Transcript Document

Chemistry 20
Chapter 10
Carboxylic Acids
Carboxylic Acids
A carboxylic acid contains a carboxyl group, which is a
carbonyl group attach to a hydroxyl group.
carbonyl
group
O

CH3 — C—OH hydroxyl group or CH3COOH
carboxyl group
CH3CO2H
Naming Carboxylic Acids
• In the IUPAC name of carboxylic acids, the “-e” in the
name of the longest chain is replaced by “-oic acid”.
• The common names use prefixes “form-” and “acet-” for the first
two carboxylic acids.
H-COOH
CH3-COOH
methanoic acid
ethanoic acid
CH3-CH2-COOH
formic acid
acetic acid
propanoic acid
CH3-CH2-CH2-COOH butanoic acid
Naming Carboxylic Acids
– Number the chain beginning with the carbon of the carboxyl group.
– Because the carboxyl carbon is understood to be carbon 1, there is no
need to give it a number.
CH2 – CH3
CH3
1
3
2
1
CH3─CH─CH2─COOH
CH3─CH2─CH─COOH
3-Methylbutanoic acid
2-Ethylbutanoic acid
OH
5
O
1
OH
5-Hydroxylhexanoic acid
H2 N
4
1
COOH
4-Aminobenzoic acid
Naming Dicarboxylic Acids
– Add the suffix “-dioic acid” to the name of the parent alkane that
contains both carboxyl groups; thus, “-ane” becomes “-anedioic acid”.
– The numbers of the carboxyl carbons are not indicated because they
can be only at the ends of the chain.
O
HO
O
1
2
3
OH
HO
O
1
OH
O
Ehanedioic acid
O
HO
4
O
5
1
OH
HO
Propanedioic acid
O
O
1
OH
6
O
O
Butanedioic acid
HO
1
Pentanedioic acid
Hexanedioic acid
OH
Physical properties of Carboxylic Acids
1- The carboxyl group contains three polar covalent bonds;
C=O, C-O, and O-H. So they are so polar.
2- Carboxylic acids have higher boiling points than other types of organic
compounds (with the same molecular weight) because of hydrogen bonding.
Hydrogen bonding
between two molecules
H3 C
dO
d+
H O
C
C
O
H
d+
CH3
O
d-
3- They are more soluble in water than alcohols, ethers, aldehydes, and
ketones because of stronger hydrogen bonding.
4- Liquid carboxylic acids have sharp and disagreeable odors.
5- They taste sour (exist in pickle, lime, and lemon).
Fatty Acids
• Long, unbranched chain carboxylic acids and they are found in animal
fats, vegetable oils, or phospholipids of biological membranes.
COOH S te aric acid (18:0)
(mp 70°C )
•
COOH O l e ic acid (18;1)
Most have between 12 and 20 carbons in an unbranched chain.
(mp 16°C )
• In most unsaturated fatty acids, the cis isomer is usually
existed
and
the
COOH Lin
ol
e
ic
acid
COOH S te aric acid (18:0) (18:2)
trans isomer is rare.
(mp-5°C )
(mp 70°C )
COOHCOOH
O l e icLin
acid
ol e(18;1)
ni c aci d (18:3
(mp Cis
16°C
) -11°C )
(mp
•
COOH Lin ol e ic acid (18:2)
Unsaturated fatty acids have lower melting points than their
saturated
(mp-5°C
)
counterparts.
COOH Lin ol e ni c aci d (18:3)
Fatty Acids
Saturated fatty acids are solids at room temperature.
Packed together  Maximum London dispersion forces
COOH
COOH
COOH
COOH
COOH
Fatty Acids
Unsaturated fatty acids are liquids at room temperature.
Can not packed together  London dispersion forces
COOH
COOH
Cis
COOH
COOH
COOH
Esters
In an ester, the H in the
carboxyl group is replaced
by an alkyl group.
O

CH3 — C—O —CH3
ester group
Soaps
• Natural soaps are sodium or potassium salts of fatty acids.
• They are prepared from a blend of tallow and coconut oils
(triglycerides).
CH2 – CH – CH2
OH
• Triglycerides are triesters of glycerol.
OH
OH
1,2,3-Propanetriol
(glycerol, glycerin)
• the solid fats are melted with steam and the water insoluble
triglyceride layer that forms on the top is removed.
Soaps
• Preparation of soaps begins by boiling the triglycerides with
NaOH. The reaction that takes place is called saponification.
• Boiling with KOH gives a potassium soap.
O
O
CH2 OH
O
O CH2 OCR
saponification
+
CH2 OH +
CH2 OCR+ 3 N aOH
O
O
3
RCO
N
a
CHOH
RCOCH
saponification
+
O +
+
3
N
aOH
3
RCO
N
a
CHOH
RCOCH
O
CH2 OH
CH2 OCR
CH2 OHetriol S odiu m soaps
1,2,3-Propan
A triglCH
yce
ri de
2 OCR
1,2,3-Propan
etriol
(Glyce
rol; gl yce
rin )S odiu m soaps
de rol )
( a triAe trigl
ste r yce
of glriyce
(Glyce rol; gl yce rin )
( a tri e ste r of gl yce rol )
Soaps
Hydrophobic part: nonpolar
Hydrophilic part: polar (remains in contact with environment)
O
+
3 RCO N a
riol S odiu m soaps
e rin )
Soaps
When soap is mixed with dirt (grease, oil, and …), soap
micelles “dissolve” these nonpolar, water-insoluble molecules.
Soaps
• Natural soaps form water-insoluble salts in hard water.
• Hard water contains Ca(II), Mg(II) and Fe(III) ions.
-
2 CH3 ( CH2 ) 1 4 COO Na + + Ca
A sodium soap
(sol ubl e i n wate r as mi cel le s)
2+
-
2+
+
[ CH3 ( CH2 ) 1 4 COO ] 2 Ca
+ 2 Na
Cal ci um salt of a fatty aci d
(insol uble i n wate r)
Solution:
Using Synthetic detergents.
-SO3- (sulfonate) instead of COO- (carboxylate)
Chemical properties of Carboxylic Acids
1- They are weak acids.
Substituents of high electronegativity, especially -OH, -Cl, and -NH3+, near
the carboxyl group increase the acidity of carboxylic acids.
Formula: CH3 COOH
N ame:
pK a:
Acetic
acid
4.76
ClCH2 COOH
Cl2 CHCOOH
Cl3 CCOOH
Chloroacetic D ichloroacetic Trich loroacetic
acid
acid
acid
2.86
1.48
0.70
In creasing acid strength
Chemical properties of Carboxylic Acids
2- Reaction with bases:
They react with NaOH, KOH, NH3, and other strong bases to form watersoluble salts.
COOH
+
NaOH
Ben zoic acid
(slightly soluble in water)
COOH
+
H2 O
+
COO Na + H2 O
Sodium b enzoate
(60 g/100 mL water)
NH3
Benzoic acid
(s ligh tly solub le in w ater)
H2 O
-
COO NH4
+
Ammoniu m b enzoate
(20 g/100 mL water)
Chemical properties of Carboxylic Acids
3- Reduction:
Resistant to reduction
Using a powerful reducing agent: LiAlH4 (Lithium aluminum hydride).
1° alcohol
O
COH
3-cyclopentenecarboxylic acid
LiAlH4, ether
H2O
CH2OH
4-Hydroxymethylcyclopentene
Chemical properties of Carboxylic Acids
3- Fischer Esterification:
- A carboxylic acid reacts with an alcohols to form an ester.
- Using an acid catalyst such as concentrated sulfuric acid.
O
H2 SO4
CH3 C-OH + H-OCH2 CH3
Ethanoic acid
Ethanol
(Acetic acid) (Ethyl alcohol)
O
CH3 COCH2 CH3 + H2 O
Ethyl ethanoate
(Ethyl acetate)
The best way to prepare an ester.
Chemical properties of Carboxylic Acids
5- Decarboxylation:
Loss of CO2 from a carboxyl group.
O
RCOH
de carboxylation
Heat
RH + CO 2