WM - Reaction mechanisms

Question 1

Elimination reaction

Answer 1

a small group of atoms break away from the larger molecule

the small group is not replaced by anything else

Question 2

How do you make an alkene from ethanol

Answer 2

Make an alkene by eliminating water from an alcohol in a dehydration reaction

Question 3

Two ways of dehydrating alcohols to form alkenes

Answer 3

1. Ethanol vapour is passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3 - the catalyst provides a large surface area for the reaction.
2. reflux ethanol with excess concentrated sulfuric acid at 170degreesC.

Question 4

Dehydrating alcohols - using a catalyst experient

Answer 4

ceramic wool is soaked in ethanol, pumice stone or Al2O3 is heated, the alkene gas collects in an inverted cylinder in a water bath

Question 5

Dehydrating alcohols - reflux experiment

Answer 5

• heat solution in a flask fitted with a vertical Liebig condenser - this causes the solution to continuously boil/eveaporate and then condense back into the flask, giving it time to react
• heat solution electronically; hot plates, heating mantles.

Question 6

dehydrating alcohols - reflux reaction

Answer 6

DRAW THIS
The conc. sulfuric acid acts as a dehydration agent in the elimination reaction

1. the hydroxyl group will bond to the H+ ions from the strong acid.
   - the alcohol is protonated, giving the atom a +ve charge
2. the +vely charged oxygen will pull electrons away from the neighbouring carbon, and water will ‘fall off’
   - creates an unstable carbon intermediate
3. the carbocation loses H+ and the alkene is formed