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Chapter 29 Alkanols

Chapter 29 Alkanols. 29.1 Introducing alkanols. 29.2 Manufacture of ethanol. 29.3 Uses of alkanols. 29.4 Properties of alkanols. 29.5 Alcohol power. 29.6 Problems associated with alcoholic drinks. 29.7 How much is one unit of alcohol?. CONTENTS OF CHAPTER 29. 29.1 INTRODUCING ALKANOLS

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Chapter 29 Alkanols

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  1. Chapter 29 Alkanols 29.1Introducing alkanols 29.2Manufacture of ethanol 29.3Uses of alkanols 29.4Properties of alkanols 29.5Alcohol power 29.6Problems associated with alcoholic drinks 29.7How much is one unit of alcohol? CONTENTS OF CHAPTER 29

  2. 29.1 INTRODUCING ALKANOLS WHAT ARE ALKANOLS? Alkanols (or alcohols) are a homologous series of organic compounds with the general formula CnH2n+1OH or simply ROH. Their molecules consist of a functional group — the hydroxyl group (—OH) joined to an alkyl group (R—). The two simplest alkanols are methanol and ethanol. 29.1 INTRODUCING ALKANOLS

  3. 29.1 INTRODUCING ALKANOLS

  4. Figure 29.1 The two simplest alkanols. ETHANOL — THE MOST IMPORTANT ALKANOL Ethanol is the most important alkanol. 29.1 INTRODUCING ALKANOLS

  5. unreacted ethene and steam recirculated ethene a mixture of ethanol and water REACTOR (300oC, 65 atm, catalyst) HEATER CONDENSER steam 29.2 MANUFACTURE OF ETHANOL In general, industrial ethanol is formed from ethene, a petroleum product. Ethanol in alcoholic drinks is made from agricultural products by fermentation. ETHANOL FROM CATALYTIC HYDRATION OF ETHENE Figure 29.2 A flow diagram for ethanol manufacture by the catalytic hydration of ethene. 29.2 MANUFACTURE OF ETHANOL

  6. The process produces a mixture of ethanol and water. Ethanol can be separated out by fractional distillation. ETHANOL FROM FERMENTATION OF STARCH OR SUGAR FERMENTATION is the slow breakdown of large organic molecules (e.g. starch) to smaller molecules (e.g. ethanol) by micro-organisms (e.g. yeast). 29.2 MANUFACTURE OF ETHANOL

  7. Grape Wheat Potato Apple Barley Rice Maize Figure 29.4 Some raw materials for fermentation. 29.2 MANUFACTURE OF ETHANOL

  8. (a) (b) Figure 29.5 (a) Yeast is a living plant. It can supply enzymes for fermentation. (b) Yeast under microscope. Note the oval-shaped cells. 29.2 MANUFACTURE OF ETHANOL

  9. diastase 2 —C6H10O5 — (s) + nH2O(l) nC12H22O11(aq) starch maltose [ ]n maltase C12H22O11(aq) + H2O(l) 2C6H12O6(aq) maltose water glucose zymase C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g) glucose ethanol carbon dioxide To produce beer, use barley (or maize) as the starch source. 29.2 MANUFACTURE OF ETHANOL

  10. (a) (b) Figure 29.6 (a) Brewing beer by the traditional method of fermentation. (b) Brewing beer in a local brewery. 29.2 MANUFACTURE OF ETHANOL

  11. The result of fermentation is a dilute (roughly 10%) solution of ethanol in water. The concentration of alcohol cannot be greater than 15%. At concentrations higher than this, the yeast dies and fermentation stops. We can increase the concentration of ethanol in the product by distillation. 29.2 MANUFACTURE OF ETHANOL

  12. short rubber tubing solution of glucose with yeast limewater Figure 29.7 Fermentation of glucose in the laboratory. 29.2 MANUFACTURE OF ETHANOL

  13. A29.1 (a) The mixture in the flask smells of ethanol. (b) The limewater can test for the carbon dioxide given out in the fermentation process. Besides, the arrangement serves as an air-lock to prevent oxidation of ethanol to ethanoic acid by air. 29.2 MANUFACTURE OF ETHANOL

  14. To prepare ethanol by fermentation. 29.2 MANUFACTURE OF ETHANOL

  15. 29.3 USES OF ALKANOLS ALKANOLS AS FUELS Methanol and ethanol burn readily in air with a clean flame. In a few countries, ethanol (in a pure form or mixed with petrol) is used as a motor vehicle fuel. 29.3 USES OF ALKANOLS

  16. Figure 29.8 Ethanol burns with a clean flame in a good supply of air. Figure 29.9 Ethanol is used as a motor vehicle fuel in Brazil. 29.3 USES OF ALKANOLS

  17. Methylated spirit is the most widely used industrial alcohol. Its main use is as a fuel. Figure 29.10 Methylated spirit is the most widely used industrial alcohol. 29.3 USES OF ALKANOLS

  18. ALKANOLS AS SOLVENTS Alkanols are very good solvents. Ethanol is used as a solvent for cosmetics, perfumes and tincture of iodine. Methylated spirit is an industrial solvent for paints and dyes. 29.3 USES OF ALKANOLS

  19. Figure 29.11 These products contain ethanol as the solvent. 29.3 USES OF ALKANOLS

  20. ETHANOL IN ALCOHOLIC DRINKS All alcoholic drinks contain ethanol to a greater or lesser extent. Table 29.2 Starch/sugar source and approximate percentage volume of ethanol in some alcoholic drinks. 29.3 USES OF ALKANOLS

  21. Figure 29.13 Beer and wine are produced by fermentation alone. Brandy has to be obtained by distillation of wine. 29.3 USES OF ALKANOLS

  22. PRODUCTION OF VINEGAR Vinegar is a dilute solution (~6%) of ethanoic acid. To make vinegar, add suitable micro-organisms to a dilute solution of ethanol. Then expose the mixture to air for one or two weeks. The following reaction occurs: [O] CH3CH2OH CH3COOH from air 29.3 USES OF ALKANOLS

  23. Figure 29.14 Ordinary vinegar is colourless. It may be brown due to a colouring matter added. 29.3 USES OF ALKANOLS

  24. PRODUCTION OF ESTERS Esters are usually pleasant-smelling liquid compounds. Each ester has its own characteristic sweet fruity smell. Many synthetic esters are used in cosmetics and artificial flavourings (added to food and drinks). Esters are also good solvents for organic compounds. 29.3 USES OF ALKANOLS

  25. Figure 29.15 Fruits contain natural esters. 29.3 USES OF ALKANOLS

  26. Figure 29.16 Cosmetics contain synthetic esters. 29.3 USES OF ALKANOLS

  27. Figure 29.17 Synthetic esters are often added to food and drinks as flavourings. 29.3 USES OF ALKANOLS

  28. Figure 29.18 This nail varnish remover contains an ester. 29.3 USES OF ALKANOLS

  29. 29.4 PROPERTIES OF ALKANOLS WHAT INFLUENCE PROPERTIES? An alkanol molecule can be represented as: As the size of the alkyl group increases, there is a gradual change in physical properties. 29.4 PROPERTIES OF ALKANOLS

  30. Chemical properties of an alkanol are mainly due to the hydroxyl group. PHYSICAL PROPERTIES OF ALKANOLS Simple alkanols are liquids at room conditions. Melting point, boiling point and density increase steadily as the number of carbon atoms increases. Solubility The lower alkanols (methanol, ethanol, propan-l-ol and propan-2-ol) are miscible with water in all proportions. But as the number of carbon atoms increases, the solubility rapidly decreases. 29.4 PROPERTIES OF ALKANOLS

  31. insoluble hexan-1-ol layer uniform mixture (water + ethanol) water Figure 29.19 Different solubilities of ethanol and hexan-1-ol in water. 29.4 PROPERTIES OF ALKANOLS

  32. Figure 29.20 This after-shave lotion contains ethanol. 29.4 PROPERTIES OF ALKANOLS

  33. CHEMICAL PROPERTIES OF ALKANOLS All alkanols are non-electrolytes. They are neutral (pH value = 7). Most of their properties are due to the —OH functional group. A29.2 No; no. Combustion Alkanols burn readily in air to form carbon dioxide and water, giving a lot of heat. For example, CH3CH2OH(l) + 3O2(g)  2CO2(g) + 3H2O(l) 29.4 PROPERTIES OF ALKANOLS

  34. Figure 29.21 Ethanol burns in air. 29.4 PROPERTIES OF ALKANOLS

  35. [O] [O] e.g. CH3CH2OH CH3CHO CH3COOH ethanol ethanal ethanoic acid Oxidation Alkanols in the form of RCH2OH can be oxidized in two stages: 29.4 PROPERTIES OF ALKANOLS

  36. solution containing Cr3+(aq) ions ethanol acidified potassium dichromate solution Figure 29.23 shows how the oxidation can be performed on a test-tube scale. Figure 29.23 Oxidizing ethanol with acidified potassium dichromate solution. 29.4 PROPERTIES OF ALKANOLS

  37. In the laboratory, the above reaction is better carried out using Quickfit apparatus. Step 1: Heating the reaction mixture under reflux 29.4 PROPERTIES OF ALKANOLS

  38. Figure 29.24 Oxidizing ethanol to ethanoic acid by heating under reflux. 29.4 PROPERTIES OF ALKANOLS

  39. Step 2: Distilling the product mixture Figure 29.25 Distilling ethanoic acid from the product mixture. 29.4 PROPERTIES OF ALKANOLS

  40. Oxidation of ethanol to ethanoic acid by acidified potassium dichromate solution. 29.4 PROPERTIES OF ALKANOLS

  41. A29.3 Ethanol in wine is slowly oxidized in air by the action of micro-organisms. It is changed to ethanoic acid, which is sour. On the other hand, brandy has an ethanol content much higher than wine. Micro-organisms cannot function in such a high ethanol concentration. Esterification ESTERIFICATION is the reversible reaction of an alkanoic acid with an alkanol to form an ester and water. 29.4 PROPERTIES OF ALKANOLS

  42. 29.4 PROPERTIES OF ALKANOLS

  43. Take an example: Figure 29.28 Reaction between ethanoic acid and ethanol (in the presence of a little concentrated sulphuric acid) to form ethyl ethanoate. 29.4 PROPERTIES OF ALKANOLS

  44. A29.4 29.4 PROPERTIES OF ALKANOLS

  45. For example, methyl propanoate Naming of esters 29.4 PROPERTIES OF ALKANOLS

  46. A29.5 29.4 PROPERTIES OF ALKANOLS

  47. 29.5 ALCOHOL POWER ALCOHOL POWER FROM CROPS Crops can be fermented and distilled to produce ethanol. ETHANOL AS A FUEL FOR MOTOR VEHICLES Sugar cane is a fast-growing tropical plant. The sugar it provides can be fermented to make ethanol. Brazil is a country that extensively uses ethanol as a fuel for motor vehicles. Most vehicles use gasohol. Gasohol is a mixture of petrol (78%) and ethanol (22%). 29.5 ALCOHOL POWER

  48. Figure 29.30 Sugar cane farm. 29.5 ALCOHOL POWER

  49. Figure 29.31 Making ethanol fuel from sugar cane. 29.5 ALCOHOL POWER

  50. Activity 6 For the affirmative side:  Ethanol burns to form carbon dioxide and water only, so it is a cleaner fuel than petrol.  Ethanol has a higher octane number (a measure of anti-knock characteristics) than ordinary petrol.  Ethanol can be produced from the fermentation of various crops (e.g. cane sugar), which are renewable energy sources. (But petrol is a non-renewable fuel.) 29.5 ALCOHOL POWER

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