Aldehydes, Ketones,
And
Carboxylic Acids
IUG, Fall 2012
Dr. Tarek Zaida
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Aldehydes
• Aldehydes are characterized by the presence of
the carbonyl group CO
• Aldehydes have at least one hydrogen atom
attached to the carbonyl carbon atom. The
remaining group may be another hydrogen atom
or any aliphatic or aromatic organic group.
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Preparation
• Aldehydes are prepared by oxidation of a
primary alcohol:
• Formaldehyde is supplied as 37% aqueous
solution and is called formalin.
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• Acetaldehyde is manufactured mainly by the
oxidation of ethylene H2C=CH2 over a
palladium–copper catalyst:
• Acetaldehyde is partially responsible for the
damage of liver in cirrhosis.
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Naming Aldehydes
• The term aldehyde means
• In the IUPAC system, the
characteristic ending for
aldehydes is -al (from the
first syllable of aldehyde).
The following examples
illustrate the system:
alcohol
dehydrogenation
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6
• For substituted aldehydes, the aldehyde is
numbered first as the following examples
illustrate:
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For cyclic aldehydes, the suffix -carbaldehyde is
used.
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• Draw the structural formula of the following:
1. 6-bromo-5,7-dimethyloctanal
2. 4,4-dichloro-2,3-dimmethylpentanal
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Uses of Aldehydes
1. Formalin is used as a disinfectant and
preservative (used to preserve biologic
specimens).
2. Formaldehyde is mostly used in the
manufacture of plastics, building insulation.
3. Fumes of formaldehyde solutions are very
irritating, so should not be used directly on a
patient skin
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4. Glutaraldehyde is used as
a good sterilizing agent.
5. Paraldehyde is used as a
hypnotic. Is formed by
polymerization of 3
molecules of acetaldehydes
6. Glyceraldehyde is an
important in carbohydrate
metabolism
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Tests for Aldehydes
• Aldehydes are good reducing agents.
• Lab tests for the presence of aldehydes are
based on their ability to reduce Cu2+ to Cu+
• R-CHO + Cu2+
aldehyde
Cupric ion
R-CO-OH + Cu+
Carboxylic acid
Cuprous ion
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Benedict’s Test
• R-CHO + Benedict’s reagent (Cu2+)
red precipitate + RCOOH
• Fehling’s reagent or clini tablet will give same reaction as the
above.
• Another test for reducing aldehydes is Tollen’s reagent which
contains Ag+:
R-CHO + Tollen’s reagent (Ag+)
bright shiny mirror (Ago)
Note: The above reactions are used to detect for diabetes, since
urine should have no glucose.
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Reactions of aldehydes
1. Oxidation:
R-CHO + [O]
RCOOH
acid
2. Reduction:
R-CHO + [H]
RCH2-OH
alcohol
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Ketones
• The general structural formula for ketones:
R-CO-R
Preparation:
By oxidation of secondary alcohols:
OH
O
[O]
R
C
R
R
C
R
H
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Naming ketones
1. Take the name of the longest alkane
containing the carbonyl group.
2. Drop the ending –e and add –one
2
1
H3C-CH2-CO-CH3
butanone
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Draw the structures of:
•
•
•
•
1.
2.
3.
4.
2,2-dimethyl-3-pentanone
methylethylketone
3-chlorobutanone
hydroxyacetone
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Uses of ketones
• 1. Acetone is a good solvent for fats and oils
• 2. Acetone is used in fingernail polish and
polish removal
• 3. Acetone is normally present in small
amounts in blood & urine. But in diabetes
mellitus it is present in higher concentration.
• 4. Dihydroxyacetone is an intermediate in
carbohydrate metabolism HO-CH2-CO-CH2OH
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Reactions of Ketones
• Ketones are not oxidized because there is no
hydrogen atom attahed to the carbon atom of
carbonyl group.
• Ketones can be reduced to the corresponding
secondary alcohols.
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and
1. Reaction of an aldehyde with an alcohol yields
compounds known as
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• 2. Reactions of a ketone with an alcohol yields
compounds known as
21
• If a
or a
a second alcohol, an
respectively is formed.
RO
•
R’
C
R’’
reacts with
or
OR
OH + R”’-OH
R’-C-OR”’
R”
Ketal
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• The Hemiacetals/Acetals & Hemiketal/Ketals
are important in understanding the structures
of monosaccharides
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Carboxylic Acids
Functional group is (-COOH)
• Preparation by oxidation of an aldehyde:
H
R-C=O + [ O ]
OH
R-C=O
Acid
CH3-CHO + [O]
CH3-CO-OH
acetic acid
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• Oxidation CH3-OH yields CH2=O
• Oxidation of aldehyde yields carbooxylic acid
(HCOOH; formic acid)
• Formic acid is also named as methanoic acid
• CH3CH2-OH
Ethanol
[O]
CH3COOH
acetic acid
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Naming Carboxylic acids
• IUPAC names for organic acids end in –oic acid
• CH3COOH Ethanoic acid or acetic acid
Name
• COOH
• COOH
Oxalic acid Ethanedioic acid
• COOH
CH2
Malonic acid Propanedioic aicd
COOH
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COOH
CH2
CH2
COOH
Succinic acid
Butanedioic acid
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Properties & Reactions of Organic Acids
• 1. Most organic acids are relatively weak acids,
since they dissociate only slightly in water:
CH3COOH
H+ + CH3COO-
2. Organic acids react with bases to form salts
and water:
RCOOH + NaOH
RCOONa + H2O
CH3COOH + NaOH
CH3COONa + H2O
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3. They react with bicarbonates and carbonates:
CH3COOH + NaHCO3
CH3COONa+CO2(g) +
H2O
2 HCOOH + NaCO3
2HCOONa + CO2(g) + H2O
4. Organic acids with few carbon atoms are
soluble in water. As the length of the carbon
chain increases, the solubility in water
decreases.
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• 5. Organic acid react with alcohols to form
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HCOOH is formed in bees sting
& ants, and causes the characteristic pain and
swelling when it is injected into tissues.
, CH3COOH found in vinegar in 4
to 5 % solution.
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Found in citrus fruits
- Magnesium citrate, a salt of citric acid
Is used as a cathartic to stimulate evacuation of bowels
- Sodium citrate, used as a blood anticoagulant (it removes Ca2+
needed for coagulation from the blood)
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CH3-CH(OH)-COOH
• Found in sour milk.
• It is formed whenever the body produces
energy anaerobically
HOOC-COOH
• A strong naturally occurring acid
• Used to remove stains from clothing
• It is poisonous when taken internally
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• Oxalate salts prevent clotting by chelating Ca2+
From blood (however it should not be applied
directly on the blood due to it’s toxicity)
- Produced during glycolysis.
- In muscle pyruvate is reduced to lactic acid
during anaerobic exercise
- In tissues pyruvate is converted to acetylCoenzyme A, which enters the Krebs cycle.
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• It is both an acid & alcohol
HOOC-CH-CH-COOH
OH OH
2, 3-dihydroxysuccinic acid
Found in several fruits such as grapes and bananas
Potassium hydrogen tartarate is used in making
baking powder.
Rochelle salt or potassium sodium tartarate used as a
mild cathartic.
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- Is a fatty acid, insoluble in water
- Is a solid greasy like acid
- Sodium stearate is the commonly used soap
- C17H35COOH +NaOH
+ H2O
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