Organic Chemistry Chapter 14

1. Organic ChemistryChapter 14 Science 10 CT03D04 Resource: Brown, Ford, Ryan, IB Chem

2. Organic “Carbon” Chemistry • Chemistry for you, Lawrie Ryan • Chapter 13 • Pages 159-177 • Hydrocarbons, Fossil Fuels, Distillation of Crude Oil, Cracking, Plastics, Polymers • Chapter 14 • Pages 178-185 • Alcohols, Isomers, Ethanol, Alcohol Reactions, Carboxylic Acids

3. 14.1 - Alcohols

4. 14.1 - Alcohols • Ethanol, C2H5OH is what we find in beer, wine, and spirits • Methanol, if ingested, can be toxic and leads to blindness • The addition of an –OH group to a hydrocarbon increases the boiling point and the solubility in water: hydrogen bonds

5. 14.2 - Structural Isomers • Different arrangements of the same atoms make different molecules • Molecular formula shows the atoms that are present in a molecule, but gives no information on how they are arranged. Consider, for example, C4H10 • Each isomer is a distinct compound, having unique physical and chemical properties.

6. Structural Isomers of Alkenes • Isomers (although similar) have different physical and chemical properties • Propan-1-ol , BP 97.5oC • Propan-2-ol, BP 82.5oC

7. 14.3 – Making ethanol (1) • Ethanol can be made through fermentation of simple sugars such as glucose • Ethanol can be used to make alcoholic beverages • Yeast, water, sugar, and flavorings are added in a series of steps. • The ethanol, which is what makes the drink alcoholic, is made when the yeast feeds on sugar in the absence of oxygen (anaerobic respiration) C6H12O6 2 C2H5OH + 2CO2

8. 14.3 – Ethanol from alkene (2) • There are five main reactions that can take place with alkenes (slides to come) and one of them allows for the formation of an alcohol. + H2O This compound is simply an intermediate

9. 14.3 – Which method is best? • We can make ethanol from fermentation of carbohydrates (C6H12O6) or from the addition of water to ethene (C2H4). Which process is best? • Ethanol from ethenerequires crude oil supplies which are in short supply. Cheap for now! • In Brazil where no natural oil supplies exist, they have relied on the manufacturing of ethanol through fermentation to fuel cars along with petrol. Sugar cane is used in this case.

10. 14.4 – Reactions of alcohols • Combustion of alcohols is simple as they are flammable. Alcohols are often added to petrol to make them easier to ignite • Oxidationis common, especially in wine and beer. The taste changes as its left exposed to oxygen in the air. Wine tastes sharp or sour after this process as the ethanol has been converted to ethanoic acid (acids taste sour, think citrus).

11. 14.5 – Carboxylic Acids • We will not be dealing with carboxylic acids in this unit, but materials with this functional group have many uses and applications.

12. 14.6 – Reactions with Ethene • This section is not in your book, but is very important. • As discussed, ethene is much more reactive than ethane due to the presence of the double bond • There are five major reactions for ethene • Formation of alkanes • Formation of alcohols (mentioned earlier) • Formation of halogenalkanes • Formation of dihalogenalkanes • Formation of polymers (discussed in Ch. 13)

13. 14.6 - Alkenes • General formula is CnH2n • Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond • The double bond can be broken resulting in a new bonding site on each carbon atom.

14. Alkene addition with Hydrogen • With the presence of a nickel catalyst at about 150oc, for example • Known as hydrogenation, used in the margarine industry to convert oils containing unsaturated hydrocarbon chains into more stable saturated compounds with higher melting points CH3CHCH2 + H2 ----> CH3CH2CH3 Ni catalyst propene hydrogen gas propane

15. 14.6 - Alkene addition with water • The reaction with water is known as hydration and converts the alkene into an alcohol. • Use of concentrated sulfuric acid as catalyst. • Involves intermediate in which H+ and HSO4- ions are added across the double bond. H2SO4 needed H2O + H2SO4 (conc) H2O CH2CH2 CH3CH2(HSO4)  CH3CH2OH + H2SO4 ethene ethyl hydrogen sulfate ethanol

16. 14.6 - Alkene addition with hydrogen halides • Hydrogen halides (HCl, HBr, etc) react with alkenes to produce hydrogenalkanes. • Take place rapidly in solution at room temperature. • All halogens are able to react in this manner, but the reactivity is in the order HI>HBr>HCl, per the decreasing strength of the hydrogen halide bond. CH2CH2 + HCl ----> CH3CH2Clethenechloroethane

17. 14.6 - Alkene addition with halogens • Halogens react with alkenes to produce dihalgeno compounds. • Occur quickly at room temperature and are accompanied by the loss of color of the reacting compound. CH3CHCH2 + Br2 ----> CH3CHBrCH2Brpropene bromine gas 1,2-dibromopropane

18. 14.6 - Polymerization of alkenes • Since alkenes readily undergo addition reactions by breaking their double bonds, they can be joined together to produce long chains known as polymers. The alkene is known as the monomer. • Example: • Ethene polymerizes to form polyethene, commonly known as polythene. First discovered by accident in 1935, was used extensively as an insulator in the WWII.

19. 14.6 - Repeating Units for Polymers • Poly(ethene): • Insulator, water tanks, piping.. • Poly(propylene): • Manufature clothing, especially thermal wear

20. 14.6 - PVC (poly vinyl chloride) • Poly(chloroethene) (PVC) is widely used in construction materials, packaging, electrical cable sheathing, etc. • Synthesis is associated with toxic byproducts known as dioxins, which are linked to reproductive disorders and a variety of cancers.

21. 14.6 – Distinguishing between Alkanes and Alkenes • Alkenes readily undergo addition reactions, alkanes will not (only in UV light) • Shake separate samples of alkanes and alkenes with bromine water at room temperature, red-brown color of bromine water is decolorized by the alkene (but not the alkane) • Color of a burned flame. Alkenes have high ratio of C:H and leave unburned carbon. Results in a smokier, dirtier flame from alkenes.