Want to know more… (Further Reading) ‏

1. Credits What will you learn Radio buttons (if any)/Drop down (if any)‏ Play/pause Restart Lets Learn! Interactivity options Sliders(IO1)‏ / Input Boxes(IO2)‏ /Drop down(IO3)‏ (if any)‏ Definitions Process Diagram‏ Animation Area Facts Test your understanding (questionnaire)‏ Lets Sum up (summary)‏ Want to know more… (Further Reading)‏ Output result of interactivity (if any)‏ Instructions/ Working area

2. Catalytic Hydrogenation It is the reduction of compounds by hydrogen adsorbed onto the surface of metals‏. This Learning Object shows the mechanism of catalytic hydrogenation of ethene (C2H4) using platinum catalyst. Author: Sukumar Honkote Department of Chemistry, IIT Bombay

3. Learning objectives: • After interacting with this learning object, the user will be able to: • explain the process of catalytic hydrogenation of ethene

4. Definitions of the components: 1 1) Catalyst: a substance that causes or accelerates a chemical reaction without itself being affected. 2) Adsorption: the binding of molecules or particles to a surface. 3) Adsorbate: An adsorbed substance. 4) Adsorbent: An substance on which chemicals adsorb. 5) Physisorption: is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption. 6) Chemisorption: To take up and chemically bind (a substance) onto the surface of the adsorbent. 2 3 4 5

5. Process: 1 Hydrogenation is a reaction where a given compound reacts with hydrogen. In this process, metals like nickel or platinum are used as adsorbents. Hydrogen molecule gets chemically adsorbed (binds) onto the metal surface. The bond between the two hydrogen atoms is broken and a bond between the metal surface and hydrogen atom forms. A compound (in this case ethene) comes near the hydrogen atoms adsorbed to the metal. The bond between metal surface and hydrogen atom is broken and a bond between ethene and hydrogen is created. Thus ethene reacts with hydrogen to form ethane. 2 3 4 5

6. Table/Facts: • The adjacent diagram shows the ease of hydrogenation reaction with the compounds given and their products.

7. Diagrams: 1 This is Ethene molecule. All the C-C-H angles are 120°. All the C and the 4 H are in the same plane. There is a double bond between the C atoms. 2 3 Lets call this figure H-Ethene. This is when ethene is rotated nearly parallel to the horizontal plane. 4 5

8. Diagrams 1 This is Ethane molecule. All the bond angles are 109°. When viewed along the C-C bond, the HCH bonds appear to be at 120° with each other. 2 3 4 5

9. Diagrams 1 This is Hydrogen molecule. This is called the H Atom. It is connected to the catalyst (as shown in the animation figure). 2 3 This is the surface of the catalyst. 4 Lets call figures like this in pair of H atoms attached to the surface as Adsorbed H Atoms. 5

10. Master Layout 1 2 Ethene molecule Ethane molecule Hydrogen molecule Ethene molecule rotated to be parallel to catalyst surface 3 4 Surface of the catalyst Hydrogen atom 5

11. For the animator: 1) All molecules are 3D. 2) The molecules should be randomly moving and rotating. 3) The molecules can also leave the animation area. 4) The animation should have 2-3 molecules of ethene reacting with the adsorbed H Atoms at different points on the catalyst surface. In this IDD the animation has been shown for only 1 molecule at a time

12. Step 1: Reaction 1 Hydrogenation of Ethene 2 Ethene Ethane 3 4 5

13. Step 2: Adsorption of Hydrogen 1 2 3 4 5

14. Step 3: Formation and breaking of bonds 1 2 3 4 5

15. Step 4: 1 1 2 2 3 4 5

16. Step 5.1: Formation and breaking of bonds 1 2 3 4 5

17. Step 5.2: Formation and breaking of bonds 1 2 3 4 5

18. Step 5.3: Formation and breaking of bonds 1 2 3 4 5

19. Step 5.4: Formation of ethane 1 2 3 4 5

20. Summary: 1 • Hydrogenation is the chemical reaction that results from the • addition of hydrogen (H2). • Hydrogenation is a process highly dependent on temperature and • pressure. • Catalysts are required for the reaction to be useful; non-catalytic hydrogenation takes place only at very high temperatures. • Process: • Hydrogen molecule gets chemically adsorbed (binds) onto • the metal surface. The bond between the two hydrogen • atoms is broken and a bond between the metal surface and • hydrogen atom forms. • A compound (in this case ethene) comes near the hydrogen • atoms adsorbed to the metal. The bond between metal • surface and hydrogen atom is broken and a bond between • ethene and hydrogen is created. • Thus ethene reacts with hydrogen to form ethane. • On hydrogenating an alkyne with Lindlar’s catalyst (Pt + BaSO4) • we get only a cisalkene. • Vanaspatighee is obtained by hydrogenating vegetable oil with • nickel catalyst. 2 3 4 5

21. Questionnaire 1 1. Hydrogenation is an example of __________ a) Physisorption b) Chemisorption ‏ 2. Which of these compounds cannot get hydrogenated? a) Hexene b) Cyclohexane c) Cyclopentene d) 1- Pentyne 3. Which is the correct parameter to measure the amount of catalyst for a hydrogenation reaction? a. Surface area/ gram b. Moles 4. Which of these compounds is easier to hydrogenate? a. aromatic compound b. ketone c. aldehyde 2 3 4 5

22. Questionnaire (contd..) 1 5. What is the major product on hydrogenating the following product using Lindlar’s catalyst (Pt + BaSO4) ? (the answer is a) a) b) c) d) e) 2 3 4 5