Download Carboxylic acid-Group A

PPT 102 ORGANIC CHEMISTRY 1
SEM 1 (2012/2013)
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Outline
• Nomenclature
• Physical Properties
• General Mechanism for Nucleophile
Addition-Elimination Reaction
• Acid Catalyzed Esterification
• Reaction of Carboxylic acids
• Reaction of Amides
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Compound that containing carbonyl groups –called
carbonyl compound.
An acyl group consists of a carbonyl group
attached to an alkyl group ( R) or an aryl group
(Ar)
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Carbonyl compound can be divide into 2 classes:
Class 1: carbonyl compounds are those in which the
acyl group is attach to a group (or atom)
that can be replace by another group.
Which compound belong to this class?
• Carboxylic acid
• Acyl halides
• Acid anhydride
• Ester
• Amides
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Class I Carbonyl Compounds
Carboxylic Acid Deritives
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Why it called as carboxylic acid derivatives ?
Because they differ from carboxylic acid only the
nature of the group or atom that has replace the
OH group of the carboxylic acid.
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Class II : Carbonyl compounds are those in which
the acyl is attached to a group that cannot
be readily replaced by another group.
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Carboxylic Acid Nomenclature
The functional group of a carboxylic acid is called a
carboxyl group
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Carboxylic Acid Nomenclature
In IUPAC nomenclature, a carboxylic acid is named
by replacing the terminal “e” of the alkane with “oic
acid”
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In systematic nomenclature, the carbonyl carbon is
always C-1
In common nomenclature, the carbon next to the
carbonyl is the a-carbon
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Carboxylic Acid Nomenclature
Carboxylic acid in which a carboxyl group is
attached to a ring are named by adding “carboxylic
acid” to the name of the cyclic compound.
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Salts of Carboxylic Acids
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Acyl Halides
Acyl halides have a Cl or Br in place of OH.
Acyl halides are named by replacing “ic acid” with the “yl
chloride”
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Acid Anhydrides
Loss of water from 2 molecules of a carboxylic
results of acid anhydride.
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There are 2 types of acid anhydride:
Symmetrical anhydride
when R1 the same as R2
Mixed (unsymmetrical
anhydride) when R1 the not the
same as R2
Ethanoic Anhydride
Acetic Anhydride
Ethanoic Methanoic Anhydride
Acetic Formic Anhydride
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Esters
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Amides
An amide has an NH2, NHR, or NHR2 group in
place of OH group.
Amides are named by replacing “oic acid”, “ic
acid” or “ylic acid” of the acid name with “amide”
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Nitriles
Nitriles are compound that contain C≡N
functional group, called a cyno group.
In common nomenclature, nitriles are named
by replacing “ ic acid” with the “onitrile”
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Physical Properties
• The carboxyl group contains three polar
covalent bonds; C=O, C-O, and O-H
– the polarity of these bonds determines the
major physical properties of carboxylic acids
δ-O
– Hδ+
δ+C=Oδ-
R
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Physical Properties
– The carbonyl group has a large dipole
– The hydroxy group is capable of hydrogen bonding.
– The molecules can H-bond to each other
hydrogen bondin g
betw een tw o
molecules
H3 C
O
+
H O
C
C
O
H
+
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O
-
CH3
Solubility in Water
• Carboxylic acids are similar to alcohols in
respect to their solubility in water
• Form hydrogen bonds to water
H
O
H
O
H3CC
H
O
H
O
H
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Physical Properties
– Carboxylic acids are more soluble in water than are
alcohols,
ethers,
aldehydes,
and
ketones
comparable molecular weight
– Sharp and or sour odor/taste
Vinegar, rancid butter, sweat, sauerkraut.
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of
Carboxylic acids have relatively high boiling points
because…
Amides have the highest boiling points:
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How the carbonyl
compound react?
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The reactivity of the carbonyl compound is due to the
polarity of the carbonyl group that result from oxygen being
more
electronegative
than
carbon.
So the carbonyl carbon is therefore electron deficient
(electrophile)
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When nucleophile adds to the carbonyl carbon, the weakest
bond in the molecule- the carbon-oxygen π bond- breaks
=tetrahedral intermediate
The tetrahedral intermediate is a transient species that
eliminates the leaving group Y– or the nucleophile Z–:
This is a nucleophilic acyl substitution reaction
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Z– will be expelled if it is a much weaker base than
Y–; that is, Z– is a better leaving group than Y– (k–1
>> k2):
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Y– will be expelled if it is a weaker base than Z–; that is,
Y– is a better leaving group than Z– (k2 >> k–1):
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The reactivity of a carboxylic acid derivative
depends on the basicity of the substituent attached
to the acyl group:
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General Mechanism for Nucleophile
Addition-Elimination Reaction
• All carboxylic acids derivatives undergo
nucleophilic addition-elimination reaction
by the same mechanism.
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Mechanism: Negatively charge nucleophile
1. The nucleophile adds to the carbonyl carbon,
forming a tetrahedral intermediates.
2. The tetrahedral intermediates collapse,
eliminating the weaker base
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If the nucleophile is neutral…
Where :B represent any spesies in the solution that is capable of removing a
proton, and HB+ Represent any spesies in solution that is capable of donation a
proton.
1.
2.
3.
The nucleophile adds to the carbonyl carbon, forming a tetrahedral
intermediate.
A proton is loss from the tetrahedral intermediate, resulting in a
tetrahedral intermediate equivalent to the one formed by a negatively
charge nucleophile.
The π bond re-form and the weaker of the two base is eliminated.
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Reaction of Carboxylic Acid
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Nucleophililic Acyl Substitutution
Reactions
1. Preparation of Acyl Chloride
2. Preparation of Acid Anhydride
3. Preparation of ester
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4. Preparation of Amide
5.Reduction Of Carboxylic Acid
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Reactions of Carboxylic Acids
• Carboxylic acid can undergo nucleophilic
acyl substitution reactions only when they
are in their acidic form.
• The basic form of a carboxylic acid cannot
undergo nucleophilic acyl substitution
reactions because the negatively charge
carboxylate ion is resistant to nucleophilic
reaction
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Reactions of Carboxylic Acids
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Carboxylic acid react with alcohol to form esters.
The reaction must carried out in an acidic solution, not
only to catalyze the reaction but also to keep the
carboxylic acid in its acidic form so that the nucleophilic
will react with it.
Since the tetrahedral intermediate formed in this reaction
has two potential leaving groups of aproximately the same
basicity, the reaction must carried out with excess alcohol
to drive it towards product.
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• Emil Fischer was the first to discover that
an ester could be prepared by treating a
carboxylic acids with excess alcohol in the
presence of an acid catalyst.
• The reaction is called, FISCHER
ESTERIFICATION.
• Its mechanism is the exact reverse of the
mechanism for the acid catalyzed
hydrolysis of an ester.
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Carboxylic acids do not undergo nucleophilic acyl
substitution reactions with amines at room temperature
Because a carboxylic acid is an acid and an amine is
base, the carboxylic acid immediately donates a proton
to the amine.
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Reactions of Amides
Amides are very unreactive carboxylative
derivatives.
Amides do not react with halide ions,
carboxylate ions, alcohols, or water because in
each case, the incoming nucleophile is a weaker
base than the leaving group of the amide ( Table
17.1)
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Amides can react with water and alcohols if an acid
catalyst is present:
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Dehydration of an Amide
Dehydration reagents commonly used are SOCl2, P2O5,
or POCl3
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Acid catalyzed Esterification
• Ester hydrolyzed slowly because water is
a poor nucleophile and ester have very
basic leaving groups.
• However the rate of hydrolysis can be
increased by either acid or hydroxide ion.
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• When you examine the mechanisms for
these reactions, notice the two following
features that hold for all organic reactions:
• 1. All organic intermediates and products
in acidic solution are positively charge or
neutral
• 2. All organic intermediates and products
in basic solutions are negatively charge.
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MECHANISM FOR ACID CATALYZED ESTER
HYDROLYSIS
Hydrolysis of an ester with primary or secondary
alkyl groups can be catalyzed by an acid
The carbonyl oxygen is first protonated,
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There are no negatively charged species in the reaction:
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Because tetrahedral intermediate I and III are
equally likely to collapse, both ester and carboxylic
acid will present in approximately equal amounts
when the reaction reach equilibrium
Excess water will force the equilibrium to the right
Excess alcohol will force the equilibrium to the left
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Esters with tertiary alkyl groups undergo hydrolysis
much more rapidly than do others:
1. An acid protonates the carbonyl oxygen
2. The leaving group departs, forming the tertiary
carbocation
3. A nucleophile react with the carbocation
4. A base removes a proton fronm the strongly
acidic protonated alcohol
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TRANSESTERIFICATION
The reaction of an ester with an alcohol.
The mechanism is identical to the mechanism
for acid catalyzed ester hydrolysis (for ester with
primary or secondary alkyl groups), except that
the nucleophile is ROH rather than H20
Transesterification is also catalyzed by acid:
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• Biodiesel ProductionTransesterification.
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Rudolf Diesel (1893)
“The use of vegetable oils for
engine fuels may seem
insignificant today,” he argued,
“but such oils may become, in
the course of time, as important
as petroleum and the coal-tar
products of the present time."
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Biodiesel
• Biodiesel is not the same thing as raw vegetable oil. It is
produced by a chemical process which removes the
glycerol from the oil.
• Biodiesel
–
–
–
–
Domestic
Renewable
For diesel engines
Derived from oils and fats
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Biodiesel production
• Biodiesel is typically produced by a
reaction of a vegetable oil or animal fat
with an alcohol such as methanol or
ethanol in the presence of a catalyst to
yield mono-alkyl esters and glycerol, which
is removed.
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How?
• Tranesterification: alcohol + ester →
different alcohol + different ester
– Base of acid as a catalyst
– The oil is mixed with an alcohol, usually
methanol or ethanol, and separated into
methyl esters (biodiesel) and glycerol.
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Transesterification
Methyl esters
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Biodiesel technology
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Possible sources
• Vegetable oil (soy, canola, palm, rapeseed,
coconut etc.)
• Non food plants (jatropha)
• Recycled oil (McDonald’s fryer)
• Animal fats (fish oil)
• Algae
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