1. Reactions of Alkenes Section 10.3

2. Introduction Alkenes are unsaturated The double bond in ethene, for example, has one sigma bond and one pi bond (2 nd bond) The pi bond is weaker than the sigma bond and can be broken without the molecule falling apart

3. Types of Reaction Addition reactions occur. There are 5 types: 1. hydrogenation 2. halogenation 3. reaction with hydrogen halides 4. hydration 5. polymerization

4. Hydrogenation Addition of H across C=C bond to produce an alkane A nickel catalyst is used and a temp. of 180° C See examples for you on notes in class Hydrogenation is used to convert vegetable oil that contains unsaturated hydrocarbon chains into more saturated compounds with higher melting points This will make margarine be a solid at room temperature

5. Halogenation Halogens reacting with alkenes Occurs at room temperature Halogen loses color Halogens are added across the double bond so they are on adjacent C atoms Use the examples on class notes

6. Reaction of Symmetrical Alkenes with Hydrogen Halides React with alkenes to produce halogenoalkanes Occurs rapidly in solution at room temperature See the examples from class notes

7. Hydration Alkene is converted to an alcohol Water does not react directly with the alkene Concentrated H 2 SO 4 is used to form an addition product An intermediate product as H + and HSO 4 - are added across the double bond Cold water is added, hydrolysis takes place, and the sulfuric acid is re-formed See the example from class

8. Industrial Process of Synthesizing Ethanol by Hydration of Ethene Pass ethene and steam at high pressure over a catalyst of phosphoric acid at 300° C Phosphoric acid is adsorbed on SiO 2 pellets Equilibrium is achieved and there is a conversion to ethanol of about 5% Unconverted ethene is recycled in the process until all is reacted High degree of purity is achieved Ethanol is an important solvent in other processes

9. Test for Saturation Add the compound to bromine water Alkane produces no reaction (saturated) Alkene reacts and the bromine water discolors (unsaturated)

10. Polymerization Alkenes can join together in addition reactions to form long chains called polymers Beginning alkene is called a monomer Chemical nature of the monomer determines the properties of the polymer Typically are thousands of molecules long Major product of the organic chemical industry Most common and useful plastics are polymers of alkenes

11. Continued Remember the video from class (You can access MIT open course ware, solid state chemistry lectures with Donald Sadoway, lectures 27, 28 and 29 deal with organic) Poly(chloroethene) is PVC Poly (tetrafluoroethene) is PTFE, known as Teflon See the examples from class notes.

14. Source: Oil and Gas Journal http://www.ogj.com/articles/print/vol-110/issue-07/special-report-ethylene-report/global-ethylene-capacity.html

15. Ethene Products Polystyrene PVC polyethene