Transcript Lecture Notes

Chapter Sixteen
Carboxylic Acids,
Esters, and Other
Acid Derivatives
• Carboxylic acid: An organic compound with carboxyl functional
group
• Carboxyl group: A carbonyl group (C=O) with a hydroxyl group (—
OH) bonded to the carbonyl carbon atom
• A general structural representation for a carboxyl group is shown
below
Carbonyl group
O
R
C
OH
Carboxylic acid
Chapter 16 | Slide 2 of 52
Carboxylic Acids
Fig. 16.1
The three simplest carboxylic acids: methanoic acid, ethanoic
acid, and propanoic acid.
Chapter 16 | Slide 3 of 52
Carboxylic Acids
→ Fig. 16.2
Benzoic acid molecule
Chapter 16 | Slide 4 of 52
Carboxylic Acids
Carboxylic acids always contain the carboxyl group on
__________ ____.
• A carboxyl group is a carbonyl attached to a hydroxyl
• Acts differently than an alcohol or a carbonyl compound
O

CH3 — C—OH
=
CH3—COOH
carboxyl group
Chapter 16 | Slide 5 of 52
IUPAC Rules for Naming
Monocarboxylic Acids
• Rule 1: Select the longest carbon chain that includes the
carbon atom of the carboxyl group as the parent chain.
• Rule 2: Name the parent chain by changing the “-e”
ending of the corresponding alkane to “-oic” acid.
• Rule 3: Number the parent chain by assigning the #1 to
the carboxyl carbon atom.
• Rule 4: Determine the identity and location of any
substituents in the usual manner, and append this
information to the front of the parent chain name.
Chapter 16 | Slide 6 of 52
Naming Rules
• Identify longest chain containing the ___________ group
• (IUPAC) Number ____________ carbon as 1
• (Common) Assign , , g to carbon atoms adjacent to
____________ carbon
CH3
|
CH3 — CH—CH2 —COOH
IUPAC
3-methylbutanoic acid
Common -methylbutryic acid
Chapter 16 | Slide 7 of 52
Naming Carboxylic Acids
Formula
IUPAC
alkan -oic acid
Common
prefix – ic acid
HCOOH
methanoic acid
formic acid
CH3COOH
ethanoic acid
acetic acid
CH3CH2COOH
propanoic acid
propionic acid
CH3CH2CH2COOH
butanoic acid
butyric acid
Chapter 16 | Slide 8 of 52
First Six Unbranched Monocarboxylic
Acids
Chapter 16 | Slide 9 of 52
First Six Unbranched Dicarboxylic Acids
Chapter 16 | Slide 10 of 52
Aromatic Carboxylic Acids
• Benzoic Acid is the ______________ carboxylic acid
• Locates substituents by assigning 1 to the carbon with the
carboxyl group
O
OH
C
O
OH
O
C
OH
C
Cl
Benzoic acid
3-chlorobenzoic acid
CH3
4-methylbenzoic acid
Chapter 16 | Slide 11 of 52
Common Acids
• Acetic Acid: CH3COOH
– Vinegar is 4%-8% (v/v) acetic acid solution
– Colorless liquid with sharp odor
• Oxalic acid: HOOC-COOH - found in spinach
and cabbage
– Harmful at high concentrations
– Used to remove rust, bleach straw, and leather and
ink stains
Chapter 16 | Slide 12 of 52
Polyfunctional Carboxylic Acids
• PCAs contain at least one or more functional groups
other than carboxyl group
• PCAs are commonly found in living organisms an play
an important role in human body
– Occur in many fruits
– Used in over the counter skin care products and prescription
drugs
• Common types of PCAs:
– Unsaturated acids
– Hydroxy acids
– Keto acids
Chapter 16 | Slide 13 of 52
Unsaturated Acids
• Contain at least one carbon-carbon double bond (C=C):
• Two types of monounsaturated carboxylic acids:
– Trans - unsaturated carboxylic acids
– Cis – unsaturated carboxylic acids
• Examples:
– Propenoic acid (acrylic acid) used in the manufacture of
polymeric materials.
– Futenedioic acid - has two forms
•
•
Fumaric acid : trans-form
Maleic acid: cis-form
Chapter 16 | Slide 14 of 52
Hydroxy Acids
• Contain at least one hydroxyl group and are
naturally present in many foods
• Examples:
– Glycolic acid: present in juice from sugar cane and
sugar beets
– Lactic acid: Present sour milk, sauerkraut, and dill
pickles
– Malic acid and tartaric acid occur naturally in fruits
Chapter 16 | Slide 15 of 52
Keto Acids
• Contain a carbonyl (C=O) group within a carbon
chain.
• Example:
– Pyruvic acid - simplest keto acid with odor resembling
that of vinegar (acetic acid) and it is also a metabolic
acid
Chapter 16 | Slide 16 of 52
• Metabolic acids: Polyfunctional acids formed as intermediates
of ________________ reactions in the human body.
• There are eight such acids that will appear repeatedly in the
biochemistry chapters
• Metabolic acids are derived from:
− Propionic acid, (C3 mono acids): lactic, glyceric, and
pyruvic acids
− Succinic acid (C4 diacid): fumaric, oxaloacetic, and malic
acids
− Glutaric acid (C5 diacid): -ketoglutaric and citric acids
Chapter 16 | Slide 17 of 52
Chapter 16 | Slide 18 of 52
At Room Temperature and Pressure
• Straight chain carboxylic acids with 1-9 carbon
atoms are liquids and strong odors
• Straight chain carboxylic acids with >10 C atoms
are waxy solids with no odor.
• Aromatic and dicarboxylic acids: Odorless solids
Chapter 16 | Slide 19 of 52
Properties of Carboxylic Acids
• Like alcohols, carboxylic acids form ___________
intermolecular hydrogen bonds.
• Most carboxylic acids exist as ___________.
– Boiling points higher than alkanes of similar MW.
– Small carboxylic acids (1-4 carbons) are soluble in
water
O
H
O
H3C
CH 3
O
H
O
Chapter 16 | Slide 20 of 52
Boiling Points
Chapter 16 | Slide 21 of 52
Chapter 16 | Slide 22 of 52
Synthesis of Carboxylic Acids
• Synthesized from
aromatic rings,
primary alcohols
and aldehydes.
• Oxidizing Agents:
K2Cr2O7 / H2SO4
or
KMnO4
R
Oxidizing agent
R
OH
Carboxylic
Acid
O
R
Chapter 16 | Slide 23 of 52
Oxidation of Aromatic Compounds
• Benzene does not react with KMnO4.
• Alkyl groups on the ring (-R) are readily
oxidized though.
• One product for all reactions.
O
R
OH
+ KMnO4
Chapter 16 | Slide 24 of 52
Oxidation of Aromatic Compounds
with KMnO4
O
OH
Chapter 16 | Slide 25 of 52
• Oxidation of primary alcohols and
aldehydes:
O
OH
CrO3, H3O+
or Na2Cr2O7, H2O, CH3CO2H
R
O
R
R
OH
O
H
AgNO3
NH4OH
R
OH
Chapter 16 | Slide 26 of 52
• Oxidation of alcohols to carboxylic acids.
O
OH
CrO3, H3O+
HO
CrO3, H3O+
OH
OH
O
Chapter 16 | Slide 27 of 52
Properties
• Carboxylic acids are ________ acids
– Stronger acids than alcohols
• In water they dissociate to release ___________ (H+) and
form carboxylate ion (RCOO-) -- equilibrium reactions and
equilibrium lies towards the left indicating that small
amount of acid is ionized
CH3COOH + H2O
CH3COO– + H3O+
• Neutralized by a base
CH3COOH + NaOH
CH3COO– Na+ + H2O
Chapter 16 | Slide 28 of 52
• Monocarboxylic acids release ______ H+ to form
carboxylate ion with _______ negative charge
• Dicarboxylic acids release ______ H+ ions to
form carboxylate ion with _____ negative
charges and so on
Chapter 16 | Slide 29 of 52
• Carboxylic acids are obviously _________.
• Stronger acids than alcohols, but __________ than
mineral acids.
• Will react with _________ to give metal carboxylates.
• There is a large range of acidities depending on the
substituents on a carboxylic acid.
O
O
+ NaOH
R
OH
+ H2O
R
O-Na +
Chapter 16 | Slide 30 of 52
Carboxylate Ions
• The conjugate base of a carboxylic acid
– Formed when a carboxylic acid loses a proton
– Named by dropping the -ic acid ending and replacing it
with –ate
• CH3CH2COO• CH3COO• CH3CH2CH2COO-
Propionate
Ethanoate (Acetate)
Butanoate
Chapter 16 | Slide 31 of 52
Carboxylate Salts
• An ionic compound in which the negative ion is a
carboxylate ion
– Naming: the positive ion is named first, followed by a
separate word giving the name of the negative ion
– Converted back to a carboxylic acid by the addition of a
strong acid
• CH3CH2COO-Na+
• CH3COO-K+
• CH3CH2CH2COO-Li+
Sodium Propionate
Potassium Ethanoate
Lithium Butanoate
Chapter 16 | Slide 32 of 52
Uses of Carboxylic Acid Salts
• Good antimicrobial and antifungal agents
• Benzoate salts: Effective (0.1%, m/m) against yeast and
mold in beverages, jams and jellies, etc.
• Sodium sorbate: Inhibits mold and yeast in dairy
products, dried fruits, some meat and fish products
• Propionate: Used in preservation of baked goods
• Benzoate and sorbate can’t be used in yeast leavened
baked goods as they inhibit mold and yeast
Chapter 16 | Slide 33 of 52
Carboxylic Acids
Chapter 16 | Slide 34 of 52
Esters
← Fig. 16.12
Methyl and ethyl esters
of acetic acid.
Chapter 16 | Slide 35 of 52
Ester
In an ester, the _______ in the carboxyl group is replaced
with an ________ group
O

CH3 — C—O —CH3
= CH3—COO —CH3
ester group
Sulfur analogs of esters are called thioesters (sulfur replaces
the hydroxyl oxygen)
Chapter 16 | Slide 36 of 52
• The name for the alcohol part of the ester appears
_________ and is _____________ by a separate word
giving the name for the acid part of the ester.
• The name for the alcohol part of the ester is simply the
name of the R group (alkyl, cycloalkyl, or aryl) present in
the —OR portion of the ester.
• The name for the acid part of the ester is obtained by
dropping the “-ic” acid ending for the acid’s name and
adding the suffix “-ate.”
Chapter 16 | Slide 37 of 52
Naming Esters
• Name the alkyl from the alcohol –O• Name the acid with the C=O with –ate
acid
alcohol
O

methyl
CH3 — C—O —CH3
Ethanoate
(acetate)
methyl ethanoate (IUPAC)
methyl acetate (common)
Chapter 16 | Slide 38 of 52
Chapter 16 | Slide 39 of 52
Esters
Chapter 16 | Slide 40 of 52
Esterification: Preparation of Esters
• Reaction of a carboxylic acid and alcohol
• Acid catalyst
O

CH3 — C—OH + HO—CH2CH3
H+
O

CH3 — C—O—CH2CH3 + H2O
Chapter 16 | Slide 41 of 52
Hydrolysis: Breaking Up Esters
• Esters react with water and acid catalyst
• Split into carboxylic acid and alcohol
O

H+
H — C—O—CH2CH3 + H2O
O

H — C—OH
+ HO—CH2CH3
Chapter 16 | Slide 42 of 52
Hydrolysis
Chapter 16 | Slide 43 of 52
Saponification
• Esters react with bases
• Produce the salt of the carboxylic acid and alcohol
O

H 2O
CH3C—OCH2CH3 + NaOH
O

CH3C—O– Na+
+
HOCH2CH3
salt of carboxylic acid
• Saponification reactions produce soaps
Chapter 16 | Slide 44 of 52
Soaps
• Carboxylate salts
Chapter 16 | Slide 45 of 52
• The following figure represents soap.
• Which end of the anion is hydrophobic?
Chapter 16 | Slide 46 of 52
• How does soap interact with grease?
Chapter 16 | Slide 47 of 52
Chapter 16 | Slide 48 of 52
Chapter 16 | Slide 49 of 52
Chapter 16 | Slide 50 of 52
Dicarboxylic Acids
Chapter 16 | Slide 51 of 52
The C2 dicarboxylic acid, oxalic acid, contributes to the tart taste of
rhubarb stalks.
Chapter 16 | Slide 52 of 52