1.

Explain dehydration of alcohols.

Answer»

Solution :In the presence of strong dehydrating agents such as conc. `H_(2)SO_(4)` or `H_(3)PO_(4)`, the alcohols dehydrate to form alkenes. The reaction is also carried out in presence of catalyst such as alumina or anhydrous zinc chloride. The alkene is formed as per Saitzev.s rule.
`to` The reaction proceeds by formation of carbocation intermediate. Thus, the relative ease of dehydration of alcohols is `3^(@) gt2^(@) gt1^(@)`

`to ` Ethanol dehydrates to form ethene by heating with conc. `H_(2)SO_(4)` at 443 K TEMPERATURE.
`C_(2)H_(5)OH underset(443K)overset(H_(2)SO_(4))to CH_(2)= CH_(2)H_(2)O`
`to` Secondary and tertiary alcohols are dehydrated under milder CONDITIONS. For EXAMPLE,
`CH_(3)overset(OH)overset(|)CHCH_(3) underset(440K)overset(85% of H_(3)PO_(4))to CH_(3)-CH= CH_(2)+ H_(2)O`
`CH_(3)- underset(CH_(3))underset(|)overset(CH_(3))overset(|)C0OH underset(358K)overset(20% of H_(3)PO_(4))to CH_(3)-overset(CH_(2))overset(||)C-CH_(3)+H_(2)O`


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