1) Why does this reaction provide predominantly the elimination product whereas
ID: 509595 • Letter: 1
Question
1) Why does this reaction provide predominantly the elimination product whereas the reaction performed with the EXACT same alcohol with an acid (HCl) provides predominantly the substitution product? Be SPECIFIC. Show mechanism to highlight the specific difference.
2) In both distillations the receiving flasks were to be kept on ice, why?
3) Why were two distillations required?
4) What is the rate limiting step for this reaction (be specific)?
Procedure: 1) In a 50mL round bottomed flask add 15mL of 2-methyl-2-butanol, 8mL of 9M sulfuric acid and a magnetic stir bar 2) Set up the fractional distillation apparatus, use low heat on the heating mantle and place the Erlenmeyer receiving flask in an ice water bath. 3) Distill until 900C 4) Take the collected product and dry with potassium carbonate until clear 5) Decant the dried liquid into a dry tared 25mL round bottom flask. Get the weight of the liquid 6) Set up a simple distillation apparatus with the collection flask on ice. Record the boiling point. 7) Perform a bromine test on the collected liquid. Record observations and results. Post Lab Questions: 1) Why does this reaction provide predominantly the elimination product whereas the reaction performed with the EXACT same alcohol with an acid (HCI) provides predominantly the substitution product? Be SPECIFIC. Show mechanism to highlight the specific difference 2) In both distillations the receiving flasks were to be kept on ice, why? 3) Why were two distillations required? 4) What is the rate limiting step for this reaction (be specific)?Explanation / Answer
1) the reaction done above, provides predominantly the elimination product as H2SO4 is a dehydrating agent, the water formed in the reaction is removed and thus the carbocation intermediate does not get stabilized in the reaction ad looses a hydrogen immediately to form the elimination product. Whereas, in case when HCl is used, the carbocation intermediate is stabilized and gets attacked by Cl- in solution to form substitution product.
2) In both receiving flasks are kept dry to avoid reversible reaction and formation of starting materials or likewise.
3) Distillation is perfoformed to remobe the product in both cases from the starting material as it is formed and to avoid product going back to reactants while reacting.
4) Rate limiting step is protonation and formation of carbocation intermediate.
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