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

1. Reduce alkene to alkane
2. Prepare reagent “in situ”
3. 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

1. Cyclohexene-4E dicarboxylic acid (solid at RT)
2. Hydrogen generated in situ using NaBH4 and HCl
3. Platinum catalyst from chloroplatinic acid (
   H2PtCl6)
4. Vacuum flask and other lab equipment

Experimental Procedure

1. Set up reaction vessel with serum cap and balloon
2. Prepare hydrogenation reagents and catalyst
3. Conduct reaction while ensuring safety measures regarding hydrogen gas
4. 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

1. Identify oxidized and reduced atoms in the hydrogenation reaction
2. Discuss roles of NaBH4 and its potential substitution with LiAlH4
3. Explain how hydrochloric acid affects carboxylic acid solubility in water