1. Organic Chemistry
William H. Brown &
Christopher S. Foote

2. Carboxylic Acids Chapter 17

3. Structure
The functional group of a carboxylic acid is a carboxyl group
the general formula of an aliphatic carboxylic acid is RCOOH; that of an aromatic carboxylic acid is ArCOOH

4. Nomenclature - IUPAC
IUPAC names: drop the -e from the parent alkane and add the suffix -oic acid
if the compound contains a carbon-carbon double bond, change the infix -an- to -en-

5. Nomenclature - IUPAC
The carboxyl group takes precedence over most other functional groups

6. Nomenclature - IUPAC
dicarboxylic acids: add the suffix -dioic acid to the name of the parent alkane containing both carboxyl groups

7. Nomenclature - IUPAC
if the carboxyl group is attached to a ring, name the ring compound and add the suffix -carboxylic acid

8. Nomenclature - IUPAC
benzoic acid is the simplest aromatic carboxylic acid
use numbers to show the location of substituents

9. Nomenclature-Common
when common names are used, the letters etc. are often used to locate substituents

10. Physical Properties
In the liquid and solid states, carboxylic acids are associated by hydrogen bonding into dimeric structures

11. Physical Properties
Carboxylic acids have significantly higher boiling points than other types of organic compounds of comparable molecular weight
they are polar compounds and form very strong intermolecular hydrogen bonds
Carboxylic acids are more soluble in water than alcohols, ethers, aldehydes, and ketones of comparable molecular weight
they form hydrogen bonds with water molecules through their C=O and OH groups

12. Physical Properties
water solubility decreases as the relative size of the hydrophobic portion of the molecule increases

13. Acidity Carboxylic acids are weak acids
values of pKa for most aliphatic and aromatic carboxylic acids fall within the range 4 to 5
The greater acidity of carboxylic acids relative to alcohols, both compounds containing an OH group is due to resonance stabilization of the carboxylate anion

14. Acidity
electron-withdrawing substituents near the carboxyl group increase acidity through their inductive effect

15. Reaction with Bases
Carboxylic acids, whether soluble or insoluble in water, react with NaOH, KOH, and other strong bases to give water-soluble salts
They also form water-soluble salts with ammonia and amines

16. Reaction with Bases
Carboxylic acids react with sodium bicarbonate and sodium carbonate to form water-soluble salts and carbonic acid
carbonic acid, in turn, breaks down to carbon dioxide and water

17. Reaction with Bases

18. Preparation Carbonation of Grignard reagents
treatment of a Grignard reagent with carbon dioxide followed by acidification gives a carboxylic acid

19. Methanol to Acetic Acid
Acetic acid is synthesized by carbonylation of methanol
the carbonylation is exothermic
the Monsanto process uses a soluble rhodium(III) salt and HI to catalyze the reaction

20. Methanol to Acetic Acid
Steps 1 and 2: preparation of the catalyst:
Steps 3 and 4: the catalytic cycle

21. Reduction The carboxyl group is very resistant to reduction
it is not affected by catalytic hydrogenation under conditions that easily reduce aldehydes and ketones to alcohols, and reduce alkenes and alkynes to alkanes
it is not reduced by NaBH4

22. Reduction by LiAlH4
Lithium aluminum hydride reduces a carboxyl group to a 1° alcohol
reduction is carried out in diethyl ether, THF, or other nonreactive, aprotic solvent

23. Selective Reduction
carboxyl groups are not affected by catalytic reduction under conditions that reduce aldehydes and ketones

24. Selective Reduction
using the less reactive NaBH4, it is possible to reduce the carbonyl group of an aldehyde or ketone without affecting a carboxyl group

25. Fischer Esterification
Esters can be prepared by treatment of a carboxylic acid with an alcohol in the presence of an acid catalyst, commonly H2SO4 or gaseous HCl

26. Fischer Esterification
Fischer esterification is an equilibrium reaction
by careful control of experimental conditions, it is possible to prepare esters in high yield
if the alcohol is inexpensive relative to the carboxylic acid, it can be used in excess to drive the equilibrium to the right
alternatively, water can be removed by azeotropic distillation and a Dean-Stark trap

27. Fischer Esterification
a key intermediate in Fischer esterification is the tetrahedral carbonyl addition intermediate formed by addition of ROH to the C=O group

28. Diazomethane Diazomethane, CH2N2
a potentially explosive, toxic yellow gas, is best drawn as a hybrid of two contributing structures
treatment of a carboxylic acid with diazomethane gives a methyl ester

29. Diazomethane Esterification occurs in two steps
Step 1: proton transfer to diazomethane
Step 2: nucleophilic displacement of N2

30. Acid Chlorides
The functional group of an acid halide is a carbonyl group bonded to a halogen atom
among the acid halides, acid chlorides are by far the most common and the most widely used

31. Acid Chlorides
acid chlorides are most often prepared by treatment of a carboxylic acid with thionyl chloride

32. Acid Chlorides
The mechanism for this reaction is divided into two steps.
Step 1: OH-, a poor leaving group, is transformed into a chlorosulfite group, a good leaving group

33. Acid Halides
Step 2: attack of chloride ion gives a tetrahedral carbonyl addition intermediate, which collapses to give the acid chloride

34. Decarboxylation Decarboxylation: loss of CO2 from a carboxyl group
most carboxylic acids, if heated to a very high temperature, undergo thermal decarboxylation
most carboxylic acids, however, are quite resistant to moderate heat and melt or even boil without decarboxylation

35. Decarboxylation
Exceptions are carboxylic acids that have a carbonyl group beta to the carboxyl group
this type of carboxylic acid undergoes decarboxylation on mild heating

36. Decarboxylation
thermal decarboxylation of a -ketoacid involves rearrangement of six electrons in a cyclic six-membered transition state

37. Decarboxylation
decarboxylation occurs if there is any carbonyl group beta to the carboxyl
malonic acid and substituted malonic acids, for example, also undergo thermal decarboxylation

38. Decarboxylation
thermal decarboxylation of malonic acids also involves rearrangement of six electrons in a cyclic six-membered transition state

39. Prob 17.17
Each compound shows strong absorption between 1720 and 1700 cm-1, and strong broad absorption over the region cm-1. Propose a structural formula for each compound.

40. Prob (cont’d)

41. Prob (cont’d)

42. Prob 17.18
Complete these reactions.

43. Prob 17.19
Show how to bring about each conversion.

44. Prob 17.21
Draw a structural formula for each starting compound.

45. Prob 17.22
Show reagents to bring about each conversion.

46. Prob 17.23
Show how to synthesize butanedioic acid starting with acetylene and formaldehyde.

47. Prob 17.24
Propose a mechanism for the rearrangement of benzil to sodium benzilate.

48. Prob 17.33
Show how to convert trans-3-phenyl-2-propenoic (cinnamic acid) to each compound.

49. Prob 17.34
Show how to convert 3-oxobutanoic acid to these compounds.

50. Prob 17.35
Complete each example of Fischer esterification.

51. Prob 17.37
Name the carboxylic acid and alcohol from which each ester is derived.

52. Prob 17.39
Propose a mechanism for this reaction.

53. Prob 17.40
Draw a structural formula for the product of thermal decarboxylation of each compound.

54. Prob 17.41
Propose a mechanism for each decarboxylation. Compare your mechanisms with the mechanism for decarboxylation of a b-ketoacid.

55. Prob 17.43
Show how to convert cyclohexane to cyclohexanecarboxylic acid.

56. Carboxylic Acids
End Chapter 17