Mechanism: The formation of ethylene and diethyl ether from ethanol and conc. H₂SO₄ may be explained as follows:

(a) Formation of ethene or ethylene:

Step 1. Due to the presence of two lone pairs of electrons on oxygen, alcohols act as weak bases. Therefore, they react with strong mineral acids (HCl, H₂SO₄ etc.) to form oxonium salts.




Step 2. The presence of a positive charge on the highly electronegative oxygen atom weakens the C—O bond. Thus, the protonated ethanol readily eliminates a molecule of H₂O to form ethyl carbocation.



This step is slow and hence is the rate-determining step of the reaction.

Step 3. The ethyl carbocation formed in step 2 being a reactive chemical species, readily loses a proton to form the ethene molecule.