1. Carboxylic Acids and Esters
Chapter 24
Carboxylic Acids and Esters
The sour tang in fruit
juice comes from
carboxylic acids.
Introduction to General, Organic, and Biochemistry, 10e
John Wiley & Sons, Inc
Morris Hein, Scott Pattison, and Susan Arena 1

2. Course Outline 24.1 Carboxylic Acids
24.2 Nomenclature and Sources of Aliphatic Carboxylic Acids
24.3 Physical Properties of Carboxylic Acids
24.4 Classification of Carboxylic Acids
24.5 Preparation of Carboxylic Acids
24.6 Chemical Properties of Carboxylic Acids
25.7 Nomenclature of Esters 2 2

3. Course Outline 24.8 Occurrence and Physical Properties of Esters
24.9 Polyesters: Condensation Polymers
24.10 Chemical Properties of Esters
24.11 Glycerol Esters
24.12 Soaps and Synthetic Detergents
24.13 Esters and Anhydrides of Phosphoric Acid
Chapter 24 Summary 3 3

4. Carboxylic Acids
Carboxylic acids are organic compounds that contain the carboxyl functional group as shown here.
These are three different ways to represent the carboxyl group.
Carboxylic acids can be aliphatic or aromatic . . . 4

5. Carboxylic Acids benzoic acid This is the general formula
(an aromatic carboxylic acid)
This is the general formula
for an aromatic carboxylic acid. 5

6. Nomenclature and Sources of Aliphatic Carboxylic Acids
IUPAC Rules for Naming Carboxylic Acids
1. Name the longest continuous carbon chain of carbon atoms containing the –COOH group.
2. The –COOH carbon is the #1 carbon atom because the carboxyl group is always at the beginning of the carbon chain. 6 6

7. Nomenclature and Sources of Aliphatic Carboxylic Acids
3. Drop the –e from the name of the parent alkane and add the suffix –oic acid as shown below. 7 7

8. Nomenclature and Sources of Aliphatic Carboxylic Acids
Carboxylic acids can be named using the IUPAC system or given common names. Sometimes Greek letters are used to in common names to locate groups attached to the molecules. 8 8

9. Nomenclature and Sources of Aliphatic Carboxylic Acids
Table 24.1 on the next slide is a list of the common and IUPAC names for many other carboxylic acids . . . 9 9

10. 10

11. Your Turn!
Write formulas for 3-chloro-4-methylhexanoic acid and α-aminobutyric acid. 11

12. Your Turn!
Write formulas for 3-chloro-4-methylhexanoic acid and α-aminobutyric acid. 12

13. Physical Properties of Carboxylic Acids
The solubility of carboxylic acids is determined by which of the two groups (the nonpolar R group or the polar –COOH group) of the molecule is the most dominant in the chemical structure.
Carboxylic acids with:
1-4 carbon atoms are water soluble
5-7 carbon atoms are slightly water soluble
8 and more carbon atoms are water insoluble

14. Physical Properties of Carboxylic Acids
The relative high boiling points of carboxylic acids are due to intermolecular attractions resulting from hydrogen bonding. 14

15. Physical Properties of Carboxylic Acids
Acid-Base Properties of Carboxylic Acids
Carboxylic acids and phenols like mineral acids ionize in water to produce hydronium ions and anions. 15

16. Physical Properties of Carboxylic Acids
Carboxylic acids are generally weak acids; that is, they are only slightly ionized in water. Phenols are, in general, even weaker acids than carboxylic acids. 16

17. Physical Properties of Carboxylic Acids
Carboxylic Acids in Biochemistry
Carboxylic acids are released in the blood by the liver in an excessive amount during ketoacidosis which is a condition associated with uncontrolled diabetes.
Normal amounts of carboxylic acid can be controlled by blood buffers and by respiration rate and kidney function. 17

18. Physical Properties of Carboxylic Acids
L-Dopa (levodopa) is a carboxylic acid that is a derivative of dopamine and is used in the treatment of Parkinson’s disease. 18

19. Classification of Carboxylic Acids
There are five major types of carboxylic acids in addition to the saturated monocarboxylic acids like acetic acid (CH3COOH ).
These acids are summarized and discussed in this section . . . 19

20. Classification of Carboxylic Acids
These major types are:
Unsaturated carboxylic acids
Aromatic carboxylic acids
Dicarboxylic acids
Hydroxy acids
Amino acids 20 20

21. Classification of Carboxylic Acids
An unsaturated carboxylic acid contains one or more C=C bonds. The C=C bond affects the physical and chemical properties of the acid.
For example stearic acid, CH3(CH2)16COOH, and oleic acid, CH3(CH2)7CH=CH(CH2)7COOH, both contain 18 carbon atoms.
Stearic acid has no C=C bonds and melts at 70C where as oleic acid, CH3(CH2)7CH=CH(CH2)7COOH, has one C=C bond and melts at 16C. 21

22. Classification of Carboxylic Acids
Aromatic acids have a –COOH group bonded to a carbon in the aromatic ring. Benzoic acid and the three isomers of toluic acid are examples. 22

23. Classification of Carboxylic Acids
Dicarboxylic acids have two carboxyl (– COOH) groups. Examples of some dicarboxylic acids are shown below. 23

24. Classification of Carboxylic Acids
Dicarboxylic acids are subject to decarboxylation (loss of CO2 ) to form a monocarboxylic acid. They will also undergo internal dehydration to form anhydrides when heated. 24

25. Classification of Carboxylic Acids
Citric acid is a hydroxytricarboxylic acid. It is 5-8% of lemon juice and widely distributed in plant and animal tissues 25

26. Classification of Carboxylic Acids
Hydroxy acids have hydroxyl (–OH) and carboxyl (– COOH) functional groups. Two important -hydroxy acids are lactic acid and salicylic acid. 26

27. Classification of Carboxylic Acids
Lactic acid is found in sour milk as well as in muscle tissue after strenuous exercise.
Salicyclic acid and its derivatives are found in analgesics like aspirin. 27

28. Classification of Carboxylic Acids
Malic acid and tartaric acid are two other common -hydroxy acids found in apples and grapes respectively. 28

29. Classification of Carboxylic Acids
Amino acids have a carboxyl group (–COOH) and an amino group (–NH2). The –COOH group acts as an acid while the – NH2 acts as a base.
Most amino acids in nature have the –NH2 in the -position as shown here. 29

30. Classification of Carboxylic Acids
Amino acid units are the building blocks of proteins. Approximately 20 amino acids are biologically significant. 30

31. Your Turn! Write the structural formulas of the following.
1) A dicarboxylic acid with three carbon atoms.
2) An -amino acid with three carbon atoms. 31

32. Your Turn! Write the structural formulas of the following.
1) A dicarboxylic acid with three carbon atoms.
2) An -amino acid with three carbon atoms. 32

33. Preparation of Carboxylic Acids
Carboxylic acids can be prepared by various methods. Three methods we will discuss are the:
Oxidation of primary alcohols or aldehydes
Oxidation of alkyl groups attached to aromatic rings
Hydrolysis of nitriles 33

34. Preparation of Carboxylic Acids
Primary alcohols are oxidized to carboxylic acids.
(general reaction) 34

35. Preparation of Carboxylic Acids
Primary alcohols like benzyl alcohol can also be oxidized to a carboxylic acid. 35

36. Preparation of Carboxylic Acids
Aldehydes also oxidize to carboxylic acids
( general reaction) 36

37. Preparation of Carboxylic Acids
Alkyl benzenes are oxidized in basic solution to the carboxylate salt and then protonated with acid to form benzoic acid. 37

38. Preparation of Carboxylic Acids
Nitriles can be hydrolyzed to form carboxylic acids.
Nitriles can be prepared by reacting an alkyl halide and a cyanide salt. 38

39. Preparation of Carboxylic Acids
Nitriles can also be prepared by reacting an aldehyde or a ketone with HCN. The specific types of molecules formed in these reactions are cyanohydrins. 39

40. Preparation of Carboxylic Acids
Once formed nitriles can be hydrolyzed to form carboxylic acids. 40

41. Your Turn!
What primary alcohol can be oxidized to form pentanoic acid? 41

42. Your Turn!
What primary alcohol can be oxidized to form pentanoic acid?
1-Pentanol is a primary alcohol that oxidizes to pentanoic acid. 42

43. Your Turn!
1-Chlorobutane reacts with KCN. The product of this reaction is hydrolyzed to form a carboxylic acid. Write the equations for these reactions. 43

44. Your Turn!
1-Chlorobutane reacts with KCN. The product of this reaction is hydrolyzed to form a carboxylic acid. Write the equations for these reactions.
Notice that the resulting carboxylic acid has one more carbon atom than the starting alkyl halide. 44

45. Chemical Properties of Carboxylic Acids
Carboxylic acids undergo two broad classes of reactions which are acid-base reactions and substitution reactions.
1. Acid-base reactions occur because the –OH on the –COOH group can act as a proton donor
2. The C=O on the –COOH group serves as a site for substitution reactions. 45

46. Chemical Properties of Carboxylic Acids
Acid-Base Properties
Low molar-mass carboxylic acids release H+ ions in solution and as a result have the following properties unique to acids in general.
Sour taste
Blue litmus paper changes to red in an acidic solution
Forms solutions with a pH < 7
Reacts with bases in neutralization reactions 46

47. Chemical Properties of Carboxylic Acids
The characteristics listed on the previous slide are not true of higher molar-mass carboxylic acids because the dominant nonpolar R group makes these higher molar- mass carboxylic acids insoluble in water . . . 47

48. Chemical Properties of Carboxylic Acids
However the higher molar-mass carboxylic acids do react with strong bases like NaOH. The sodium and potassium salts of the carboxylic acids are soluble in water. 48

49. Chemical Properties of Carboxylic Acids
There are four major types of substitution reactions of carboxylic acids. 49

50. Chemical Properties of Carboxylic Acids
Acid Chloride Formation
Acid chlorides are prepared by reacting thionyl chloride (SOCl2) with a carboxylic acid. 50

51. Chemical Properties of Carboxylic Acids
Acid chlorides are very reactive and will hydrolyze back to the carboxylic acid if exposed to moisture. 51

52. Chemical Properties of Carboxylic Acids
Acid chlorides can be used to prepare esters like methyl acetate or amides like acetamide. 52

53. Chemical Properties of Carboxylic Acids
Acid Anhydride Formation
Acid anhydrides can be prepared by reacting two molecules of a carboxylic acid and eliminating a molecule of water. 53

54. Chemical Properties of Carboxylic Acids
Acid anhydrides can also prepared by reacting an acid chloride with a carboxylate anion. 54

55. Chemical Properties of Carboxylic Acids
Ester Formation
Esters can be prepared by a reacting a carboxylic acid and an alcohol or a phenol in the presence of a strong acid catalyst. 55

56. Chemical Properties of Carboxylic Acids
The specific reaction of formic acid and ethanol is shown here. 56

57. Nomenclature of Esters
Naming Esters
Name the alkoxy alkyl group. This is the alcohol portion of the molecule.
2. Name the carboxylic acid portion of the molecule. Change the -ic in the name of the acid to –ate. 57 57

58. Nomenclature of Esters
3. The alcohol portion is named first followed by the name of the acid portion.
The IUPAC name for this ester is methyl ethanoate. The common name is methyl acetate. 58 58

59. Nomenclature of Esters
The ester formed by the reaction of propanoic acid and methanol is methyl propanoate. The common name is methyl propionate.
Table 24.3 on the next slide lists the IUPAC and common names of other esters . . . 59 59

60. 60

61. Your Turn!
Give IUPAC and common names for the following esters. 61 61

62. Your Turn!
Give IUPAC and common names for the following esters. 62 62

63. Occurrence and Physical Properties of Esters
Low molar mass esters are volatile nonpolar liquids at room temperature.
For example esters such as ethyl acetate, butyl acetate, and isoamyl acetate are used extensively in paints, varnishes, and lacquers. 63

64. Occurrence and Physical Properties of Esters
Low- and intermediate-molar-mass esters have characteristic fragrant or fruity odors.
The difference in properties between an acid and its esters is remarkable. 64

65. Occurrence and Physical Properties of Esters
High molar mass esters are nonpolar solids at room temperature. Many of these esters are waxes. Carnauba wax is an ester that can have a 28-carbon fatty acid chain and a 34-carbon alcohol chain.
High molar mass esters are used in furniture and automobile wax preparations.
Very high molar mass esters include polyesters such as Dacron. 65

66. Polyesters: Condensation Polymers
A polyester is a polymer formed between an alcohol monomer and a carboxylic acid monomer.
Polyesters are classified as condensation polymers. An example of a general polymerization reaction to produce a polyester is shown here. 66

67. Polyesters: Condensation Polymers
This is a polymerization reaction that produces the polyethylene terephthalate (PETE) polyester. 67

68. Polyesters: Condensation Polymers
Polyethylene terephthalate is a common polyester found in Mylar films and soft drink bottles.
This is the plastic recycle code for polethylene terephthalate. 68

69. Polyesters: Condensation Polymers
When trifunctional acids or alcohols are used as monomers, cross-linked thermosetting polyesters are obtained.
One common example is the reaction of glycerol and o- phthalic acid. The polymer formed is one of a group of polymers known as alkyd resins. 69

70. Polyesters: Condensation Polymers
Glycerol has three functional groups, and phthalic acid has two functional COOH groups making the formation of the cross-linked polymer possible.
Glycerol o-phthalic acid 70

71. Chemical Properties of Esters
The principal reaction of esters is hydrolysis.
Ester hydrolysis is either acid-catalyzed (acid hydrolysis) or base-promoted (alkaline hydrolysis/saponification). 71

72. Chemical Properties of Esters
An ester hydrolyzed in the presence of an acid catalyst forms an alcohol and a carboxylic acid. The acid is a catalyst so it isn’t consumed during the reaction. 72

73. Chemical Properties of Esters
Specific examples of acid-catalyzed ester hydrolysis are shown here. 73

74. Chemical Properties of Esters
The ester hydrolysis in the presence of a strong base to form an alcohol and a salt is called saponification. 74

75. Chemical Properties of Esters
The carboxylic acid may be obtained by reacting the salt obtained from the hydrolysis with a strong acid.
Notice that in saponification, the base is a reactant, not a catalyst. 75

76. Your Turn!
Write equations for the acid hydrolysis and the base hydrolysis of ethyl butyrate. 76

77. Your Turn!
Write equations for the acid hydrolysis and the base hydrolysis of ethyl butyrate. 77

78. Glycerol Esters
Esters of glycerol (glycerol esters) are known as triacylglycerols and triglycerides. 78

79. Glycerol Esters Fats and oils are triacylglycerols.
Fats originating from animal sources are solids at room temperature because they have a higher percentage of saturated fatty acid derivatives in their triacylglycerol structure.
Oils originating from plant sources are liquids at room temperature because they have a higher percentage of unsaturated fatty acid derivatives in their triacylglycerol structure. 79

80. Glycerol Esters
Some common unsaturated fatty acid derivatives found in oils include the corresponding parent fatty acids oleic acid, linoleic acid, and linolenic acid.
Table 24.4 is a list of the types of fatty acids in various
fats and oils by percent composition . . . 80

81. 81

82. Glycerol Esters Triacylglycerols undergo two basic types of reactions.
Reduction which includes hydrogenation and hydrogenolysis.
Acid and basic hydrolysis. 82

83. Glycerol Esters Hydrogenation of Glycerides
Oils can be partially hydrogenated using a metal catalyst and hydrogen gas to obtain a solid like the shortening found in Crisco. 83

84. Glycerol Esters
During partial hydrogenation some of the cis bonds change to trans bonds which is the basis for the term “trans fat”.
Research has shown these unnatural fats to be unhealthy and to increase the risk of heart disease. 84

85. Glycerol Esters Hydrogenolysis
Long-chain alcohols are prepared by reducing triacylglycerols with hydrogen gas and a copper chromite catalyst. 85

86. Glycerol Esters Acid Hydrolysis
Fatty acids can be prepared by hydrolyzing triacylglycerols with either enzymes or mineral acid catalysts. 86

87. Glycerol Esters Alkaline Hydrolysis (Saponification)
Soap (i.e. carboxylate salts) is prepared by the alkaline hydrolysis of triacylglycerols. 87

88. Your Turn!
Write the structure of a triacylglycerol that has one unit each of stearic, palmitic and lauric acids. How many isomers of this molecule exists? 88

89. Your Turn!
Write the structure of a triacylglycerol that has one unit each of stearic, palmitic and lauric acids. How many isomers of this molecule exists?
There are three isomers of this molecule. 89

90. Your Turn!
Write the structure of a triacylglycerol that has one unit each of stearic, palmitic and lauric acids. How many isomers of this molecule exists? 90

91. Soaps and Synthetic Detergents
Soaps are salts of long-chain fatty acids that are prepared by reacting fat or oil with sodium hydroxide.
Sodium palmitate is a soap that is the sodium salt of palmitic acid. 91

92. Soaps and Synthetic Detergents
The hydrocarbon tail of the carboxylate ion is nonpolar and dissolves the nonpolar grease. The hydrocarbon tail is hydrophobic (i.e. water-fearing).
The polar head of the carboxylate ion allows the ion to remain soluble in water which is also polar. The polar head is hydrophilic (i.e. water-loving).
Figure 24.1 shows the cleansing action of the hydrocarbon tails and the polar heads of the carboxylate ions . . . 92

93. Soaps and Synthetic Detergents93

94. Soaps and Synthetic Detergents
The cleansing action of soaps in hard water is limited because hard water contains ions that react with carboxylate ions to form insoluble salts (soap scum) as shown in the reaction below. These ions include Ca2+, Fe3+, and Mg2+. 94

95. Soaps and Synthetic Detergents
Soaps are also ineffective in acidic solutions because insoluble fatty acids are formed. 95

96. Soaps and Synthetic Detergents
Synthetic detergents (syndets) are synthetic organic products that act as cleansing agents. These synthetic detergents are effective in soft water and hard water. Two examples are shown below. 96

97. Soaps and Synthetic Detergents
Synthetic detergents can be ionic (either anionic or cationic) or nonionic.
Sodium lauryl sulfate is an anionic detergent because it contains long-chain negatively-charged ions. 97

98. Soaps and Synthetic Detergents
A cationic detergent has a long hydrocarbon chain and a positive charge. 98

99. Soaps and Synthetic Detergents
Nonionic detergents are molecular substances. The molecule of a nonionic detergent contains a grease-soluble component and a water-soluble component. 99

100. Soaps and Synthetic Detergents
Biodegradable organic substances are those that can be readily decomposed by microorganisms in the environment into simple inorganic ions and molecules.
Detergents with straight-chain alkyl benzenes are biodegradable.
100

101. Soaps and Synthetic Detergents
Detergents with branched-chain alkyl benzenes are not biodegradable.
101

102. Esters and Anhydrides of Phosphoric Acid
Phosphoric acid and a carboxylic acid have similar structures. Because of this structural similarity phosphoric acid can form esters and anhydrides just like a carboxylic acid.
102

103. Esters and Anhydrides of Phosphoric Acid
Here a phosphate ester is formed by the reaction of phosphoric acid and ethanol in the presence of a strong acid catalyst.
103

104. Esters and Anhydrides of Phosphoric Acid
Because phosphoric acid has more than one –OH, it can form more than one ester.
104

105. Esters and Anhydrides of Phosphoric Acid
In living cells, the phosphoric acid often connects different biochemicals by two ester bonds (phosphodiesters).
Our cells’ genetic material (DNA and RNA) is linked by phosphodiesters.
105

106. Esters and Anhydrides of Phosphoric Acid
Pyrophosphoric acid is a phosphoric acid anhydride formed by the reaction of two molecules of phosphoric acid and the elimination of a water molecule.
Phosphoric acid anhydrides are biologically important because they temporarily store metabolic energy in the form of molecules like ATP.
106

107. Esters and Anhydrides of Phosphoric Acid
The “energy currency” of the cell, adenosine triphosphate (ATP), carries its energy in phosphoric acid anhydride bonds.
107

108. Chapter 24 Summary Carboxylic acids contain the carboxyl group.
The IUPAC naming of carboxylic acids follows a similar process to that used for other organic molecules.
Many carboxylic acids are known by common names. Each common name generally refers to a natural source for the carboxylic acid.
The polar carboxyl group causes the small carboxylic acids to be water-soluble.
108
108

109. Chapter 24 Summary
Carboxyl groups can hydrogen-bond to each other at two places. This strong noncovalent bonding causes high boiling points for carboxylic acids.
Carboxylic acids are weak acids.
Strong oxidizing agents will convert aldehydes and primary alcohols to carboxylic acids.
Alkyl chains on benzene rings can be oxidized by strong oxidizing agents to form benzoic acid.
109
109

110. Chapter 24 Summary
Nitriles, RCN, will react with water plus hydrogen ion to yield carboxylic acids.
Carboxylic acids have a sour taste, affect pH indicators, form water solutions with a pH of less than 7, and undergo neutralization reactions.
Carboxylic acids react with bases to form salts.
Many common carboxylic acid reactions involve substitution of the hydroxyl group for another atom or group of atoms.
110
110

111. Chapter 24 Summary
An ester is formed when an alcohol or phenol substitutes for the carboxylic acid hydroxyl group.
Esters are named as alcohol derivatives of carboxylic acids.
Condensation polymers are produced when monomers combine with the loss of a small molecule. Polyesters are formed when alcohol monomers react with carboxylic acid monomers with the loss of water.
111
111

112. Chapter 24 Summary
The most important reaction of esters is hydrolysis.
Fats and oils are esters of glycerol and long-chain carboxylic acids (fatty acids).
A triacylglycerol or triglyceride is a glycerol that has been esterified with three fatty acids molecules.
112
112

113. Chapter 24 Summary
Fats are solids at room temperature, while oils are liquids.
Triacylglycerols are the principal energy-storage molecules in the human body.
Hydrogenation of unsaturated fatty acids results in the addition of hydrogen to carbon–carbon double bonds.
Hydrogenolysis breaks a triacylglycerol into glycerol and three long-chain primary alcohols.
113
113

114. Chapter 24 Summary
Triacylglycerols can be hydrolyzed in acid to form fatty acids and glycerol or in base to form soaps and glycerol.
A synthetic detergent is an organic molecule that has been synthesized in a chemical factory and acts as a cleansing agent.
Soaps are salts of long-chain fatty acids.
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