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ORGANIC CHEMISTRY
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General, Organic and Biochemistry
7th Edition
Functional Group Formulas
14.1 Carboxylic Acids
Structure
• Carboxylic acid groups consist of two
very polar functional groups
– Carbonyl group
– Hydroxyl group
• Carboxylic acid groups are very polar
Carboxylic acid –
propanoic acid
Ester –
methyl ethanoate
1
14.1 Carboxylic Acids
Physical Properties
• Low molecular weight carboxylic acids
– Sharp, sour taste
– Unpleasant aromas
• High molecular weight carboxylic acids
– Fatty acids important in biochemistry
• Low molecular weight carboxylic acids are water
soluble due to hydrogen bonding with:
– Water
– Each other
14.1 Carboxylic Acids
Physical Properties
Due to carboxylic acids forming intermolecular
hydrogen bonds boiling points are at higher
temperatures than those of any other functional
group studied
14.1 Carboxylic Acids
Nomenclature
2
• Determine the parent compound: 4C – butane
• Number the chain so that the carboxyl carbon is
carbon 1: from right to left
• Replace the –e ending with –oic acid
– Butanoic acid
– If two carboxyl groups are present use –dioic acid
• Complete naming as usual – bromine on C-3
O
Br
CH
CH
CH
C
OH
4
2
3 3
2 1
14.1 Carboxylic Acids
Carboxylic Acid
Naming Examples
14.1 Carboxylic Acids
Common Names
• Use Latin or Greek prefixes
• Suffix is –ic acid
• Greek letters indicate the position of the
substituents
14.1 Carboxylic Acids
Names and Structures of Some
Common Carboxylic Acids
14.1 Carboxylic Acids
Some Important Carboxylic Acids
O
CH3 CH2 16C OH
Stearic acid
found in beef fat
3
14.1 Carboxylic Acids
Reactions Involving
Carboxylic Acids
4
• Carboxylic acids are prepared by oxidation of
primary alcohols and aldehydes
CH3CH2CH2OH
O
H2CrO4
O
CH3CH2C OH
Warm
CH3CH2CH
14.1 Carboxylic Acids
Acid-Base Reactions
5
• Carboxylic acids behave as acids because
when they are dissolved in water they will
deprotonate to form a carboxylate ion and
the hydronium ion
• Carboxylic acids are weak acids with
dissociations of less than 5%
14.1 Carboxylic Acids
Acid-Base Reactions
• Carboxylic acids DO react with strong bases
to form carboxylate salts
– A process of neutralization
– Acid protons are removed by the –OH- to form
H2O and carboxylate ion
– Equilibrium shifts to the right with removal of
H+
14.1 Carboxylic Acids
Acid-Base Reactions
• What is the product of each of the
following reactions?
14.1 Carboxylic Acids
Salts of Carboxylic Acids
• Nomenclature
– First add the cation’s name
• Sodium
– Then drop the –oic acid and add –ate
• Sodium benzoate
• Uses of carboxylic acids
•
•
•
•
Soaps like sodium stearate
Preservatives
Anti-fungal medicines
Used to control food pH
14.1 Carboxylic Acids
Esterification
• Carboxylic acids react with alcohols to form:
– Esters
– Water
6
14.2 Esters
Structure and physical properties
• Esters are mildly polar, somewhat water soluble
• Frequently found in natural foodstuffs
• Many have pleasant aromas
– Isoamyl acetate = banana oil
3-methylbutyl ethanoate
– Ethyl butanoate = pineapple aroma
Ethyl butanoate
– Isobutyl formate = raspberry aroma
Isobutyl methanoate
• Boil at approximately the same temperature as
carbonyls with comparable molecular weight
7
14.2 Esters
Nomenclature
8
Form from the reaction of a carboxylic acid with an
alcohol, which is reflected in the naming
1. Use the alkyl group as the first name
(Alcohol part of the ester)
2. Base the name for the acid part of the structure
from the longest chain ending in the C=O
(Carboxylic acid part of the ester)
3. Change the –oic acid of the acid name to –oate
Naming Esters
14.2 Esters
Name the following esters:
• Alkyl portion = first name ethyl
• Parent carboxylic acid = butanoic acid
• Change suffix to reflect ester = Ethyl butanoate
• Alkyl portion = first name proply
• Parent carboxylic acid = ethanoic acid
• Change suffix to reflect ester = Propyl
ethanoate
Naming Esters
14.2 Esters
Naming esters is much like naming the salts
of carboxylic acids:
• Alkyl portion = first name ethyl
• Parent carboxylic acid = ethanoic acid
• Change suffix to reflect ester =
Ethyl ethanoate
Reactions Involving Esters
14.2 Esters
Preparation
•
•
•
•
6
Carboxylic acids react with alcohols to produce esters
The reaction is catalyzed by strong mineral acid
Heat is required
A molecule of water is also released as a product:
reaction is a dehydration
Reactions Involving Esters
14.2 Esters
Another example:
6
O
O
+
H3O
CH3CH2C O CH3
CH3CH2C OH
H3PO4
+ CH3 OH
+ H2O
Hydrolysis of Esters
14.2 Esters
• The main reaction of esters is hydrolysis,
reaction with water
– This reaction is also called hydration =
cleavage of any bond by the addition of a
water molecule
• However, the uncatalyzed reaction is
slow and requires heat
• Mineral acid is used as a catalyst
9
14.2 Esters
Acid hydrolysis of Esters
Acid hydrolysis products are:
• Acid
• Alcohol
14.2 Esters
Base Hydrolysis of Esters
10
The base catalyzed hydrolysis of an ester:
• Saponification or soap-making
• Products are:
– Acid salt
– Alcohol
• Acid can’t exist in basic conditions, so the
product is the salt of the carboxylic acid
using the cation of the base catalyst
Saponification
• Saponification (soap-making) is:
– Base-catalyzed hydrolysis of fats (glycerol triesters)
14.2 Esters
Simplified Action of Soap
14.2 Esters
Condensation Polymers
• Polyesters are condensation polymers
• They are formed by eliminating a small
molecule (e.g., H2O) when combining:
– Diacid
– Diol
• Each of the combining molecules has two
reactive functional groups, highlighted in red
Polethylene terphthalate, PETE
COOH + n HO CH2CH2OH
HOOC
Terphthalic acid
HOOC
PETE is used in:
•Mylar
•Plastic bottles
•Polyester fabric
*
O
C
H+
1,2-ethanediol
O
C O CH2CH2OH
+ H2O
O
C O CH2CH2O
Continued
condensation
at each end
n*
Repeating unit of the polymer
14.3 Acid Chlorides and
Acid Anhydrides
11
• Acid chlorides are derivatives of carboxylic
acids having the general formula:
• Are named:
– by replacing the –oic acid ending of the IUPAC
name with –oyl chloride
O
CH3C Cl
Cl
O
C Cl
ethanoyl chloride
(acetyl chloride)
4-chlorobenzoyl chloride
(p-chlorobenzoyl chloride)
Acid Anhydrides
14.3 Acid Chlorides and
Acids Chlorides
12
Acid chlorides
• Noxious, irritating chemicals requiring great
care in handling
• Slightly polar, boiling near the corresponding
carbonyl’s temperature
• React violently with water
• Are good acyl group transfer reagents
12
Another Example:
Acid Anhydrides
14.3 Acid Chlorides and
Acids Chlorides
PCl3
O
PCl
5
CH3CH2 C Cl
CH3 CH2C OH
SOCl2
O
Acid Anhydrides
14.3 Acid Chlorides and
Hydrolysis of Acid Chlorides
Acid chlorides react violently with water in a
hydrolysis reaction
• Reforming the acid and HCl
• Substitution of the –OH for the –Cl occurs at
the acyl carbon
O
CH3CH2C Cl + H2O
Substitution
O
here
CH3CH2C OH +HCl
Acid Anhydrides
14.3 Acid Chlorides and
Acid Chloride Substitution
• Acid chlorides react with alcohols to form esters
and HCl
• Substitution of the –OR for the –Cl occurs at the
acyl carbon
O
CH3CH2C Cl + CH3OH
Substitution
here
O
CH3CH2C O CH3 + HCl
Acid Anhydrides
14.3 Acid Chlorides and
Acid Anhydrides
13
• Acid anhydrides have the formula:
• The molecule is 2 carboxylic acid molecules with
a water molecule removed
– Anhydride means without water
• Symmetrical anhydrides are those with both acyl
groups the same
• Symmetrical anhydrides are named by replacing
the -acid ending of the acid with –anhydride
O O
CH3C O C CH3
ethanoic anhydride
acetic anhydride
14
• Acid anhydrides are not typically formed in a
reaction between the parent carboxylic acids
• One pathway is the reaction between:
Anhydrides
14.3 Acid Chlorides and Acid
Formation of Acid Anhydrides
– Acid chloride
– Carboxylate anion
O O
O
O
warm
+
CH3C OH HO C CH3 H3PO4 CH3C O C CH3
O
CH3C O
+
O
Cl C CH3
SOCl2
O
HO C CH3
O O
CH3C O C CH3
• Acid anhydride reacts with alcohol to
produce:
Anhydrides
14.3 Acid Chlorides and Acid
Acid Anhydride Reactions
With Alcohols
– Ester
– Carboxylic acid
– An acyl group transfer reaction
O O
CH3C O C CH3
+ CH3
HO CH
CH3
CH3
O
CH3C O CH
+
CH3
O
HO C CH3
14.4 Nature’s High Energy Compounds:
Phosphoesters and Thioesters
15
• Phosphoric acid reacts with alcohols to
produce a phosphate ester or
phosphoester
• The ester can then react with a second or
third acid to give phosphoric acid
anhydrides
• ADP and ATP of biochemistry fame are
important examples of phosphate esters
and Thioesters
14.4 Nature’s High Energy
Compounds: Phosphoesters
Phosphoric Acid Esters
Ester bond
NH2
Anhydride bonds
O
O
N
N
O
O P O P O P O CH2
O O O
adenosine
triphosphate, ATP
N
N
OH
O
OH
• In biochemistry, acetyl coenzyme A (acetyl
CoA-SH) reacts with acyl groups to “activate”
them for further biological reaction by
forming a thioester
and Thioesters
14.4 Nature’s High Energy
Compounds: Phosphoesters
Thioesters
-
COO
CH2
O
COO
CoA-S C CH3 + C O HO C COO
CH2
Acetyl CoA CH2 COO
COO
+ CoA-SH
Reaction Schematic
Aldehyde Oxidation
Carboxylic
Acid
Esterification
Oxidation
1º Alcohol
Dissociation
Neutralization
Carboxylate anion
Esterification
Carboxylic Acid salt
Summary of Reactions
1. Carboxylic acids
a. Preparation
b. Dissociation
c. Neutralization
d. Esterification
2. Esters
a. Acid hydrolysis
b. Saponification
3. Acid chloride synthesis
4. Acid anhydride synthesis
5. Phosphoester formation
Summary of Reactions