Synthesis of 4-Methylcyclohexene

Abstract:

In this lab, 4-methylcyclohexene was synthesize from 4-methylcyclohexanol with phosphoric acids via the E1 mechanism. With a fair percent yield of 52.16%, success of our reaction was verified by IR spectroscopy analysis and unsaturation tests.

Our IR showed C-H vinyl stretches near 3050 cm-1, aliphatic C-H stretches near 2900 cm-1, C=C stretches near 1650 cm-1, C-H bending vibrations near 1455 cm-1, and no broad absorption peak at 3200-3700 cm-1, where the OH functional group of the original 4-methylcyclohexanol should show itself.

Success of the alcohol dehydration was further verified with unsaturation tests. When the first ten Br2 drops were added, the product remained clear because the double bond reacted with the red bromine solution to decolorize it. Furthermore, when the first thirty-five drops of KMnO4 were added, we observed brown precipitate formation because the double bond reacted with purple potassium permanganate to discharge its color and produce the brown precipitate.

Introduction:

Nucleophilic elimination via the E1 mechanism is a first order reaction with a unimolecular rate determining step. It is favored by tertiary alkyl groups and big, bulky bases because the bimolecular transition state of E2 cannot form when too sterically hindered. Both elimination mechanisms were proposed by British scientist Sir Christopher Ingold in the 1920’s and 1930’s, when he discovered the difference in reaction kinetics between the reaction of primary and tertiary alkyl-halides.

Reaction Mechanism:

General:

Mechanism:

Results & discussion:

Mass Data:

4-methylcyclohexanol: 4-methylcyclohexene:

1.233 g 0.542 g

0.011 mol 0.006 mol

Theoretical Yield: 1.039 g 4-methylcyclohexene

Actual Yield: 0.542 g 4-methylcyclohexene

1.233 g 4-methylcyclohexanol was reacted with 0.4 mL of 85% phosphoric acide and 6 drops of sulfuric acid to produce 0.542 g 4-methylcyclohexene. This was only a 52.16%...