the nature of the alcohol.
$1.$ Dehydration of $1^{\circ}$ alcohols: Alcohols are heated in the presence of protic acids like $H_2SO_4$ or $H_3PO_4$ to form ethers.
$2.$ Example: Dehydration of ethanol $(CH_3CH_2OH)$:
- At $443 \ K$ in the presence of concentrated $H_2SO_4$,ethanol undergoes $\beta$-elimination to form ethene $(CH_2=CH_2)$ as the major product.
- At $413 \ K$ in the presence of concentrated $H_2SO_4$,ethanol undergoes bimolecular nucleophilic substitution $(S_N2)$ to form ethoxyethane $(C_2H_5-O-C_2H_5)$ as the major product.
Mechanism for ether formation $(S_N2)$:
Step $1$: Protonation of alcohol: $CH_3CH_2OH + H^+ \rightarrow CH_3CH_2OH_2^+$
Step $2$: Nucleophilic attack by another molecule of alcohol: $CH_3CH_2OH + CH_3CH_2OH_2^+ \rightarrow CH_3CH_2-O^+(H)-CH_2CH_3 + H_2O$
Step $3$: Deprotonation: $CH_3CH_2-O^+(H)-CH_2CH_3 \rightarrow CH_3CH_2-O-CH_2CH_3 + H^+$