0

Guest

Courses New

why alcoholic.KOH gives elimination reaction but aqueous.KOH gives substitution reaction?

why alcoholic.KOH gives elimination reaction but aqueous.KOH gives substitution reaction?

Grade:12

3 Answers

sumit kumar
askIITians Faculty 13 Points
9 years ago
Aqueous KOH is alkaline in nature i.e. It gives OH-.
These hydroxyde ions ions which act as strong nucleophile and replace halogen atom from alkyl halide.
RCl + KOH (aq.) → ROH.
This results in the formation of alcohol molecules and the reaction is known as nucleophil substitution reaction.
Alcoholic, KOH , specially in ethylene alcohol, produce C2H5O- ions. These ions are stronger base than OH- ion. Thus they abstracts the ß-hydrogen of alkyl halide to produce alkene. This reaction is known as elemenation reaction.
CH3CH2Br + KOH (alc.) → H2C=CH2 + KBr + H2O
Thanks & Regards
Sumit Kumar
askIITians Faculty
Sukhjot
11 Points
6 years ago
In aqueous medium that water KOH will be completely dissociated to give OH negative ions. They being strong nucleophile,will bring about the substitution of alkyl halides to form alcohols. At the same time the OH negative i o n s will be hydrated also they will not be able to abstract a Proton from the beta carbon atom to form alkenes. In other words, in aqueous medium oh negative i o n s will behave as weak base and elimination leading T0 alkenes will not be feasible.In alcoholic KOH, the solution will also contain ethoxide ions in addition to OH negative ions. They being a stronger base then OH negative ions,will abstract a H positive ion from the beta carbon atom giving alkene as the product as a result of dehydrohalogenation.
Yash Chourasiya
askIITians Faculty 256 Points
3 years ago
Hello Student


Aqueous KOH is alkaline in naturei.e.It gives OH-ions.

These hydroxyde ions ions which act as strong nucleophile and replace halogen atom from alkyl halide.
RCl + KOH (aq.) → ROH.

This results in the formation of alcohol molecules and the reaction is known as nucleophil substitution reaction.

Alcoholic, KOH , specially in ethylene alcohol, produce C2H5O-ions. These ions are stronger base than OH-ion. Thus they abstracts the ß-hydrogen of alkyl halide to produce alkene. This reaction is known as elemenation reaction.
CH3CH2Br + KOH (alc.) → H2C=CH2+ KBr + H2O

I hope this Answer will help you.

Think You Can Provide A Better Answer ?

Other Related Questions on Organic Chemistry

View all Questions »

ASK QUESTION

Get your questions answered by the expert for free

Answer and earn gift vouchers

Win Gift vouchers upto Rs 500/-

View courses by askIITians

Design classes One-on-One in your own way with Top IITians/Medical Professionals

Click Here Know More

Complete Self Study Package designed by Industry Leading Experts

Click Here Know More

Live 1-1 coding classes to unleash the Creator in your Child

Click Here Know More

a Complete All-in-One Study package Fully Loaded inside a Tablet!

Click Here Know More