Transcript 20.4 Acid-Base Properties of Carboxylic Acids

Acidity of Carboxylic Acids
• Carboxylic acids are weakly acidic
– One of their most important properties
20.4 Acid-Base Properties of Carboxylic Acids
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pKa Values of Some Carboxylic Acids
20.4 Acid-Base Properties of Carboxylic Acids
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Effects of Substitution on Acidity
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• Conjugate bases of carboxylic acids are called
carboxylate ions
– More soluble than carboxylic acids
• Naming carboxylic acid salts
– Name the cation
– Name the anion by removing the “-ic acid” and
replacing it with “-ate”
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Basicity of Carboxylic Acids
• The carbonyl oxygen is weakly basic
– plays an important role in many reactions
• Note: Carboxylate protonation is less favorable
20.4 Acid-Base Properties of Carboxylic Acids
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Problems
1) You have a mixture of naphthalene and benzoic acid that you
wish to separate. How might you take advantage of the
acidity of one component in the mixture to accomplish the
separation?
2) Without looking at a table of pKa values, rank the substances
in each of the following groups in order of increasing acidity:
fluoroacetic acid, 3-fluoropropanoic acid, iodoacetic acid
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Synthesis of Carboxylic Acids
1) Oxidation of primary alcohols
2) Side-chain oxidation of alkylbenzenes
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3) Grignard or organolithium with carbon dioxide
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Problem
• How would you prepare butanoic acid using
two different methods?
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Carboxylic Acid Reactions
• There are four main types of reactions:
1. Reactions at the carbonyl group
2. Reactions at the carboxylate oxygen
3. Loss of the carboxy group as CO2
(decarboxylation)
4. Reactions involving the a-carbon (Ch 22)
20.7 Introduction to Carboxylic Acids Reactions
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Acid-Catalyzed Esterification
• Ester:
• Carboxylic acid + alcohol + acid catalyst = Ester
• Also referred to as the Fischer esterification
• Equilibrium is favorable, but not large
• The alcohol needs to be present in large excess
(commonly as the solvent)
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Problem
• Write out the complete mechanism for the following reaction
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Esterification via SN2 Rxn with Carboxylate Anion
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Esterification by Alkylation
• The carboxylate oxygen acts as a nucleophile
20.8 Conversion of Carboxylic Acids into Esters
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Problems
1) What reactants can you use to form the following ester using
an SN2 reaction?
2) Draw the mechanism for the esterification of benzoic acid
via alkylation using diazomethane.
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