Transcript Carboxylic Acids

Carboxylic Acids,
Esters,
Amides
Unit 13
Carboxylic Acids
 When a carbonyl carbon also bears a hydroxyl group, then these
compounds are appreciably acidic, and are called carboxylic
acids.
 Carboxylic acids are classified according to the substituent
bonded to the carboxyl carbon:
 Aliphatic acids have an alkyl group bound to the carboxyl group
 An aromatic acid has an aryl group bound to the carboxyl group
 The simplest acid is formic acid
Introduction
The functional group of carboxylic acids
consists of a C═O with —OH bonded to the
same carbon.
Carboxyl group is usually written —COOH.
Aliphatic acids have an alkyl group bonded
to —COOH.
Aromatic acids have an aryl group.
Fatty acids are long-chain aliphatic acids.
Common Names
Many aliphatic acids have historical names.
Positions of substituents on the chain are
labeled with Greek letters starting at the
carbon attached to the carboxylic carbon.
Carboxylic Acids
 IUPAC Formulation:
 The root name is based on the longest continuous
chain of carbon atoms bearing the carboxyl
group
 The –e is replaced by –oic acid
 The chain is numbered starting with the carboxyl
carbon atom
 The carboxyl group takes priority over any other
functional groups previously discussed
Carboxylic Acids
 Unsaturated acids are named using the name of
the alkene with –e replaced with –oic acid
 The chain is numbered starting with the
carboxyl group; a number designates the
location of the multiple bond
 Aromatic acids of the form Ar-COOH are
typically named as derivatives of benzoic acids,
with ortho, meta and para indicating the location
relative to the carboxyl group (non-IUPAC)
IUPAC Names
Remove the final -e from alkane name, add
the ending -oic acid.
The carbon of the carboxyl group is #1.
Unsaturated Acids
Remove the final -e from alkene name,
add the ending -oic acid.
Stereochemistry is specified.
Aromatic Acids
 Aromatic acids are named as derivatives of
benzoic acid.
 Ortho-, meta- and para- prefixes are used to
specify the location of a second substituent.
 Numbers are used to specify locations when
more than 2 substituents are present.
Carboxylic Acids
 Dicarbolylic Acids are named by adding the suffix
dioic acid to the root name.
 The root name comes from the longest carbon chain
containing both carboxyl groups.
 Numbering starts at the end closest to a
substituent.
3-bromohexanedioic acid
Carboxylic Acid Derivatives
 Carboxylic derivatives are described as
compounds that can be converted to carboxylic
acids via simple acidic or basis hydrolysis
 The most important acid derivatives are esters,
amides and nitriles, although acid halides and
anhydrides are also derivatives (activated forms
of a carboxylic acid)
 Esters of carboxylic acids are derivatives where
the hydroxyl group of replaced by an alkoxy group
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Most anhydrides are named by
dropping the word acid from the
name of the carboxylic acid and
then adding the word “anhydride”
Acid chloride as parent (suffix):
ending with “–oyl chloride”
Ester as parent (suffix): ending with
“–oate”
Amide as parent (suffix): ending
with “amide”
Nitrile as parent (suffix): ending
with “nitrile”
Examples
O
O
OH
Ethanoic acid
(acetic acid)
O
O
O
Ethanoic anhydride
(acetic anhydride)
OCH3
Methyl propanoate
O
NH'2
Ethanamide
Examples
O
O
O
Cl
Na
Sodium benzoate
Benzoyl chloride
H3C
C
N
Ethanenitrile
Carboxylic Esters
 Nomenclature of carboxylic esters are
derived from the names of the compounds
that are used to create them.
 The first word of the name comes from the
alkyl group of the alcohol and the second part
comes from the carboxylate group of the
acid used.
 A cyclic ester is called a lactone. IUPAC
names of lactones are derived by adding the
term lactone at the end of the name of the
parent hydroxycarboxylic acid from which it
came.
Carboxylic Amide
An amide is a composite of a
carboxylic acid and an amine (or
ammonia).
Heating the salt formed when an amine
and carboxylic acid react together,
drives off the water produced and an
amide is formed.
Amides are much less basic than their
parent amines since the lone pairs of
electrons on Nitrogen are delocalized
onto the carbonyl carbon.
Carboxylic Amide
 To name a primary amide, identify the acid part
and remove the –oic acid suffix and add –amide
 To name a secondary or tertiary amide, the alkyl
groups on nitrogen are treated as substituents,
and are given the prefix N (since they are on
the nitrogen)
 Cyclic amides are known as Lactams.
 Lactams are produced from amino acids, where
the amino acid and the carboxylic acid groups
react together to form an amide linkage.
 They are named by adding the word lactam to
the correct IUPAC name of the parent amino
acid.
Boiling Points
Higher boiling points than similar
alcohols, due to the formation of a
hydrogen-bonded dimer.
Melting Points
 Aliphatic acids with more than 8 carbons are
solids at room temperature.
 Double bonds (especially cis) lower the melting
point. The following acids all have 18 carbons:
Stearic acid (saturated): 72C
Oleic acid (one cis double bond): 16C
Linoleic acid (two cis double bonds): -5C
Solubility
Water solubility decreases with the length
of the carbon chain.
With up to 4 carbons, acid is miscible in
water.
Very soluble in alcohols.
Also soluble in relatively nonpolar solvents
like chloroform because the hydrogen bonds
of the dimer are not disrupted by the
nonpolar solvent.
Acidity of Carboxylic Acids
 A carboxylic acid may dissociate in water to give a
proton and a carboxylate ion.
 The equilibrium constant Ka for this reaction is
called the acid-dissociation constant.
 The acid will be mostly dissociated if the pH of the
solution is higher than the pKa of the acid.