Download Carboxylic Acids

Chem 2642
Chapter 19
I.
Carboxylic Acids
Structure of carboxylic acids
A. R – CO- OH
B. The carbon of the carbonyl is electron-poor.
C. The oxygen of the carbonyl is electron-rich.
II.
Nomenclature
A. IUPAC system
1. The parent name comes by replacing the ending of the
longest chain with –oic acid.
2. C-1 is the carbonyl carbon.
3. Examples
O
Methanoic acid
H
OH
O
Hexanoic acid
OH
4. If the COOH group is bonded to a ring, the words
carboxylic acid are added to the parent ring name. The
carbon where the COOH is bonded is C-1.
5. Examples
COOH
2-methylcyclohexancarboxylic acid
2
COOH
3,3-dimethylcyclopentanecarboxylic acid
B. Common naming system
COOH
Benzoic acid
Formic acid
H-COOH
Acetic acid
CH3-COOH
Propionic acid
CH3-CH2-COOH
Butyric acid
CH3-CH2-CH2-COOH
Valeric acid
CH3-CH2-CH2-CH2-COOH
Caproic acid
CH3-CH2-CH2-CH2-CH2-COOH
1. The carbon next to the COOH is called the -carbon.
2. Substituents are located using the greek letters , ,
, , , etc.
3. Examples
O
,-dimethylbutyric acid
OH
O
-bromobutyric acid
Br
OH
3
C. Diacids
1. IUPAC system – replace the ending of the longest chain
with –dioic acid
2. Common naming system
Oxalic acid
HOOC-COOH
Malonic acid
HOOC-CH2-COOH
Succinic acid
HOOC-CH2-CH2-COOH
Maleic acid
HOOC
COOH
COOH
Fumaric acid
HOOC
D. Carboxylates
1. The structure is R-CO-O- M+ where the metal ion is
commonly sodium or potassium
2. The metal name comes first, followed by the
carboxylate name
3. The carboxylate name is named by replacing –ic acid
with –ate.
4. Examples
COO-Na+
Sodium benzoate
Sodium acetate
CH3COO-Na+
4
III.
Preparation of carboxylic acids
A. Oxidation of 1o alcohols with Na2Cr2O7 or CrO3
B. Oxidation of alkyl benzenes that have a benzylic carbon, with
KMnO4
COOH
KMnO4
heat
C. Oxidative cleavage of alkynes using ozone followed by H2O
R-CC-R + ozone then H2O
2 R-COOH
D. Acid hydrolysis of a nitrile
R-CN
IV.
+ H+/H2O
R-COOH
Reactions of carboxylic acids
A. with the bases NaOH, hydride, or methoxide
RCOO-Na+
R-COOH + NaOH
B. with the acids HCl, H2SO4 or HNO3
OH+
R-COOH + HCl
R
OH
5
V.
Acidity of carboxylic acids
A. They are weak acids with pKa ‘s about 5
1. acetic acid has pKa 4.7
2. benzoic acid has pKa 4.2
3. carboxylic acids can be deprotonated using a base that
has a conjugate acid with a pKa greater than 5, such as
NaOH or NaHCO3
B. Electron withdrawing groups near the COOH group will weaken
the OH bond, making the compound more acidic (lower pKa).
1. This is an inductive effect, through the sigma bond
system.
2. Inductive effects weaken with distance.
3. Electron withdrawing groups include X, CO, CN, NO2
C. Electron donor groups near the COOH group will strengthen the
OH bond, making he compound less acidic (higher pKa).
1. also an inductive effect
2. also weakens with distance
3. groups include R and Z:
D. For benzoic acids
1. If put an electronegative group on the meta or para
carbon, the compound will be more acidic than benzoic
acid
2. If put an electron donor group on the meta or para
carbon, the compound will be less acidic than benzoic
acid.
3. If put any group on the ortho carbon, the compound will
be more acidic than benzoic acid (ortho effect)