Inter-conversions of carbon compounds Inter-conversions between the functional groups Considerations in planning a synthetic route

Transcription

1 Chapter 45 Inter-conversions of carbon compounds 45.1 Inter-conversions between the functional groups 45.2 Considerations in planning a synthetic route 45.3 Laboratory preparation of simple carbon compounds P. 1 / 70

2 Key terms Progress check Summary Concept map P. 2 / 70

3 45.1 Inter-conversions between the functional groups Carbon compounds possessing different functional groups usually have different physical and chemical properties. Example: chloroethane (CH 3 CH 2 Cl) and ethanol (CH 3 CH 2 OH) Same structure except the difference in functional groups. P. 3 / 70

4 Chloroethane: gas under room conditions slightly soluble in water soluble in organic solvents Ethanol: liquid under room conditions soluble in both water and organic solvents 45.1 Inter-conversions between the functional groups P. 4 / 70

5 (a) (b) Figure 45.1 (a) Chloroethane is a gas under room conditions. It is largely used as a blowing agent in foamed plastics. (b) Ethanol is very soluble in water. It is dissolved in water in alcoholic drinks. By converting one or more functional groups to another, we can synthesize compounds with desired properties (e.g. solubility, melting and boiling points, chemical reactivity, etc.) Inter-conversions between the functional groups P. 5 / 70

6 Chemists have been working hard to make new carbon compounds that are more useful. In organic synthesis, chemists change the functional groups of carbon compounds. They cannot do this without knowledge of the inter-conversions of functional groups Inter-conversions between the functional groups P. 6 / 70

7 Reactions of alkanes Conversion Alkane haloalkane Reactions of alkenes Conversion Alkene alkane Alkene dihaloalkane Alkene haloalkane Example CH 3 CH 2 CH 2 CH 3 (excess) CH 3 CH 2 CH 2 CH 2 X (major product) Example Reagents and conditions X 2 (X: Cl or Br), UV light or heat Reagents and conditions P. 7 / 70 Type of reaction Substitution Type of reaction CH 3 CH=CH 2 H 2, Pt Addition CH 3 CH 2 CH 3 CH 3 CH=CH 2 CH 3 CHXCH 2 X CH 3 CH=CH 2 CH 3 CHXCH 3 (major product) 45.1 Inter-conversions between the functional groups X 2 (X: Cl, Br or I) in organic solvent HX (X: F, Cl, Br or I) Addition Addition Table 45.1 Summary of typical reactions of different functional groups.

8 Reactions of haloalkanes Conversion Haloalkane alcohol Reactions of alcohols Example CH 3 CH 2 CH 2 X CH 3 CH 2 CH 2 OH (X: F, Cl, Br or I) Reagents and conditions NaOH(aq) Type of reaction Substitution Conversion Alcohol haloalkane Alcohol alkene 1 alcohol aldehyde 1 alcohol carboxylic acid 2 alcohol ketone Example CH 3 CH 2 CH 2 OH CH 3 CH 2 CH 2 X CH 3 CH 2 CH 2 OH CH 3 CH=CH 2 CH 3 CH 2 CH 2 OH CH 3 CH 2 CHO CH 3 CH 2 CH 2 OH CH 3 CH 2 COOH Reagents and conditions HX or PX 3 (X: Cl, Br or I) Conc. H 2 SO 4, heat or Al 2 O 3, heat Cr 2 O 7 2 (aq)/h + (aq), heat Cr 2 O 7 2 (aq)/h + (aq), heat P. 8 / 70 Type of reaction Substitution Dehydration Oxidation Oxidation CH 3 CH(OH)CH 3 CH 3 COCH 3 Cr 2 O 7 2 (aq)/h + (aq), heat Oxidation Table 45.1 Summary of typical reactions of different functional groups Inter-conversions between the functional groups

9 Reactions of aldehydes and ketones Conversion Aldehyde carboxylic acid Aldehyde 1 alcohol Ketone 2 alcohol Example CH 3 CH 2 CHO CH 3 CH 2 COOH CH 3 CH 2 CHO CH 3 CH 2 CH 2 OH CH 3 COCH 3 CH 3 CH(OH)CH 3 Reactions of carboxylic acids Conversion Carboxylic acid ester Carboxylic acid 1 alcohol Example CH 3 CH 2 COOH CH 3 CH 2 COOCH 2 CH 3 CH 3 CH 2 COOH CH 3 CH 2 CH 2 OH 45.1 Inter-conversions between the functional groups Reagents and conditions Cr 2 O 7 2 (aq)/h + (aq), heat 1. LiAlH 4, dry ether 2. H + (aq) or NaBH 4, H 2 O 1. LiAlH 4, dry ether 2. H + (aq) or NaBH 4, H 2 O Reagents and conditions CH 3 CH 2 OH, conc. H 2 SO 4, heat 1. LiAlH 4, dry ether 2. H + (aq) P. 9 / 70 Type of reaction Oxidation Reduction Reduction Type of reaction Esterification Reduction Table 45.1 Summary of typical reactions of different functional groups.

10 Carboxylic acid amide Reactions of esters Conversion Ester carboxylic acid + alcohol Ester carboxylic acid + alcohol Reactions of amides Conversion Amide carboxylic acid Amide carboxylic acid CH 3 CH 2 COOH 1. PCl 3 Amide CH 3 CH 2 CONH 2 2. NH 3 formation Example CH 3 CH 2 COOCH 2 CH 3 CH 3 CH 2 COOH + CH 3 CH 2 OH CH 3 CH 2 COOCH 2 CH 3 CH 3 CH 2 COOH + CH 3 CH 2 OH Example CH 3 CH 2 CONH 2 CH 3 CH 2 COOH + NH 4 + CH 3 CH 2 CONH 2 CH 3 CH 2 COOH + NH 4 + Reagents and conditions H + (aq), heat 1. OH (aq), heat 2. H + (aq) Reagents and conditions H + (aq), heat 1. OH (aq), heat 2. H + (aq) P. 10 / 70 Type of reaction Acid hydrolysis Alkaline hydrolysis Type of reaction Acid hydrolysis Alkaline hydrolysis Table 45.1 Summary of typical reactions of different functional groups Inter-conversions between the functional groups

11 Dihaloalkanes Esters Amides X 2 (in organic solvent) Carboxylic acids H 2, Pt Alkenes (C n H 2n ) conc. H 2 SO 4, or Al 2 O 3, Alcohols (ROH) For 1º [O], [R] or [R] [O], Aldehydes Alkanes (C n H 2n+2 ) X 2 UV light or HX Haloalkanes (RX) [O] Cr 2 O 2 7 (aq)/h + (aq) [R] 1. LiAlH 4, dry ether 2. H + (aq) [R] NaBH 4, water * = heat P. 11 / 70 Ketones Figure 45.2 Summary of methods of converting one functional group to another Inter-conversions between the functional groups

12 Multi-step synthesis Some functional groups can be converted to another directly but some cannot. Multi-step synthesis is needed. An alkane can be converted to a haloalkane first. Haloalkane is then allowed to react with sodium hydroxide solution to give the required alcohol. The synthesis involves two steps Inter-conversions between the functional groups P. 12 / 70

13 Multi-step syntheses require more than one step, and so one or more intermediate compounds are produced. Example 3 steps are required to convert compound W to compound Z. 2 intermediate compounds (X and Y) are produced. reagent W X Y Z condition reagent condition reagent condition 45.1 Inter-conversions between the functional groups P. 13 / 70

14 Key point In order to convert a chosen starting material to a target molecule, it requires a single step or multiple steps. In either case, interconversions between functional groups are usually needed Inter-conversions between the functional groups P. 14 / 70

15 Inter-conversions between alkanes, alkenes, haloalkanes and alcohols Alkanes and alkenes are important starting materials in organic syntheses. Alkanes are obtained from the fractional distillation of petroleum. Alkenes are obtained from the cracking of higher members of the homologous series of alkanes Inter-conversions between the functional groups P. 15 / 70

16 H 2, Pt Dihaloalkanes Alkenes X 2 (in organic solvent) HX conc. H 2 SO 4, or Al 2 O 3, Alcohols Alkanes X 2 UV light or Haloalkanes * = heat Figure 45.3 Inter-conversions between alkanes, alkenes, haloalkanes and alcohols Inter-conversions between the functional groups P. 16 / 70

17 The following route can be used to convert ethane (an alkane) to ethanol (an alcohol). Alcohols Alkanes Haloalkanes 1 st step: conversion of ethane to chloroethane. CH 3 CH 3 ethane Cl 2 UV light or heat CH 3 CH 2 Cl chloroethane 45.1 Inter-conversions between the functional groups P. 17 / 70

18 2 nd step: conversion of chloroethane (the intermediate compound) to ethanol (the end product). CH 3 CH 2 Cl chloroethane NaOH(aq) CH 3 CH 2 OH ethanol The overall process can then be represented by the following synthetic route. CH 3 CH 3 CH 3 CH 2 Cl CH 3 CH 2 OH ethane Cl 2 UV light or heat chloroethane NaOH(aq) ethanol 45.1 Inter-conversions between the functional groups P. 18 / 70

19 Ethanol can also be converted to ethane. The synthetic route is: conc. H 2 SO 4 H CH 3 CH 2 OH CH 2 =CH 2, Pt 2 CH 3 CH 3 ethanol heat ethene ethane In the above examples, two compounds, ethane and ethanol, can be inter-converted by using different reagents and conditions. Example 45.1 Example 45.2 Class practice Inter-conversions between the functional groups P. 19 / 70

20 Inter-conversions between alcohols, aldehydes, ketones, carboxylic acids, esters and amides Many organic compounds find important uses as pharmaceuticals, pesticides, perfumes and dyes. Figure 45.4 Many synthetic dyes are organic compounds containing oxygen and nitrogen. They can be used to colour fabrics Inter-conversions between the functional groups P. 20 / 70

21 These compounds include alcohols, aldehydes, ketones, carboxylic acids, esters and amides. The inter-conversions between alcohols, aldehydes and carboxylic acids are redox reactions. Carboxylic acids can be converted to esters and amides, and vice versa Inter-conversions between the functional groups P. 21 / 70

22 Esters Amides Alcohols Carboxylic acids [O], For 1º [O], Aldehydes [R] or [R] Ketones [O] Cr 2 O 7 2 (aq)/h + (aq) [R] 1. LiAlH 4, dry ether 2. H + (aq) [R] NaBH 4, water * = heat Figure 45.5 Inter-conversions between alcohols, aldehydes, ketones, carboxylic acids, esters and amides. Concept check 45.1 Inter-conversions between the functional groups P. 22 / 70

23 Alcohols are often used as the starting materials for different oxygen-containing compounds. Example: Convert propan-1-ol (an alcohol) to ethyl propanoate (an ester) Esters Carboxylic acids Alcohols Aldehydes 45.1 Inter-conversions between the functional groups P. 23 / 70

24 Learning tip A primary alcohol can be oxidized to carboxylic acid by heating the reaction mixture under reflux. The synthetic route is: Cr 2 O 7 2 (aq)/h + (aq) CH 3 CH 2 OH, H + (aq) heat propan-1-ol heat ethyl propanoate propanoic acid Example 45.3 Class practice Inter-conversions between the functional groups P. 24 / 70

25 Inter-conversions between functional groups of common homologous series To convert a compound without oxygen to a compound with oxygen, a synthetic pathway that includes an alcohol as one of the intermediates should be taken Inter-conversions between the functional groups P. 25 / 70

26 Compounds without oxygen Compounds with oxygen Esters Amides Dihaloalkanes H 2, Pt X 2 (in organic solvent) Alkenes HX conc. H 2 SO 4, or Al 2 O 3, Alcohols For 1º [O], [R] or [R] Carboxylic acids [O], Aldehydes Alkanes X 2 UV light or Haloalkanes P. 26 / 70 Ketones [O] Cr 2 O 7 2 (aq)/h + (aq) [R] 1. LiAlH 4, dry ether [R] NaBH 4, water * = heat 2. H + (aq) Figure 45.6 Inter-conversions between alcohols and other functional groups Inter-conversions between the functional groups

27 Example: Convert ethene (an alkene) to ethanal (an aldehyde) Alkenes Alcohols Aldehydes Haloalkanes 45.1 Inter-conversions between the functional groups P. 27 / 70

28 The synthetic route is: HCl NaOH(aq) ethene chloroethane ethanol distil off Cr 2 O 2 7 (aq)/h + (aq) when formed ethanal Example 45.4 Example 45.5 Class practice Inter-conversions between the functional groups P. 28 / 70

29 45.2 Considerations in planning a synthetic route Chemists try to synthesize the desired compounds with the lowest costs in organic syntheses. They would consider a number of factors in planning a synthetic route. 1. Availability of starting materials and reagents The starting materials and reagents of a synthetic route should be readily available and cheap. P. 29 / 70

30 2. Rate of reactions Many organic reactions are slow. Reactions can be speeded up by using catalysts and a high temperature. Lead to a higher production cost. 3. Percentage yield of the synthetic route Organic syntheses seldom give a 100% yield since organic reactions seldom go to completion or by-products may be produced Considerations in planning a synthetic route P. 30 / 70

31 Example: Direct conversion of chloroethane to ethanol by sodium hydroxide solution CH 3 CH 2 Cl NaOH(aq) CH 3 CH 2 OH One mole (64.5 g) of chloroethane never gives one mole (46.0 g) of ethanol Considerations in planning a synthetic route P. 31 / 70

32 = If only 23.0 g of ethanol is produced, the percentage yield of ethanol = = = actual mass of ethanol obtained theoretical mass of ethanol calculated 23.0 g 46.0 g 100% 50% Key point Percentage yield of a product 100% actual mass of the product obtained theoretical mass of the product calculated 100% 45.2 Considerations in planning a synthetic route P. 32 / 70

33 4. Number of steps in the synthetic route If an organic synthesis consists of several steps, the overall yield will be reduced after each step. Example Three-step synthesis in which each step has a yield of 60%: 60% 60% 60% W X Y Z 45.2 Considerations in planning a synthetic route P. 33 / 70

34 The overall yield will be = 21.6% Therefore, a synthetic route should include as few steps as possible. Ethene Ethanol Ethane Ethene Ethanol Chloroethane Chloroethane Route (1) Route (2) Figure 45.7 Possible synthetic routes for the conversion of ethene to ethanol Considerations in planning a synthetic route P. 34 / 70

35 Ethene is converted to chloroethane in two steps in route (1) but in three steps in route (2). Yield of route (1) is higher than that of route (2). 5. By-products formed in the synthetic route ethane chloroethane ethanol... Route (3) ethene chloroethane ethanol... Route (4) Both routes involve two steps Considerations in planning a synthetic route P. 35 / 70

36 First step of route (3) produces not only the desired intermediate (chloroethane), but a mixture of haloalkane by-products such as 1,1- dichloroethane, 1,2-dichloroethane, 1,1,1- trichloroethane, etc. Formation of by-products reduces the efficiency of the synthesis. Some of the unwanted haloalkanes may cause the depletion of the ozone layer. They are harmful to the environment. Think about 45.2 Considerations in planning a synthetic route P. 36 / 70

37 Hydrohalogenation of ethene in route (4) produces only the desired intermediate (chloroethane) which will then be converted. The best synthetic route should produce little or no by-products. Harmful by-products should be avoided in organic syntheses Considerations in planning a synthetic route P. 37 / 70

38 Key point In planning a synthetic route for carbon compounds, the following factors have to be considered: Availability of starting materials and reagents Rate of reaction Percentage yield Number of steps By-products formed STSE connections 45.1 Activity Considerations in planning a synthetic route P. 38 / 70

39 45.3 Laboratory preparation of simple carbon compounds Preparation of ethanoic acid In the laboratory, ethanoic acid is usually prepared by the oxidation of ethanol. An acidified potassium dichromate solution can be used as the oxidizing agent. Ethanol is first oxidized to ethanal, and then to ethanoic acid. P. 39 / 70

40 To ensure complete oxidation of ethanol to ethanoic acid, excess oxidizing agent is used. The reaction mixture is heated under reflux for 20 to 30 minutes. ethanol loses 2 hydrogen atoms ethanal gains 1 oxygen atom 45.3 Laboratory preparation of simple carbon compounds ethanoic acid P. 40 / 70

41 Step 1: Heating the reaction mixture under reflux Function of the reflux condenser is to condense vapour formed from the mixture during heating. It helps to prevent the loss of volatile organic substances by evaporation on prolonged heating Laboratory preparation of simple carbon compounds P. 41 / 70

42 reflux condenser water in pear-shaped flask anti-bumping granule water bath heat water out hot vapour condenses on the cold inner wall of the condenser condensed liquid returns to the flask ethanol + acidified potassium dichromate solution reflux condenser pearshaped flask antibumping granule water out water in Figure 45.8 Oxidizing ethanol to ethanoic acid by heating under reflux. water bath ethanol + acidified potassium dichromate solution 45.3 Laboratory preparation of simple carbon compounds P. 42 / 70

43 Ethanol is first oxidized to ethanal. The ethanal vaporizes and condenses in the reflux condenser. The liquid drops back into the reaction flask and is then further oxidized to ethanoic acid Laboratory preparation of simple carbon compounds P. 43 / 70

44 Step 2: Distilling the product mixture pear-shaped flask anti-bumping granule heat thermometer water out (to sink) product mixture Liebig condenser water in (from tap) thermometer pear-shaped flask product mixture receiver adaptor test tube (as receiver) aqueous solution of ethanoic acid Liebig condenser water out anti-bumping granule aqueous solution of ethanoic acid Figure 45.9 Distilling ethanoic acid from the product mixture. water in receiver adaptor 45.3 Laboratory preparation of simple carbon compounds P. 44 / 70

45 Distil the product mixture and collect the liquid that boils between 110 C and 114 C. The distillate obtained is an aqueous solution of ethanoic acid and it has a strong smell of vinegar. To obtain pure ethanoic acid, the aqueous solution of ethanoic acid is redistilled. The liquid that boils between 116 C and 118 C is collected as distillate Laboratory preparation of simple carbon compounds P. 45 / 70

46 The percentage yield of ethanoic acid can be calculated from the amount of ethanoic acid obtained. Percentage yield of ethanoic acid = actual mass of ethanoic acid obtained theoretical mass of ethanoic acid calculated 100% Example 45.6 Experiment 45.1 Experiment Laboratory preparation of simple carbon compounds P. 46 / 70

47 Preparation of ethyl ethanoate In the laboratory, ethyl ethanoate is prepared by heating a mixture of ethanoic acid and ethanol in the presence of an acid catalyst. The process is known as esterification. H + (aq) ethanoic acid ethanol heat ethyl ethanoate water 45.3 Laboratory preparation of simple carbon compounds P. 47 / 70

48 Learning tip Concentrated sulphuric acid has two functions in the laboratory preparation of ethyl ethanoate: 1. It acts as a catalyst. 2. It removes water, shifting the equilibrium of esterification to the product side. Esterification is a reversible reaction Laboratory preparation of simple carbon compounds P. 48 / 70

49 Step 1: Heating the reaction mixture under reflux Equal volumes of ethanoic acid and ethanol are mixed and concentrated sulphuric acid is added to the mixture. The mixture is then heated under reflux. SBA note Addition of concentrated sulphuric acid to the mixture of ethanol and ethanoic acid is highly exothermic. Hence, the acid should be added to the mixture slowly with cooling (in an ice-water bath) and shaking Laboratory preparation of simple carbon compounds P. 49 / 70

50 reflux condenser water out reflux condenser water out water in pear-shaped flask anti-bumping granule heat hot vapour condenses on the cold inner wall of the condenser condensed liquid returns to the flask a mixture of ethanol, ethanoic acid and conc. H 2 SO 4 pear-shaped flask anti-bumping granule Figure Heating a mixture of ethanol, ethanoic acid and concentrated sulphuric acid under reflux. water in a mixture of ethanol, ethanoic acid and conc. H 2 SO Laboratory preparation of simple carbon compounds P. 50 / 70

51 Step 2: Distilling the product mixture To separate the organic compounds (i.e. unreacted ethanol, unreacted ethanoic acid and the product ethyl ethanoate) from the aqueous solution, twothirds of the product mixture is distilled off. This distillate should have a much lower percentage of water and relatively higher percentages of ethanol, ethanoic acid and ethyl ethanoate Laboratory preparation of simple carbon compounds P. 51 / 70

52 thermometer thermometer pearshaped flask anti-bumping granule heat water out (to sink) product mixture Liebig condenser water in (from tap) pear-shaped flask product mixture receiver adaptor test tube (as receiver) Liebig condenser water out anti-bumping granule water in receiver adaptor solution of organic compounds Figure Distilling off two-thirds of the reaction mixture in order to separate the carbon compounds from the aqueous solution of the product mixture Laboratory preparation of simple carbon compounds P. 52 / 70

53 Step 3: Removing unreactedethanoicacid and traces of sulphuric acid from the distillate The distillate is mixed with excess sodium carbonate solution. Sodium carbonate reacts and removes any acidic substances (unreacted ethanoic acid and traces of sulphuric acid) in the distillate. The lower aqueous layer is discarded Laboratory preparation of simple carbon compounds P. 53 / 70

54 2CH 3 COOH(aq) + CO 3 2 (aq) 2CH 3 COO (aq) + H 2 O(l) + CO 2 (g) 2H + (aq) + CO 3 2 (aq) H 2 O(l) + CO 2 (g) filter funnel separating funnel excess sodium carbonate solution distillate obtained in step 2 organic layer aqueous layer beaker (a) Figure (a) Adding excess sodium carbonate solution removes unreacted ethanoic acid and traces of sulphuric acid in the distillate. (b) Discarding the aqueous layer Laboratory preparation of simple carbon compounds (b) P. 54 / 70

55 Step 4: Removing unreacted ethanol from the distillate The organic layer is then mixed with excess calcium chloride solution. Calcium chloride reacts and removes any unreacted ethanol in the organic layer. An aqueous layer forms and is discarded Laboratory preparation of simple carbon compounds P. 55 / 70

56 CaCl 2 (aq) + 4CH 3 CH 2 OH(l) CaCl 2 4CH 3 CH 2 OH(aq) filter funnel separating funnel organic layer excess calcium chloride solution organic layer aqueous layer beaker (a) (b) Figure (a) Adding excess calcium chloride solution removes unreacted ethanol in the organic layer. (b) Discarding the aqueous layer Laboratory preparation of simple carbon compounds P. 56 / 70

57 Step 5: Removing traces of water from the distillate Add a few lumps of anhydrous calcium chloride to the organic layer. The anhydrous calcium chloride is a drying agent that removes remaining traces of water from the organic layer. Filter the organic layer and obtain the filtrate Laboratory preparation of simple carbon compounds P. 57 / 70

58 separating funnel anhydrous calcium chloride spatula conical flask (a) organic layer (b) organic layer Figure (a) Pouring the organic layer to a conical flask. (b) Adding anhydrous calcium chloride removes traces of water in the organic layer Laboratory preparation of simple carbon compounds P. 58 / 70

59 glass rod fluted filter paper residue filter funnel pear-shaped flask filtrate Figure Filtering the organic layer into a pear-shaped flask to obtain filtrate for further distillation Laboratory preparation of simple carbon compounds P. 59 / 70

60 Step 6: Re-distillation to obtain a second distillate (pure ethyl ethanoate) The filtrate obtained is then redistilled and the liquid that boils between 74 C and 79 C is collected as distillate. The distillate is ethyl ethanoate. Class practice 45.4 Experiment 45.2 Experiment Laboratory preparation of simple carbon compounds P. 60 / 70

61 Key terms 1. inter-conversion 互換 2. intermediate compound 中間化合物 3. multi-step synthesis 多步驟合成 4. organic synthesis 有機合成 5. percentage yield 百分產率 6. reflux condenser 回流冷凝器 7. synthetic route 合成路線 P. 61 / 70

62 Progress check 1. What is the importance of inter-conversions between functional groups in organic compounds? 2. What is a multi-step synthesis? 3. What reagents and conditions are needed for the inter-conversions between alkanes, alkenes, haloalkanes and alcohols? 4. What reagents and conditions are needed for the inter-conversions between alcohols, aldehydes, carboxylic acids, esters and amides? P. 62 / 70

63 5. What is the role of alcohols for the interconversions between compounds with oxygen and compounds without oxygen? 6. What are the essential features of a good synthetic route? 7. What is the percentage yield of a product in a synthetic process? 8. What are the steps in the laboratory preparation of ethanoic acid? 9. What are the steps in the laboratory preparation of ethyl ethanoate? Progress check P. 63 / 70

64 Summary 45.1 Inter-conversions between the functional groups 1. Some common reactions that can bring about a change in functional groups are summarized infigure 45.2 on p Multi-step synthesis is the process of converting a readily available compound into the desired product in more than one step. 3. The inter-conversions between alkanes, alkenes, haloalkanes and alcohols are summarized in Figure 45.3 on p.7. P. 64 / 70

65 4. The inter-conversions between alcohols, aldehydes, ketones, carboxylic acids, esters and amides in Figure 45.5 on p We can divide carbon compounds into two main groups: one with oxygen and one without. If we want to convert a compound without oxygen to a compound with oxygen, a synthetic pathway that includes an alcohol as one of the intermediates should be taken. Refer to Figure 45.6 on p.13 Summary P. 65 / 70

66 45.2 Considerations in planning a synthetic route 6. Percentage yield of a product actual mass of the product obtained = theoretical mass of the product calculated 100% 7. In planning a synthetic route for carbon compounds, the following factors have to be considered: - Availability of starting materials and reagents - Rate of reaction Summary P. 66 / 70

67 - Percentage yield - Number of steps - By-products formed 45.3 Laboratory preparation of simple carbon compounds 8. In the laboratory, ethanoic acid is usually prepared by heating ethanol under reflux with acidified potassium dichromate solution. Ethanoic acid is collected in the distillate by distillation of the product mixture. It is then purified by redistillation. Summary P. 67 / 70

68 9. In the laboratory, ethyl ethanoate is prepared by heating a mixture of ethanoic acid and ethanol under reflux in the presence of an acid catalyst. Ethyl ethanoate is collected in the distillate by distillation of the product mixture. Unreacted ethanol, ethanoic acid and water are removed from the distillate. Ethyl ethanoate is then purified by redistillation. Summary P. 68 / 70

69 Concept map Dihaloalkanes HX or PX 3 Alkanes H 2, Pt X 2 (in organic solvent) Alkenes NaOH(aq) conc. H 2 SO 4 or Al 2 O 3, Alcohols X 2, UV light or HX Haloalkanes HX or PX 3 NaOH(aq) P. 69 / 70

70 Esters R OH, H + (aq), H + (aq), or 1. OH (aq), 2. H + (aq) (For 1 ) Cr 2 O 7 2 (aq)/h + (aq), Alcohols (1) LiAlH 4, dry ether (2) H + (aq) (For 1 ) Cr 2 O 7 2 (aq)/h + (aq), (1) LiAlH 4, dry ether (2) H + (aq) or NaBH 4, H 2 O (For 2 ) Cr 2 O 2 7 (aq)/h + (aq), (1) LiAlH 4, dry ether (2) H + (aq) or NaBH 4, H 2 O Concept map Carboxylic acids Cr 2 O 7 2 (aq)/ H + (aq), Aldehydes Ketones 1. PCl 3 2. NH 3 H + (aq), or 1. OH (aq), 2. H + (aq) P. 70 / 70 Amides