1. Introduction to carboxylic acids 1

2. Learning Objectives Identify the general structure of carboxylic acids Give the IUPAC and the common names Explain the physical properties of the carboxylic acids ; e.g solubility, boiling point, etc Give examples and uses of carboxylic acids 2

3. Functional Groups 3

4. R = Alkyl Groups 4

5. Carboxylic Acids A class of organic compounds containing at least one carboxyl group Introduction 5

6. R = alkyl group  Aliphatic acid R = aryl group  aromatic acid 6

7. (1) The IUPAC names of carboxylic acids Replace the ‘e’ with ‘oic acid’ at the end of the name of the hydrocarbon Naming Carboxylic Acids H H H C C H H H ethane H O H C C O H H ethanoic acid 7

8. 8 Number substituents from the carboxyl carbon 1. CH 3 O | ║ CH 3 —CH—CH 2 —C—OH 4 3 2 1 3-methylbutanoic acid IUPAC Names

9. 9 The common names of simple carboxylic acids HCOOH formic acid, CH 3 —COOH acetic acid Locate substituents using greek letters , , γ for the carbon atoms adjacent to the carboxyl carbon. CH 3 γ  α | CH 3 —CH—CH 2 —COOH α-methylbutryic acid ( IUPAC ; 2-methylbutanoic acid ) (2) Common Names  -phenylcaproic acid ε δ γ  α

10. Common and IUPAC Names of Some Carboxylic Acids 10

11. (3) Naming Cyclic Acids Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids 11 Cyclohexanecarboxylic acid

12. 12 (4) Naming Aromatic Acids 3-chlorobenzoic acid 4-aminobenzoic acid m-chlorobenzoic acid p-aminobenzoic acid Locates substituent by assigning 1 to the carbon attached to the carboxyl group. Prefixes ortho, meta, and para for 2 substituents: ortho1, 2 location meta 1, 3 location para1, 4 location Benzoic acid o-hydroxybenzoic acid 2-hydroxybenzoic acid (salicylic acid)

13. 13 Dicarboxylic Acids Aliphatic diacids are usually called by their common names. For IUPAC name, number the chain from the end closest to a substituent. 3-bromohexanedioic acid  -bromoadipic acid HOOCCH 2 CHCH 2 CH 2 COOH Br

14. Some examples of dicarboxylic acid Common nameIUPAC name (Historical name) alkanedioic acid HOOC-COOH HOOCCH 2 COOH HOOC(CH 2 ) 2 COOH oxalic acid malonic acid succinic acid ethanedioic acid propanedioic acid butanedioic acid 14

15. phthalic acid O -phthalic acid 1,3-benzenedicarboxylic acid 1,4-benzenedicarboxylic acid Common name IUPAC name 1,2-benzenedicarboxylic acid isophthalic acid m-phthalic acid terephthalic acid p-phthalic acid 15

16. PHYSICAL PROPERTIES carboxylic acids are soluble in organic solvents ; e.g alcohols they are also soluble in water due to hydrogen bonding small ones dissolve readily in cold water ( up to 4 carbons) as mass increases, the solubility decreases benzoic acid is fairly insoluble in cold, but soluble in hot water Solubility 16

17. 17 The boiling points of carboxylic acids Are higher than alcohols, ketones, and aldehydes of similar mass. Are high because they form dimers in which hydrogen bonds form between the polar groups in the two carboxyl groups. O H—O || | CH 3 —C C—CH 3 | || O—H O A dimer of acetic acid Boiling Points

18. Melting Points Aliphatic acids with more than 8 carbons are solids at room temperature. Double bonds (especially cis) lower the melting point. The following acids all have 18 carbons: – Stearic acid (saturated): 72  C – Oleic acid (one cis double bond): 16  C – Linoleic acid (two cis double bonds): -5  C 18

19. Polarity of Carboxylic Acids Polarity is Carboxylic acids are strongly polar because they have two polar groups hydroxyl (  OH) and carbonyl (C=O) 19

20. 20 Acidity of Carboxylic Acids A carboxylic acid may dissociate in water to give a proton and a carboxylate ion (known as conjugate base). The equilibrium constant K a for this reaction is called the acid- dissociation constant, The acidity constant, K a,, is about 10 -5 for a typical carboxylic acid (pK a ~ 5) The acid will be mostly dissociated if the pH of the solution is higher than the pK a of the acid. are weak acids compared to inorganic acids

21. 21 Acidity of Carboxylic Acids Carboxylic acids are significantly more acidic than water or alcohols.

22. 22 4  -electrons delocalized over three p-prbitals C-O bond length of a carboxylates are the same This greater acidity of carboxylic acids is attributed to greater stabilization of carboxylate ion by: a.Inductive effect of the C=O group b. Resonance stabilization of the carboxylate ion

23. Electron delocalization stabilizes carbonyl group Carbon is sp 2 hybridized. Bond angles are close to 120 . R C O H O R C O H O + – R C O H O + – Electron delocalization; resonance 23

24. Electronegative substituents increase acidity X CH 2 C-OH O XKaKa pKapKa H F Cl 1.8 x 10 -5 4.7 2.5 x 10 -3 2.6 1.4 x 10 -3 2.9 Substituent Effects on Acidity 24

25. 25 Substituent Effects on Acidity

26. Multiple electronegative substituents have synergistic effects on acidity Fluoroacetic, chloroacetic, bromoacetic, and iodoacetic acids are stronger acids than acetic acid 26 The magnitude of a substituent effect depends on its distance from the carboxyl group. Substituent Effects on Acidity

27. 27 Aromatic Carboxylic Acids Electron-withdrawing groups (e.g NO 2 ) enhance the acid strength while electron-donating groups ( e.g alkyl ) decrease the acid strength. Effects are strongest for substituents in the ortho and para positions.

28. Substituent Effects An electronegative group will drive the ionization equilibrium toward dissociation, increasing acidity An electron-withdrawing group (-NO 2 ) increases acidity by stabilizing the carboxylate anion, and an electron-donating (activating) group (OCH 3 ) decreases acidity by destabilizing the carboxylate anion 28

29. Substituent Effects in Substituted Benzoic Acids 29

30. So: Carboxylic acids are weak acids, average pH = 5 Are Polar because of ( the high electronegative O) Soluble in water Have high boiling and melting points 30

31. Learning Check Write the balanced equation for the ionization of butanoic acid in water and identify the carboxylate ion. 31

32. Solution Write the balanced equation for the ionization of butanoic acid in water and identify the carboxylate ion. O O CH 3  CH 2  C  OH + H 2 O CH 3  CH 2  C  O – + H 3 O + carboxylic acid carboxylate ion 32

33. 33 Naming Carboxylic Acid Salts First name the cation. Then name the anion by replacing the -ic acid with -ate. potassium 3-chloropentanoate CH 3 CH 2 CHCH 2 COO - K + Cl

34. Neutralization of Carboxylic Acids Carboxylic acid salts are a product of the neutralization of a carboxylic acid with a strong base CH 3 —COOH + NaOH CH 3 —COO – Na + + H 2 O acetic acid sodium acetate (carboxylic acid salt) are used as : preservatives and flavor enhancers 34

35. 35 Properties of Acid Salts Usually solids with no odor. Carboxylate salts of Na +, K +, Li +, and NH 4 + are soluble in water. Soap is the soluble sodium salt of a long chain fatty acid. Salts can be formed by the reaction of an acid with NaHCO 3, releasing CO 2.

36. Uses of Organic Acids Alpha hydroxy acids Acetic acid skin care products. in vinegar as preservative and flavourings 36

37. Uses of Organic Acids 37 Making of drugs, dyes, paints, insecticides, plastics. Making of esters.

38. 38 Limes, lemons Citric acid Formic acid Insects Other Important Organic Acids Malic acid Apples and pears Lactic acid Sour milk Tartaric acid Grape juice Oxalic acid Spinch

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