1. Carboxylic Acids and Carboxylic Acid Derivatives
Chapter 14
Carboxylic Acids and Carboxylic Acid Derivatives

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. 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. 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. 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. 1. Carboxylic acids: boiling points
Compare molecules with similar molar masses and different functional groups:

7. 1. Carboxylic acids: boiling points
Boiling point (oC) vs. number of carbons for acids, alcohols, aldehydes, and alkanes.

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.
In alcohols, the polar hydroxyl group and its ability to hydrogen bond make small alcohols completely miscible with water. As the nonpolar alkyl chain of the alcohol gets larger, it is harder and harder for the polar –OH to provide enough interaction with water to get the entire nonpolar “tail” into solution.
The same thing is going on with carboxylic acids; the carboxyl group is very polar and can hydrogen bond with water. As the molar mass increases, the nonpolar hydrocarbon “tail” is harder and harder for the carboxyl group to get into solution. ♫

9. 1. Carboxylic acids: solubility
Solubility (g acid/g H2O) vs. number of carbons for saturated, unbranched-chain carboxylic acids.
Note that “complete solubility” means the same thing as “miscible.”
The graph applies only to straight-chain carboxylic acids with no multiple bonds.
The carboxylic acids with one through four carbons are completely soluble in water. These are methanoic acid, ethanoic acid, propanoic acid, and butanoic acid.
At 5 carbons and beyond, the solubility drops off rapidly; hexadecanoic acid, with a 16-carbon chain, is insoluble in water. ♫

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. 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. 1. Carboxylic acids: nomenclature
pencast
pentanoic acid
3-methylbutanoic acid
3-bromo-2-ethylbutanoic acid ♫

13. 1. Carboxylic acids: nomenclature
Name the following compounds:
cyclopentanoic acid methylcyclohexanoic acid benzoic acid ethyl-4-hydroxybenzoic acid
4-phenylbutanoic acid phenylbutanoic acid
pencast ♫

14. 1. Carboxylic acids: nomenclature
Draw structures for the following compounds:
2,5-dimethylhexanoic acid
3-bromo-5-chlorooctanoic acid
2,2-dimethylbutanedioic acid
3-methylcyclohexanecarboxylic acid
2,4-dichlorobenzoic acid
3-phenylpentanoic acid
pencast

15. ♫ 1. Carboxylic acids Is “alpha-hydroxy” an actual substance?
glycolic acid
lactic acid
tartaric acid
Many cream and lotion bottles say, “with alpha-hydroxy!” You may be remembering that, when we have an –OH on a compound that is not an alcohol, the –OH substituent is called hydroxy-. In non-IUPAC nomenclature, the carbon next to the carboxyl carbon is called the alpha carbon. [The carbon two over from the carboxyl carbon is called the beta carbon.] A carboxylic acid with a hydroxyl group on the alpha carbon is called an alpha hydroxy acid.
So, when a product claims it contains “alpha hydroxy,” it is claiming to have a molecule-less substituent. The correct term is “alpha hydroxy acid.” ♫

16. 1. Carboxylic acids
The last paragraph in the inset box on pages 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
We have been using BioBags for quite some time, and they work just fine and are not prohibitively expensive, especially if you consider the environmental cost of regular plastic bags. ♫

17. 1. Carboxylic acids: reactions
Preparation is by complete oxidation of primary alcohols or oxidation of aldehydes.
1o alcohol
aldehyde
carboxylic acid

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. 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. 1. Carboxylic acids: reactions
Acid-base reaction
carboxylic acid + strong base  carboxylic acid salt + water

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
potassium ethanoate
lithium benzoate
sodium hexanoate
pencast ♫

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. 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. 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. 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.
Precede this name with the name of the alkyl or aryl portion of the alcohol.

26. ♫ 2. Esters: nomenclature Name the following esters. pencast
ethyl propanoate methyl benzoate
phenyl butanoate ethyl ethanoate ♫

27. 2. Esters: nomenclature Draw the structures of the following esters.
propyl ethanoate
octyl decanoate
methyl methanoate
2-methylpropyl propanoate
3-methylbutyl ethanoate
phenyl pentanoate
pencast

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. 2. Esters: reactions
Show the esterification reaction that would produce butyl propanoate.
pencast

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).
For pentyl butanoate:
Begin with butanol and oxidize it to butanoic acid. React butanoic acid with pentanol and a trace of acid to produce pentyl butanoate.
For octyl ethanoate:
Begin with ethanol and oxidize it to ethanoic acid. React ethanoic acid with octanol and a trace of acid to produce octyl ethanoate.
pencast ♫

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. 2. Esters: reactions
Hydrolysis of esters, when it is base-catalyzed, is called saponification.
ester carboxylic acid salt alcohol

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. 2. Esters: reactions
What are the products of the following reactions?
+ H2O
pencast
+ H2O
1. ethanoic acid and propanol
2. potassium hexanoate and propanol
3. sodium pentanoate and methanol
4. hexanoic acid and 2-pentanol
+ H2O ♫
+ H2O

35. 2. Esters: saponification
(salts of carboxylic acids)
Old fashioned soap was made from animal fat and lye, the equivalent of triglycerides and strong base shown in this slide. A triglyceride is a molecule with three esters attached.
Each of these three esters detaches in the presence of base to form a carboxylic acid salt. The other product is glycerol, properly called 1,2,3-propanetriol according to IUPAC rules. The salts of carboxylic acids act as soaps. + + ♫

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. 2. Esters: saponification

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. 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. 3. Acid chlorides and acid anhydrides
Examples
ethanoic acid
ethanoyl chloride
benzoic acid
benzoyl chloride

41. 3. Acid chlorides and acid anhydrides
Name the following acid chlorides.
Draw structures for the following acid chlorides.
heptanoyl chloride
2-hydroxypropanoyl chloride
pencast ♫
3-bromobutanoyl chloride, 3-hydroxypentanoyl chloride

42. 3. Acid chlorides and acid anhydrides
Preparation of acid chlorides
The reagents PCl3, PCl5, and SOCl2 are inorganic acid chlorides
PCl3 or
+ PCl5 or
SOCl2
+ inorganic products

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!
Don’t worry about knowing the mechanism. I just put it on the slide to show you the amazing things that happen between reactant and product! ♫

44. 3. Acid chlorides and acid anhydrides
Write an equation for the reaction of benzoic acid with SOCl2 and name the organic product.
SOCl2
benzoyl chloride
pencast

45. 3. Acid chlorides and acid anhydrides
Acid anhydrides are two carboxylic acid molecules with a water molecule removed.
+ H2O

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. 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. 3. Acid chlorides and acid anhydrides
Name the following acid anhydrides.
pencast

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. 3. Acid chlorides and acid anhydrides
Write equations for the synthesis of butanoic anhydride, beginning with butanoic acid.
pencast

51. 3. Acid chlorides and acid anhydrides
Acid anhydrides react with water, if it is present, to produce two carboxylic acids.
+ H2O

52. 3. Acid chlorides and acid anhydrides
What are the products of the hydrolysis of
ethanoic anhydride?
ethanoic methanoic anhydride?
pencast

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.