1. Bettelheim, Brown Campbell and Farrell Chapter 18
Carboxylic Acids
Bettelheim, Brown Campbell and Farrell
Chapter 18

2. Introduction to Carboxylic Acids
Derivatives of carboxylic acids
Anhydrides, Esters, and Amides
Made by reacting a carboxyl acid group with another molecule. H2O is formed in each reaction

3. Carboxylic Acids
The functional group of a carboxylic acid is a carboxyl group, which can be represented in any one of three ways

4. Naming Carboxylic Acids
IUPAC names
Take longest carbon chain that contains the carboxyl group as the parent alkane
Change the final -e from the name of the parent alkane to -oic acid
Number the chain so that the carboxyl group carbon is number 1
Carboxyl carbon is understood to be carbon 1, so we don’t need to include the number in the name

5. Nomenclature Examples: (common name shown in parentheses)
an -OH substituent is indicated by the prefix hydroxy-
an -NH2 substituent by the prefix amino-

6. Dicarboxylic Acids
Add the suffix -dioic acid to the name of the parent alkane that contains both carboxyl groups
Carboxylic acid groups must be at ends of chain, so we do not need to number them

8. Nomenclature
Common names use the Greek letters alpha (a), beta (b), gamma (g), etc. to locate substituents

9. Physical Properties
The carboxyl group contains three polar covalent bonds; C=O, C-O, and O-H
Polarity of carboxyl group determines the major physical properties of carboxylic acids

10. Physical Properties Highly polar group
Two hydrogen bonds can form between groups
Two carboxyl groups create a dimer that behaves as a higher-molecular-weight compound
Much higher boiling points than other types of organic compounds of comparable molecular weight

11. Physical Properties
More soluble in water than comparable alcohols, ethers, aldehydes, and ketones

12. Fatty Acids (carboxylic acids)
Fatty acids: long chain carboxylic acids
derived from animal fats, vegetable oils, or phospholipids of biological membranes.
Over 500 have been isolated from various cells and tissues.
Generally 12 and 20 carbons in an unbranched chain—with even number of carbons
May be unsaturated:
cis isomer predominates; trans isomers are rare.
Unsaturated fatty acids have lower melting points than saturated fatty acids.

13. Fatty Acids

14. Fatty Acids
Unsaturated fatty acids generally have lower melting points than their saturated counterparts.

15. Fatty Acids Saturated fatty acids are solids at room temperature
Hydrocarbon chains can to pack together in such a way as to maximize interactions (by London dispersion forces) between their chains.

16. Fatty Acids
Unsaturated fatty acids are liquids at room temperature because the cis double bonds interrupt the regular packing of their hydrocarbon chains.

17. Fatty Acids
Fatty acid: an unbranched-chain carboxylic acid derived from hydrolysis of animal fats, vegetable oils, or membrane phospholipids
Usually unbranched chain with carbons
EVEN number of carbons
May be saturated or unsaturated (C=C)
Unsaturated generally have cis double bonds
Unsaturated fatty acids have lower melting points than their saturated fatty acids
Most abundant are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1)

18. Notation of fatty acids
Numbers in parentheses show number of carbons and double bonds
(carbons, double bonds)
Palmitic acid (16:0) has 16 carbons and no double bonds
Oleic acid (18:1) has 18 carbons and 1 double bond

19. Fatty Acids

20. Reactions of Carboxylic Acids
Chapter 18: Carboxylic Acids
Acid-Base Properties
Ionization and pH
Reaction with base
Esterification (Reaction with Alcohol)
Reduction (NaBH4 or LiAlH4 )
Decarboxylation
Chapter 19: Derivatives of Carboxylic Acids
Reaction with Acids: Anhydride formation
Reaction with Amines: Amide formation

21. Acidity of Carboxylic Acids
Carboxylic acids are weak acids
Ka generally in range of 10-4 to 10-5 for most unsubstituted aliphatic and aromatic carboxylic acids
pKa is pH at which half of acid has lost its H
pKa range is 4 - 5
Example:
Acetic Acid

22. Acidity of RCOOH
Highly electronegative substituents, such as -OH, -Cl, and -NH3+, near the carboxyl group increase the acidity of carboxylic acids
Pull electron density away from carboxyl group
Both dichloroacetic acid and trichloroacetic acid are stronger acids than H3PO4 (pKa 2.1)

24. Ionization versus pH
The form in which a carboxylic acid exist in an aqueous solution depends on the solution’s pH
Very important in biological systems

25. Reaction With Bases
All carboxylic acids, whether soluble or insoluble in water, react with strong bases (NaOH, KOH) to form water-soluble salts
Also form water-soluble salts with ammonia and amines (weak bases)

26. Reaction With Bases
Carboxylic acids react with sodium bicarbonate and sodium carbonate to form water-soluble sodium salts and carbonic acid, H2CO3
Carbonic acid then decomposes to give water and carbon dioxide gas CO2

27. Reduction of Carboxylic Acids

28. Fischer Esterification
Fischer esterification is commonly used to make esters
Carboxylic acid is reacted with an alcohol in the presence of an acid catalyst, such as concentrated sulfuric acid
Fischer esterification is reversible
Can drive reaction in either direction by altering experimental conditions (Le Chatelier’s principle)

29. Fischer Esterification
Alcohol adds to the carbonyl group of the carboxylic acid to form a tetrahedral carbonyl addition intermediate
Intermediate then loses H2O to form an ester

30. Soaps
Natural soaps are prepared by boiling lard or other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap)

31. Soaps
In water, soap molecules spontaneously cluster into micelles, a spherical arrangement of molecules such that their hydrophobic parts are shielded from the aqueous environment, and their hydrophilic parts are in contact with the aqueous environment.

32. Soaps Soaps clean by acting as emulsifying agents
Long hydrophobic hydrocarbon chains cluster so as to minimize their contact with water
Polar hydrophilic carboxylate groups remain in contact with the surrounding water molecules
These two forces cause soap molecules to form micelles

33. Soaps
When soap is mixed with dirt (grease, oil, and fat stains), soap micelles “dissolve” these nonpolar, water-insoluble molecules.

34. Soaps Natural soaps form water-insoluble salts in hard water.
Hard water contains Ca(II), Mg(II) and Fe(III) ions.

35. Detergents
Can overcome problem of precipitates in by using a molecule containing a -SO3- group (sulfonic acid group) in the place of a -CO2- group.
Calcium, magnesium and iron salts of sulfonic acids, RSO3H, are more soluble in water than salts of fatty acids.
Synthetic detergents can be synthesized from SDS, a linear alkylbenzene sulfonate (LAS), an anionic detergent.