Transcript Chem 150 Unit 7 - Organic Molecules II Carboxylic Acids

Chem 150
Unit 7 - Organic Molecules II
Carboxylic Acids, Phenols & Amines
In this unit and the next we look at the chemical and
physical properties of a variety of organic families, all of
which play important roles in biochemistry. These
include the carboxylic acids, phenols, amines and
amides. We also look at a new type of stereoisomer
that figures predominantly in biological chemistry; the
optical isomer.
Introduction
The organic groups covered in this Unit all have important
biological roles
• Carboxylic acids
• Fatty acids
• Amino acids and proteins
• Phenols
• Colors and flavorings
• Amino acids and proteins
• Signal molecules
• Amines
• Amino acids and proteins
• Signal molecules
• Drugs
• Amides
• Amino acids and proteins
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Carboxylic Acids
Naming carboxylic acids
• The IUPAC ending is -oic acid.
4
Question
Give the IUPAC names for the following carboxylic acids:
O
A)
CH3 CH2 CH2 CH2 C
O
B)
HO
C
CH3
CH2 CH
CH3
5
OH
CH2 CH
CH3
Carboxylic Acids
•
•
6
Carboxylic acid have high melting points
Small carboxylic acids are quite soluble in water
Carboxylic Acids
Small (volatile) carboxylic acids have noticeable odors.
• Ethanoic acid (acetic acid) vinegar
O
CH3 C
•
OH
Butanoic acid (butyric acid) vomit, dirty socks
O
CH3 CH2 CH2 C
•
OH
Hexanoic acid (caproic acid) goats, ripe cheese
O
CH3 CH2 CH2 CH2 CH2 C
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OH
Phenols
Simplest phenol is phenol.
• A hydroxyl group attached to a benzene ring.
OH
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Phenols
All phenols contain hydroxyl groups attached to aromatic
rings.
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Phenols
All phenols contain hydroxyl groups attached to aromatic
rings.
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These have
2 hydroxyl
groups
attached to a
benzene ring
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Carboxylic Acids & Phenols as Weak Acids
Both carboxylic acids and phenols are weak acids
pKa ≈ 5
O
CH3 C
OH
+
acid
O
CH3 C
H2O
base
O
+
base
H3O+
acid
pKa ≈ 10
OH
acid
12
+
H2O
base
O
base
+
H3O+
acid
Carboxylic Acids & Phenols as Weak Acids
The acidity of hydroxyl groups depend on what they are
connected to:
carboxylic
acids
phenols
alcohols
O
C
O
acidic
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H
O
weakly acidic
H
C
O
H
non-acidic
Carboxylic Acids & Phenols as Weak Acids
•
•
At pH 7, the carboxylate ion of carboxylic acids predominate
At pH 7, the phenol of phenol predominate
O
CH3 C
O
OH
+
acid
CH3 C
H2O
base
pKa ≈ 5
OH
acid
pH = 7
14
+
H2O
O
base
pH = 7
O
base
base
pKa ≈ 10
+
H3O+
acid
+
H3O+
acid
Carboxylic Acids & Phenols as Weak Acids
Strong bases can be used to convert carboxylic acids and
phenols to their corresponding carboxylate and phenoxide
ions
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Carboxylic Acids & Phenols as Weak Acids
Fatty acids are carboxylate ions at pH 7
• Fatty acids with less that 12 carbons are soluble in water
• Fatty acids with greater than 12 carbons are amphipathic,
and form micelles when mixed with water.
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Carboxylic Acids & Phenols as Weak Acids
IUPAC names for carboxylate ions:
• Remove the “-ic acid” from the corresponding conjugate
acids name and replace it with “-ate ion”.
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Carboxylic Acids & Phenols as Weak Acids
Examples:
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Carboxylic Acids & Phenols, Other Reactions
We have already seen how carboxylic acids and
carboxylate ions can be made from from the hydrolysis of
esters.
• Base-catalyzed hydrolysis of esters:
•
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Acid-catalyzed hydrolysis of esters:
Carboxylic Acids & Phenols, Other Reactions
The acid-catalyzed hydrolysis of esters is reversible and can
be used to make esters from carboxylic acids and alcohols:
• Synthesis of esters from carboxylic acids and alcohols:
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Carboxylic Acids & Phenols, Other Reactions
A biologically important reaction involving carboxylic acids is
the decarboxylation of α-keto and β-keto acids:
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Carboxylic Acids & Phenols, Other Reactions
The decarboxylation of β-keto acids produces ketones
The decarboxylation of α-keto acids produces aldehydes
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Carboxylic Acids & Phenols, Other Reactions
The oxidation of
hydroquinones is also
an important biological
reaction.
• A chemical oxidation
of hydroquinones
can be carried out
the oxidizing agent
K2Cr2O7 (potassium
dichromate)
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Carboxylic Acids & Phenols, Other Reactions
Example:
• Coenzyme Q and the Electron Transport Chain
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Carboxylic Acids & Phenols, Other Reactions
Example:
• Coenzyme Q and the Electron Transport Chain
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Amines
Amines are a nitrogen with one or more carbons attached:
• Amines are classified based on the number of carbons that
are attached to the nitrogen.
• Primary amine (1°): 1 carbons
• Secondary amine (2°): 2 carbons
• Tertiary amine (3°): 3 carbons
N
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Amines
It is possible for a fourth carbon to attach to the nitrogen
• The nitrogen will take on a positive charge to become an
ion.
• Quaternary (4°) ammonium ions: 4 carbon atoms
N
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Amines
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Amines
The IUPAC names for 1°, 2°, and 3° amines.
• Create the parent name by picking the longest chain of
carbons that is attached to the nitrogen.
• Replace the “-e” in the parent with the ending “-amine”.
• Number the longest chain from the end that gets you to the
the carbon to which the nitrogen is attached in the fewest
number of carbons.
• Use a numbered prefix to indicate which the carbon in the
longest chain the nitrogen is bonded to.
• If other substituents are attached to the nitrogen, list them
and use the prefix “N-” to indicate that they are attached to
the nitrogen.
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Questions
Give the IUPAC names for the following amines:
CH3
A)
CH3 CH2 CH
CH3 CH2 CH
NH2
N
CH2 CH3
CH3 CH2 CH2 CH3
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Questions
Give the IUPAC names for the following amines:
CH3
A)
CH3 CH2 CH
NH2
2-butanamine
2-butanamine
CH3 CH2 CH
N
CH2 CH3
CH3 CH2 CH2 CH3
N-ethyl-N-propyl-2-butanamine
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N-ethylN-propyl
Amines
For heterocyclic amines the nitrogen is part of a ring.
• The ring can be either aromatic or not.
• The nucleic acid nucleotide bases are good examples of
hetoercyclic amines
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Amines
Hydrogen Bonding
• 1° and 2° amines can serve as both a hydrogen bond
donor and acceptor.
• 3° amines can server as a hydrogen bond acceptors, but
not donors.
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Amines
Hydrogen Bonding
• 4° ammonium ion cannot form hydrogen bonds, but
because they are charged, form ionic bonds:
CH3
CH3
N
CH3
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CH3
Cl-
Amines
The ability to hydrogen bond give amines moderately high
boiling points and high solubilities in water.
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Amines
Another notable property of amines is their odor.
• Like carboxylic acids, they can also produce foul odor.
• The produce a “fishy” smell.
• Examples of amines, whose names imply their odoriferous
properties, include
H2N
putrescine
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NH2
H2N
NH2
cadaverine
Amines as Weak Bases
In Unit 6, while discussing the definitions of acids and bases,
we saw that ammonia, NH3, is operationally a base
• That is, when added to water ammonia causes the pH to
rise above pH 7.
NH3 (aq)
•
+
H2O (l)
NH4+ (aq)
+
Ammonia was the example we used to demonstrate the need for the
Brønsted-Lowry definition of acids and bases.
See the Unit 6 Elaboration Definitions of Acids and Bases - Part III:
Brønsted-Lowry Definition
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OH- (aq)
Amines as Weak Bases
Like ammonia, 1°, 2° and 3°, act as Brønsted-Lowry bases.
H
CH3 N
H (aq)
H
methanamine
(base)
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+
H2O (l)
CH3 N
H (aq)
H
methylammonium ion
(acid)
+
OH- (aq)
Amines as Weak Bases
The conjugate acids are called ammonium ions
• When placed in water, these ammonium ions will behave
like acids.
H
CH3 N
pKa - 10
H (aq)
H
methylammonium ion
(acid)
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+
H2O (l)
CH3 N
H (aq)
H
methanamine
(base)
+
H3O+ (aq)
Amines as Weak Bases
Because it is charged, the conjugate acid is even more
soluble that the amine.
• Many drugs are amines and are sold the ammonium salts,
which are more readily absorbed, due to their increased
solubility.
• Ephedrine is used as a decongestant.
CH3
CH
CH
OH
N
+
CH3
HCl
H
CH
OH
ephedrine
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CH
CH
N
CH3
Cl-
H
ephedrine HCl
CH3
CH
H
OH
ephedrine
2
CH3
N
H
CH3
+
H2SO4
CH
CH3
H
CH
N
OH
ephedrine sulfate
H
CH3
SO422
Amines as Weak Bases
Ephedrine is an example of an alkaloid.
• Alkaloids are alkaline molecules that are derived from
plants.
• “alkaline” and another name for basic.
• Ephedrine is isolated from the Chinese ma huang
plant(Ephedra sinica)hyperlink
CH3
CH
CH
OH
ephedrine
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CH3
N
H
CH3
CH2
CH
N
H
methamphetamine
CH3
Amides
•
•
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When a carboxylic acid reacts with an amine it also
produces and ammonium salt
If the ammonium salt is then heated, an amide is
produced.
Amides
Amides are important in
biochemistry.
• For example, amino
acids are connected
together to form
proteins using amide
groups.
amino acid
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Amides
Amides can be hydrolyzed back to carboxylic acids and
amines by heating them in the presence of an acid
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Stereoisomers
So far we have encountered two different types of isomers.
• Constitutional Isomers
• Stereoisomers
• cis/trans isomers with alkenes and cycloalkanes, that arise from
restricted rotation about bonds.
There is one more type of stereoisomer, which is important in
biochemistry.
• optical isomers
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Stereoisomers
Optical isomers arise when a carbon atom has four different
things attached to it.
• These carbons are called chiral carbons.
• The a molecule containing a chiral carbon is non
superimposable on its mirror image.
• The molecule and its mirror image are referred to as enantiomers
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Stereoisomers
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Stereoisomers
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Stereoisomers
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Stereoisomers
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Stereoisomers
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Stereoisomers
When developing drugs that are chiral, it is important to look
at the effects of both the enantiomers.
O
O
H
H
N
O
NH
O
O
O
N
NH
O
O
R-thalidomide
S-thalidomide
is effective in
treating morning
sickness in pregnant
women
is a teratogen,
causing birth
defects
R and S are another way of distinguishing enantiomers; R is
the rectus (right) isomer, while S is the sinister (evil) isomer!
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Stereoisomers
When chiral molecules contain more than one chiral carbon,
it is possible for two molecules to be stereoisomers without
being mirror images.
• Such molecules are referred to as diastereomers.
CH3
C
OH
CH
H
ephedrine
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CH3
N
H
C
CH3
H
CH
OH
N
H
pseudoephedrine
CH3
Stereoisomers
Each chiral carbon that a chiral molecule contains doubles
the number of stereoisomers for that molecule.
• Ephedrine has two chiral carbons, it therefore has 2 x 2 = 4
stereoisomers.
• pseudoephedrine is one of 4 stereoisomers.
CH3
C
OH
CH
H
ephedrine
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CH3
N
H
C
CH3
H
CH
OH
N
H
pseudoephedrine
CH3
The End