Chapter 46 Important organic substances 46.1 Acetylsalicylic acid (aspirin) 46.2 Soaps and soapless detergents 46.3 Nylon and polyesters Key terms Progress check Summary Concept map P. 1 / 69
46.1 Acetylsalicylic acid (Aspirin) Carbon compounds are found around us. Some of them are found naturally. Some of them are artificially made to be used for various purposes. Examples of important organic substances: acetylsalicylic acid soaps and soapless detergents nylon and polyesters P. 2 / 69
Structure of acetylsalicylic acid Acetylsalicylic acid: commonly known as aspirin. Figure 46.1 Structural formula of acetylsalicylic acid. 46.1 Acetylsalicylic acid (Aspirin) P. 3 / 69
Functional groups of aspirin include benzene ring, carboxyl group and ester group. carboxyl group benzene ring ester group Figure 46.2 Different functional groups of an acetylsalicylic acid molecule. 46.1 Acetylsalicylic acid (Aspirin) P. 4 / 69
Medical applications of acetylsalicylic acid Aspirin is a common over-the-counter drug. Used to relieve pains (as an analgesic) such as headache and toothache and reduce fever. Anti-inflammatory drug used in the treatment of arthritis. Has an anti-platelet ( blood-thinning ) effect. 46.1 Acetylsalicylic acid (Aspirin) P. 5 / 69
Low dose of aspirin prevents heart attack. Side-effects: stomach upset and ulcer, and increased bleeding. Figure 46.3 Aspirin is the active ingredient in some analgesics. Activity 46.1 Think about Experiment 46.1 P. 6 / 69 STSE connections 46.1 Example 46.1 Class practice 46.1 46.1 Acetylsalicylic acid (Aspirin) Experiment 46.1
46.2 Soaps and soapless detergents Defining detergents In the broadest sense, a detergent is any substance which has cleansing power. Key point A detergent is a substance which improves the cleansing properties of water. Water is good at dissolving many things. It cannot dissolve oil or grease. This is where detergents can help in cleansing. P. 7 / 69
toothpaste soap liquid body wash face cleansing foam shampoo washing powder dish-washing liquid car wash Figure 46.4 Detergents for different cleansing purposes. 46.2 Soaps and soapless detergents P. 8 / 69
Types of detergents Two types of detergents: Soapy detergents (or soaps) made from fats or oils like butter or palm oil Soapless detergents (or synthetic detergents) made from hydrocarbons derived from petroleum 46.2 Soaps and soapless detergents P. 9 / 69
Figure 46.5 Soapy detergents are made from fats or oils. These include bath soap, laundry soap and liquid soap. Figure 46.6 Soapless detergents include washing powder, dishwashing liquid, shampoo, etc. They are called soapless because they contain no soap. Activity 46.2 46.2 Soaps and soapless detergents P. 10 / 69
Structures of soaps and soapless detergents General structure of detergent particles Detergents are usually sodium (or potassium) salts of long-chain organic acids. hydrophobic tail (water-insoluble part) hydrophilic head (water-soluble part) Figure 46.7 General structure of a detergent anion. 46.2 Soaps and soapless detergents P. 11 / 69
The detergent anion consists of two parts: An ionic group (the head ) hydrophilic (water-loving) soluble in water, but not in oil A hydrocarbon chain (the tail ) hydrophobic (water-hating) soluble in oil, but not in water Detergent anions are therefore attracted to both water and oil molecules. 46.2 Soaps and soapless detergents P. 12 / 69
Two important properties of detergents: wetting property emulsifying property Structure of soap particles Soaps are sodium (or potassium) salts of longchain carboxylic acids. The ionic head of soaps is always a carboxylate group ( COO ). 46.2 Soaps and soapless detergents P. 13 / 69
Common soap is sodium stearate: CH 3 (CH 2 ) 16 COO Na + hydrocarbon tail ionic head carbon atom oxygen atom sodium ion hydrogen atom 46.2 Soaps and soapless detergents P. 14 / 69
Making soaps saponification Soaps are made by saponification of animal fats and vegetable oils. Fats and oils are triesters. They are hydrolysed by boiling with sodium hydroxide solution (i.e. alkaline hydrolysis). Figure 46.8 The castor oil from the seeds of castor plant can be used to make soaps. 46.2 Soaps and soapless detergents P. 15 / 69
Example Sodium stearate can be prepared by saponification of glyceryl triestearate. glyceryl tristearate (an animal fat) sodium hydroxide glycerol sodium stearate (a soap) 46.2 Soaps and soapless detergents P. 16 / 69
General equation: heat triester (fat or oil) alkali glycerol soap where R 1, R 2 and R 3 are hydrocarbon chains of triesters and they may be the same or different. 46.2 Soaps and soapless detergents P. 17 / 69
Soap can be prepared in the school laboratory. To prepare soap from castor oil (an example of vegetable oil), follow the main steps below: 1. Boil a mixture of castor oil and concentrated sodium hydroxide solution gently with stirring. 2. When saponification is complete, add saturated sodium chloride solution to the hot mixture with stirring. This is to separate the soap from water. 46.2 Soaps and soapless detergents P. 18 / 69
3. A white, creamy solid (i.e. soap) forms and it floats on the solution surface. Collect it by filtration later. Learning tip The process of separating soap from solution by reducing its solubility in water is known as salting-out. Key point Soapy detergents (or soaps) are made from fats or oils. They are sodium (or potassium) salts of long-chain carboxylic acids. 46.2 Soaps and soapless detergents P. 19 / 69
castor oil and NaOH(aq) magnetic stirrerhotplate (a) beaker magnetic stirring bar soap forms but much has been dissolved in water (b) saturated sodium chloride solution magnetic stirring bar a white, creamy solid floats on the solution surface (c) Figure 46.9 Laboratory preparation of soap from castor oil. 46.2 Soaps and soapless detergents P. 20 / 69
Structure of soapless detergent particles Two common soapless detergents are: Sodium alkylbenzenesulphonate hydrocarbon tail ionic head carbon atom oxygen atom sodium ion hydrogen atom 46.2 Soaps and soapless detergents sulphur atom P. 21 / 69
Sodium alkylsulphate CH 3 (CH 2 ) 11 O SO 3 Na + hydrocarbon tail ionic head carbon atom oxygen atom sodium ion hydrogen atom sulphur atom Concept check 46.2 Soaps and soapless detergents P. 22 / 69
Ionic heads of common soapless detergent anions are usually a sulphonate group ( SO 3 ) or a sulphate group ( OSO 3 ). Making soapless detergents Soapless detergents are made from hydrocarbons derived from petroleum. Hydrocarbons may be treated with concentrated sulphuric acid, followed by sodium hydroxide solution. 46.2 Soaps and soapless detergents P. 23 / 69
Example conc. H 2 SO 4 NaOH(aq) from petroleum industry Key point Soapless detergents are made from hydrocarbons derived from petroleum. They are usually sodium salts of long-chain alkylbenzenesulphonate or alkylsulphate. Example 46.2 Class practice 46.2 46.2 Soaps and soapless detergents P. 24 / 69
Properties of detergents Wetting property of detergents Water has a high surface tension. A little water tends to form drops on a surface, rather than spreading out to wet the surface. 46.2 Soaps and soapless detergents Figure 46.10 The detergent particles increase the wetting power of water by reducing its surface tension. P. 25 / 69
Detergent reduces the surface tension of water. It loosens the skin of the water surface. Water spreads over the surface and wets it more easily. A detergent acts as a wetting agent. Because of its ability to lower the surface tension of a liquid, a detergent is sometimes known as a surfactant. 46.2 Soaps and soapless detergents P. 26 / 69
water molecule a water drop a drop of detergent solution detergent particle a piece of cloth water molecule a piece of cloth (a) (b) Figure 46.11 (a) Intermolecular forces between water molecules hold them into a drop (Note: only the water molecules at the water surface are shown and denotes the intermolecular forces). (b) A detergent increases the wetting power of water. Tap water does not wet this piece of cloth easily, but a detergent does. Activity 46.3 46.2 Soaps and soapless detergents P. 27 / 69
Emulsifying property of detergents The oil breaks up into droplets and the droplets suspend in water. This forms an unstable emulsion. On standing, the oil droplets rapidly join together and grow larger to form a separate oily layer again. Animation (Detergent as an emulsifying agent in an oil-water mixture) 46.2 Soaps and soapless detergents P. 28 / 69
shake allow it to stand oil oil water emulsion tiny oil droplets water Figure 46.12 Shaking a mixture of water and oil and allowing it to stand. 46.2 Soaps and soapless detergents P. 29 / 69
When we add a little detergent to the oil-water mixture and shake it, the emulsion remains as a single layer even on standing. This illustrates that a detergent acts as an emulsifying agent. Learning tip An emulsion is a mixture of two or more liquids. These liquids are mixed together in such a way that one forms tiny droplets dispersed throughout the other. 46.2 Soaps and soapless detergents P. 30 / 69
detergent shake allow it to stand foam foam oil water emulsion tiny oil droplets emulsion tiny oil droplets Figure 46.13 Shaking a mixture of water and oil (with a little detergent added) and allowing it to stand. 46.2 Soaps and soapless detergents P. 31 / 69
When we add a detergent to an oil-water mixture, the heads of the detergent anions dissolve in the water and the tails dissolve in the oil. When we shake the mixture, oil droplets form. Each oil droplet is negatively charged, as detergent anions spread over the surface of the droplet. The negatively charged oil droplets repel each other, and cannot join together. 46.2 Soaps and soapless detergents P. 32 / 69
detergent anion hydrophobic hydrocarbon tail in oil hydrophilic ionic head in water oil water oil droplet repulsion between oil droplets (a) (b) (c) Figure 46.14 How detergent anions arrange themselves in an oil-water mixture: (a) before the mixture is shaken, (b) after shaking, (c) negatively charged oil droplets repel each other. 46.2 Soaps and soapless detergents P. 33 / 69
Oil droplets remain dispersed throughout the water. Oil-water emulsion is stabilized by the detergent. foam oil water oil/water emulsion stabilized by detergent (a) Figure 46.15 (a) Oil and water do not mix. (b) An oil-water emulsion is stabilized by a detergent solution. (b) Experiment 46.2 Experiment 46.2 46.2 Soaps and soapless detergents P. 34 / 69
Cleansing action of soaps and soapless detergents Since grease is insoluble in water, cleansing with water alone is not effective. When a detergent is added, the surface tension of water is reduced. The object to be cleaned can be wetted more thoroughly. Hydrophobic tails of detergent anions dissolve in grease, with the hydrophilic heads in water. Animation (Cleansing action of soaps and soapless detergents) 46.2 Soaps and soapless detergents P. 35 / 69
The surrounding water molecules attract the ionic heads. The grease is lifted off the surface to be cleansed. By stirring, the grease (carrying the dirt) is broken down into tiny droplets (negatively charged). These droplets are dispersed throughout water to form an emulsion. The lather produced when mixing detergent and water also helps to suspend grease and dirt particles. 46.2 Soaps and soapless detergents Think about P. 36 / 69
A detergent enables water to wet the object thoroughly. detergent anion water The hydrophobic tails of detergent anions dissolve in grease. Water molecules attract the hydrophilic heads of detergent anions, lifting up the grease from the surface. grease dirt particles surface (a) (b) (c) By stirring, the grease forms tiny droplets, forming an emulsion. detergent (d) tiny grease droplets (negatively charged) (e) lather Figure 46.16 How detergent removes grease and dirt from a surface. 46.2 Soaps and soapless detergents P. 37 / 69
Key point Detergents are cleansing agents. They work by reducing the surface tension of water, enabling it to wet things more effectively, and by emulsifying grease. 46.2 Soaps and soapless detergents P. 38 / 69
Effect of length of hydrocarbon tail on properties of a detergent The length of the hydrocarbon tail has important effects on properties of a detergent. Too short: the detergent will dissolve well in water but not in oil. Too long: the detergent will dissolve well in oil, but not in water. In general, detergent particles with 12 to 20 carbon atoms in their hydrocarbon chains have good detergent properties. Experiment 46.4 Class practice 46.3 Experiment 46.3 Experiment 46.3 Experiment 46.4 Activity 46.4 46.2 Soaps and soapless detergents P. 39 / 69
46.3 Nylon and polyesters Nylon Nylon: the first synthetic substitute for natural fibres (e.g. wool and silk). It is a polymer and is a kind of polyamide containing many amide linkage, called amide linkages. R, R hydrocarbon chains P. 40 / 69
Formation of nylon There are many different types of nylons. Nylon 6.6 is the most popular among all. It can be produced from two monomers hexanedioic acid and hexane-1,6-diamine. and hexanedioic acid (a dioic acid) hexane-1,6-diamine (a diamine) 46.3 Nylon and polyesters P. 41 / 69
When these two monomer molecules react, water is eliminated and an amide forms. hexanedioic acid hexanediamine amide This is an example of condensation reaction. Two or more molecules join together to form a larger molecule with the elimination of small molecules (such as H 2 O or HCl). 46.3 Nylon and polyesters P. 42 / 69
The amide molecule formed still has unreacted functional groups at both ends. There is a carboxyl group at one end of the molecule and an amine group at the other end. Repeated condensations thus lead to the formation of a long polymer chain. from dioic acid from diamine from dioic acid from diamine 46.3 Nylon and polyesters P. 43 / 69
Condensation polymerization: reaction in which monomers molecules join together repeatedly to form polymer molecules with the elimination of small molecules (such as HCl and H 2 O). The polymer formed from this kind of polymerization is called condensation polymer. The polymer and the repeating unit of nylon 6.6: Polymer: Repeating unit: 46.3 Nylon and polyesters Think about P. 44 / 69
If hexanedioyl dichloride instead of hexanedioic acid is used, hydrogen chloride is eliminated. The structural formula of hexanedioyl dichloride is: hexanedioyl dichloride (a dioyl dichloride) 46.3 Nylon and polyesters P. 45 / 69
The formation of nylon can be represented by the general equation: dioic acid diamine nylon (polymer) Key point Condensation polymerization is a reaction in which monomer molecules join together to form polymer molecules with the elimination of small molecules (such as H 2 O or HCl). 46.3 Nylon and polyesters P. 46 / 69
Properties and uses of nylon Tough, very strong and elastic Water-proof and oil-proof Has a high tensile strength and its surface is usually very smooth Easy to wash and can be dyed in a wide range of colours Nylon was synthesized as a substitute for silk during World War II. 46.3 Nylon and polyesters P. 47 / 69
Used to make parachutes, ropes and shoelaces for army boots at that time Today, nylon is still used for making ropes, fishing lines and nets. Also used as tennis racket strings Figure 46.17 Common uses of nylon in daily life. Class practice 46.4 Experiment 46.5 46.3 Nylon and polyesters P. 48 / 69
Polyesters Polyester is another synthetic fibre, which is a polymer containing many called ester linkages. linkages, ester linkage R and R are hydrocarbon chains n 46.3 Nylon and polyesters P. 49 / 69
Formation of polyesters Poly(ethylene terephthalate) or PET is kind of polyester, can be produced from two monomers. terephthalic acid (systematic name: benzene- 1,4-dicarboxylic acid) and ethane-1,2-diol. terephthalic acid (a dioic acid) ethane-1,2-diol (a diol) Learning tip Poly(ethylene terephthalate) is also commercially known as Terylene or Dacron. 46.3 Nylon and polyesters P. 50 / 69
When the two monomer molecules react, water is eliminated and an ester forms. terephthalic acid (a dioic acid) ethane-1,2-diol (a diol) ester The ester molecule formed still has unreacted functional groups at both ends. There is a carboxyl group at one end of the molecule and a hydroxyl group at the other end. 46.3 Nylon and polyesters P. 51 / 69
Repeated condensations thus lead to the formation of a long polymer chain. The structure of the chain is shown below: from dioic acid from diol from dioic acid from diol The polymer formed here is poly(ethylene terephthalate). 46.3 Nylon and polyesters P. 52 / 69
As it is produced by condensation polymerization, it is a condensation polymer. The polymer and the repeating unit of PET: Polymer: Repeating unit: The formation of PET can be represented by the following equation: 46.3 Nylon and polyesters P. 53 / 69 PET (polymer)
Properties and uses of polyesters Strong, tough and smooth Resistant to water and chemicals Suitable for making fibres and clothes Have low density, they are used for making lightweight sails and bottles for water and drinks 46.3 Nylon and polyesters P. 54 / 69
Figure 46.18 Some clothes are made of 100% polyester. Figure 46.19 PET can be used to make sails. Class practice 46.5 46.3 Nylon and polyesters P. 55 / 69
Aspirin Structure Uses relieves pain reduces fever and inflammation prevents heart attack Soaps Soapless detergents e.g. sodium stearate CH 3 (CH 2 ) 16 COO Na + e.g. sodium alkylbenzenesulphonate improves the cleansing properties of water e.g. sodium alkylsulphate CH 3 (CH 2 ) 11 O SO 3 Na + Table 46.1 Structures and uses of aspirin, soaps, soapless detergents, nylon and polyesters. 46.3 Nylon and polyesters P. 56 / 69
Nylon (e.g. nylon 6.6) Polyester (e.g. PET) Structure Uses making fibres for clothing making ropes making fishing lines and nets making tennis racket strings making fibres making clothes making food containers making bottles for water and drinks Table 46.1 Structures and uses of aspirin, soaps, soapless detergents, nylon and polyesters. Activity 46.5 46.3 Nylon and polyesters P. 57 / 69
Key terms 1. acetylsalicylic acid 乙酰水楊酸 2. amide linkage 酰胺鍵合 3. aspirin 阿士匹靈 4. carboxylate group 羧酸基團 5. condensation polymer 縮合聚合物 6. condensation polymerization 縮合聚合作用 7. condensation reaction 縮合反應 8. detergent 清潔劑 9. emulsifying agent 乳化劑 10. emulsifying property 乳化性質 P. 58 / 69
11. emulsion 乳狀物 12. ester linkage 酯鍵合 13. hydrophilic 親水性 14. hydrophobic 疏水性 15. lather 泡沫 16. nylon 尼龍 17. polyamide 聚酰胺 18. polyester 聚酯 19. poly(ethylene terephthalate)/pet 聚對苯二甲酸乙二酯 20. saponification 皂化作用 Key terms P. 59 / 69
21. soapless detergent/synthetic detergent 非皂性清潔劑 / 合成清潔劑 22. soapy detergent/soap 皂性清潔劑 / 肥皂 23. sulphate group 硫酸基團 24. sulphonate group 磺酸基團 25. surfactant 表面活性劑 26. surface tension 表面張力 27. wetting property 濕潤性質 Key terms P. 60 / 69
Progress check 1. What is the structure of acetylsalicylic acid (aspirin)? 2. What are the uses of acetylsalicylic acid (aspirin)? 3. What is the general structure of a detergent particle? 4. What are the structural differences between a soapy detergent and a soapless detergent? 5. How can soaps be prepared from fats and oils? 6. How can soapless detergents be prepared from the chemicals derived from petroleum? 7. How do detergents help water wet a surface? P. 61 / 69
8. How do detergents emulsify a mixture of water and oil? 9. How do detergents clean dirt particles in grease? 10.What is condensation polymerization? 11.What are the structures, properties and uses of the condensation polymers? (a) nylon (b) polyesters Progress check P. 62 / 69
Summary 46.1 Acetylsalicylic acid (Aspirin) 1. Acetylsalicylic acid is commonly known as aspirin. The functional groups of aspirin include benzene ring, carboxylic group and ester group. 2. Aspirin is used to relieve pain and reduce fever. It is also an anti-inflammatory drug. Low doses of aspirin prevent heart attacks. 46.2 Soaps and soapless detergents 3. A detergent is a substance which improves the cleansing properties of water. P. 63 / 69
4. The hydrophilic head of a detergent particle is soluble in water but not in oil. However, the hydrophobic tail of a detergent particle is soluble in oil, but not in water. 5. Soapy detergents (or soaps) are made from fats or oils. They are sodium (or potassium) salts of long-chain carboxylic acids. 6. Soapless detergents are derived from the chemicals from petroleum. They are usually sodium salts of long-chain alkylbenzenesulphonate or alkylsulphate. Summary P. 64 / 69
7. A detergent reduces the surface tension of water. It is a wetting agent. 8. A detergent mixes oil and water. It is an emulsifying agent. 9. The hydrophobic tails of detergent anions dissolve in grease, with the hydrophilic heads in water. When stirred, the surrounding water molecules attract the ionic heads. As a result, the grease is lifted off the surface to be cleaned. Summary P. 65 / 69
46.3 Nylon and polyesters 10. Nylon is a kind of polyamide. It is a polymer containing amide linkage, chain. Summary P. 66 / 69, along its 11. Nylon is tough, very strong and elastic. Besides, it is water-proof and oil-proof. Nylon has a high tensile strength and its surface is usually very smooth. Also, it is easy to wash and can be dyed in a wide range of colours. Therefore, nylon is ideal for making ropes, fishing lines and nets. It is also used for making tennis racket strings.
12. Polyester is a polymer containing ester linkage,, along its chain. 13. Polyesters are strong, tough, smooth, resistant to water and chemicals. They are suitable for making fibres and clothes. Besides, as polyesters have low density, they are used for making lightweight sails and bottles for water and drinks. Summary P. 67 / 69
Concept map IMPORTANT ORGANIC SUBSTANCES include Acetylsalicylic acid ( ) Aspirin functional groups Soaps ionic head Soapless detergents ionic head Benzene ring Carboxyl group Ester group Carboxylate group Alkylbenzenesulphonate or alkylsulphate group P. 68 / 69
IMPORTANT ORGANIC SUBSTANCES include Nylon Polyester functional group functional group Amide group Ester group Concept map P. 69 / 69