Introduction to carboxylic acids 1. Learning Objectives Identify the general structure of carboxylic...
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Transcript of Introduction to carboxylic acids 1. Learning Objectives Identify the general structure of carboxylic...
![Page 1: Introduction to carboxylic acids 1. Learning Objectives Identify the general structure of carboxylic acids Give the IUPAC and the common names Explain.](https://reader036.fdocuments.in/reader036/viewer/2022070403/56649f305503460f94c4af80/html5/thumbnails/1.jpg)
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Introduction to carboxylic acids
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Learning Objectives
• Identify the general structure of carboxylic acids
• Give the IUPAC and the common names• Explain the physical properties of the
carboxylic acids ; e.g solubility , boiling point, etc
• Give examples and uses of carboxylic acids
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Functional Groups
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R = Alkyl Groups
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Carboxylic Acids
A class of organic compounds containing at least one carboxyl group
Introduction
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R C
O
OH
R = alkyl group Aliphatic acid
R = aryl group aromatic acid
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(1) The IUPAC names of carboxylic acids
Replace the ‘e’ with ‘oic acid’ at the end of the name of the hydrocarbon
Naming Carboxylic Acids
H H
H C C H
H Hethane
H O
H C C O H
Hethan oic acid
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• Number substituents from the carboxyl carbon 1.
CH3 O | ║
CH3—CH—CH2—C—OH 4 3 2 1
3-methylbutanoic acid
IUPAC Names
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The common names of simple carboxylic acids HCOOH formic acid, CH3—COOH acetic acid
• Locate substituents using greek letters , , γ for the carbon atoms adjacent to the carboxyl carbon.
CH3
γ α | CH3—CH—CH2—COOH
α-methylbutryic acid ( IUPAC ; 2-methylbutanoic acid )
(2) Common Names
CH3CH2CH2CHCH2COOH
Ph
-phenylcaproic acid ε δ γ α
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Common and IUPAC Names of Some Carboxylic Acids
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(3) Naming Cyclic Acids
Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids
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Br
O
HO
3-bromo-cyclohexane carboxylic acid
O
OH
1-cyclopentene carboxylic acid
COOH
Cyclohexanecarboxylic acid
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(4) Naming Aromatic Acids
OHC
O
3-chlorobenzoic acid 4-aminobenzoic acid m-chlorobenzoic acid p-aminobenzoic acid
Locates substituent by assigning 1 to the carbon attached to the carboxyl group. Prefixes ortho, meta, and para for 2 substituents:
ortho 1, 2 locationmeta 1, 3 location para 1, 4 location
Benzoic acid
o-hydroxybenzoic acid2-hydroxybenzoic acid
(salicylic acid)
OHC
O
OHC
O
ClNH2
COOH
OH
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Dicarboxylic Acids• Aliphatic diacids are usually called by their
common names.• For IUPAC name, number the chain from the
end closest to a substituent.
3-bromohexanedioic acid-bromoadipic acid
HOOCCH2CHCH2CH2COOH
Br
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Some examples of dicarboxylic acid
Common name IUPAC name(Historical name) alkanedioic acid
HOOC-COOH
HOOCCH2COOH
HOOC(CH2)2COOH
oxalic acid
malonic acid
succinic acid
ethanedioic acid
propanedioic acid
butanedioic acid
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COOH
COOH
phthalic acidO-phthalic acid
COOHHOOC 1,3-benzenedicarboxylic acid
HOOC
COOH
1,4-benzenedicarboxylic acid
Common name IUPAC name
1,2-benzenedicarboxylic acid
isophthalic acidm-phthalic acid
terephthalic acidp-phthalic acid
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PHYSICAL PROPERTIES
carboxylic acids are soluble in organic solvents ; e.g alcohols they are also soluble in water due to hydrogen bonding
small ones dissolve readily in cold water ( up to 4 carbons) as mass increases, the solubility decreases
benzoic acid is fairly insoluble in cold, but soluble in hot water
Solubility
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The boiling points of carboxylic acids• Are higher than alcohols, ketones, and aldehydes of similar
mass.
• Are high because they form dimers in which hydrogen bonds form between the polar groups in the two carboxyl groups.
O H—O || |
CH3—C C—CH3
| ||
O—H O
A dimer of acetic acid
Boiling Points
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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): 72C
– Oleic acid (one cis double bond): 16C
– Linoleic acid (two cis double bonds): -5C
CO2H
CO2H
CO2H
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Polarity of Carboxylic Acids
Polarity isCarboxylic acids are strongly polar because they have
two polar groups hydroxyl (OH) and carbonyl (C=O)
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Acidity of Carboxylic Acids
• A carboxylic acid may dissociate in water to give a proton and a carboxylate ion (known as conjugate base).
• The equilibrium constant Ka for this reaction is called the acid-dissociation constant, The acidity constant, Ka,, is about 10-5 for a typical carboxylic acid (pKa ~ 5)
• The acid will be mostly dissociated if the pH of the solution is higher than the pKa of the acid.
• are weak acids compared to inorganic acids
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Acidity of Carboxylic Acids Carboxylic acids are significantly more acidic than water or alcohols.
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4 -electrons delocalizedover three p-prbitals
C-O bond length of a carboxylates are the same
This greater acidity of carboxylic acids is attributed to greater stabilization of carboxylate ion by:
a. Inductive effect of the C=O group
b. Resonance stabilization of the carboxylate ion
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Electron delocalization stabilizes carbonyl group
Carbon is sp2 hybridized.
Bond angles are close to 120.
RC
OH
O••
•• ••
•• RC
OH
O••
•• ••
••+••
– RC
OH
O••
••
••
+
••
–
Electron delocalization; resonance
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Electronegative substituents increase acidity
X CH2C-OH
O X Ka pKa
HF
Cl
1.8 x 10-5 4.72.5 x 10-3 2.6
1.4 x 10-3 2.9
Substituent Effects on Acidity
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Substituent Effects on Acidity
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• Multiple electronegative substituents have synergistic effects on acidity
• Fluoroacetic, chloroacetic, bromoacetic, and iodoacetic acids are stronger acids than acetic acid
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The magnitude of a substituent effect depends on its distance from the carboxyl group.
Substituent Effects on Acidity
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Aromatic Carboxylic Acids
Electron-withdrawing groups (e.g NO2) enhance the acid strength while electron-donating groups ( e.g alkyl ) decrease the acid strength.
Effects are strongest for substituents in the ortho and para positions.
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Substituent Effects
• An electronegative group will drive the ionization equilibrium toward dissociation, increasing acidity
• An electron-withdrawing group (-NO2) increases acidity by stabilizing the carboxylate anion, and an electron-donating (activating) group (OCH3) decreases acidity by destabilizing the carboxylate anion
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Substituent Effects in Substituted Benzoic Acids
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So:• Carboxylic acids are weak acids, average
pH = 5• Are Polar because of ( the high
electronegative O)• Soluble in water• Have high boiling and melting points
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Learning Check
Write the balanced equation for the ionization of butanoic acid in water and identify the carboxylate ion.
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Solution
Write the balanced equation for the ionization of butanoic acid in water and identify the carboxylate ion.
O O
CH3CH2COH + H2O CH3CH2CO– + H3O+
carboxylic acid carboxylate ion
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Naming Carboxylic Acid Salts
• First name the cation.• Then name the anion by replacing the
-ic acid with -ate.
potassium 3-chloropentanoate
C H3 C H2 C HC H2 C O O- K
+
C l
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Neutralization of Carboxylic Acids
Carboxylic acid salts • are a product of the neutralization of a carboxylic acid with a
strong base
CH3—COOH + NaOH CH3—COO– Na+ + H2Oacetic acid sodium acetate
(carboxylic acid salt)• are used as :• preservatives and flavor enhancers
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Properties of Acid Salts
• Usually solids with no odor.
• Carboxylate salts of Na+, K+, Li+, and NH4+
are soluble in water.• Soap is the soluble sodium salt of a long
chain fatty acid.• Salts can be formed by the reaction of an
acid with NaHCO3, releasing CO2.
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Uses of Organic Acids
Alpha hydroxy acids Acetic acid
skin care products. in vinegar as preservative and flavourings
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Uses of Organic Acids
Making of drugs, dyes, paints, insecticides, plastics.
Making of esters.
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Limes, lemons
Citric acid
Formic acid
Insects
Other Important Organic Acids
Malic acid
Apples and pears
Lactic acid
Sour milkTartaric acid
Grape juice
Oxalic acid
Spinch
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VITAMIN C (Ascorbic
acid)