Download Carboxylic Acids

Carboxylic Acids
Carboxyl Group
The carboxyl group:
 Is a carbonyl group (C=O) attached to a
hydroxyl group (OH).
 Is found on carbon 1 in carboxylic
acids.
 Is written in different ways.
O

CH3—C—OH CH3—COOH CH3—CO2H
Properties
• Weak acids
• In a pure carboxylic acid, hydrogen
bonding can occur between two molecules
of acid to produce a dimer.
• Thus carboxylic acids have a much higher boiling point
than alkanes of a similar mass.
propan-1-ol
CH3CH2CH2OH
97.2°C
ethanoic acid
CH3COOH
118°C
• Low mass carboxylic acids are soluble in water
IUPAC Names
The IUPAC names of carboxylic acids:
• Replace the -e in the alkane name with -oic
acid.
CH4 methane
HCOOH methanoic acid
CH3—CH3 ethane CH3—COOH ethanoic acid
• Number substituents from the carboxyl
carbon 1.
CH3
|
CH3—CH—CH2—COOH
4
3
2
1
3-methylbutanoic acid
IUPAC Names
The IUPAC names of carboxylic acids:
• Replace the -e in the alkane name with -oic
acid.
Models of Carboxylic Acids
• The three-dimensional models show the
geometry of atoms in carboxylic acid
molecules.
Names and Sources of Some
Carboxylic Acids
Reactions
• Neutralise bases
• React with metals metal carbonates and
metal oxides to form ionic salts
• React with PCl5 or SOCl2 to form acid
chlorides (substitution)
• Reacts with alcohols to form esters
• Reacts with ammonia to form amides
Neutralisation
• Organic acids will react with bases to form
a salt and water
E.g.
CH3COOH + NaOH
CH3COONa + H2O
When the acids form salts, H+ is lost and replaced by a
metal. Sodium ethanoate, for example, has the structure:
The bond between the sodium and the ethanoate
is ionic. Don't draw a line between the two
(implying a covalent bond).
Although the name is written with the sodium first,
the formula is always written in one of the ways
shown (CH3COO- Na+ or CH3COONa)
Acid Chlorides
• This is a substitution reaction where Cl replaces
OH on the carboxylic acid.
• Also referred to as alkanoyl chloride
• Are very reactive and so can be used to make
other products
• Suffix for naming is -oyl chloride e.g.
Properties of Acid Chlorides
• Low melting points (No H bonding)
• Pungent fuming liquids
Formation of Acid Chlorides
• PCl5 (phosphorous pentachloride) or
SOCl2 (thionyl chloride) are the reagents
• The acyl chloride can be separated by
fractional distillation.
• Conc HCl can not be use as the water would react
with acid chloride to produce the carboxylic acid
Equations
Reactivity of Acid Chlorides
Acid chlorides are highly reactive because the
carbon of the acid chloride group, COCl, is
attached to two highly electronegative atoms, ie:
• Oxygen (of the C=0 carbonyl group).
• Chlorine (of the C-Cl bond).
• This allows NH3 and H2O to react with them in
nucleophilic substitution reactions.
Reaction with Water
Produces a carboxylic acid
Reaction with Ammonia
Produces an amide and ammonium chloride
Reaction with Primary Aminoalkanes
Produces a secondary amide
Reaction with Alcohols
Produces an ester and hydrogen chloride
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