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14 carboxylic-acids-and-derivatives

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Chapter 14 in General, Organic, and Biological Chemistry, 7th edition, by Denniston.

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14 carboxylic-acids-and-derivatives

  1. 1. Chapter 14Carboxylic Acids and Derivatives 1
  2. 2. 1. Carboxylic acidsThe carboxyl group consists of carbonyl and hydroxylgroups attached to the same carbon. carbonyl + hydroxyl = carboxyl An aliphatic or aromatic group can be attached to the carboxyl group. 2
  3. 3. 1. Carboxylic acidsThe acyl group is a carboxyl group with either a hydroxylor alkoxy group. If R is a hydroxyl group, the compound is a carboxylic acid. If R is an alkoxy group, the compound is an ester. 3
  4. 4. 1. Carboxylic acids: boiling pointsIntermolecular forcesare strong in carboxylicacids due to the high polarity of the carboxyl group; the presence of hydrogen-bonding between carboxylic acid molecules. 4
  5. 5. 1. Carboxylic acids: boiling pointsWhen two hydrogen bonds form between two carboxylicacid molecules, the result is a dimer.Dimer formation can cause carboxylic acids to seem tohave double their actual molecular mass. 5
  6. 6. 1. Carboxylic acids: boiling pointsCompare molecules with similar molar masses anddifferent functional groups: 6
  7. 7. 1. Carboxylic acids: boiling pointsBoiling point (oC) vs.number of carbons foracids, alcohols, aldehydes,and alkanes. 7
  8. 8. 1. Carboxylic acids: solubilityLower molecular weight carboxylic acids are very solublein water. Vinegar is a solution of ethanoic acid.Solubility falls off as molecular weight increases. Why? Hexadecanoic acid is insoluble in water. 8
  9. 9. 1. Carboxylic acids: solubilitySolubility (g acid/g H2O)vs. number of carbons forsaturated, unbranched-chain carboxylic acids. 9
  10. 10. 1. Carboxylic acids: nomenclatureDetermine the parent compound from the longestchain that includes the carboxyl carbon.Number the chain so that the carboxyl carbon iscarbon 1.Replace the –e ending with –oic acid.Assign numbers to any remaining substituents. 10
  11. 11. 1. Carboxylic acids: nomenclatureAdditional notes: If two carboxyl groups are present use –dioic acid. For cycloalkanes, add carboxylic acid to the name of the cycloalkane. For aromatic acids, the simplest acid is benzoic acid. If the acid group is attached to the aromatic ring, name after benzoic acid. If the acid group is not attached to the aromatic ring, name after the longest chain, with a –phenyl substituent. 11
  12. 12. 1. Carboxylic acids: nomenclature pencast 12
  13. 13. 1. Carboxylic acids: nomenclatureName the following compounds: pencast 13
  14. 14. 1. Carboxylic acids: nomenclatureDraw structures for the following compounds: 2,5-dimethylhexanoic acid 3-bromo-5-chlorooctanoic acid pencast 2,2-dimethylbutanedioic acid 3-methylcyclohexanecarboxylic acid 2,4-dichlorobenzoic acid 3-phenylpentanoic acid 14
  15. 15. 1. Carboxylic acidsIs “alpha-hydroxy” an actual substance? glycolic acid α carbon lactic acid tartaric acid 15
  16. 16. 1. Carboxylic acidsThe last paragraph in the inset box on pages 460-461 ofyour textbook states: "For the time being, biodegradable plastics cannot outcompete their nonbiodegradable counterparts. Future research and development will be required to reduce the cost of commercial production and fulfill the promise of an environmentally friendly garbage bag.” This statement gives the impression that there are no biodegradable plastics available to consumers at a reasonable cost. Compostable plastic bags 16
  17. 17. 1. Carboxylic acids: reactionsPreparation is by complete oxidation of primary alcoholsor oxidation of aldehydes. 1o alcohol aldehyde carboxylic acid 17
  18. 18. 1. Carboxylic acids: reactionsCarboxylic acids are proton donors and therefore react asacids.Carboxylic acids are weak acids, dissociating only slightlyin solution. >95% <5% 18
  19. 19. 1. Carboxylic acids: reactionsWhen a strong base is added to a carboxylic (weak) acid,water and salt are formed.Although the carboxylic acid isn’t initially completelydissociated, as H+ is removed by reaction with OH-, moreacid dissociates. 19
  20. 20. 1. Carboxylic acids: reactionsRemember le Chatelier’s principle?When product (H+) is removed, the equilibrium shifts tomake more product (and less undissociated acid). 20
  21. 21. 1. Carboxylic acids: reactionsAcid-base reactioncarboxylic acid + strong base  carboxylic acid salt + water 21
  22. 22. 1. Carboxylic acids: reactionsNaming salts of carboxylic acids Name the carboxylic acid. Replace the –ic acid ending with –ate. Precede this name with the name of the cation.Name the salts formed in the following reactions: ethanoic acid + KOH benzoic acid + LiOH pencast hexanoic acid + NaOH 22
  23. 23. 1. Carboxylic acids: reactionsEsterification is the formation of water and an ester froma carboxylic acid and an alcohol. More about this in the next section… 23
  24. 24. 2. EstersEsters are carboxylic acid derivatives, in which the acidic-H of the acid has been replaced by an alkyl or aryl group–R. carboxylic acid ester derivative 24
  25. 25. 2. Esters: propertiesEsters are slightly polar; boil at about the same temperature as corresponding aldehydes and ketones; are somewhat soluble in water when they are small. have pleasant aromas. 25
  26. 26. 2. Esters: nomenclatureRecall nomenclature of salts of carboxylic acids. Name the carboxylic acid. Replace the –ic acid ending with –ate. Precede this name with the name of the cation.Esters are named in the same way, except the alkyl or arylportion of the alcohol is used in place of the cation name. Name the carboxylic acid. Replace the –ic acid ending with –ate. Precede this name with the name of the alkyl or aryl portion of the alcohol. 26
  27. 27. 2. Esters: nomenclatureName the following esters. pencast 27
  28. 28. 2. Esters: nomenclatureDraw the structures of the following esters. propyl ethanoate octyl decanoate methyl methanoate pencast 2-methylpropyl propanoate 3-methylbutyl ethanoate phenyl pentanoate 28
  29. 29. 2. Esters: reactionsPreparation of esters is by reaction of a carboxylic acidand an alcohol to produce an ester and water. This is a dehydration reaction. [water is lost] Heat and a trace of acid catalyst (H+) are required. The reaction produces an equilibrium mixture. heat 29
  30. 30. 2. Esters: reactions 30
  31. 31. 2. Esters: reactionsShow the esterification reaction that would producebutyl propanoate. pencast 31
  32. 32. 2. Esters: reactionsEsters can be synthesized starting from alcohols only. An alcohol can be oxidized to an aldehyde, and further oxidized to a carboxylic acid. This carboxylic acid can undergo an esterification reaction with another alcohol.Name the required alcohols and show the necessaryreactions to produce pentyl butanoate (apricots). pencast octyl ethanoate (oranges). 32
  33. 33. 2. Esters: reactionsHydrolysis (hydration) of esters, when it is acid-catalyzed,is the reverse of the esterification reaction. H2O ester carboxylic acid alcohol 33
  34. 34. 2. Esters: reactionsHydrolysis of esters, when it is base-catalyzed, is calledsaponification. ester carboxylic acid salt alcohol 34
  35. 35. 2. Esters: reactionsThe carboxylic acid that forms when the ester breaks upreacts immediately with the base, forming thecarboxylate anion, associated with the cation of the base. 35
  36. 36. 2. Esters: reactionsWhat are the products of the following reactions? + H2O pencast + H2O + H2O + H2O 36
  37. 37. 2. Esters: saponification (salts of carboxylic acids) + + 37
  38. 38. 2. Esters: saponificationA soap (carboxylic acid salt) has a nonpolar end that dissolves in nonpolar fats and oils, and a polar end that dissolves in water. forms groups of soap molecules called micelles that dissolve in water and are washed away. 38
  39. 39. 2. Esters: saponification 39
  40. 40. EXTRA CREDIT QUESTIONRadioactive isotopes of an element behave chemically in exactly thesame manner as the nonradioactive isotopes. As a result, they can beused as tracers to investigate the details of chemical reactions. Ascientist is curious about the origin of the bridging oxygen atom in anester molecule. She has chosen to use the radioactive isotope 18O tostudy the following reaction:Design experiments using 18O that will demonstrate whether the oxygenin the water molecule came from the –OH of the alcohol or the –OH ofthe carboxylic acid.Post your answer in the Journal for this module with tag = isotopes. 40
  41. 41. 3. Acid chlorides and acid anhydridesAcid chlorides are carboxylic acid derivatives in which thehydroxyl group, -OH, has been replaced by –Cl.Naming Name the corresponding carboxylic acid. Replace the -oic acid ending with –oyl chloride. 41
  42. 42. 3. Acid chlorides and acid anhydridesExamples ethanoic acid ethanoyl chloride benzoic acid benzoyl chloride 42
  43. 43. 3. Acid chlorides and acid anhydridesName the following acid chlorides. pencastDraw structures for the following acid chlorides. heptanoyl chloride 2-hydroxypropanoyl chloride 43
  44. 44. 3. Acid chlorides and acid anhydridesPreparation of acid chlorides PCl3 or + PCl5 or + inorganic products SOCl2 The reagents PCl3, PCl5, and SOCl2 are inorganic acid chlorides. 44
  45. 45. 3. Acid chlorides and acid anhydridesPCl3, PCl5, and SOCl2 replace the hydroxyl group on theacid with a chloride, by the following mechanism! 45
  46. 46. 3. Acid chlorides and acid anhydridesWrite an equation for the reaction of benzoic acid withSOCl2 and name the organic product. pencast SOCl2 benzoyl chloride 46
  47. 47. 3. Acid chlorides and acid anhydridesAcid anhydrides are two carboxylic acid molecules with awater molecule removed. + H2O 47
  48. 48. 3. Acid chlorides and acid anhydridesAcid anhydrides with identical acyl groups are symmetrical.Symmetrical acid anhydrides are named after the acid fromwhich they are made, with the acid ending replaced withanhydride. The molecule above, made from two molecules of ethanoic acid, is called ethanoic anhydride. 48
  49. 49. 3. Acid chlorides and acid anhydridesUnsymmetrical anhydrides have two different acyl groups.Unsymmetrical anhydrides are named using both parentcarboxylic acid names, in alphabetical order, followed by theword anhydride. The molecule above is called butanoic ethanoic anhydride. 49
  50. 50. 3. Acid chlorides and acid anhydridesName the following acid anhydrides. pencast 50
  51. 51. 3. Acid chlorides and acid anhydridesAcid anhydrides can be prepared from an acid chlorideand a carboxylate anion. Direct reaction of the two parent carboxylic acids is usually not possible.acid chloride carboxylate anion acid anhydride 51
  52. 52. 3. Acid chlorides and acid anhydridesWrite equations for the synthesis of butanoic anhydride,beginning with butanoic acid. pencast 52
  53. 53. 3. Acid chlorides and acid anhydridesAcid anhydrides react with water, if it is present, toproduce two carboxylic acids. + H2O 53
  54. 54. 3. Acid chlorides and acid anhydridesWhat are the products of the hydrolysis of ethanoic anhydride? pencast ethanoic methanoic anhydride? 54
  55. 55. 3. Acid chlorides and acid anhydridesAn acid anhydride can also react with an alcohol, in areaction analogous to hydrolysis. Hydrolysis: products are two carboxylic acids. Reaction with alcohol: products are an ester and an acid. 55

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