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Carboxylic Acids and Carboxylic Acid Derivatives

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Chapter 14 in General, Organic, and Biological Chemistry, 7th ed, Dennistron.

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Carboxylic Acids and Carboxylic Acid Derivatives

  1. 1. Chapter 14 Carboxylic Acids andCarboxylic Acid Derivatives
  2. 2. 1. Carboxylic acids The carboxyl group consists of carbonyl and hydroxyl groups attached to the same carbon.  carbonyl + hydroxyl = carboxyl  An aliphatic or aromatic group can be attached to the carboxyl group.
  3. 3. 1. Carboxylic acids The acyl group is a carboxyl group with either a hydroxyl or 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.
  4. 4. 1. Carboxylic acids: boiling points Intermolecular forces are strong in carboxylic acids due to  the high polarity of the carboxyl group;  the presence of hydrogen- bonding between carboxylic acid molecules.
  5. 5. 1. Carboxylic acids: boiling points  When two hydrogen bonds form between two carboxylic acid molecules, the result is a dimer.  Dimer formation can cause carboxylic acids to seem to have double their actual molecular mass.
  6. 6. 1. Carboxylic acids: boiling points Compare molecules with similar molar masses and different functional groups:
  7. 7. 1. Carboxylic acids: boiling points Boiling point (oC) vs. number of carbons for acids, alcohols, aldehydes, and alkanes.
  8. 8. 1. Carboxylic acids: solubility Lower molecular weight carboxylic acids are very soluble in water.  Vinegar is a solution of ethanoic acid. Solubility falls off as molecular weight increases.  Why?  Hexadecanoic acid is insoluble in water.
  9. 9. 1. Carboxylic acids: solubility Solubility (g acid/g H2O) vs. number of carbons for saturated, unbranched- chain carboxylic acids.
  10. 10. 1. Carboxylic acids: nomenclature Determine the parent compound from the longest chain that includes the carboxyl carbon. Number the chain so that the carboxyl carbon is carbon 1. Replace the –e ending with –oic acid. Assign numbers to any remaining substituents.
  11. 11. 1. Carboxylic acids: nomenclature Additional 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.
  12. 12. 1. Carboxylic acids: nomenclature pencast
  13. 13. 1. Carboxylic acids: nomenclature Name the following compounds: pencast
  14. 14. 1. Carboxylic acids: nomenclature Draw 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
  15. 15. 1. Carboxylic acids Is “alpha-hydroxy” an actual substance?  glycolic acid  lactic acid  tartaric acid
  16. 16. 1. Carboxylic acids The last paragraph in the inset box on pages 460-461 of your 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
  17. 17. 1. Carboxylic acids: reactions Preparation is by complete oxidation of primary alcohols or oxidation of aldehydes. 1o alcohol aldehyde carboxylic acid
  18. 18. 1. Carboxylic acids: reactions Carboxylic acids are proton donors and therefore react as acids. Carboxylic acids are weak acids, dissociating only slightly in solution. >95% <5%
  19. 19. 1. Carboxylic acids: reactions When a strong base is added to a carboxylic (weak) acid, water and salt are formed. Although the carboxylic acid isn’t initially completely dissociated, as H+ is removed by reaction with OH-, more acid dissociates.  Remember le Chatelier’s principle?  When product (H+) is removed, the equilibrium shifts to make more product (and less undissociated acid).
  20. 20. 1. Carboxylic acids: reactions Acid-base reactioncarboxylic acid + strong base  carboxylic acid salt + water
  21. 21. 1. Carboxylic acids: reactions Naming 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  hexanoic acid + NaOH pencast
  22. 22. 1. Carboxylic acids: reactions Esterification is the formation of water and an ester from a carboxylic acid and an alcohol. More about this in the next section…
  23. 23. 2. Esters Esters 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. 24. 2. Esters: properties Esters  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. 25. 2. Esters: nomenclature Recall 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 aryl portion 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. 26. 2. Esters: nomenclature Name the following esters. pencast
  27. 27. 2. Esters: nomenclature Draw the structures of the following esters.  propyl ethanoate  octyl decanoate  methyl methanoate  2-methylpropyl propanoate pencast  3-methylbutyl ethanoate  phenyl pentanoate
  28. 28. 2. Esters: reactions Preparation of esters is by reaction of a carboxylic acid and 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. 29. 2. Esters: reactions Show the esterification reaction that would produce butyl propanoate. pencast
  30. 30. 2. Esters: reactions Esters 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 necessary reactions to produce  pentyl butanoate (apricots).  octyl ethanoate (oranges). pencast
  31. 31. 2. Esters: reactions Hydrolysis (hydration) of esters, when it is acid-catalyzed, is the reverse of the esterification reaction. H2O ester carboxylic acid alcohol
  32. 32. 2. Esters: reactions Hydrolysis of esters, when it is base-catalyzed, is called saponification. ester carboxylic acid salt alcohol
  33. 33. 2. Esters: reactions The carboxylic acid that forms when the ester breaks up reacts immediately with the base, forming the carboxylate anion, associated with the cation of the base.
  34. 34. 2. Esters: reactions What are the products of the following reactions? + H2O pencast + H2O + H2O + H2O
  35. 35. 2. Esters: saponification (salts of carboxylic acids) + +
  36. 36. 2. Esters: saponification A 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.
  37. 37. 2. Esters: saponification
  38. 38. EXTRA CREDIT QUESTION Radioactive isotopes of an element behave chemically in exactly the same manner as the nonradioactive isotopes. As a result, they can be used as tracers to investigate the details of chemical reactions. A scientist is curious about the origin of the bridging oxygen atom in an ester molecule. She has chosen to use the radioactive isotope 18O to study the following reaction: Design experiments using 18O that will demonstrate whether the oxygen in the water molecule came from the –OH of the alcohol or the –OH of the carboxylic acid. Post your answer in the Journal for this module with tag = XC.
  39. 39. 3. Acid chlorides and acid anhydrides Acid chlorides are carboxylic acid derivatives in which the hydroxyl group, -OH, has been replaced by –Cl. Naming  Name the corresponding carboxylic acid.  Replace the -oic acid ending with –oyl chloride.
  40. 40. 3. Acid chlorides and acid anhydrides Examples ethanoic acid ethanoyl chloride benzoic acid benzoyl chloride
  41. 41. 3. Acid chlorides and acid anhydrides Name the following acid chlorides. pencast Draw structures for the following acid chlorides.  heptanoyl chloride  2-hydroxypropanoyl chloride
  42. 42. 3. Acid chlorides and acid anhydrides Preparation of acid chlorides PCl3 or + PCl5 or + inorganic products SOCl2  The reagents PCl3, PCl5, and SOCl2 are inorganic acid chlorides
  43. 43. 3. Acid chlorides and acid anhydrides PCl3, PCl5, and SOCl2 replace the hydroxyl group on the acid with a chloride, by the following mechanism!
  44. 44. 3. Acid chlorides and acid anhydrides Write an equation for the reaction of benzoic acid with SOCl2 and name the organic product. pencast SOCl2 benzoyl chloride
  45. 45. 3. Acid chlorides and acid anhydrides Acid anhydrides are two carboxylic acid molecules with a water molecule removed. + H2O
  46. 46. 3. Acid chlorides and acid anhydrides Acid anhydrides with identical acyl groups are symmetrical. Symmetrical acid anhydrides are named after the acid from which they are made, with the acid ending replaced with anhydride.  The molecule above, made from two molecules of ethanoic acid, is called ethanoic anhydride.
  47. 47. 3. Acid chlorides and acid anhydrides Unsymmetrical anhydrides have two different acyl groups. Unsymmetrical anhydrides are named using both parent carboxylic acid names, in alphabetical order, followed by the word anhydride.  The molecule above is called butanoic ethanoic anhydride.
  48. 48. 3. Acid chlorides and acid anhydrides Name the following acid anhydrides. pencast
  49. 49. 3. Acid chlorides and acid anhydrides Acid anhydrides can be prepared from an acid chloride and a carboxylate anion.  Direct reaction of the two parent carboxylic acids is usually not possible. acid chloride carboxylate anion acid anhydride
  50. 50. 3. Acid chlorides and acid anhydrides Write equations for the synthesis of butanoic anhydride, beginning with butanoic acid. pencast
  51. 51. 3. Acid chlorides and acid anhydrides Acid anhydrides react with water, if it is present, to produce two carboxylic acids. + H2O
  52. 52. 3. Acid chlorides and acid anhydrides What are the products of the hydrolysis of  ethanoic anhydride? pencast  ethanoic methanoic anhydride?
  53. 53. 3. Acid chlorides and acid anhydrides An acid anhydride can also react with an alcohol, in a reaction analogous to hydrolysis.  Hydrolysis: products are two carboxylic acids.  Reaction with alcohol: products are an ester and an acid.

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