Presentation on theme: "1 Chapter 29Alkanols 29.1Introducing alkanols 29.2Manufacture of ethanol 29.3Uses of alkanols 29.4Properties of alkanols 29.5Alcohol power 29.6Problems."— Presentation transcript:
1 Chapter 29Alkanols 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 C n H 2n+1 OH 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.
4 Figure 29.1 The two simplest alkanols. ETHANOL — THE MOST IMPORTANT ALKANOL Ethanol is the most important alkanol. 29.1 INTRODUCING ALKANOLS
5 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 HEATER REACTOR (300 o C, 65 atm, catalyst) CONDENSER a mixture of ethanol and water ethene steam unreacted ethene and steam recirculated Figure 29.2 A flow diagram for ethanol manufacture by the catalytic hydration of ethene.
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 Figure 29.4 Some raw materials for fermentation. 29.2 MANUFACTURE OF ETHANOL Grape Wheat Potato Apple Barley Rice Maize
8 (a)(b) Figure 29.5 (a)Yeast is a living plant. It can supply enzymes for fermentation. 29.2 MANUFACTURE OF ETHANOL (b)Yeast under microscope. Note the oval-shaped cells.
9 29.2 MANUFACTURE OF ETHANOL diastase 2 —C 6 H 10 O 5 — (s) + nH 2 O(l) nC 12 H 22 O 11 (aq) starch maltose maltase C 12 H 22 O 11 (aq) + H 2 O(l)2C 6 H 12 O 6 (aq) maltose waterglucose zymase C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) glucoseethanol carbon dioxide To produce beer, use barley (or maize) as the starch source. [ ] n
10 (a)(b) Figure 29.6 (a)Brewing beer by the traditional method of fermentation. 29.2 MANUFACTURE OF ETHANOL (b)Brewing beer in a local brewery.
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 solution of glucose with yeast limewater short rubber tubing 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 29.2 MANUFACTURE OF ETHANOL To prepare ethanol by fermentation.
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.
16 Figure 29.8 Ethanol burns with a clean flame in a good supply of air. 29.3 USES OF ALKANOLS Figure 29.9 Ethanol is used as a motor vehicle fuel in Brazil.
17 Figure 29.10 Methylated spirit is the most widely used industrial alcohol. Methylated spirit is the most widely used industrial alcohol. Its main use is as a fuel. 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] CH 3 CH 2 OH CH 3 COOH 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
27 29.3 USES OF ALKANOLS Figure 29.17 Synthetic esters are often added to food and drinks as flavourings.
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.
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 water uniform mixture (water + ethanol) 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, CH 3 CH 2 OH(l) + 3O 2 (g) 2CO 2 (g) + 3H 2 O(l) 29.4 PROPERTIES OF ALKANOLS
34 Figure 29.21 Ethanol burns in air. 29.4 PROPERTIES OF ALKANOLS
35 Oxidation Alkanols in the form of RCH 2 OH can be oxidized in two stages: [O] e.g.CH 3 CH 2 OH CH 3 CHO CH 3 COOH ethanol ethanal ethanoic acid 29.4 PROPERTIES OF ALKANOLS
36 Figure 29.23 shows how the oxidation can be performed on a test-tube scale. ethanol acidified potassium dichromate solution solution containing Cr 3+ (aq) ions 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 29.4 PROPERTIES OF ALKANOLS Oxidation of ethanol to ethanoic acid by acidified potassium dichromate solution.
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
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%).
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 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 Activity 6
51 In some places (e.g. Brazil), ethanol is much cheaper than petrol. Ethanol is easy to transport within and between nations. A petrol engine would take 10% ethanol in the petrol without any carburetor adjustments. Even engines specially designed to run on pure ethanol are only slightly more expensive than ordinary engines. 29.5 ALCOHOL POWER
52 For the negative side: The calorific value of ethanol is only 60% that of petrol. Ethanol has different burning characteristics compared with petrol. As a result, car engines need to be modified or specially designed before pure ethanol can be used. The above two points may have serious economic implications. In many places, ethanol is even more expensive than petrol. Ethanol can be reserved for other purposes, e.g. alcoholic drinks, solvents and making chemicals. Poisonous effluents from distilleries may cause pollution to nearby rivers. 29.5 ALCOHOL POWER
53 A little ethanal is produced on burning ethanol. Ethanal is toxic, causing damage to the skin, eyes and lungs and harming vegetation. Huge areas of arable land would have to be cultivated to produce ethanol, at the expense of other agricultural uses. Besides, land disturbance is high and soil erosion is increased. 29.5 ALCOHOL POWER
54 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS Most alkanols are poisonous. The first member of the series, methanol, is very toxic.
55 Figure 29.32 Methanol is toxic! 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS WHAT HAPPENS AFTER DRINKING ALCOHOL?
56 Figure 29.34 How alcohol goes around the body. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
57 Alcohol is removed from the blood mainly by action of the liver. PHYSIOLOGICAL EFFECTS OF ALCOHOL Alcohol can suppress feelings of fear and tension, making people feel relaxed. Excessive drinking would be harmful. Blood alcohol concentration (BAC) Drinking affects the blood alcohol concentration (BAC). BAC is the mass of alcohol (in mg) present in 100 cm 3 of blood. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
58 Table 29.3 Typical physiological effects at various blood alcohol concentrations. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
59 HEALTH PROBLEMS ASSOCIATED WITH DRINKING Excessive drinking over a number of years can cause many health problems: hepatitis (inflammation of the liver) cirrhosis (scarring of the liver) brain damage depression, forgetfulness and other psychiatric and emotional disorders problems with the nervous system high blood pressure alcohol increases the workload of the liver and kills liver cells alcohol can destroy brain cells, and dead brain cells cannot be renewed 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
60 stomach ulcer (alcohol irritates stomach linings) vitamin deficiency muscle disease cancer of the mouth, throat and gullet body weight problem A29.6 Alcohol in a pregnant woman‘s blood can pass into the blood of the unborn baby, causing much harm. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
61 SOCIAL PROBLEMS ASSOCIATED WITH ALCOHOL Social problems with alcoholics Besides having bad health, alcoholics often have family and social problems. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
62 Figure 29.35 An alcoholic sleeping in the street. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
63 Drinking and driving Alcohol is one of the main causes of traffic accidents. Figure 29.36 Drinking and driving don’t mix. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
64 Figure 29.37 A scene of a car accident. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
65 Figure 29.38 One type of breathalyser tube contains potassium dichromate. Its colour changes from orange to green with ethanol. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
66 Activity 7 Students may be divided into 3 groups: One works on the physiological effects of alcoholic drinks; One works on the health problems associated with excessive drinking; One works on the social problems associated with excessive drinking. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
67 Some useful guiding questions for the library search and subsequent discussion: (a)On physiological effect: (1)What is the constituent in wine that causes the physiological effects? (2)How does the body cope with the intake of wine? (3)Which parts of the body or organs are affected by drinking wine? (4)What are the symptoms of excessive drinking? (5)How are the symptoms/effects changed with the amount of wine drunk? (6)Does excessive drinking cause addiction? 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
68 (b)On health problem: (1)Which parts of the body or organs would be damaged by excessive drinking? (2)What are the diseases likely to be induced by excessive drinking? (3)What are the bad effects of excessive drinking on a pregnant woman? 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
69 (c)On social problem: (1)How does excessive drinking affect our society on the aspects of (i)family relationship (ii)law and order (iii)economy? (2)Do you think that the problem is serious in Hong Kong? 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
70 Some additional information: The life expectancy of heavy drinkers is estimated to be 10 – 12 years shorter than the general public. Children of alcoholics are 3 – 4 times more likely to become alcoholics. In the U.S.A., about 15% of the people suffer from desertion, divorce, impoverishment or child displacement due to alcoholism. 29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS
71 SUMMARY 1.Alkanols (or alcohols) are a homologous series of organic compounds with the general formula C n H 2n+1 OH. 2.Ethanol (CH 3 CH 2 OH) is the most important alkanol. 3.Ethanol can be manufactured by the catalytic hydration of ethene: SUMMARY
72 SUMMARY 4.Ethanol in alcoholic drinks is made from starch/sugars by fermentation. The reaction is catalysed by enzymes in yeast. 5.Fermentation is the slow breakdown of large organic molecules (e.g. starch) to smaller molecules (e.g. ethanol) by micro-organisms (e.g. yeast). 6.General uses of lower alkanols: As fuels As solvents Production of esters In addition, ethanol is present in all alcoholic drinks can be oxidized to produce vinegar
73 SUMMARY 7.Chemical properties of an alkanol are mainly due to the — OH functional group. 8.Ethanol can be oxidized first to ethanal and then to ethanoic acid in the laboratory. The oxidizing agent commonly used is acidified potassium dichromate solution. 9.Esterification is the reversible reaction of an alkanoic acid with an alkanol to form an ester and water.
74 SUMMARY 10.Esters have the general formula RCOOR’. Lower esters are liquids with pleasant sweet fruity smell. They are often used in flavourings and solvents. 11.Ethanol is used as a fuel for vehicles in some countries (e.g. Brazil, USA). Ethanol is a cleaner fuel than petrol. It is also a renewable energy source. 12.Excessive drinking causes many health and social problems. 13.Drink driving is very dangerous.