4-Methylcyclohexene Synthesis

4-Methylcyclohexene Synthesis

Objective

To develop organic laboratory techniques, to synthesize 4-methylcyclohexene, and to gain experience using Fourier Transform Infrared (FTIR) Spectroscopy to characterize the product of a reaction.

Background

As we have previously noted, alcohols are not good leaving groups. However, the addition of an acid to an alcohol can convert a bad leaving group, hydroxide, to an effective leaving group, water. In the absence of a nucleophile, a protonated alcohol can undergo an elimination reaction. The synthesis of 4-methylcyclohexene can be accomplished in this way.

H2SO4, H3PO4 OH

Δ

+ H2O

eq 1

Although the synthesis of 4-methylcyclohexene is straight forward, isolation of the product is complicated by the formation of many byproducts. Since the boiling point of the product is lower than the boiling point of the starting material and the many byproducts, the 4methylcyclohexene is isolated from the reaction mixture by distillation. Of course, one byproduct of the reaction, water, has a boiling point similar to the boiling point of 4methylcyclohexene. Thus, the distillate will contain both water and 4-methylcyclohexene.

Procedure1

Warning: concentrated sulfuric acid is corrosive and it will cause burns on contact with skin. Wear protective gloves. Synthesis of 4-methylcyclohexene Place 1.5 mL of 4-methylcyclohexanol in a tared 5-mL conical vial. After determining the mass of the 4-methylcyclohexanol in the vial, add 0.40 mL of 85% phosphoric acid and six drops of concentrated sulfuric acid. Mix the liquids and add a spin vane to the vial. Attach a Hickman distillation head equipped with a water-cooled condenser to the vial. Cap the apparatus with a drying tube filled with calcium chloride. Turn on the cooling water and stirrer, and slowly heat the reaction to 160 to 180 °C. Periodically transfer the distillate that collects in the well of the Hickman head to a clean 3Adapted from Pavia, Lampman, Kiz, and Engel,...