Reaction of 2Chloro2Methylbutane with Alcoholic Potassium Hydroxide

1
Reaction of 2-Chloro-2-Methylbutane with
Alcoholic Potassium Hydroxide
2
Outline

• Dehydrohalogenation of 2-Chloro-2-Methylbutane a
  base.
• Purification of the product by distillation.
• Confirmation of the product formation by IR.
• Characterization by 1H NMR Spectrum.

3
Introduction

• Removal of hydrogen halide from an alkyl halide
  in which a hydrogen atom and halogen atoms from
  adjacent carbon in presence of a base to form an
  alkene .

4
Introduction

• Alkyl halide is the starting material
• Hydrogen and halogen are attached in adjacent
  carbon atom.
• Alkene is the product
• Alcoholic KOH is the catalyst.

5
Mechanism

• This reaction follows E2 mechanism.

6
Mechanism

• This is another possibility

7
Possible Products
8
Procedure

• Take 10 mL of 2-Chloro-2-Methylbutane in a 100 mL
  dry RB.
• Add 50 mL of 4M Alcoholic Potassium Hydroxide.
• Set up a Fractional Distillation apparatus with
  Hempel Column.

9
Hempel Column

• Normal condenser packed with thin copper wire
  called Hempel Column.
• Increasing the surface area of the column.

10
Procedure

• Circulate cold water through Hempel Column.
• Heat the reaction mixture using hot plate for 1
  hour.
• Cool it to room temperature.

11
Procedure

• Remove the water hoses and now its ready for
  fractional distillation.
• Keep the receiving RB in an ice bath and collect
  all the distillate at 45 ?C.
• Transfer the product into another dry Erlenmeyer
  Flask or RB.

12
Confirmation

• Product formation can be easily confirmed from
  its IR spectrum.
• Starting material does not have double bond.
• But both products has a double bond.
• You can see a medium band at 1670 1640 cm-1

13
Characterization

• GC Mass spectrum is not the suitable instrument
  to find which product is obtained.
• Why????
• Because both products has the same molecular
  weight.
• Molecular weight is very low so it may merges
  with solvent peak.

14
Characterization

• Proton NMR is the ideal one to characterize the
  product.
• Take few drops of the final product and make
  solution for 1H NMR using CDCl3.

15
Characterization

• Three different peaks in 1H NMR
• Singlet with intensity of 6 protons
• Quartet with intensity of 1 proton
• Doublet with intensity of 3 protons

16
Characterization

• Four different signals in 1H NMR spectrum
• Singlet with intensity of 3 protons
• Singlet with intensity of 2 protons
• Triplet with intensity of 3 protons
• Quartet with intensity of 2 protons

17
Notes

• Please circulate cold water in Hempel column.
• Why????
• You are refluxing the reaction mixture and if you
  do not circulate cold water, then the volatile
  alkyl halide may go off and finally there wont
  be any reaction.

18
Notes

• Use clean and dry RB flask when set up for
  distillation.
• Why???
• Reaction of alkyl halide with water in presence
  of base may yield alcohol.

19
Notes

• Use most of the 2-Chloro-2-Methylbutane (Keep 0.5
  mL for next lab).
• Alcoholic KOH is very aggressive, so please do
  not remove your safety glass.

20
Notes

• Use hot plate instead of Burner.
• Add boil seizer when you do the distillation.
• Work in pair.