Advices For Studying Organic Chemistry

1) Dehydration to an ether usually takes place at a lower temperature than

dehydration to an alkene.

i) The dehydration to an ether can be aided by distilling the ether as it is formed.

ii) Et 2 O is the predominant product at 140°C; ethane is the major product at 180°C

CH 3 CH 2 OH

H 2 SO 4

180 oC CH^2 CH^2

CH 3 CH 2 OCH 2 CH 3

Ethene

Diethyl ether

H 2 SO 4

140 oC

2. The formation of the ether occurs by an SN2 mechanism with one molecule of the
   alcohol acting as the nucleophile and with another protonated molecule of the
   alcohol acting as the substrate.

A Mechanism for the Reaction

Intermolecular Dehydration of Alcohols to Form an Ether

Step 1

RCH 2 OH

H

++H OSO 3 H RCH 2 O+ H −OSO 3 H

This is an acid-base reaction in which the alcohol accepts a proton from the sulfuric

acid.

Step 2

RCH 2 OH

H

++O

H

+ O

H

RCH 2 O+ H RCH 2 CH 2 R H

Another molecule of alcohol acts as a nucleophile and attacks the protonnated

alcohol in SN2 reaction.

Step 3

RCH 2 O + O

H

O

H

+ O

H

RCH 2 CH 2 R + H CH 2 R H + H

Another acid-base reaction converts the protonated ether to an ether by

transferring a proton to a molecule of water (or to another molecule of alcohol).