Grade 11 Chemistry: Alcohols and Ethers - Past Notes PDF

6 CHEMISTRY GRADE 11 O R C O H + H O R'  R O C O...

6 CHEMISTRY GRADE 11 O R C O H + H O R'  R O C O R' + H+ H O H SOME IMPORTANT OXYGEN-CONTAINING ORGANIC COMPOUNDS Unit Outcomes At the end of this unit, you will be able to: ) classify organic compounds ) write the structural formula and IUPAC names of alcohols, ethers, aldehydes, ketones, carboxylic acids and esters ) give the general formulas of alcohols, ethers, aldehydes, ketones, carboxylic acids and esters ) describe some physical and chemical properties of alcohols, ethers, aldehydes, ketones, carboxylic acids and esters ) develop skills in naming and writing the molecular and structural formulas of alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, anhydrides, amides, and acid chlorides ) predict and correctly name the products of organic reactions, including substitution, addition, elimination, esterification, hydrolysis and oxidation reactions ) perform activities to prepare an alcohol (Katikalla), and a carboxylic acid ) test for the carboxylic acid and ester functional groups ) write the general formula of fats and oil and the structures for some common triglycerides ) give the structures, properties and uses of fats and oils, and demonstrate scientific enquiry skills, including: observing, classifying, comparing and contrasting, asking questions, drawing conclusions, applying concepts and problem solving. 264 UNIT 6  Introduction Start-up Activity Perform the following activity in groups and present your response to the rest of the class. Take turns to name an item that contains organic molecules that we use in daily life, and identify what class of organic compound (s) it contains. 6.1  At the end of this section, you will be able to: ) classify organic compounds. Classification of organic compounds Why is classification of organic compounds needed? What is the basis of the classification? In Grade 10, you have learned about some general organic reactions of hydrocarbons. In this unit, you will continue to learn about more functional groups: oxygen- containing functional groups. The oxygenated hydrocarbons include alcohols, ethers, aldehydes, ketones, carboxylic acids and esters. Alcohols occur widely in nature and have many industrial and pharmaceutical applications. Methanol, for example, is one of the most important of all industrial chemicals. Ethers are relatively resistant to chemical transformation and are often used as solvents in chemical reactions. Can you name the common functional groups and give an example for each functional group? Aldehydes and ketones contain a carbonyl group that consists of a carbon–oxygen double bond (C=O). Many compounds found in nature have aldehyde or ketone functional groups. Aldehydes have pungent odors, whereas ketones tend to smell sweet. Carboxylic acids and esters are present in many fruits and flowers. Many carboxylic acids are used as food additives in jams, jellies, candies and pickles, etc. In this unit, you will also learn about fats and oils which are esters. UNIT 6 265  CHEMISTRY GRADE 11 6.2  At the end of this section, you will be able to: ) define alcohols ) tell the functional group of alcohols ) classify alcohols based on the number of hydroxyl groups ) write the general formulas of monohydric alcohols ) write the molecular formulas and the names of the first six members of the monohydric alcohols ) give the IUPAC names for the given alcohols ) classify monohydric alcohols based on the number of alkyl groups attached to the carbon atom carrying the hydroxyl group ) give some examples for primary, secondary and tertiary alcohols ) describe the physical properties of alcohols ) explain general methods of preparation of alcohols ) explain the industrial preparation of ethanol ) perform an experiment to prepare ethanol from sugar ) explain the chemical reactions of alcohols such as oxidation, reaction with active metals, esterification and dehydration ) carry out an activity to show chemical reactions of alcohols with active metals ) write the molecular formulas and names of the first six members of ethers ) give the IUPAC names for given ethers ) describe the physical properties of ethers ) explain the general methods of preparation of ethers ) explain the use of ethers, such as solvent inorganic reactions. 266 UNIT 6  Alcohols and Ethers Activity 6.1 Discuss the following questions in groups, and write a report. Present your report to the class. 1. List some alcohols you know. Name the alcohol used in alcoholic beverages. What are the uses of alcohols in industry? 2. Ethiopia uses an alcohol blended with gasoline to drive cars. What is the name of the alcohol? 3. Hand sanitizers are used as an alternative to washing hands to kill most bacteria and viruses that spread colds and flu. Which alcohol (s) is present in hand sanitizers? 4. Explain the effects of using carbon-based fuels on the increase in carbon dioxide in the atmosphere and its consequences. What do you think when you hear the word “alcohol”? Can you define alcohol? Give a few examples of the uses of alcohols. Most people think of two common alcohols: the substance that intoxicates people, and the one used in clinics and hospitals. However, there are many types of alcohol. The only alcohol present in all alcoholic beverages is called ethanol. Other alcohols are used for different purposes. Alcohols are derivatives of hydrocarbons in which one or more of the hydrogen atoms in the hydrocarbon have been replaced by a hydroxyl group (–OH). The functional group in an alcohol is an –OH (hydroxyl) group, which is responsible for imparting certain chemical and/or physical properties to the compound. In alcohols, the hydroxyl group is directly attached to carbon atom(s) of an aliphatic system. Example 6.1 H H H H H H H C OH H C C OH H C C C OH H H H H H H Methanol Ethanol 1-Propanol (Propan-1-ol) UNIT 6 267  CHEMISTRY GRADE 11   Alcohols may be classified as mono–, di–, tri- or polyhydric compounds depending on whether they contain one, two, three or many hydroxyl (–OH) groups respectively in their structures. i. Monohydric alcohols are alcohols containing only one hydroxyl group. Example 6.2 CH3 CH2 OH CH3 CH2 CH2 OH CH3 CH2 CH2 CH2 OH Ethanol 1-Propanol 1-Butanol (Butan-1-ol) Which one of the above monohydric alcohols is present in any drinking alcohol? ii. Dihydric alcohols are those containing two hydroxyl groups per molecule. They are also named glycols or diols. Example 6.3 H2C CH2 OH OH Ethane-1,2-diol (Ethylene glycol) Can you give more examples of dihydric alcohols? iii. Trihydric alcohols are those containing three hydroxyl groups in their molecular structure. Example 6.4 H2C CH CH2 OH OH OH Propane-1,2,3-triol (Glycerine or glycerol) iv. Polyhydric alcohols are those alcohols containing three or more hydroxyl groups in their molecular structure. 268 UNIT 6  Alcohols and Ethers Can you give examples of polyhydric alcohols? Classification of Monohydric Alcohols Monohydric alcohols may be further classified according to the carbon atom to which the hydroxyl group is attached. Primary alcohols In a primary alcohol, the carbon with the hydroxyl group is only attached to one alkyl group. H General structure: R C OH H Primary (1o) alcohol Example 6.5 CH3 CH3-CH2-OH CH3-CH2-CH2-OH CH3-CH2-CH-CH2-OH Ethanol 1-Propanol 2-Methyl-1-butanol Secondary alcohols In a secondary alcohol, the carbon with the hydroxyl group is attached to two alkyl groups. OH General structure: R C R' Where, R and R' may be the same or dif f erent H Secondary (2o) alcohol Example 6.6 OH OH OH CH3-CH-CH3 CH3-CH2-CH-CH3 CH3-CH2-CH-CH2-CH3 2-Propanol 2-Butanol 3-Pentanol UNIT 6 269  CHEMISTRY GRADE 11 Tertiary alcohols In a tertiary alcohol, the carbon with the hydroxyl group is attached to three other alkyl groups. OH General structure: R C R' Where, R, R' and R'' may be the same or dif f erent R'' Tertiary (3o) alcohol Example 6.7 OH OH CH3 C CH3 CH3CH2 C CH3 CH3 CH3 2-Methyl-2-propanol 2-Methyl-2-butanol   The common name of an alcohol is derived from the common name of the alkyl group and adding the word alcohol to it. In the IUPAC system, an alcohol is named by replacing the e of the corresponding alkane name with ol. Example 6.8 CH3 H CH3 OH CH3 CH2 H CH3 CH2 OH Methane Methanol Ethane Ethanol (methyl alcohol) (ethyl alcohol) When an alcohol consists of a chain with three or more carbon atoms, the chain is numbered to give the position for the –OH group and any substituents on the chain. For this, the longest carbon chain (parent chain) is numbered starting at the end nearest to the hydroxyl group. The positions of the –OH group and other substituents are indicated by using the numbers of carbon atoms to which these are attached. 270 UNIT 6  Alcohols and Ethers Example 6.9 OH CH3 CH2 CH2 OH CH3 CH CH3 3 2 1 3 2 1 1-Propanol 2-Propanol (propyl alcohol) (isopropyl alcohol) Is neopentyl alcohol a 1°, 2°, or 3° alcohol? For naming polyhydric alcohols, the ‘e’ of alkane is retained and the ending ‘ol’ is added. The number of –OH groups is indicated by adding the multiplicative prefix, di, tri, etc., before ‘ol’. Example 6.10 OH HO CH2 CH2 OH HO CH2 CH CH2 OH 2 1 3 2 1 1,2-Ethanediol 1,2,3-Propanetriol (ethylene glycol) (glycerol) Exercise 6.1 1. Give the general formula for the homologous series of monohydric alcohols. 2. Classify the following alcohols as monohydric, dihydric and trihydric alcohols. a. 2-propanol b. 1,3-propanediol c. 1,2,3-butanetriol 3. Classify the following monohydric alcohols as primary, secondary or tertiary alcohols. a. 1-pentanol b. 2-pentanol c. 2-methyl-2-butanol 4. Give the IUPAC name for the following alcohols: a. OH b. HO OH c. OH UNIT 6 271  CHEMISTRY GRADE 11     Activity 6.2 Answer the following questions in groups, and share your answers with the whole class. 1. Is the bond in −O−H polar or non-polar? Why? 2. Compare the physical state of the first four members of monohydric alcohols and alkanes. 3. Lower alcohols, like methanol and ethanol, are miscible with water in all proportions, while lower hydrocarbons are not so. Explain. The hydroxyl group in an alcohol is polar due to the high electronegativity of oxygen. As a result, there is significant hydrogen bonding in alcohols (Figure 6.1). δ δ R δ H O H δ δ δ δ δ O H O H O R R Hydrogen R bonding         Due to the hydrogen bonding in alcohols, they have higher melting and boiling points than hydrocarbons of comparable molecular size (mass). Table 6.1 gives some physical constants of the first six monohydric alcohols. Hydrogen bonding is also the cause for even lower members to be liquids at room temperature. 272 UNIT 6  Alcohols and Ethers Group Assignment 6.1 Form a group of five and explain the following facts by searching information from the internet and any other sources. Submit your report inWord and PDF formats. 1. Dihydric and the trihydric alcohols have higher boiling points than monohydric alcohols of similar molecular size (mass). 2. The solubility of alcohols in water decreases with increasing carbon number. 3. The water solubilities of dihydric and trihydric alcohols are higher than those of monohydric alcohols of similar molecular mass. 4. The boiling point of a branched isomer is lower than that of its isomeric straight-chain alcohol. Table 6.1: IUPAC Names, Condensed Structure and Physical Constants of the First Six Monohydric Alcohol Structure of monohy- IUPAC name Melting Boiling Density dric alcohol point (°C) point (°C) (g/mL) CH3OH Methanol −97 64.7 0.792 CH3CH2OH Ethanol −117 78.3 0.789 CH3CH2CH2OH 1-Propanol −126 97.2 0.804 CH3(CH2)2CH2OH 1-Butanol −90 117.7 0.810 CH3(CH2)3CH2OH 1-Pentanol −78.5 138 0.817 CH3(CH2)4CH2OH 1-Hexanol −52 156.5 0.819 UNIT 6 273  CHEMISTRY GRADE 11    The general laboratory methods of preparation of alcohols are: A. Acid-catalyzed hydration of alkenes: Water is added to the double bond of an alkene in the presence of dilute acid such as H2SO4 or H3PO4. General Reaction: H3O+ C C + HOH C C H OH Alkene Alcohol Example 6.11 CH3 H3C H3O+ C CH2 + HOH H3C C CH2 H 25 °C H3C OH 2-Methylpropene (isobutylene) tert-Butyl alcohol Note that hydrogen of the water goes to the carbon of the alkene that contains more hydrogens. Does addition reaction change the hybridization of the carbon items initially held by the double bond? Explain. B. Hydrolysis of alkyl halides: Warming alkyl halides with sodium hydroxide forms alcohols. What does hydrolysis mean? General Reaction: R CH2X heat R CH2OH + NaX + NaOH (X = Cl, Br, I) Alcohol Alkyl halide 274 UNIT 6  Alcohols and Ethers Example 6.12 CH3 CH2Cl + heat NaCl NaOH CH3 CH2OH + Ethyl chloride Ethanol C. Hydrolysis of Esters: Heating esters with potassium hydroxide produces alcohols. General reaction: RCOOR' + KOH heat RCOOK + R'OH Ester Alcohol Example 6.13 heat CH3COOCH2CH3 + KOH CH3COOK + CH3CH2OH Ethyl acetate Ethanol Methods B and C involve the replacement of other groups by the –OH group. Hence, they are examples of substitution reactions. Ethanol (Ethyl Alcohol), CH3CH2OH Activity 6.3 Answer the following questions individually and share your answers with others in the class. 1. Why is the shelf-life of some alcoholic beverages low, while for others it is high? 2. How can you improve the shelf-life of those alcoholic beverages with a low shelf-life? Ethanol is the second member of the homologous series of monohydric alcohols. It is one of the constituents of all alcoholic beverages. ‘Tella’, ‘Tej’, Beer, Wine, ‘Katikalla’, Ouzo, Gin and Whisky contain ethanol. There are a number of methods for preparing ethanol using different materials. Can you categorize the alcoholic beverages as distilled and non-distilled? UNIT 6 275  CHEMISTRY GRADE 11 Industrial preparation of ethanol Ethanol is manufactured industrially by: 1. Fermentation of carbohydrates such as sugar. Fermentation is the slow decomposition of carbohydrates such as sucrose, starch and cellulose in the presence of a suitable enzyme. It results in the formation of ethanol and carbon dioxide: C12H22O11 + invertase C6H12O6 + C6H12O6 H2O Sucrose Glucose Fructose C6H12O6 2CH3CH2OH + 2CO2 Glucose Ethanol Fermentation can produce an alcoholic beverage whose ethanol content is 12– 15% only. Why is it that difficult to produce a higher percentage of alcohols by fermentation? How can a higher ethanol-containing beverage be produced? Most liquor factories in Ethiopia use molasses, a by-product of sugar industries, as a raw material to produce ethanol. In the brewing industry, germinated barley called malt is used as the starting material. The whole process taking place in breweries is summarized as follows: 2(C6H10O5)n + nH2O Diastase nC12H22O11 nH2O 2nC6H12O6 Starch Maltose Maltase Glucose Zymase C6H12O6 2CH3CH2OH + 2CO2 Glucose Ethanol 2. Catalytic Hydration of Ethene: Most ethanol is manufactured at present by this method. In this process, ethene is treated with steam at 573 °K and 60 atm pressures in the presence of phosphoric acid, H3PO4, catalyst. H3PO4 CH2 CH2 (g) + H2O (g) CH3CH2OH (g) Ethene 573 K/60 atm Ethanol 276 UNIT 6  Alcohols and Ethers Experiment 6.1 Preparation of Ethanol by Fermentation Objective: To prepare ethanol from sugar. Materials and chemicals: Conical flask, glass rod, distillation flask, condenser, spatula, thermometer, watch glass, Bunsen burner, tripod, boiling chips, beaker, stopper and delivery tube. Sugar, ammonium phosphate or ammonium sulphate, yeast, Ca(OH)2. Procedure: 1. Take 50 mL of distilled water in a conical flask, add 15 g of sugar to it and stir. Add about 1 gram of yeast and a small amount of ammonium phosphate or ammonium sulphate to the solution. Arrange the setup, as shown in   and let the flask stand for three days at a warm place.       Observations and analysis: A. What is the purpose of adding yeast to the solution? B. Why do we add ammonium phosphate or ammonium sulphate to the sugar solution? C. What happened to the calcium hydroxide solution at the end of the first or second day? Which gas is produced? D. What is the smell of the solution in the flask after three days? E. What has happened in the flask containing the sugar solution as it stood for three days? UNIT 6 277  CHEMISTRY GRADE 11 F. After three days, filter the solution, and arrange the set up as in  Pour 20 mL of the filtrate in a distilling flask, with a few boiling chips, heat the solution, and collect the liquid in a receiver.       Points to observe: A. Observe the colour and identify the smell of the distillate. B. Pour a small amount of the distillate on a watch glass, strike a match and bring the flame close to the distillate. Does it catch fire? C. Write a complete laboratory report on this experiment and submit it to your teacher. 278 UNIT 6  Alcohols and Ethers Project 6.1 Form a group of five and do the following activities. Submit Word and PDF documents to your teacher. 1. Search the preparation of “Katikalla”, “Tela”, “Tej”, and other locally prepared alcoholic beverages in your community by interviewing elders. Report your findings to the whole class. 2. Choose one locally prepared non-distilled alcoholic beverage in your community and illustrate its preparation. 3. Compare the traditional and industrial methods of preparing alcoholic beverages. 4. Search the internet or any other sources to summarize the properties and uses of ethanol.      Activity 6.4 Discuss the following questions in groups, and write a report. Present your report to the class. 1. Why do alcoholic beverages such as “Tela”, “Tej”, beer and wine turn sour if they are not properly stored? Which reaction of alcohols is responsible for this? Write a chemical equation to support your answer. 2. What types of reactions do alcohols undergo? Alcohols contain a hydrocarbon group and a functional group (–OH). Which part of alcohols is responsible for most of their chemical reactions? Reactions of alcohols may involve the cleavage of the oxygen–hydrogen bond (– O–H) or the carbon-oxygen bond (–C–O). 1. Reactions of alcohols involving cleavage of –O–H bond a. Reaction with Active Metals Alcohols react with Li, Na, K, Mg, and other active metals to liberate hydrogen and to form metal alkoxides. UNIT 6 279  CHEMISTRY GRADE 11 General reaction: 2 R CH2 O H + 2 Na 2 R CH2 O Na + H2 Alcohol Sodium alkoxide Example 6.14 - 2 CH3 CH2 O H + 2 Na 2 CH3 CH2 O Na + + H2 Ethanol Sodium ethoxide Experiment 6.2 Reactions of Alcohols with Active Metals Objective: To observe the reaction of alcohols with sodium and magnesium. Materials required: Ethanol, sodium and magnesium metal. Test tubes, test tube holder, test tube rack, measuring cylinder, Bunsen burner, scissors or knife. Procedure: Take two test tubes and add 2-5 mL of ethanol to each of the test tubes. Cut a very small piece of sodium with a knife and drop it into the first test tube. Take magnesium ribbon and drop it in the second test tube. Observations and analysis: A. What do you observe a. in the first test tube? b. in the second test tube? B. Is there an evolution of gas? How do you check this gas is hydrogen? C. If no reaction occurs in any of the test tubes, heat the mixture gently using a Bunsen burner and write your observation. D. Which bond of the alcohol is broken in the reaction? E. Write a general reaction for such reactions. F. What type of metals reacts in this manner? b. Oxidation of alcohols The oxidation products of alcohols depend on the type of alcohol and the nature of oxidizing agents. Oxidation of alcohols is a very important method for the production of other oxygen-containing organic compounds, such as aldehydes, ketones and carboxylic acids. 280 UNIT 6  Alcohols and Ethers i. Oxidation of primary alcohols Depending on the oxidizing agent used, a primary alcohol is oxidized to an aldehyde which in turn is oxidized to a carboxylic acid in the presence of mild oxidizing agents such as copper metal, primary alcohols yield aldehydes. General reaction: O Cu R CH2 OH R C H Primary alcohol 360 °C Aldehyde Example 6.15 O Cu CH3 CH2 OH CH3 C H Ethanol 360 °C Ethanal Strong oxidizing agents, such as acidified KMnO4 or K2Cr2O7 or CrO3 in H2SO4, oxidize primary alcohol first to aldehydes and then to carboxylic acids. It is difficult to stop the reaction at the aldehyde stage. General reaction: O O KMnO4/ H KMnO4/ H R CH2 OH R C H R C OH Primary alcohol Aldehyde Carboxylic acid Example 6.16 O O KMnO4/ H KMnO4/ H CH3 CH2 OH CH3 C H CH3 C OH Ethanol Ethanal Ethanoic acid Is there any possibility to prepare aldehydes from primary alcohols? ii. Oxidation of secondary alcohols yields ketones General reaction: OH O [O] R C R' R C R' H Secondary alcohol Ketone UNIT 6 281  CHEMISTRY GRADE 11 Example 6.17 OH O + KMnO4/H H3C C H H3C C CH3 CH3 Propanol 2-Propanol (acetone) iii. Tertiary alcohols and ketones are generally resistant to oxidation OH [O] R C R' No reaction under normal conditions R'' Tertiary alcohol What happens if 3° alcohols subject to oxidation under drastic conditions? Group Assignment 6.2 Do the following activity in a group of five and share your responses with the whole class. Alcohols A, B, and C all have the composition C4H10O. Molecules of alcohol A contain a branched carbon chain and can be oxidized to an aldehyde; molecules of alcohol B contain a linear carbon chain and can be oxidized to a ketone; and molecules of alcohol C can be oxidized to neither an aldehyde nor a ketone. Predict the structural formulas of these molecules. 2. Reactions involving cleavage of carbon–oxygen (C – O) bond in alcohols a. Dehydration of alcohols: Alcohols undergo dehydration (removal of a molecule of water) to form alkenes on treating with an acid such as concentrated H2SO4 or H3PO4 and heating. 282 UNIT 6  Alcohols and Ethers General reaction: H H Conc.H2SO4 R H R C C OH C C + H2O ∆ H H H H Alcohol Alkene In general, dehydration of primary alcohols is difficult and requires concentrated acid and high temperature. Example 6. 18 Ethanol dehydrates in the presence of concentrated H2SO4 and heating at 170 °C. H H Conc.H2SO4 H H H C C OH C C + H2O 170 °C H H H H Ethanol Ethene Secondary and tertiary alcohols dehydrate under milder conditions. Example 6.19 OH 85% H3PO4 CH3 CH CH3 CH3 CH CH2 + H2O 167 °C 2-Propanol Propene CH3 CH2 20% H3PO4 CH3 C OH CH3 C CH3 + H2O 85 °C CH3 2-Methyl-2-propanol 2-Methylpropene Arrange primary, secondary, and tertiary alcohols in the degree of dehydration order. b. Reactions of alcohols with hydrogen halides: Alcohols react with hydrogen halides to form alkyl halides. UNIT 6 283  CHEMISTRY GRADE 11 General reaction: R CH2 OH + HX R CH2 X + H2O Alcohol (X = Cl, Br, I) Alkyl halide Example 6.20 CH3 CH2 OH + HBr CH3 CH2 Br + H2O Ethanol Ethyl bromide (1-bromoethane) Is it possible to produce alcohols from alkyl halides? Exercise 6.2 1. What is the functional group in alcohols? 2. Classify the following alcohols as primary, secondary and tertiary alcohols: a. 3-hexanol b. 2-methyl-2-pentanol c. 3-methyl-2-butanol d. 1-heptanol e. 2-methyl-1-propanol f. 2,3-dimethyl-2-butanol 3. Compare boiling points of alcohols and hydrocarbons of similar molecular mass. Explain if there is any difference. 4. Complete the following chemical reactions in your exercise book: CrO3/H2SO4 a. CH3CH2CH2CH2OH OH b. H3C CH2 K2Cr2O7/ H CH CH2CH3 284 UNIT 6  Alcohols and Ethers     Activity 6.5 Try to answer the following questions in groups, and present your responses to the whole class. 1. Diethyl ether (CH 3CH 2-O-CH 2CH 3) is prepared from ethyl alcohol (CH 3CH 2-OH). Based on these information and your prior knowledge of molecular structures, discuss these questions. a. From CH 3CH 2-OH and CH 3CH 2-O-CH 2CH 3, which one do you expect to have higher boiling point? b. Which one of these compounds is more soluble in water? Why? Ethers are compounds in which an oxygen is bonded to two alkyl substituents (R− O−R’), where R and R’ may be the same or different. If the alkyl substituents are identical, the ether is a symmetrical ether. If the substituents are different, the ether is an unsymmetrical ether. R −O−R R − O − R' a symmetrical ether an unsymmetrical ether The common name of an ether consists of the names of the two alkyl substituents (in alphabetical order), followed by the word “ether”. The smallest ethers are almost always named by their common names. Example: 6.21 CH3 a. CH3 O CH2CH3 b. CH3CH2 O CH2CH3 c. CH3CH O CH2CH3 ethylmethyl ether diethyl ether ethylisopropyl ether The IUPAC system names ether as an alkane with an RO− substituent. The substituents are named by replacing the “yl” ending in the name of the alkyl substituent with “oxy”. CH3O CH3CH2O CH3CHO methoxy ethoxy CH3 isopropoxy UNIT 6 285  CHEMISTRY GRADE 11 Example 6.22 OCH3 a. CH3CHCH2CH3 b. CH3CH2CH2CH2CH2 OCH2CH3 2-methoxybutane 1-ethoxypentane Exercise 6.3 1. Give the systematic (IUPAC) name for each of the following ethers: a. CH3CH2CH2OCH2CH2CH2CH3 b. CH3CH2CH2CH2CHCH2CH3 OCH3 2. What are the common names of the compounds given in question 1?     Ethers are polar compounds in which oxygen bears a partial negative charge and each carbon bonded to it bears a partial positive charge (Figure 6.4). How do ethers differ from alcohols? The boiling points of ethers are much lower than those of alcohols of comparable molecular weight. For example, the boiling points of ethanol (78 °C) is much higher than its constitutional isomer dimethyl ether (-24 °C). The difference in boiling points between these two compounds is due to the polar O−H group in the alcohol, which is capable of forming intermolecular hydrogen bonds. How do you rate the boiling points of ethers and hydrocarbons of comparable molecular weight? only very weak dipole-dipole interaction H H H δ H C H O δ C C Oδ δ δ Cδ H H H H H H H                  286 UNIT 6  Alcohols and Ethers Because the oxygen atom of ether carries a partial negative charge, ethers form hydrogen bonds with water (Figure 6.5) and are more soluble in water than are hydrocarbons of comparable molecular weight and shape. H H δ C H δ O δ δ H H Oδ Cδ H hydrogen bonding H H        Exercise 6.4 1. Arrange these compounds in order of increasing solubility in water: a. CH 3OCH 2CH 2OCH 3 b. CH 3CH 2OCH 2CH 3 c. CH 3CH 2CH 2CH 2CH 2CH 3 2. Arrange these compounds in order of increasing boiling point: a. CH 3OCH 2CH 2OCH 3 b. HOCH 2CH 2OH c. CH 3OCH 2CH 2OH 3. Write the condensed structures of both isomers with the formula C2H 6O. Label the functional group of each isomer.   1. Dehydration of alcohols Alcohol undergoes dehydration in the presence of protic acids (sulphuric acid, phosphoric acid) to produce alkenes and ethers under different conditions. For example, ethanol is dehydrated to ethene at 170 °C in the presence of sulphuric acid. On the other hand, ethanol yields ethoxyethane in the presence of sulphuric acid at 140 °C. The method is limited to use with primary alcohols. H2SO4 CH3CH2OH CH2 CH2 + H2O ο Ethanol 170 C water Ethene H2SO4 2CH3CH2OH CH3CH2OCH2CH3 + H2O Ethanol 140 οC Diethyl ether water UNIT 6 287  CHEMISTRY GRADE 11 What is the problem if we use secondary and tertiary alcohols? Does this method work for the synthesis of both symmetrical and unsymmetrical ethers? 2. Williamson ether synthesis In this method, an alkyl halide is made to react with an alkoxide which leads to the formation of ether. R X + R O R O R + X Alkyl halide Alkoxide ion Ether Can this method be used for the preparation of both symmetrical and unsymmetrical ethers? Example 6.23 CH3CH2Br + CH3O CH3CH2OCH3 + Br ethyl bromide methoxide ion ethyl methyl ether CH3CH2CH2CH2I + CH3CH2O CH3CH2CH2CH2OCH2CH3 + I butyl iodide ethoxide ion butyl ethyl ether   Ethers, R−O−R, resemble hydrocarbons in their resistance to chemical reaction. They do not react with oxidizing agents, such as K2Cr2O7 or KMnO4. Ethers are not affected by bases, however, they can react with proton donors to form oxonium salts. Example 6.24 CH3CH2OCH2CH3 + HBr CH2CH3 O CH2CH3 Br H An oxonium salt Heating dialkyl ethers with very strong acids (HI, HBr, and H2SO4) cleaves the ether linkage: ∆ CH3CH2OCH2CH3 + 2 HBr 2 CH3CH2Br + H2O 288 UNIT 6  Aldehydes and Ketones Ethers are not affected by most reagents at moderate temperatures. Because of their good solvent properties and general inertness to chemical reaction, ethers are excellent solvents in which to carry out many organic reactions. Exercise 6.5 1. What are the common uses of ethers in medicine and industry? 2. Outline how the alkoxide ion is prepared for the Williamson ether synthesis using a chemical equation. 6.3  At the end of this section, you will be able to: ) write the general structural formulas of aldehydes and ketones ) give the structures and names of common members of each group ) describe the physical properties of aldehydes and ketones ) explain some methods of preparation of aldehydes and ketones ) explain the chemical reactions of aldehydes and ketones such as addition, oxidation and reduction ) give some chemical tests that differentiate aldehydes from ketones. Activity 6.6 Answer the following questions in groups then present your response to the whole class. 1. What functional group form if one of the carbon in the C=C is replaced by an oxygen atom? 2. What is the common type of reaction for alkenes? 3. Which type of reaction do you expect for aldehydes and ketones? The functional group of an aldehyde is a carbonyl group (C=O) bonded to a hydrogen atom. In methanal (formaldehyde), the carbonyl group is bonded to two hydrogen atoms. In other aldehydes, it is bonded to one hydrogen atom and one carbon atom. The functional group of a ketone is a carbonyl group bonded to two carbon atoms. UNIT 6 289  CHEMISTRY GRADE 11 O O or RCHO C or RCOR' where R and R' may be C R R H R' same or different. Aldehyde Ketone What are the simplest ketone and simplest aldehyde?   The IUPAC system of nomenclature for aldehydes and ketones follows the familiar pattern of selecting the longest chain of carbon atoms that contains the functional group as the parent alkane. Aldehydes are named by changing the suffix -e of the parent alkane to –al. The suffix “-al” indicates the functional group –CHO. Example 6.25 O O O H C H CH3 C H CH3 CH2 C H Methanal Ethanal Propanal Because the carbonyl group of an aldehyde can appear only at the end of a parent chain and numbering must start with that group as carbon-1, its position is unambiguous; there is no need to use a number to locate it. Example 6.26 CH3 O C2H5 O 4 3 2 1 5 4 3 2 1 CH3 CH CH2 C H H3C CH2 CH2 CH C H 3-Methylbutanal 2-Ethylpentanal The functional group of a ketone is a carbonyl group bonded to two carbon atoms. The IUPAC names of ketones are obtained by using the suffix -one to replace the terminal -e in the corresponding alkane name. The suffix ‘-one’ indicates the functional group –RCOR’. Example 6.27 O O CH3 C CH3 CH3 C CH2 CH3 Propanone Butanone 290 UNIT 6  Aldehydes and Ketones Unlike aldehydes, the position of the functional group must be indicated in the name of higher ketones. To do so, the longest chain containing the functional group is chosen as a parent structure and then the carbon atoms of the chain are numbered starting from the end closer to the carbonyl group. Example 6.28 O H H H O H 1 2 3 C 4C 5 1 2 3 4 5 CH3 C CH3 H3C C C C CH3 H H H H 2-Pentanone or pentan-2-one 3-Pentanone or pentan-3-one Give structures and name of ketones containing six (6) carbon atoms. Hint: consider isomeric forms including cyclic ones.          Oxygen is more electronegative than carbon; therefore, a carbon–oxygen double bond is polar, with oxygen bearing a partial negative charge and carbon bearing a partial positive charge: δ δ C O Polarity of a carbonyl group Because of the polarity of the carbonyl group, aldehydes and ketones are polar compounds and interact in the liquid state by dipole–dipole interactions. As a result, aldehydes and ketones have higher boiling points than those of non-polar compounds with comparable molecular weight. For example, butanal and butanone both have a molecular mass (MM) of 72. The boiling point of butanal is 76 °C and of butanone is 80 °C, which is much higher than the boiling points of diethyl ether (MM) 74, 34 °C and pentane (MM) 72, 36 °C. Because the carbonyl groups of aldehydes and ketones interact with water molecules by hydrogen bonding, low-molecular-weight aldehydes and ketones are more soluble in water than are non-polar compounds of comparable molecular weight. Table 6.2 lists the boiling points and solubilities in water of several low-molecular-weight aldehydes and ketones. UNIT 6 291  CHEMISTRY GRADE 11 Table 6.2: Physical properties of selected aldehydes and ketones Name Common Name Structural Formula Boiling Solubility Point (°C) (g/100 g water) Methanal Formaldehyde HCHO -21 infinity Ethanal Acetaldehyde CH3CHO 20 infinity Propanal Propionaldehyde CH3CH2CHO 49 16 Butanal Butyraldehyde CH3CH2CH2CHO 76 7 Hexanal Caproaldehyde CH3(CH2)4CHO 129 slight Propanone Acetone CH3COCH3 56 infinity Methyl ethyl 2-Butanone CH3COCH2CH3 80 26 ketone 3-pentanone Diethyl ketone CH3CH2COCH2CH3 101 5 Project 6.2 Form a group of five and write on the following topics by searching information from the internet or any other sources. For each case, give the general reaction and specific examples. i. Method of preparation of aldehydes and ketones. These may include: a. ozonolysis of alkenes b. oxidation of alcohols: oxidation of a primary alcohols using mild oxidizing agents oxidation of a secondary alcohol ii. Reactions of aldehydes and ketones. Here focus on addition, oxidation, and reduction reactions. a. Addition Addition of Grignard reagents to aldehydes and ketone Addition of alcohol: formation of hemiacetals and acetals b. Oxidation Oxidation of aldehydes and ketones c. Reduction Catalytic reduction of aldehydes and ketones Metal hydride reductions 292 UNIT 6  Aldehydes and Ketones Exercise 6.6 1. Which of the following statements is false? Give your reason. a. The carbonyl carbon in all aldehydes is bonded to a hydrogen and to an alkyl group. b. Ketones are more soluble in water than alcohols of comparable molecular weight. c. Any reaction that oxidizes an aldehyde to a carboxylic acid will also oxidize a ketone to a carboxylic acid. 2. Draw a structural formula for the one ketone with molecular formula C4H 8O and for the two aldehydes with molecular formula C4H 8O. 3. Draw structural formulas for these compounds: a. 1-Chloro-2-propanone b. 3-Hydroxybutanal c. 4-Hydroxy-4-methyl-2-pentanone 4. Give the IUPAC name of the following compounds: O O a. b. H 5. Formalin helps in the preservation of biological specimens. What is the main constituent of formalin? UNIT 6 293  CHEMISTRY GRADE 11 6.4  At the end of this section, you will be able to: ) list common organic acids and name their sources ) write the general formula of saturated monocarboxylic acids ) write the molecular formulas and names of the first six members of the saturated monocarboxylic acids ) give the structural formula for the first four members of the saturated monocarboxylic acids ) give the examples of mono, di and tricarboxylic acids ) name some branched carboxylic acids] ) explain why “Tella” or “Tej” turns sour ) describe the physical and chemical properties of saturated monocarboxylic acids ) explain the general methods of preparation of saturated monocarboxylic acids ) explain the industrial and laboratory preparation of acetic acid ) conduct an experiment to prepare acetic acid in the laboratory ) name and write structural formulas of some fatty acids ) describe some uses of common carboxylic acids.          Activity 6.7 Discuss the following questions in groups, then present your response to the whole class. 1. What are acids? 2. Name some common house-hold carboxylic acids. 294 UNIT 6  Carboxylic Acids     Carboxylic acid is one of the class of organic compounds containing the carbonyl functional group (C=O). A carboxyl group (COOH) is a functional group consisting of a carbonyl group (C=O) with a hydroxyl group (O−H) attached to the same carbon atom. It is usually written as —COOH or —CO2H. O C OH Carboxyl group A. Saturated monocarboxylic acids The general formula for saturated monocarboxylic acids can be written as: O R C OH where R is either hydrogen or an alkyl group for aliphatic carboxylic acids. When R is phenyl (aryl) group, the structure represents aromatic carboxylic acids. Example 6.29 1. The structure of the first three saturated monocarboxylic acids are written as follows: O a. H C OH Methanoic acid O b. CH3 C OH Ethanoic acid O c. CH3 CH2 C OH Propanoic acid 2. The simplest aromatic acid is benzoic acid. COOH Benzene carboxylic acid (Benzoic acid) UNIT 6 295  CHEMISTRY GRADE 11 B. Di- and tricarboxylic acids Carboxylic acids containing two carboxyl groups in their structure are called dicarboxylic acids. Example 6.30 1. The structure of the first three saturated dicarboxylic acids are shown below: O O a. HO C C OH Ethanedioic acid O O b. HO C CH2 C OH Propanedioic acid O O c. HO C CH2 CH2 C OH Butanedioic acid 2. The simplest aromatic dicarboxylic acid occurs in three isomeric forms. One of these is phthalic acid; its structure and IUPAC name are shown below. COOH COOH 1, 2- Benzenedicarboxylic acid (phthalic acid) Give the structures, IUPAC and common names of the other two isomers. Similarly, carboxylic acids that contain three carboxyl groups in their structure are called tricarboxylic acids. Example: citric acid is a typical tricarboxylic acid. Can you give the structure of citric acid? Activity 6.8 Form a group and make a list of some fruits containing carboxylic acid. Which acid is commonly present in most fruits? Which carboxylic acid is present in wine fruits? Is this acid a monocarboxylic, a dicarboxylic or a tricarboxylic acid? Present your responses to the whole class. 296 UNIT 6  Carboxylic Acids Exercise 6.7 1. Write the structure of the following monocarboxylic acids: a. Butanoic acid b. Pentanoic acid 2. Write the structure of the following dicarboxylic acids: a. Pentanedioic acid b. Hexanedioic acid c. 1,3-Benzenedicarboxylic acid 3. A great many carboxylic acids are encountered in nature. List some of them and their respective sources.        i. Common names carboxylic acids A. Straight chain monocarboxylic acids A large number of carboxylic acids have widely used common names which need to be learned. The common names of some basic carboxylic acids are derived from Latin names that indicate the first original natural source of the carboxylic acid. Table 6.3 lists common names of some of the most important monocarboxylic acids. Table 6.3: Common names of some monocarboxylic acids. Structure of Acid Natural Source Common Name HCOOH Ants (Formica) Formic acid CH3COOH Vinegar (Acetum) Acetic acid CH3CH2COOH Basic Fat (Propio) Propionic acid CH3CH2CH2COOH Rancid butter (Butyrum) Butyric acid CH3CH2CH2CH2COOH Present in a Valerian herb Valeric acid CH3CH2CH2CH2CH2COOH Goat (Caper) Caproic acid Note that the common name of carboxylic acids end with the suffix –ic acid. UNIT 6 297  CHEMISTRY GRADE 11 B. Branched chain and substituted carboxylic acids In common naming system, the branched chain and substituted acids are named as derivatives of straight chain carboxylic acids. In this case, the position of the side chain or substituents is indicated by Greek letters, α, β, γ, δ... for designating the 1st, 2nd, 3rd,… position of carbon atoms as shown below: O δ γ β α C C C C C OH 5 4 3 2 1 Example 6.31 β α δ γ β α a. CH3 CH COOH b. CH3 CH CH2 CH COOH Cl CH3 CH3 α-chloropropionic acid α,γ-dimethyvaleric acid C. Dicarboxylic acids Dicarboxylic acids also possess common names which are based on their sources. Table 6.4 lists common and IUPAC names of some of the most important dicarboxylic acids. Table 6.4: Common and IUPAC names of some dicarboxylic acids. Structure Common Name IUPAC Name HOOC−COOH Oxalic acid Ethanedioic acid HOOC−CH2−COOH Malonic acid Propanedioic acid HOOC−(CH2)2−COOH Succinic acid Butanedioic acid HOOC−(CH2)3−COOH Glutaric acid Pentanedioic acid HOOC−(CH2)4−COOH Adipic acid Hexanedioic acid HOOC−(CH2)5−COOH Pimelic acid Heptanedioic acid 298 UNIT 6  Carboxylic Acids D. Aromatic carboxylic acids Aromatic carboxylic acids are compounds which have a carboxyl group directly attached to an aromatic ring. The common name of the simplest aromatic carboxylic acid is benzoic acid. O C OH Benzoic acid In common naming system, the position of the substituent is indicated by the prefixes ortho (o-), meta (m-), para (p-) as it is shown in the structure below. O C OH ortho ortho meta meta para Example 6.32 COOH COOH CH3 a. b. Cl CH3 m-chlorobenzoic acid o,p-dimethylbenzoic acid. UNIT 6 299  CHEMISTRY GRADE 11 Exercise 6.8 1. Write the common names for the following carboxylic acids: a. CH3 CH CH2 CH COOH b. HOOC (CH2)2 CH2 COOH Br Cl 2. Write the structures of carboxylic acids for the given common names: a. β-Bromobutyric acid b. p-bromobenzoic acid c. glutaric acid ii. IUPAC names of carboxylic acids A. Straight chain monocarboxylic acid In IPUAC system, monocarboxylic acids are named by replacing the terminal “−e” of the corresponding alkane name with “−oic acid.” They are named as alkanoic acids. Example 6.33 1. Write the IPUAC names for: a. H-COOH b. CH3-CH2-COOH c. CH3-CH2-CH2 CH2-COOH methanoic acid propanoic acid pentanoic acid 2. Write the structure of the following carboxylic acids: a. Ethanoic acid b. Butanoic acid c. Hexanoic acid O O O a. CH3 C OH b. CH3 CH2 CH2 C OH c. CH3 CH2 CH2 CH2 CH2 C OH B. Branched chain and substituted monocarboxylic acids The IUPAC name of a branched carboxylic acid is derived from that of the longest carbon chain that contains the carboxyl group. The positions of the substitutes are indicated by Arabic numerals as 1, 2, 3. The numbering of the chain starts from the carboxyl carbon and it is always assigned C-1 position. Note that C-2 position in the IUPAC system corresponds to the α-position in the common naming system. O δ γ β α Common System C C C C C OH 5 4 3 2 1 IUPAC System Example 6.34 a. CH3–CH(CH3)CH2–COOH b. CH3–CH2CH(Cl)–CH(CH3)–COOH 3-methylbutanoic acid 3-Chloro-2-methylpentanoic acid 300 UNIT 6  Carboxylic Acids C. Dicarboxylic acids In the IUPAC system, dicarboxylic acids are named as alkanedioic acids. These names are obtained by replacing the suffix ‘‘–e’’ in the name of corresponding alkane by ‘‘–dioic acid’’. Table 6.4 above gives the common and IUPAC names of the first six dicarboxylic acids. Example 6.35 HOOC–CH2–CH2–COOH Butanedioic acid Write the structure of hexaneanedioic acid. D. Aromatic carboxylic acids IUPAC name of the simplest aromatic carboxylic acid is benzenecarboxylic acids. COOH Benzenecarboxylic acid Substituted aromatic acids with one carboxyl group are named as derivatives of benzenecarboxylic acids. The position of substituents is indicated using the Arabic numerals 2,3, etc according to their position on the benzene ring relative to the carboxyl group. The carbon on which the carboxyl group is attached is by convention C-1. COOH COOH 1 1 6 2 6 2 or 5 3 5 3 4 4 Example 6.36 COOH 1 6 2 Br 5 3 4 2-bromobenzenecarboxylic acid UNIT 6 301  CHEMISTRY GRADE 11 Exercise 6.9 1. Write the IUPAC names for the following carboxylic acids: a. CH3 CH COOH b. CH3 CH CH2 CH COOH CH2CH3 CH2 CH3 CH3 c. Cl CH2 CH2 CH2 COOH d. HO CH2 CH2 CH2 COOH COOH NH2 e. Cl f. CH2CH3 COOH 2. Draw the structures of the following carboxylic acids: a. 3-chloro-2,3-dimethylpentanoic acid b. 4-bromo-2-hydroxybenzoic acid c. p-Methylbenzoic acid d. 2-ethyl-3-methylpentanedioic acid        Activity 6.9 Discuss the following questions in groups, then present your ideas to the whole class. 1. The solubility of monocarboxylic acids in water decreases with increase in molecular mass. Explain. 2. Higher members of monocarboxylic acids are almost odourless. Why? 3. Compare the boiling points of monocarboxylic acids with alcohols, aldehydes and ketones of similar molar masses? 1. State The lower aliphatic acids containing up to 9 carbon atoms are liquids, whereas the higher members are colourless waxy solids. Benzoic acid and most of its derivatives are also colourless solids. 302 UNIT 6  Carboxylic Acids 2. Odor The odors of the lower aliphatic acids progress from a sharp, irritating odor of methanoic acid and ethanoic acids to the distinctly unpleasant odor of the butanoic, pentanoic and hexanoic acids. 3. Melting and Boiling Points The melting points and boiling points of carboxylic acids are higher than those of hydrocarbons and oxygen-containing organic compounds of comparable size and shape and indicate strong intermolecular attractive forces. Figure 6.6 gives boiling point comparison of carboxylic acid with alkene, ketone, and alcohol. What is the molecular mass of each compound shown in Figure 6.6? O OH O OH 2-Methyl-1-butene 2-Butanone 2-Butanol Propanoic acid bp (1 atm): 31 °C 80 °C 99 °C 141 °C                    A unique hydrogen-bonding arrangement, shown in Figure 6.7, contributes to these attractive forces. The hydroxyl group of one carboxylic acid molecule acts as a proton donor toward the carbonyl oxygen of a second. In a reciprocal fashion, the hydroxyl proton of the second carboxyl function interacts with the carbonyl oxygen of the first. The result is that the two carboxylic acid molecules are held together by two hydrogen bonds. Hydrogen bonding δ δ δ O H O R C Carboxylic acid Carboxylic acid C R O H O δ δ δ Hydrogen bonding 
    UNIT 6 303  CHEMISTRY GRADE 11 4. Solubility In aqueous solution intermolecular association between carboxylic acid molecules is replaced by hydrogen bonding to water. The solubility properties of carboxylic acids are similar to those of alcohols. Carboxylic acids of four carbon atoms or fewer are miscible with water in all proportions. Figure 6.8 shows hydrogen bonding between carboxylic acids and water molecules. Water Hydrogen bonding δ Ο δ δ δ O Η Η δ C Η Carboxylic acid δ δ δ R O H Ο Water R δ Carboxylic acid Ηδ O C Hydrogen δ δ bonding O H                      Does the solubility carboxylic acids in water decrease or increase with increasing molecular mass? Why? Do you predict that carboxylic acids will be soluble in organic solvents? Explain. The boiling points, melting points and solubilities of some carboxylic acids are given in Table 6.5. Table 6.5: Physical constants of some carboxylic acids Boiling point Solubility (g/100 mL) Structure IUPAC Name (°C) H2O at 25 °C HCOOH Methanoic acid 100.5 ∞* CH3COOH Ethanoic acid 118 ∞* CH3CH2COOH Propanoic acid 141 ∞* CH3(CH2)2COOH Butanoic acid 164 ∞* CH3(CH2)3COOH Pentanoic acid 187 4.97 CH3(CH2)4COOH Hexanoic acid 205 1.08 304 UNIT 6  Carboxylic Acids Boiling point Solubility (g/100 mL) Structure IUPAC Name (°C) H2O at 25 °C CH3(CH2)5COOH Heptanoic acid 223 CH3(CH2)6COOH Octanoic acid 239 0.07 CH3(CH2)7COOH Nonanoic acid 253 — CH3(CH2)8COOH Decanoic acid 269 0.015 ∞* means miscible in all proportions. Exercise 6.10 1. Arrange the following aliphatic carboxylic acids in the decreasing order of boiling point: a. butanoic acid c. octanoic acid b. decanoic acid d. propanoic acid 2. Which of these aliphatic carboxylic acids has the lowest boiling point? a. pentanoic acid c. hexanoic acid b. methanoic acid d. propanoic acid 3. Arrange the following compounds in increasing order of their boiling points: a. C5H 12 c. C4H 11OH b. C2H 5COOH d. CH 3(CH 2) 4COOH       Activity 6.10 Form a group, discuss the following questions and present your responses to the whole class. 1. Why does ‘Tella’ or ‘Tej’ turn sour when kept for a longer time but not Katikalla? 2. Why does beer have a longer shell life than ‘Tella’? 3. What is the practical use of metal salts of carboxylic acids in your daily life? UNIT 6 305  CHEMISTRY GRADE 11 The carboxylic acids show reactions due to the alkyl or aryl group and the carboxyl group. The carboxyl group is further considered to be made up of a carbonyl and a hydroxyl group. All these groups modify the properties of each other due to their interaction. Some of the common reactions of carboxylic acids are: i. Reaction as an acid In aqueous solution, the cleavage of O–H bond occurs leading to the formation of carboxylate ion and hydronium ion. Carboxylic acids ionize partially and an equilibrium exists between the ionized and un-ionized forms. O O R C O H + H2O R C O + H3O Carboxylic acid Carboxylate ion Hydronium ion Carboxylic acids are weak acids and dissociates slightly. The following are examples of reactions of carboxylic acids as an acid. a. Reaction with metals: Carboxylic acids react with active metals such as Na, K, Mg, Ca, etc. to give metal carboxylate salts, RCO2−M+, and hydrogen gas. O O 2 R C O H + 2 Na 2 R C O Na + H2 Carboxylic Sodium Hydrogen acid carboxylate gas The salts of carboxylic acids are named by writing the name of the metal first, followed by the name of the acid replacing the ending -ic acid by -ate. For example, sodium reacts with ethanoic acid to form sodium ethanoate and hydrogen. 2 CH3 COOH + 2 Na 2 CH3 COO Na + H2 b. Reaction with Bases: Carboxylic acids react with strong bases like sodium hydroxide or potassium hydroxide to form the corresponding metal carboxylate salts and water. O O R C OH + NaOH R C O Na + H2O Carboxylic acid Sodium carboxylate 306 UNIT 6  Carboxylic Acids Reaction with a base is a simple neutralization reaction. Carboxylic acids react with weak bases like carbonates or bicarbonates to form salt, water and carbon dioxide. O O 2 R C OH + Na2CO3 2 R C O Na + H2O + CO2 Carboxylic acid Sodium carboxylate O O R C OH + NaHCO3 R C O Na + H2O + CO2 Carboxylic acid Sodium carboxylate They also react with ammonia to form ammonium salts of carboxylic acids. O O R C OH + NH3 R C O NH4 Carboxylic acid Ammonium carboxylate ii. Formation of Esters One of the important reactions of carboxylic acids involves the replacement of –OH group by an alkoxy group to form esters as products. In this reaction, carboxylic acids are heated with alcohols in the presence of concentrated sulphuric acid. The reaction is called esterification. O O H2SO4 R C OH + H O R' R C O R' + H2O Alcohol Ester Carboxylic acid Exercise 6.11 1. Write the chemical equations for the reaction between ethanoic acid and each of the following reagents and write the names of the products formed: a. KOH b. Na 2CO 3 c. NH 3 2. Write the chemical equations for the reaction between methanoic acid and ethanol and write the name of the product. UNIT 6 307  CHEMISTRY GRADE 11      One of the important methods for preparation of carboxylic acids is oxidation. Many saturated monocarboxylic acids are obtained by the oxidation of the corresponding primary alcohols, whereas aromatic acids are obtained from the corresponding alkylbenzenes. i. Oxidation of Primary Alcohols The primary alcohols are readily oxidized to the corresponding carboxylic acids by their reaction with common oxidizing agents like K2Cr2O7 or KMnO4. O KMnO4 R CH2 OH R C OH 1° Alcohol Carboxylic acid For example, oxidation of ethanol yields acetic acid (ethanoic acid). O KMnO4 CH3 CH2 OH CH3 C OH Ethanol Ethanoic acid ii. Oxidation of Alkylbenzenes Aromatic compounds containing alkyl group as substituent undergo oxidation to form aromatic acids. The reaction involves oxidation with KMnO4 or K2CrO7 under vigorous conditions. The alkyl group is oxidized to carboxyl group irrespective of its size. For example, toluene and ethylbenzene, both give benzoic acid on refluxing with KMnO4 in alkaline medium. 308 UNIT 6  Carboxylic Acids Example 6.37 O CH3 C OH KMnO4 / OH heat Toluene Benzoic acid Write the chemical equations for the oxidation of ethylbenzene with KMnO4 in alkaline medium. iii. Preparation of acetic acid (Ethanoic acid) Acetic acid is one of the important carboxylic acids which is used as food preservative. It can be prepared in laboratory by the oxidation of ethanol with potassium permanganate. It can also be obtained by passing the vapours of ethanol through copper oxide as described in Experiment 6.3. Experiment 6.3 Laboratory Preparation of Acetic Acid Objective: To prepare acetic acid in the laboratory by oxidation of ethanol. Apparatus: Goggles, test tubes, test tube rack, quickfit distillation apparatus, 250 mL beaker, pipettes, Bunsen burner, stand, clamp, tripod, wire gauze, digital balance, blue litmus paper, boiling chips such as fine gravels, broken porcelain pieces, etc. Chemicals: Ethanol, sodium dichromate, 1M sulphuric acid, 0.5M sodium carbonate solution. Procedure: Oxidation of ethanol to ethanoic acid 1. Set up the Quickfit distillation apparatus for refluxing as shown in  2. Place about 10 mL of 1M sulphuric acid into the 250 mL round-bottom flask. UNIT 6 309  CHEMISTRY GRADE 11 3. Add 2-3 g of sodium dichromate (Na2Cr2O7) and a few pieces of boiling chips. Swirl the contents of the flask until the solution is complete (warm if necessary). 4. Cool the mixture under a running tap since the process is exothermic. 5. Add 1 mL of ethanol dropwise into the flask. 6. Boil under refluxfor 20 minutes 7. Arrange the distillation set up as shown in (Figure 6.9 b) and distil up to 2-3 mL 8. Notice the smell of the product (distilled liquid) and compare it with that of ethanol. 9. Add a few drops of the distilled liquid to a small amount of solid sodium carbonate. 10. Add a drop of the distilled liquid to moistened blue litmus paper.   Observation and analysis 1. What happened to the colour of the solution in the flask? 2. What is the role of sodium dichromate in the above reaction? Is it oxidized or reduced? 3. Write the chemical equation for this reaction. 4. What do you conclude from this experiment? 310 UNIT 6  Carboxylic Acids         Large quantities of acetic acid are obtained in industry from fermentation of ethanol. The process is known as Quick Vinegar Fermentation Process. In the process large wooden vats are used which have a perforated bottom. They are packed with wood shavings moistened with old vinegar. Ethanol solution is poured from the top and trickles down slowly to the perforated bottom. From the lower portion, air is pumped in the vat. The bacteria present in old vinegar, ferment the ethanol into acetic acid. The liquor obtained at the bottom is recirculated through the tower. The maximum concentration of acetic acid obtained by this process is about 10%, which can be fractionated to yield glacial acetic acid (anhydrous acetic acid). UNIT 6 311  CHEMISTRY GRADE 11               Activity 6.11 Discuss the following questions in groups and present your answer to the class. You have learned about the six foodstaffs in your lower grade biology lesson. Which one of these foodstaffs produces fatty acid during digestion? Why are they named fatty acids? Fatty acids are carboxylic acids with long hydrocarbon chains. The fatty acids most frequently found in nature are shown in Table 6.6. Most naturally occurring fatty acids contain an even number of carbon atoms and are unbranched. Fatty acids can be classified as saturated or unsaturated. What is the main difference between saturated and unsaturated compounds? 312 UNIT 6  Carboxylic Acids Double bonds in naturally occurring unsaturated fatty acids are never conjugated. How many methylene (−CH2−) group(s) usually separates the double bonds in unsaturated fatty acids?(See Table 6.6). Table 6.6: Some common naturally occurring fatty acids Melting Number Common Name Structure / Formula Point of carbons ( C )  12 Lauric acid CH3(CH2)10COOH 44 14 Myristic acid CH3(CH2)12COOH 58 16 Palmitic acid CH3(CH2)14COOH 63 18 Stearic acid CH3(CH2)16COOH 69 Arachidic 20 CH3(CH2)18COOH 77 acid  Palmitoleic 16 CH3(CH2)5 CH=CH(CH2)7 COOH 0 acid 18 Oleic acid CH3(CH2)7 CH=CH(CH2)7 COOH 13 18 Linoleic acid CH3(CH2)4 CH=CHCH2CH=CH(CH2)7 COOH -5 Linolen-ic CH3CH2CH=CHCH2CH=CHCH2 18 -11 acid CH=CH(CH2)7 COOH The physical properties of a fatty acid depend on the length of the hydrocarbon chain and the degree of unsaturation. The melting points of saturated fatty acids increase with increasing molecular weight because of increased van der Waals interactions between the molecules. Why do unsaturated fatty acids have lower melting points than saturated fatty acids with comparable molecular weights? UNIT 6 313  CHEMISTRY GRADE 11 The melting points of the unsaturated fatty acids decrease as the number of double bonds increases. For example, an 18-carbon fatty acid melts at 69 °C if it is saturated, at 13 °C if it has one double bond, at -5 °C if it has two double bonds, and at -11 °C if it has three double bonds (Table 6.6).     Acetic acid is used as a solvent and as a starting material in the preparation of acetates, acetic anhydride, etc. It is also used to prepare the vinyl acetate polymer which is used in paints and adhesives. Vinegar contains about 8-10% acetic acid which is used in many food items. Perhaps one of the most important industrial applications of long chain carboxylic acid is for making soaps, detergents, and shampoos. Can you suggest some more examples of the use of carboxylic acids in daily life? Exercise 6.12 1. Explain the difference in the melting points of the following fatty acids: a. palmitic acid and stearic acid b. palmitic acid and palmitoleic acid c. oleic acid and linoleic acid 2. What are omega fatty acids? Give some examples of omega fatty acids. 3. What is the difference between omega-3-fatty acids and omega-6-fatty acids? 4. List some essential fatty acids. Why are they called ‘essential’? Project 6.3 Form a group of five and share information on some carboxylic derivatives (anhydrides, amides, and acid chloride), then submit a written word and PDF documents to your teacher. In your write-up, put the following key points into consideration: structures and naming (both IUPAC and common systems) of anhydrides, amides, and acid chloride physical properties of anhydrides, amides, and acid chloride common reactions and methods of preparations. 314 UNIT 6  Esters 6.5  By the end of this section, you will be able to: ) list common sources of esters ) write the general structural formula of esters ) write the molecular formulas and names of some simple esters ) describe physical properties of esters ) explain the chemical properties of esters ) explain the general methods of preparation of esters ) describe some uses of common esters.   Why do some fruits and flowers give out a pleasant smell? Esters are among the most widely occurring compounds in nature. Many esters are pleasant smelling substances and are responsible for the flavor and fragrance of many fruits: for example, apples, pears, bananas, pineapples, strawberries, etc. Oils, fats and waxes of plants or animal origin are all esters. Many esters are found in flowers and form the part of essential oils obtained from flowers.     Esters are derivatives of carboxylic acids in which the hydroxyl group (-OH) of a carboxylic acid is replaced by an alkoxy group (-OR). Esters can be formed by the reaction between acids and alcohols or phenols. In such cases, the hydroxyl group is replaced by an alkoxy group. Esters have the general formula RCO2R’ (or RCOOR’), which can be represented by the general formula: O R C O R' or RCO2R' or RCOOR' Where R = hydrogen, alkyl or an aryl group and R′ = alkyl or an aryl group. UNIT 6 315  CHEMISTRY GRADE 11 Esters are named by the common system and IUPAC system. In both the cases, the name consists of two parts. The first part is named using the part from alcohol. The second part of the name is based on the acid. Therefore, we have to identify the parts coming from the alcohol and the carboxylic acid. The reaction below shows the part coming from the alcohol is attached to the oxygen as an alkyl group, and the acid part is attached to the oxygen through the carbonyl group. O O H+ R C O H + H O R' R C O R' + H2O Alcohol Acid Alcohol Carboxylic acid portion Portion The names of esters are derived from the names of the alcohol (with the ending -yl) and the acid (with the ending -ate or -oate). While writing their names the part of the name derived from the alcohol comes first. When we use the common name of carboxylic acid, the name of the ester is a common name, and when the IUPAC name of the acid is used, we get the IUPAC name for the ester. See the ester formed from ethyl alcohol and ethanoic acid: O O H+ CH3 C O H + H O CH2 CH3 CH3 C O CH2 CH3 + H2O Ethanoic acid Ethyl alcohol Ethyl Ethanoate (Acetic acid) (Ethyl acetate) The common name for this ester is ethyl acetate, and the IUPAC name is ethyl ethanoate.The formulas and names of some esters are listed in Table 6.7. Table 6.7: Names and formulas of some common esters Molecular Structure/Formula Common Name IUPAC Name Formula C2O2H4 HCOOCH3 Methyl formate Methyl methanoate C3O2H6 CH3COOCH3 Methyl acetate Methyl ethanoate C3O2H6 HCOOCH2CH3 Ethyl formate Ethyl methanoate C4O2H8 CH3COOCH2CH3 Ethyl acetate Ethyl ethanoate C4O2H8 HCOOCH2CH2CH3 Propyl formate Propyl methanoate C5O2H10 CH3COOCH2CH2CH3 Propyl acetate Propyl ethanoate Note that in the given Table 6.7 molecular formulas can represent more than one structure. For example, methyl ethanoate and ethyl methanoate have the same molecular 316 UNIT 6  Esters formula, C3O2H6. Similarly, ethyl ethanoate and propyl methaoate have the same molecular formula (C4O2H8). Exercise 6.13 1. Name the following esters. O O a. H C O CH2 CH2 CH3 c. C O CH3 O O b. CH C O d. CH3 CH2 C O 3 2. Identify the acid and alcohol (or phenol) portions of carboxylic esters give in question 1. 3. Write the structure of the following esters: a. Isopropyl methanoate b. Ethyl propanoate   Activity 6.12 Form a group and discuss the following questions. After the discussion, share your ideas with the rest of the class. Which one of the following compounds do you expect to have the highest boiling point? Why? O O a. CH3 CH2 C OH b. CH3CH2 O CH2CH3 c. H C O CH2 CH3 i. Boiling points The boiling points of esters increase with increasing molecular mass. Branched- chain esters have lower boiling points than their straight-chain isomers. Esters have lower boiling points than compounds of comparable molecular mass that are capable of forming hydrogen bonds such as carboxylic acids and alcohols. Ester molecules cannot form hydrogen bonds with each other. UNIT 6 317  CHEMISTRY GRADE 11 ii. Solubility Esters of low molecular mass are fairly soluble in water. Esters have about the same solubility in water with that of the same molecular mass carboxylic acids. Because carboxylic esters can form hydrogen bonding with water Figure 6.11, the solubility of esters in water decreases as their molecular mass increase. All esters are soluble in organic solvents. δ δ O δ R O H H δ O C δ C δ O R O R' δO H δ Hδ R'         iii. Odor In sharp contrast to the disagreeable odors of carboxylic acids, esters have pleasant odors. Many of the odors of fruits and flowers result from mixtures of carboxylic esters, and many of them are used in perfumes and food flavorings.   Activity 6.13 Form a group and discuss the following questions. After the discussion, share your ideas with the rest of the class. 1. What would happen when esters are treated with water? 2. Recall the reactants that form esters. What was the by-product of the reaction? i. Hydrolysis The most important reaction of carboxylic esters is their hydrolysis, which may be catalyzed by either mineral acids or bases. The reaction yields the corresponding carboxylic acid and alcohol of the ester. The general reaction for acid-catalyzed hydrolysis of esters can be written as: O O H3O+ R C O R' + H2O R C O H + R' OH 318 UNIT 6  Esters Example 6. 38 O O H3O+ CH3 CH2 CH2 C O CH2 CH3 + H2O CH3 CH2 CH2 C OH + CH3 CH2 OH For synthetic purposes, base catalysis is often preferred because the reaction is not reversible. Base-catalyzed ester hydrolysis is called saponification. The general reaction for base-catalyzed hydrolysis of esters can be written as: O O R C O R' + NaOH R C O Na+ + R' OH Example 6.39 O O CH3 C O CH2 CH3 + NaOH CH3 C O Na+ + CH3 CH2 OH In biological systems, many ester hydrolysis reactions take place, for example, in the digestion of fats. These reactions occur under very mild conditions, and in the presence of certain biological catalysts known as enzymes. ii. Reduction Esters are reduced to primary alcohols by special reducing agents like lithium aluminum hydride, LiAlH4. The general reaction for reduction of esters is given by: O 1. LiAlH4 R C O R' R CH2 O H + R' OH 2. H+ Example 6.40 O 1. LiAlH4 CH3 CH2 CH2 CH2 C O CH3 CH3 CH2 CH2 CH2 CH2 OH + CH3 OH 2. H+ UNIT 6 319  CHEMISTRY GRADE 11   Esters can be synthesized by heating a mixture of a carboxylic acid and an alcohol in the presence of an acid (usually H2SO4) as catalyst. This reaction is called esterification and is a common method for the preparation of esters. In esterification, the -OH group from the carboxylic acid and the -H from the alcohol are removed and combine to form water molecule. O O H+ H3C C O CH3 + H2O H3C C O H + H O CH3 Ethanoic acid Methanol Methyl ethanoate In this condensation reaction, the hydroxyl group (–OH) from the acid and a hydrogen atom (–H) from the alcohol are eliminated in the form of water. In the same way, write the equation showing the preparation of acetylsalicylic acid, commonly known as aspirin from the salicylic acid and acetic acid. Exercise 6.14 1. Write the reactions for the preparation of each of the following esters using appropriate acids and alcohols: a. ethyl acetate b. ethyl butanoate c. methyl benzoate d. phenyl ethanoate 2. The esters formed from butyric acid are pleasant-smelling compounds found in fruits and used in perfumes. Draw the structural formula for the ester formed from the reaction of butyric acid with 2-propanol.   Most simple esters are pleasant-smelling substances. They are responsible for the flavors and fragrances of most fruits. They are used in the manufacture of perfumes and as flavoring agents in the confectionery (cakes, candies, and ice cream) and soft- drink industries. Esters of low molecular mass are non-toxic liquids and thus used as solvents. Esters are used as solvents for oils and fats, nail polishes, varnishes, paints, gums and resins; medicine (e.g. Aspirin); clothing, e.g. polyesters (Dacron); fragrance in perfumes; and plasticizers (e.g. octyl phthalate). Some common esters which are responsible for many pleasant fragrances in nature are presented in Table 6.8. 320 UNIT 6  Fats and Oils Table 6.8: Esters naturally available in fruits and responsible for their pleasant fragrances Fruit Formula Ester present Apple C4H9COOC5H11 Isoamyl isovalerate Pineapple C3H7COOC2H5 Ethyl butyrate Banana CH3COOC5H11 Isopentyl acetate Orange CH3COOC8H17 Octyl acetate Grape C6H4(NH2)(COOCH3) Methyl anthranilate Pear CH3CO2(CH2)2CH(CH3)2 Isopentyl acetate 6.6  By the end of this section, you will be able to: ) define fats and oils ) write the general structural formula for fats and oils ) write the structures of some common triglycerides ) describe physical properties of fats and oils ) explain hardening of oils (process of converting oils to hard fats) ) explain rancidity.     Activity 6.14 Perform the following activity in groups, then present your conclusion to the whole class. Collect samples of butter, lard, tallow, peanut oil, soybean oil and olive oil. Classify them to as vegetable or animal origin based on their physical state. Do you find any relation between the origin and the physical state? UNIT 6 321  CHEMISTRY GRADE 11 Fats and oils are esters. They are triesters of glycerol which are collectivity known as triglycerides or triacylglycerols. Glycerol contains three alcohol groups and therefore can form three ester groups. Fats and oils are widely found in nature especially in living things. They have long hydrocarbon tails which are derived from carboxylic acids, which make them hydrophobic. A triglyceride is called a fat if it is a solid or semi-solid at room temperature; it is called an oil if it is a liq