Catalytic Hydrogenation of an Alkene Study Guide
Hydrogenation Overview
- Process used to convert alkenes to alkanes
- Important in industries:
- Petroleum: Reduces low MW alkenes to alkanes
- Food: Converts unsaturated oils to solid fats (e.g., margarine)
Objectives of the Experiment
- Reduce alkene to alkane
- Prepare reagent “in situ”
- Carry out reaction under atmospheric pressure
Reaction Mechanism
- Potential energy vs reaction progress:
- Exothermic and favors formation of alkene
- High activation energy, slow reaction
- Catalyst (e.g., Pt, Pd, Ni) reduces activation energy while maintaining thermodynamics
Materials Required
- Cyclohexene-4E dicarboxylic acid (solid at RT)
- Hydrogen generated in situ using NaBH4 and HCl
- Platinum catalyst from chloroplatinic acid (
H2PtCl6) - Vacuum flask and other lab equipment
Experimental Procedure
- Set up reaction vessel with serum cap and balloon
- Prepare hydrogenation reagents and catalyst
- Conduct reaction while ensuring safety measures regarding hydrogen gas
- Perform filtration and extraction of alkane product
Post-reaction Treatment
- Extract with diethyl ether and wash with NaCl
- Dry with Na2SO4
- Remove ether and recrystallize alkane product from water
Safety Considerations
- Keep hydrogen away from flames
- Platinum catalysts can combust spontaneously in air
- Use gloves and proper disposal for waste materials
Calculations and Analysis
- Yield calculated as % yield = (actual/theoretical) x 100%
- Tests for unsaturation:
- Bromine and potassium permanganate tests
- Record melting point and conduct qualitative tests (Br2, KMnO4)
Discussion Questions
- Identify oxidized and reduced atoms in the hydrogenation reaction
- Discuss roles of NaBH4 and its potential substitution with LiAlH4
- Explain how hydrochloric acid affects carboxylic acid solubility in water