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Carboxylic Acids and Carboxylic Acid Derivatives
Chapter 15
Pages 408-438
Structure of Carboxylic Acids
R C OHO
The carboxyl group is shown in red and may be written in the condensed form: -COOH.The term carboxylic is taken from the terms carbonyl and hydroxyl, the two structures that make up the carboxyl group.
Properties of Carboxylic Acids
• Very polar compounds• Can hydrogen bond to one another and to water• Boil at higher temperatures than aldehydes,
ketones, or alcohols• Smaller carboxylic acids are soluble in water• Lower molecular weight acids have sharp, sour
tastes and unpleasant aromas• Longer chain carboxylic acids are called fatty
acids and are important components of biological membranes
Naming Carboxylic Acids - IUPAC
• Determine the name of the parent compound, the longest continuous chain containing the carboxyl group.
• Replace the –e ending with the suffix –oic acid. If there are two carboxyl groups, the suffix is –dioic acid.
• Number the chain so the carboxyl carbon is number 1.
• Name and number substituents.
Naming carboxylic acids of cycloalkanes
• Add the suffix carboxylic acid to the name of the cycloalkane or substituted cycloalkane.
• The carboxyl group is always numbered 1.
• Other substituents are named and numbered as usual.
C
O
OHCyclopentanecarboxylic acid
Name the following.
CH3CHCH2CHCOOH
CH3 CH3
CH2CH2CHCOOH
Cl Cl
COOH
CH3
COOH
CH2CH3
Name the following.
CH3CHCH2CHCOOH
CH3 CH3
CH2CH2CHCOOH
Cl Cl
COOH
CH3
COOH
CH2CH3
2,4-dimethylpentanoic acid
3-methylcyclohexanecarboxylic acid
2-ethylcyclopentanecarboxylic acid
2,4-dichlorobutanoic acid
Common Carboxylic Acids
Name Structure Source
Formic acid HCOOH Ants
Acetic acid CH3COOH Vinegar
Propionic acid CH3CH2COOH Swiss Cheese
Butyric acid CH3(CH2)2COOH Rancid butter
Stearic acid CH3(CH2)16COOH Beef fat
Draw structures for the following.
• 2,3-dihydroxybutanoic acid
• 2-bromo-3-chloro-4-methylhexanoic acid
• 1,4-cyclohexanedicarboxylic acid
• 4-hydroxycyclohexanecarboxylic acid
• Formic acid
• Acetic acid
Naming Aromatic Carboxylic Acids
• These are usually named as derivatives of benzoic acid.
• Generally, the –oic acid or –ic acid suffix is attached to the appropriate prefix.
C OH
O
Bro-bromobenzoic acid
Naming Aromatic Carboxylic Acids
• Often, the phenyl group is treated as a substituent.
H2C C
O
OH HC
CH3
H2C
H2C C
O
H
2-phenylethanoic acid 4-phenylpentanoic acid
Draw structures for the following.
• 2,4,6-tribromobenzoic acid
• 2,2,2-triphenylethanoic acid
• 3-phenylhexanoic acid
• 3-phenylcyclohexanecarboxylic acid
Preparation of Carboxylic Acids
• As discussed in Ch 14, carboxylic acids can be prepared from the oxidation of primary alcohols and/or aldehydes.
1º alcohol Aldehyde Carboxylic acid
Examples:
a)1-propanol
b)2-methylbutanal
[O ]
[O ]
Carboxylic acid - ACID
• Carboxylic acids act as acids because they are proton (H+) donors. They are weak acids that dissociate to form a carboxylate ion and a hydrogen ion as shown:
carboxylic acid carboxylate anion hydrogen ion
R
O
OH
R
O
O-
+ H+
Acid/Base Reaction
• Since a carboxylic acid acts as an acid, it will neutralize a strong base like NaOH or KOH to form water and the salt of the carboxylic acid.
R
O
OH
+ NaOH R
O
O-
Na+
+ OH2
Examples
Write a balanced equation and name the products that are formed.
Acetic acid + sodium hydroxide
Benzoic acid + potassium hydroxide
YOU TRY THESE!
• Propanoic acid + potassium hydroxide
• Ethanol
• Butanedial
• Hexanoic acid + sodium hydroxide
[O ]
[O ]
Structure of Esters
R C ORO
•Esters are carboxylic acid derivatives.•They are formed from the reaction of a carboxylic acid with an alcohol.
Formation of an Ester
R1 C OH
O
+ R2 OH R1 C O R2
O
+ H2O
Carboxylic acid alcohol Ester WaterEXAMPLE
H3C C OH
OH2C OH
H3C C O CH2CH3
O
+ H2O
H3C+
Ethanoic acid ethanol(Acetic Acid)
Ethyl ethanoate(Ethyl acetate)
H+, heat
H+, heat
Properties of Esters
• Mildly polar• Have pleasant aromas• Found in natural foodstuffs (banana oil,
pineapples, raspberries, etc.)• Boil at approximately the same
temperature as aldehydes or ketones of similar molecular weights
• Simpler ones are somewhat soluble in water
Naming Esters
• Use the alkyl portion of the alcohol as the first name.
• Remove the –ic acid ending of the carboxylic acid and replace it with –ate.
• The same naming rules apply if the common name of the carboxylic acid is used.
Examples of Ester Names
H3C C O CH3
O
H3C C O CH2CH2CH3
O
C O CH3
O
C O CH3
O
Br
Methyl ethanoate (methyl acetate)
Propyl ethanoate (propyl acetate)
Methyl benzoate Methyl m-bromobenzoate
You Try These!
H3C C O
O
H2C C O CH3
O
C O CH3
O
C O CH2CH3
O
NO2
H2CH3C
Answers to You Try These!
• Cyclopentyl ethanoate
– (cyclopentyl acetate)
• Ethyl cyclohexanecarboxylate
• Methyl p-nitrobenzoate
• Methyl butanoate
Formation of Soap - Esterification
• Fats and oils are triesters of the alcohol glycerol.
3 CH3(CH2)14COOH
3 Palmitic acid+
H2C
HC
H2C
OH
OH
OH
Glycerol
H2C O C(CH2)14CH3
O
HC
H2C
O
O
C(CH2)14CH3
C(CH2)14CH3
O
O
TriglycerideTripalmitoylglyceride
Formation of Soap - Saponification
• When they are hydrolyzed by saponification, the products are soaps.
H2C O C(CH2)14CH3
O
HC
H2C
O
O
C(CH2)14CH3
C(CH2)14CH3
O
O
NaOH
H2O, heat
+Na-O C(CH2)14CH3
O
+Na-O C(CH2)14CH3
O
+Na-O C(CH2)14CH3
O
Acid Chlorides
R C ClO
IUPAC name - Replace the –oic acid ending of the IUPAC name with –oyl chloride.Common name – Replace the –ic acid ending of the common name with –yl chloride.
Examples of Acid Chlorides
H3C C Cl
O
H2CH2C C Cl
O
Br
C ClCl
O
Ethanoyl chloride(acetyl chloride)
3-bromopropanoyl chloride
p-chlorobenzoyl chloride(4-chlorobenzoyl chloride)
Properties of Acid Chlorides
• Noxious, irritating chemicals
• Slightly polar
• Boil at approximately the same temperature as aldehydes or ketones of similar molecular weights
• React violently with water
Formation of Acid Chlorides
R C OH
O PCl3, PCl5, or SOCl2
R C Cl
O
Carboxylic acid Acid Chloride
H3C C O H
O
H3C C Cl
OPCl5
Ethanoic acid Ethanoyl chloride(acetic acid) (acetyl chloride)
Hydrolysis of Acid Chlorides
R C Cl
O
R C OH
O+ H2O
+ HCl
Acid chloride water Carboxylic acid Hydrochloric acid
H3C C Cl
O
H3C C OH
O+ H2O
+ HCl
Ethanoyl chloride ethanoic acid
(acetyl chloride) (acetic acid)
Acid Anhydrides
R C OO
C RO
An acid anhydride is two carboxylic acids with a water molecule removed.“Anhydride” means without water.
Formation of Acid Anhydrides
R C O C R
O O
R C OH
O
+ R C OH
O
Carboxylic acid Carboxylic acid
Acid anhydride
+ H OH
Water