WM - Reaction mechanisms Flashcards
1
Q
Elimination reaction
A
a small group of atoms break away from the larger molecule
the small group is not replaced by anything else
2
Q
How do you make an alkene from ethanol
A
Make an alkene by eliminating water from an alcohol in a dehydration reaction
3
Q
Two ways of dehydrating alcohols to form alkenes
A
- 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.
- reflux ethanol with excess concentrated sulfuric acid at 170degreesC.
4
Q
Dehydrating alcohols - using a catalyst experient
A
ceramic wool is soaked in ethanol, pumice stone or Al2O3 is heated, the alkene gas collects in an inverted cylinder in a water bath
5
Q
Dehydrating alcohols - reflux experiment
A
- 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.
6
Q
dehydrating alcohols - reflux reaction
A
DRAW THIS
The conc. sulfuric acid acts as a dehydration agent in the elimination reaction
- the hydroxyl group will bond to the H+ ions from the strong acid.
- the alcohol is protonated, giving the atom a +ve charge - the +vely charged oxygen will pull electrons away from the neighbouring carbon, and water will ‘fall off’
- creates an unstable carbon intermediate - the carbocation loses H+ and the alkene is formed