Question

Explain dehydrohalogenation reaction of 2-chlorobutane. Write use and environmental effect of CFC.

Hint:

Saytzeff rule favors the more substituted alkene; CFCs are phased out due to ozone depletion.

Answer 1

Dehydrohalogenation of 2-Chlorobutane: Dehydrohalogenation involves the removal of HX from an alkyl halide using a strong base (e.g., alcoholic KOH) to form an alkene. For 2-chlorobutane (\( \chemfig{CH_3-CH(Cl)-CH_2-CH_3} \)): \[ \chemfig{CH_3-CH(Cl)-CH_2-CH_3} \xrightarrow{\text{KOH (alc.), heat}} \chemfig{CH_3-CH=CH-CH_3} + \chemfig{HCl}. \] Major product (Saytzeff rule): 2-butene (more substituted alkene). Minor product: 1-butene (\( \chemfig{CH_2=CH-CH_2-CH_3} \)).
Use of CFC: Chlorofluorocarbons (CFCs) are used as refrigerants, propellants in aerosols, and solvents due to their stability and low toxicity.
Environmental Effect of CFC: CFCs deplete the ozone layer by releasing chlorine radicals upon UV exposure, catalyzing ozone (O\(_3\)) breakdown, leading to increased UV radiation reaching Earth.