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Shivendra Pandey
Dec 19, 2017

Aqueous KOH gives alcohols because of substitution reaction. While alcoholic KOH gives alkenes due to elimination reaction.

Explanation:

Alkyl chlorides with Aq.KOH :--
When an alkyl chlorides treated with Aq.KOH in solution KOH is almost ionized to give OH— ions which being a strong nucleophile, brings about a substitution reaction and give alcohols.

Ex. #"R"-"Cl" +"K"OH"#(Aq) =#"R"-"OH" +"K"Cl"#

Alkyl chlorides with alco.KOH :--
In contrast,an alcoholic solution of KOH contains alkoxide (RO–) ions which being a much stronger base than OH- ions eliminates a mol ecule of HCl from an alkyl chlorides to form alkenes.

Ex. #"CH"_3 "CH"_2"CH"_2"Cl"+"KOH"#(alc.) = #"CH"_3"CH"="CH"_2# +#"H"Cl"#

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