Chapter 29Alkanols
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Chapter 29Alkanols. 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. 29.1INTRODUCING ALKANOLS

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Chapter 29Alkanols

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Chapter 29 alkanols

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


Chapter 29 alkanols

29.1INTRODUCING 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


Chapter 29 alkanols

29.1 INTRODUCING ALKANOLS


Chapter 29 alkanols

Figure 29.1

The two simplest alkanols.

ETHANOL — THE MOST IMPORTANT ALKANOL

Ethanol is the most important alkanol.

29.1 INTRODUCING ALKANOLS


Chapter 29 alkanols

unreacted ethene and steam recirculated

ethene

a mixture of ethanol and water

REACTOR

(300oC, 65 atm, catalyst)

HEATER

CONDENSER

steam

29.2MANUFACTURE 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


Chapter 29 alkanols

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


Chapter 29 alkanols

Grape Wheat Potato

Apple Barley Rice Maize

Figure 29.4 Some raw materials for fermentation.

29.2 MANUFACTURE OF ETHANOL


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(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


Chapter 29 alkanols

diastase

2 —C6H10O5 — (s) + nH2O(l) nC12H22O11(aq)

starch maltose

[ ]n

maltase

C12H22O11(aq) + H2O(l)2C6H12O6(aq)

maltose waterglucose

zymase

C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g)

glucoseethanol carbon dioxide

To produce beer, use barley (or maize) as the starch source.

29.2 MANUFACTURE OF ETHANOL


Chapter 29 alkanols

(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


Chapter 29 alkanols

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


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short rubber tubing

solution of glucose with yeast

limewater

Figure 29.7 Fermentation of glucose in the laboratory.

29.2 MANUFACTURE OF ETHANOL


Chapter 29 alkanols

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


Chapter 29 alkanols

To prepare ethanol by fermentation.

29.2 MANUFACTURE OF ETHANOL


Chapter 29 alkanols

29.3USES 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


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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


Chapter 29 alkanols

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


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.11 These products contain ethanol as the solvent.

29.3 USES OF ALKANOLS


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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


Chapter 29 alkanols

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


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.14

Ordinary vinegar is colourless. It may be brown due to a colouring matter added.

29.3 USES OF ALKANOLS


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.15 Fruits contain natural esters.

29.3 USES OF ALKANOLS


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Figure 29.16 Cosmetics contain synthetic esters.

29.3 USES OF ALKANOLS


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Figure 29.17 Synthetic esters are often added to food and drinks as flavourings.

29.3 USES OF ALKANOLS


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Figure 29.18

This nail varnish remover contains an ester.

29.3 USES OF ALKANOLS


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29.4PROPERTIES 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


Chapter 29 alkanols

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


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.20

This after-shave lotion contains ethanol.

29.4 PROPERTIES OF ALKANOLS


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.21 Ethanol burns in air.

29.4 PROPERTIES OF ALKANOLS


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[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


Chapter 29 alkanols

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


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.24 Oxidizing ethanol to ethanoic acid by heating under reflux.

29.4 PROPERTIES OF ALKANOLS


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Step 2: Distilling the product mixture

Figure 29.25 Distilling ethanoic acid from the product mixture.

29.4 PROPERTIES OF ALKANOLS


Chapter 29 alkanols

Oxidation of ethanol to ethanoic acid by acidified potassium dichromate solution.

29.4 PROPERTIES OF ALKANOLS


Chapter 29 alkanols

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


Chapter 29 alkanols

29.4 PROPERTIES OF ALKANOLS


Chapter 29 alkanols

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


Chapter 29 alkanols

A29.4

29.4 PROPERTIES OF ALKANOLS


Chapter 29 alkanols

For example,

methyl propanoate

Naming of esters

29.4 PROPERTIES OF ALKANOLS


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A29.5

29.4 PROPERTIES OF ALKANOLS


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29.5ALCOHOL 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


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Figure 29.30

Sugar cane farm.

29.5 ALCOHOL POWER


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Figure 29.31 Making ethanol fuel from sugar cane.

29.5 ALCOHOL POWER


Chapter 29 alkanols

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


Chapter 29 alkanols

 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


Chapter 29 alkanols

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


Chapter 29 alkanols

 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


Chapter 29 alkanols

29.6PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS

Most alkanols are poisonous. The first member of the series, methanol, is very toxic.

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

Figure 29.32

Methanol is toxic!

WHAT HAPPENS AFTER DRINKING ALCOHOL?

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

Figure 29.34

How alcohol goes around the body.

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

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 cm3 of blood.

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

Table 29.3

Typical physiological effects at various blood alcohol concentrations.

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

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


Chapter 29 alkanols

 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


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.35

An alcoholic sleeping in the street.

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

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


Chapter 29 alkanols

Figure 29.37

A scene of a car accident.

29.6 PROBLEMS ASSOCIATED WITH ALCOHOLIC DRINKS


Chapter 29 alkanols

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


Chapter 29 alkanols

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


Chapter 29 alkanols

Some useful guidingquestions 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


Chapter 29 alkanols

(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


Chapter 29 alkanols

(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


Chapter 29 alkanols

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


Chapter 29 alkanols

SUMMARY

1.Alkanols(or alcohols) are a homologous series of organic compounds with the general formula CnH2n+1OH.

2.Ethanol (CH3CH2OH) is the most important alkanol.

3.Ethanol can be manufactured by the catalytic hydration of ethene:

SUMMARY


Chapter 29 alkanols

4.Ethanol in alcoholic drinks is made from starch/sugars by fermentation. The reaction is catalysed by enzymes in yeast.

5.Fermentationis 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

SUMMARY


Chapter 29 alkanols

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.

SUMMARY


Chapter 29 alkanols

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.

SUMMARY


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