Chapter 16 Carboxylic Acids

Various dilute solutions of ethanoic acid

A carboxylic acid contains a carboxyl group, which is a carbonyl group (C═O) attached to a hydroxyl group (—OH);the carbon of the carboxyl group is numbered position 1

To write the IUPAC names of a carboxylic acidSTEP 1 Replace the e in the alkane name with oic acid.

CH4 Methane HCOOH Methanoic acidCH3-CH3 Ethane CH3—COOH Ethanoic acid

STEP 2 Locate and name substituents, counting from the carboxyl carbon as carbon 1.

Alpha hydroxy acids (AHAs)occur naturally in fruit, milk, and sugarcane;they are used in skin care products

2-hydroxyethanoic acid

2-hydroxypropanoic acid

2,3-dihydroxybutanedioic acid

2-hydroxybutanoic acid

Benzoic acid is the carboxylic acid that is attached to a benzene ring

the –NH2 group is called amino; 4-aminobenzoic acid is an example of an amino acid

Some common carboxylic acids used as analgesics

Carboxylic acidsare strongly polarhave two polar groups: hydroxyl (−OH) and the carbonyl (C═O)

Carboxylic acids form very strong hydrogen bonds with themselves in the absence of water

The smaller carboxylic acids (1-4 carbons) are quite soluble in water

Carboxylic acids are weak acids that ionize in water to produce carboxylate ions and hydronium ions

A weak acid is an acid that undergoes the reaction shown above to the extent of about 5% but will react completely with stronger bases. For example:

CH3—COOH + NaOH CH3—COO– Na+ + H2O

CH3COOH + NaOH CH3COO– Na+ + H2O

Esters:

HCl + NaOH NaCl + H2O

CH3CO2H + CH3CH2OH CH3CO2CH2CH3 + H2O

Aspirinis used to relieve pain and reduce inflammationis an ester of salicylic acid and acetic acid

Oil of wintergreenis used to soothe sore musclesis an ester of salicylic acid and methanol

Naming estersThe name of an ester contains the names of the alkyl group from the alcoholthe carbon chain from the acid with -ate ending

Fats are esters of 1,2,3-trihydroxypropane (glycerol) and a long chain fatty acid

CH2O

CH

CH2O

O

C

O

C

OC

O (CH2)16CH3

(CH2)16CH3

CH3(CH2)16

The fatty acids are not necessarily all the same; some differ in the number of carbons, some have double bonds in them (unsaturated fats); upon hydrolysis they yield the salt of a fatty acid known as a soap

NaOHC O

O

CH3(CH2)16

Na+-

-

CH

CH2OH

CH2OH

HO

Soaps have a polar end and a non-polar tail and self assemble in water in a spherical fashion with the non-polar ends pointing inward and the polar ends on the outside. The non-polar ends are good for dissolving grease and oil. These small spherical balls are called micelles