Verification of alkenes with concentrated sulphuric acid

Chemicals needed

cyclohexene F Xn   R 11-22    S 9-16-23-33

sulphuric acid 96 %  C    R 35   S (1/2)-26-30-45

Instead of cyclohexene one can also use other alkenes.

Equipment needed

test tube

Test procedure

• Cyclohexene stinks, provide for ventilation! Safety goggles!
• One adds to a test tube 4-5 drops cyclohexen.
• Now one adds approx. 0.5 concentrated sulphuric acid and sways a bit back and forth. Accompanied by a slight generation of heat a unified, turgid phase is formed which quickly becomes yellow and then after 1-2 minutes orange.

Disposal

• After adding plenty of water (caution!) to the reaction mixture it can be discharged into the drainage.

Elucidation

Sulphuric acid combines as a 1,2-addition with the alkene. Cyclohexyl sulphuric acid is formed which dissolves in concentrated sulphuric acid.

Photos

Reaction mixture shortly after the addition of sulphuric acid.

Reaction mixture after about 2 minutes.

Literature

Derived from experiment 19.3 (D), "Sulfuric Acid", p. 266,[5]