which of following alcohols on dehydration with conc H2SO4 coil yeild but -2-ene
Answers
Answer:
Alcohol heated in the presence of conc. H
2
SO
4
results in the formation of ether by removal of one mole of water as:
ROH
→
H
2
SO
4
R−O−R
The reaction goes via formation of a good leaving group H
2
O after acidification of OH group thereby forms the carbocation as:
R−OH
→
H
+
R−
O
+
H
2
→R
+
+H
2
O
→
ROH
R−
R
∣
O
+
H→ROR+H
+
It is limited to symmetrical ethers. Moreover, this is for primary alcohols, which don’t form carbocations very easily. For secondary and tertiary alcohols, carbocations are much easier to form and elimination becomes an even more significant leding to alkene formation.
Among 2 - Pentanol,2 -Methyl - 2 - butanol,1- Pentanol and 2- Propanol only 1- Pentanol is a primary alcohol is suitable for ether formation.
1- Pentanol gives the best yield of dialkyl ether on being heated with a trace of sulphuric acid.