Unit 2 Module 1 Carboxylic acids and their derivatives
CARBOXYLIC ACIDS AND DERIVATIVES
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Structure of a typical carboxylic acid
This group
is the functional group
This is an example of an aliphatic acid
Aromatic carboxylic acids have a carboxyl group attached directly to an
aromatic ring.
Reactions of carboxylic acids
1. With highly reactive metals and inorganic bases/alkalis to form the
salt and hydrogen gas for highly reactive metals and a salt and
water formed from inorganic bases
2CH3COOH(aq) + Na(s)
ethanoic
sodium
acid
 CH3COONa(aq) +
sodium
ethanoate
2CH3COOH(aq) + NaOH(aq)
ethanoic
sodium
acid
hydroxide
H2(g)
hydrogen
gas
 CH3COONa(aq) + H2O(l)
sodium
water
ethanoate
2. Amide formation
With ammonia to form an ammonium
salt, which then decomposes by heat
(remember this reaction is
done in reflux) to form an amide
RCOOH + NH3  RCOO-NH4+
RCOO-NH4+  RCONH2 + H2O
Amides have the
functional group below
Unit 2 Module 1 Carboxylic acids and their derivatives
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3. Ester formation
Reflux with alcohols in the presence of conc. sulphuric acid and 170 °C
to form an ester and water (Note esters are low molecular mass
compounds, which have sweet smells and are insoluble in water)
RCOOH + R1OH conc.H2SO4
RCOOR1 + H2O
4. Acid chloride formation
With chlorinating agents e.g. dichlorosulphur
(IV) oxide SOCl2 or phosphorous (V) chloride
PCl5 to form an acid chloride
RCOOH PCl5 or SOCl2 RCOCl + HCl
5. With carbonates and hydrogen carbonates
to give a salt, carbon dioxide and water
2RCOOH + Na2CO3
Acid chlorides have
the following
functional group
O
//
--C
\
Cl
 2RCOO-Na+ + CO2 + H2O
RCOOH + NaHCO3  RCOO-Na+ + CO2 + H2O
6. Reduction
With LiAlH4 to form the corresponding alcohol
RCOOH LiAlH4 (in ether) RCH2OH
7. Anhydride formation
When 2 molecules of a carboxylic acid is reacted with a dehydrating
agent such as phosphorous (V) oxide P4O10, a molecule of water is
eliminated and an acid anhydride is formed.
2RCOOH distilled in P4O10
(RCO)2O
Unit 2 Module 1 Carboxylic acids and their derivatives
Checkpoint A
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Unit 2 Module 1 Carboxylic acids and their derivatives
Reactions of acid derivatives
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1. Hydrolysis
Acid chlorides are hydrolysed to give carboxylic acid and hydrogen
chloride gas RCOCl + H2O  RCOOH + HCl
Esters are also hydrolysed to give the original alcohol and if the reagent
is a strong mineral acid, then the carboxylic acid is formed
RCOOR1 + H+  ROH + RCOOH
If the reagent is a strong alkali, then the original alcohol is formed and
the salt of the carboxylic acid RCOOR1 + OH-  ROH + RCOO2. Ester formation
Acid and aroyl chlorides react readily with alcohols and with phenols in
alkaline solutions respectively to form esters
CH3COCl (l) + C2H5OH (l)  CH3COOC2H5 + HCl
ethanoyl
ethanol
ethyl
hydrogen
chloride
ethanoate
gas
CH3COCl +
NaCl (s)
sodium phenoxide
O-Na+ 
O—C—CH3 +
||
O
phenyl ethanoate
3. Amide formation
Amides are formed by reaction of acid chlorides with ammonia and with
primary and secondary amines
RCOCl + NH3  RCONH2 + HCl
RCOCl + R2NH  RCONR2 + HCl
4. Anhydride formation
When an acid chloride is heated with the sodium salt of a carboxylic
acid, the acid anhydride is formed
RCOCl + RCOO-Na+  (RCO)2O + NaCl
NB acid anhydrides react in a similar way to acid chlorides; they form
esters with alcohols and phenols and they form amides with ammonia
and primary and secondary amines.
Unit 2 Module 1 Carboxylic acids and their derivatives
Checkpoint B
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Saponification (alkaline hydrolysis of fats/oils)
When fats/oils are hydrolysed by an alkali, “soap” is produced.
How is a fat/oil molecule formed?
By the reaction of glycerol and long chain fatty acids (carboxylic acids with
hydrocarbon chains containing 12 or more carbon atoms)
Glycerol is propane-1,2,3-triol
Long chain fatty acids could be: C15H31COOH palmitic acid (saturated),
C17H35COOH stearic acid (saturated)
C17H33COOH oleic acid (unsaturated)
Unit 2 Module 1 Carboxylic acids and their derivatives
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When a fat/oil molecule is hydrolysis by an alkali, the glycerol is formed as
well as the sodium salt of the long chain fatty acid. The sodium salt of the
acid is the soap.
Transesterification biodiesel production
Biodiesel production is the act of producing the biofuel, biodiesel, through
either transesterification or alcoholysis. The process involves reacting
vegetable oils or animal fats catalytically with a short-chain aliphatic
alcohols (typically methanol or ethanol).
The vegetable oil is reacted with alkali in the presence of ethanol or
methanol as a catalyst under reflux, which produces the esters of the fatty
acids and glycerol. The biodiesel is the collection of the esters produced.
Checkpoint C
What advantages would there be for the use of biodiesel or biofuel in
general?
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Unit 2 Module 1 Carboxylic acids and their derivatives
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Explanation of relative acidities of acids and chlorine substituted acids
Carboxylic acids are only partially ionised in aqueous solution owing to the
predominantly covalent nature of the molecule are only weak in comparison
with mineral acids. RCOOH + H2O
RCOO- + H3O+
The relative strength of acids is attributed to the stability of the acid anion.
The more stable the acid anion, the stronger the acid.
The longer the hydrocarbon acid, the WEAKER the acid. However, the
more electronegative atoms i.e. Cl atoms present in the aliphatic chain the
STRONGER the acid.
Acidic strength of aliphatic acids decreases in the order
(Cl)3CCOOH > CH(Cl)2COOH > CH2ClCOOH > CH3COOH >
CH3CH2COOH
In aliphatic acids, the more electron withdrawing groups present, this
represents a spreading of the charge on the oxygen atom (from the anion
formed from dissociation in aqueous solution). Therefore trichloroethanoic
acid is more acidic than dichloroethanoic acid etc.
Propanoic acid is a weaker acid than ethanoic acid since there is an alkyl
group (-CH3) which is electron donating and thus increasing the charge on
the oxygen atom, making the anion formed from dissociation more unstable
i.e. a weaker acid than ethanoic acid.
NB The lower the pKa value, the stronger the acid.
Note that aliphatic alcohols are the weakest acids, then phenols are
stronger and finally carboxylic acids show the highest acidity.
The acid anion of carboxylic acids are therefore the most stable, then the
acid anion from phenols and finally the acid anion from ethanol.
Unit 2 Module 1 Carboxylic acids and their derivatives
Checkpoint C
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