organic chemistry: carboxylic acid and its derivatives
TRANSCRIPT
CHEMISTRY UPPER 6ORGANIC CHEMISTRY
CHAPTER 7 : CARBOXYLIC ACID& ITS DERIVATIVES
7.1 Nomenclature
� Organic acid containing one or more carboxyl (COOH) groups as functioning group
� Carboxylic acid has the general formula of CnH2n+1COOH or sometimes CnH2nO2.
� The naming of carboxylic acid end with –oic acid.
7.1.1 Naming carboxylic acid
1. Find the longest chain that attached to –COOH and name them accordingly. The C in COOH is C1.
2. Identify the group that attached to the parent chain and name them accordingly
3. Give the numbering of the group that attached accordingly
NameMethanoic
acid
Ethanoic
acid
Propanoic
acid
Butanoic
acid
Pentanoic
acid
Hexanoic
acid
Structure HCOOH CH3COOH C2H5COOH C3H7COOH C4H9COOH C5H11COOH
3-methylbutanoic acid 3-ethyl-3-
methylpentanoic acid
2,3,4-
trimetylpentanoic acid
Pentandioic acid
2-methylbutanoic acid6-chloro-
4,4-dimethylhexanoic acid2-ethyl-3-methylpentanoic
acid
3-hydroxy-3-
methylpentanoic acid
3,5-dibromobenzoic acid 2-phenylbutanoic acidPropanedioic acid
or malonic acid
But-2-enedioic acid
HOOCCH2CH2CH2COOH
� Practice : Draw all isomers for carboxylic acid with formula C3H7COOH
6.2 Physical properties
(A) Boiling point – The trend of the boiling points of may be caused by many factors
a) Factors of the number of carbon atom
HCOOH CH3COOH C2H5COOH C3H7COOH
Explanation :
Boiling point increase
When going down to homologous series, the boiling point increase. This is due to the increase in relative molecular mass, which increase the weak Van Der Waals forces causing boiling point increase.
Boiling point of different functioning group
Compoundpropanol
(C3H7OH)CH3COOH Butane (C4H10)
Chloroethane
(C2H5Cl)
RMM 60 60 58 64.5
Boiling
point (oC)78 117 4.4 21
Explanation : Ethanoic acid has the highest boiling point among these organic compound as it form dimer among itself using 2 hydrogen bonds. Propanol which has same molecular mass, contain only 1 hydrogen bond, has a lower boiling point. Chloroethane has higher boiling point compare to butane as it is a polar molecules which form permanent dipole while butane is a non-polar molecules which form induced dipole.
� Solubility of Carboxylic Acid
HCOOH CH3COOH C2H5COOH C3H7COOH C4H9COOH
Solubility decrease
Explanation :methanoic, ethanoic and propanoic acid are completely miscible in water as they can form hydrogen bond with water. However, the LONGER the ALKYL GROUPS ATTACHED, molecule become MORE HYDROPHOBIC. As a result, HYDROGEN BOND BECOME LESS SIGNIFICANT and cause the solubility decrease.
(C) Acidity of carboxylic acid
� Carboxylic acid is considerably weak acid since it has a small pKa value. It undergoes partial dissociation
aaa KpKRCOOH
OHRCOOK lg
][
]][[ 3−==
+−
Name Methanoic acid Ethanoic acid Propanoic acid
Structure HCOOH CH3COOH C2H5COOH
pKa 3.75 4.76 4.90
Name Benzoic acid 2-chloro-ethanoic acid 2-methyl ethanoic acid
Structure C6H5COOH CH2(Cl)COOH CH2(CH3) COOH
pKa 4.19 4.42 4.86
� Carboxylic acid is generally a stronger weak acid than alcohol, since the charge delocatisation at carboxylate ion makes the ion formed become more stable as it formed resonance structure due to mesomeric effect, hence increase the stability of carboxylate ion which result the equilibrium favour to right position (favour to position of donate proton)
� Similar to alcohol, carboxylic attached to an alkyl has lower aciditycompare to carboxylic acid attached to a phenyl. This is due to alkyl is an electron donating group, while a phenyl is an electron withdrawing group
Carboxylic acid Explanation
Carboxylic acid dissociate in water according to the equation
R-COOH + H2O R-COO- + H3O+
Alkyl group, which is an electron donating group, donate electron to O and
caused the electron density of O in R–OH increase. As a result, O is more
readily to accept proton.
Acidity decrease in the order, where
Methanoic acid > Ethanoic acid > Propanoic acid
This is due to, longer the alkyl chain, stronger the electron donating effect,
equilibrium favours more to left.
Benzoic acid
Benzoic acid dissociate in water according to the equation
C6H5–COOH + H2O C6H5–COO- + H3O+
The phenyl group is an electron-withdrawing group, which withdrawn the
electron density from partially negative charge, δ−, from O making O less
readily to accept proton. As a result, O is more readily to donate proton
which makes equilibrium favour more to right.
p-methylbenzoic acid
Since CH3 is an electron donating group to benzene ring, it will increase the
electron density in benzene ring, hence increase the polarity of -O-H bond in
the benzene ring. As a result, H is harder to dissociate, hence caused the
equilibrium to shift slightly to the left, decreasing the acidity of benzoic acid
Effect of the distance
of electron
withdrawing group
toward acidity of
butanoic acid
Due to inductive effects operate through π bonds and are dependent on distance, the effect of
halogen substitution decreases as the substituent moves farther from the carboxyl. Thus, 2-
chlorobutanoic acid has pKa = 2.86, 3-chlorobutanoic acid has pKa = 4.05, and 4-chlorobutanoic
acid has pKa = 4.52.
Effect of the number of
substituent toward
acidity of ethanoic acid
-Cl act as electron withdrawing group in carboxylic acid. Note that as the number of -Cl
increased, the acidity increased. This can be explained in term of the increment of negative
inductive effect caused by -Cl, which further stabilise the conjugate base formed. As a result,
equilibrium shift to right, increased the acidity.
7.3 Chemical Properties of Carboxylic acid
7.3.1 Preparation of carboxylic acid
Name of
reaction
Reagent used and
conditionEquation
Oxidation of
10 alcohol
Acidified KMnO4 or
acidified K2Cr2O7 +
heat Propan-1-ol propanoic acid
Oxidation of
aldehyde
Acidified KMnO4 or
acidified K2Cr2O7 +
heat Propanal propanoic acid
Hydrolysis of
nitrile
Dilute sulphuric
acid H2SO4 + H2O
under reflux2-methylbutylnitrile 2-methylbutanoic acid
Hydrolysis of
ester
Dilute HCl / NaOH
with heat
Name of
reaction
Reagent
used and
condition
Equation
Properties
of an acid
-----------
Reaction
with alkali,
metal and
metal
carbonate
Alkali, NaOH
or Na2O
Sodium, Na
Sodium
carbonate,
Na2CO3
7.3.2 Chemical reaction of carboxylic acid
Name of
reaction
Reagent used
and conditionEquation
Esterification
Alcohol
catalysed by
concentrated
sulphuric acid
Formation of
acyl chloride
Phosphorous
pentachloride(P
Cl5)
@
Thionyl chloride
(SOCl2)
Reduction –
Formation of
alcohol
Lithium
aluminium
hydride ; LiAlH4with dry ether
(1) Reaction of acid-base : Formation of salts
A. Reaction with base (metal hydroxide and metal oxide)
� Like all acid, when carboxylic acid reacts with base, it will form salt and water
Carboxylic Acid Base Salt Water
CH3COOH NaOH
CH3CH2COOH K2O
CH3CH2CH2COOH Mg(OH)2
CH3COO–Na+ H2O
CH3CH2COO–K+ H2O
Mg(CH3CH2CH2COO)2 H2O
B. Reaction with metal
� When acid react with metal, a colourless gas liberated. This gas will give “pop” sound when burning splinter is put close to the gas liberated, indicating ………… gas is released.
Carboxylic Acid Metal SaltHydroge
n
CH3COOH Zn
CH3CH2COOH Mg
Zn(CH3COO)2 H2
Mg(CH3CH2COO)2 H2
hydrogen
C. Reaction with metal carbonate
� When acid react with metal carbonate solution, an effervescence is observed and a colourless released and gas turned lime water chalky, indicating ………..……… gas is released.
Carboxylic Acid Metal carbonate SaltCarbon
dioxideWater
CH3CH(CH3)COOH K2CO3
CH3CH2COOH ZnCO3
CO2 H2O
Zn(CH3CH2COO)2
CH(CH3)2COO–K+
carbon dioxide
CO2 H2O
(2) Esterification – Formation of ester
� When alcohol reacts with carboxylic acid catalysed by concentrated sulphuric acid, ester and water is formed. The –H is donated by alcohol while –OH is given off by carboxylic acid
Carboxylic Acid
Carboxylate ion
Alcohol
Alkyl
Name of ester :
Alkyl carboxylate
carboxylic acid alcohol ester
Carboxylic Acid Alcohol Ester Water
CH3COOH CH3CH2OH
CH3CH(CH3)COOH CH3CH2CH2OH
CH3C(CH3)2COOH CH3CH(CH3)OH
H2O
H2O
H2O
H2O
(3)Formation of acyl chloride
� When carboxylic acid is reacted with a chlorine-rich compound such as phosphorous pentachloride (PCl5) or thionyl chloride (SOCl2), an acyl chloride is formed. A white fume of hydrogen chloride is given off as side product.
� The reaction take place is a nucleophilic substitution reaction.
Carboxylic acidChlorine
CompoundAcyl chloride
Side
product
Hydrogen
chloride
CH3CH2COOH PCl5
CH3CH(CH3)COOH SOCl2
CH3CH(CH3)CH2COOH HCl
PCl5
CH3CH2COCl + POCl3 + HCl
CH3CH(CH3)COCl + SO2 + HCl
CH3CH(CH3)CH2COCl + H2O
+ POCl3 + HCl
(4) Reduction of carboxylic acid : Formation of alcohol
� Using strong reducing agent such as lithium tetrahydridoluminate (LiAlH4), carboxylic acid is readily to reduce to become alcohol.
� Reagent : Lithium tetrahydridoaluminate (LiAlH4) under dry ether
CH3CH2COOH + LiAlH4
CH3CH(CH3)COOH + LiAlH4
CH3C(CH3)2COOH + LiAlH4
+ LiAlH4
→etherdry
→etherdry
→etherdry
CH3CH2CH2OH + H2O
CH3CH(CH3)CH2OH + H2O
C(CH3)3CH2OH + H2O
→etherdry
7.3.3 Simple test for carboxylic acidDifferentiate Chemical test Observation & Equation
Carboxylic
acid with
other
organic
compound
Sodium
carbonate,
Na2CO3
Positive test : Carboxylic acid
Effervescence occurs. Gas released turn lime water
chalky indicating carbon dioxide is released.
Eq. : R–COOH + Na2CO3 �
R–COO-Na+ + CO2 + H2O
Iron (III)
chloride, FeCl3
Positive test : Carboxylic acid
Dark red solution is obtained when FeCl3 is added to
carboxylic acid.
Equation :
CH3COO- + FeCl3 � Fe(CH3COO)3 + 3 Cl-
red solution
When boiled, the red solution turns to brown
precipitate.
Fe(CH3COO)3 + 2 H2O �
Fe(CH3COO)(OH)2 + 2 CH3COOH
brown precipitate
7.4 Methanoic acid (Common name : formic acid)
� Methanoic acid is the first member of carboxylic acid homologous series. Not only it shows the similar properties of carboxylic acid as proposed earlier, it also possessed other special properties.
� This special properties is due to the of having 2 functioning group at the same molecule where
Functioning Functioning as
as aldehyde carboxylic acid
� Methanoic acid is a strong reducing agent, unlike other carboxylic acid. It is easily oxidised to form carbon dioxide as shown in the following reaction (can also be its salt like HCOONa)
Reaction with Observation, Equation and explanation
Silver nitrate,
AgNO3
Observation : White precipitate is 1st formed and eventually turn to
silver
Equation : HCOONa + AgNO3 �
HCOOAg (white ppt) + NaNO3
2 HCOOAg � 2 Ag (silver) + CO2
Tollen’s Test
Due to the presence of aldehyde as functioning group, it give
positive test to
Tollen reagent (silver complex)
Observation : a silver mirror is observed
Equation : HCOOH + Ag2O �
2 Ag (silver mirror) + CO2 + H2O
Mercury (II)
chloride, HgCl2
Methanoic acid reduce mercury (II) chloride to mercury (I) chloride
(white ppt)
Equation : HCOOH + 2 HgCl2 � Hg2Cl2 + CO2 + 2 HCl
Under excess methanoic acid, a black precipitate of mercury is
observed
Equation : HCOOH + Hg2Cl2 � CO2 + 2 HCl + 2 Hg
Reaction with Observation, Equation and explanation
Dehydration :
reaction with
conc.
sulphuric acid,
H2SO4
When heated with conc. H2SO4, methanoic acid dehydrated and
produce carbon monoxide and water
Equation : HCOOH CO + H2O
Acidified
potassium
manganate
(VII).
KMnO4 / H+
As discussed earlier, when methanoic acid dissolved in KMnO4 /
H+, the purple colour of potassium manganate (VII) is decolourised
while carbon dioxide and water is formed
Equation : HCOOH + KMnO4 / H+ � CO2 + H2O
Phosphorous
pentachloride,
PCl5
Unlike other carboxylic acid, when react with phosphorous
pentachloride, it will not form acyl chloride
Equation : HCOOH + PCl5 � CO + 2 HCl + POCl3
→ 42SOH.conc
7.5 Ethanedioic acid, H2C2O4 (also known as oxalic acid)
� The structure of ethanedioic acid can be described as
� It dissolve in alcohol and water but not in organic solvent such as propanone or ether.
� It can be prepare by the following method :
Step 1 : heating sodium methanoate Step 2 : add with sulphuric acid
2 HCOONa Na2C2O4 + H2
Na2C2O4 + H2SO4
H2C2O4 + Na2SO4
→∆
→∆
� Reaction with ethanedioic acid
Reaction with Observation, Equation and explanation
Acidified potassium
manganate (VII),
KMnO4 / H+
The purple colour of potassium manganate (VII) is reduced to Mn2+
which is pink colour according to the equation
Equation : 5 C2O42- + 2 MnO4
- + 16 H+ � 2 Mn2+ + 8 H2O + 10
CO2
Concentrated
sulphuric acid,
H2SO4
Similar to methanoic acid, dehydration occur when added to conc.
H2SO4
Equation : H2C2O4 + conc. H2SO4 � CO2 + CO + H2O
Calcium chloride,
CaCl2
White precipitate is observed when reacted
Equation : Ca2+ + C2O42- � CaC2O4 (white precipitate)
7.6 Uses of Caboxylic acid
� Methanoic acid and ethanoic acid is used in rubber industries to coagulate latex
� Ethanoic acid is used as preservative and additive in food industries
� Ethanoic acid is used to manufacture ethanoic anhydride
Ethanoic anhydride is used to manufacture aspirin
� Benzoic acid is used as preservative. It is also used as an antibacterial and antifungal agent
� Calcium propanoate (react propanoic with calcium hydroxide) is used as preservative in bread to prevent the growth of mold
� Dicarboxylic acid is used mainly in manufacturing synthetic polymer such as nylon
7.7 Carboxylic Acid’s Derivatives
� In this Chapter, we’re looking into organic compounds derived from carboxylic acid. Examples of these compounds are
→acyl chlorides → esters → amides
7.7.1 Physical properties of carboxylic acid derivatives
� The boiling point of a few organic compounds are shown below
Name Molecular structure Molecular mass Boil point (0C)
Ethanoyl chloride CH3COCl 78 51
Ethyl methanoate CH3COOCH3 74 57
Butanal CH3CH2CH2COH 72 76
Butanone CH3COCH2CH3 72 80
Propanamide CH3CH2CONH2 73 213
Propanamide has the highest boiling point among these organic compound as it contain 2 hydrogen bonds. Butanal and butanone are polar molecule which are held by permanent dipole – permanent dipole, while ethanoyl chloride and ethyl methanoate is non-polar which are held by temporary dipole – induced dipole.
7.8 Acyl chloride
� Acyl chloride has the general formula of CnH2n+1COCl.
� The ending of alkyl group attached to COCl = ~noyl chloride
� Acyl chlorides are colourless liquids with pungent smell. They are very reactivecompound
� CH3COCl
� CH3CH2COCl
� CH3CH(CH3)COCl
� C6H5COCl
7.8.1 Chemical properties of acyl chlorides
� Most of the reaction of acyl chlorides are acylation reaction, where the –Cl is substitute out easily.
� This is due to the negative inductive effect (–I) of the oxygen atom, which cause the carbon atom become more positively partial charged. As a result, C–Cl carries a much higher partially positive charge and become more reactive for nucleophilicattack
Ethanoyl chloride
Propanoyl chloride
2-methylpropanoyl chloride
Benzoyl chloride
Name of
reaction
Reagent
used and
condition
Equation
Hydrolysis Water
propanoyl chloride water propanoic acid
Esterification Alcoholpropanoyl chloride ethanol
ethyl propanoate
Formation of
amide
Ammonia of
amine
propanoyl chloride ammonia propylamide
(A) Hydrolysis of acyl chloride
� Acyl chloride undergoes hydrolysis when react with water to form carboxylic acid. A white fume of hydrogen chloride is released as side product of the reaction.
� Hydrolysis occur vigorously as the –Cl is readily to leave the group. Examples of reaction
Acyl chloride Water Carboxylic acid HCl
CH3COCl + H2O HCl
CH3CH(CH3)COCl + H2O HCl
+ H2O HCl
CH3COOH
CH3CH(CH3)COOH
(B)Formation of ester
� Acyl choride react with alcohol / phenol at room temperature to form ester. Unlike carboxylic acid, which required an acidic medium, acyl chloride does not require an acidic medium.
� Similar to the hydrolysis of acyl chloride, a white fume of hydrogen chloride is released.
� When phenol react with benzoyl chloride, NaOH is used.
Acyl chloride Alcohol Ester HCl
CH3COCl CH3CH2OH HCl
CH3CH2CH2COCl CH3CH2CH2OH HCl
CH3C(CH3)2COCl CH3OH HCl
CH3COOCH2CH3
CH3CH2CH2COOCH2CH2CH3
CH3C(CH3)2COOCH3
HCl
(C) Formation of amide
� Acyl chloride form amides when reacted with ammonia, primary and secondary amine
Acyl chlorideAmmonia /
amineAmide HCl
CH3CH2COCl NH3 HCl
CH3COCl CH3CH2NH2 HCl
CH3CH2CH2COCl CH3NH(CH3) HCl
CH3CH2CONH2
CH3CONHCH2CH3
CH3CH2CH2CON(CH3)2
7.9 Ester
� Esters are the functional isomerism of carboxylic acid. Similar to carboxylic acid, it has the general formula of CnH2nO2. In naming ester, the alkyl attached to alcohol is named where the carboxylic acid is named as its anion. Examples
� Lower esters are colourless liquid with pleasant fruity odour. Larger esters are colourless solid.
� Small ester such as methyl methanoate or ethyl methanoate is soluble in water. Most of the esters are insoluble in water but soluble in organic solvent.
Methyl propanoate
Ethyl butanoate
Propyl benzoate
Phenyl benzoate
7.9.1 Preparation of ester
Name of
reaction
Reagent used
and conditionEquation
Esterification
by carboxylic
acid with
alcohol
Alcohol
catalysed by
concentrated
sulphuric acid
Esterification
by acyl
chloride with
alcohol
Alcoholpropanoyl chloride ethanol
ethyl propanoate
7.9.2 Chemical reaction of ester
Name of
reaction
Reagent used
and conditionEquation
Hydrolysis
of ester
Diluted acidic
solution
Sodium
hydroxide
(NaOH)
Name of
reaction
Reagent used
and conditionEquation
Reaction
with
ammonia
Concentrated
NH3
ethyl propanoate ammonia
propylamide ethanol
Reduction
of ester
Lithium
tetrahydrido-
aluminate
(LiAlH4)
ethyl propanoate
propan-1-ol ethanol
(A) Hydrolysis of ester
� Hydrolysis of ester is a reverse reaction of esterification. When ester is dissolved in diluted acidic solution, it will form back carboxylic acid and ester.
Ester Water Carboxylic acid Alcohol
+ H2O/
H+
+ H2O/
H+
+ H2O/
H+
CH3CH2CH2COOH
CH3CH2CH2OH
CH3CH(CH3)CH2COOH
CH3CH2CH2OH
CH3CH2COOH
CH3CH(OH)CH3
� When ester is hydrolysed under alkaline condition, metal salt is formed together with alcohol
� Example ; when ethyl propanoate is hydrolysed under alkaline condition.
� When sodium propanoate is react using acid such as sulphuric acid, the carboxylic acid formed back.
(B)Formation of amide : reaction with ammonia
� Ammonia is a weaker nucleophile compare to hydroxide ion. So, to effectively react with ester, concentrated ammonia is mixed with ester and heated. The products are an amide and alcohol
Ester Ammonia Amide Alcohol
+ NH3
+ NH3
+ NH3
CH3CH2CONH2CH3CH2OH
CH3OH
CH3CH2CONH2
(C) Reduction of ester
� When reduced using strong reducing agent such as LiAlH4, ester will formed alcohol as products
Ester LiAlH4 Alcohol Alcohol
LiAlH4 /
H+
LiAlH4 /
H+
LiAlH4 /
H+
CH3CH2CH2OH CH3CH2OH
CH3OH
CH3CH2CH2OH
7.9.3 Natural ester (Lipid) – Fats and Oils
� Lipids are organic substance found in living organisms, which is insoluble in water.
� Members of lipid include fats and oils, steroids, waxes and some vitamins.
� Fatty acids are common name for long-chain carboxylic acid obtained from fats and oils
� They are natural esters formed from propan-1,2,3-triol (known as glycerol) and long chain fatty acid.
+ 3 CH3(CH2)14COOH
� There are 2 types of fatty acid which are known as saturated fatty acid and unsaturated fatty acid.
� Saturated fatty acid – all C–C are singly bonded to each other in the long carbon chain
� Unsaturated fatty acid – contain at least 1 C=C within the long carbon chain. If there’s only one C=C in the long carbon chain, it is known as monounsaturated fat. If there’s more than one C=C, they are known as polyunsaturated fat.
� In natural product of fats and oils contain mixture of saturated fatty acid and unsaturated fatty acid
Fats / oil Saturated fat Polyunsaturated fatMonounsaturated
fat
Palm oil 51% 10% 39%
Sunflower oil 11% 69% 20%
Olive oil 14% 9% 77%
Butter fat 66% 4% 30%
Lard 41% 12% 47%
Manufacture of soap
� An important use of soap is in soap making. Soaps are sodium (Na) or potassium (K) salts of long chain of fatty acids. Hydrolysis of fats / oils in aqueous NaOH ( known as saponification) form glycerol& sodium carboxylate salt (soap).
� The cleansing action of soap is due to the hydrophobic part of soap which dissolves in grease easily and dirt are removed easily using the attraction forces between cation and the negative head of soap.
Application of ester in industries
� Used as food additive in food processing industries (taste enhancer, flavouring and preservatives)
� Solvent for drugs, antibiotics and cosmetic.
� Use to produce cosmetic, perfume / cologne and air-freshener.
� Polystyrene cement – use to bind to another type of surface in the cement
� Polyester (terylene) – synthetic fibres in textiles industries.
� Polystyrene (alkyd resin) – used in pain and surface coating
� Unsaturated polyester are readily copolymerised to give thermosetting products. They are used in the manufacture of glass fiber products for reinforcement in boat and cars.
7.10 Amides
� Amides are organic compound with the general formula of CnH2n+1CONH2. Amides are formed by replacing hydroxyl (–OH) with amine (–NH2) group.
� Naming of amide end with suffix “amide”. Examples of amides are
ethanamide
propanamide
butanamide
benzamide
20 amide
30 amide
N-propylethanamide
N-phenylpropanamide
N-ethyl-N-methylbutanamide
N,N-dimethylbenzamide
7.11 Preparation of amide
Name of
reaction
Reagent used
and conditionEquation
Reaction
with amine
Acyl chloride
with ammonia
propanoyl chloride ammonia propylamide
Acyl chloride
with amineEthanoyl chloride propylamine
Heating
ammonium
salt with
ester
Ammonium
salt with ester
ammonia ethanamide
Name of
reaction
Reagent used
and conditionEquation
Hydrolysis of
amide
Diluted HCl
under reflux ethanamide ethanoic acid
Dehydration
of amide
Distilled over
phosphorous
pentoxide,
P2O5 Propanamide propanitrile
Reaction
with nitrous
acid, HNO2
Nitrous acid,
HNO2
Propanamide nitrous acid
propanoic acid
Name of
reaction
Reagent used
and conditionEquation
Hoffmann
degradation
Bromine in
sodium
hydroxide,
NaOH
propanamide
ethylamine
Reduction of
amide
Lithium
tetrahydrido-
aluminate,
LiAlH4
propanamide
propylamine
(A) Hydrolysis of amide
� Amide slowly hydrolysed by refluxing with dilute acid / alkali solution. In both cases, the intermediate product is ammonium salt of carboxylic acid
Under acidic
medium
Step 1 : Formation of ammonium salt
Step 2 : Formation of carboxylic acid
Overall :
Under alkaline
medium
(way of
distinguish
between amine
and amide)
Step 1 : Formation of ammonium salt
Step 2 : Formation of carboxylate salt
Overall :
(B)Dehydration of amide
� When amides are distilled over P2O5, phosphorous pentoxide, nitriles are formed. So P2O5 act as dehydrating agent. The H2 from NH2 and O from C=O are withdrawn out and formed water.
� The nitrile formed can be later used to synthesis amine and carboxylic acid using suitable reagent
Amide Reagent Nitrile Reagent Compound
→ 52OP → 4LiAlH
→ 52OP →+H,OH 2
→ 52OP → 4LiAlH
(C) Reaction with nitrous acid, HNO2
� Nitrous acid, HNO2, can be prepared by treating sodium nitrite, NaNO2, with dilute HCl in cold
NaNO2 (aq) + HCl (aq) HNO2 + NaCl
� When nitrous acid, HNO2, react with amide, carboxylic acid, nitrogen and water is produced
→cold
Amide Nitrous acid Carboxylic acid Side product
HNO2
HNO2
HNO2
+ H2O+ N2
+ H2O+ N2
+ H2O+ N2
(D) Hoffmann Degradation : Way of shortening chain.
� The terms degradation mean reduce the number of carbon, an opposite of forming nitrile to increase no of carbon in an organic compound.
� The reagents used for Hoffmann degradation are bromine solution in sodium hydroxide (Br2 in NaOH)
AmideBromine in
sodium hydroxideAmine Side products
Br2 + 4 NaOH
Br2 + 4 NaOH
Br2 + 4 NaOH
CH3CH2NH2
+ Na2CO3
+ 2 NaBr+ 2 H2O
CH3CH2CH2NH2
+ Na2CO3
+ 2 NaBr+ 2 H2O
+ Na2CO3
+ 2 NaBr+ 2 H2O
(E)Reduction of amide
� Amide can be reduced to become an amine using strong reducing agent such as LiAlH4 (lithium tetrahydridoaluminate) under dry ether. The number of carbon after reduction remains the same
AmideStrong reducing
agentAmine
Side
products
LiAlH4
LiAlH4
LiAlH4
CH3CH2CH2NH2 + H2O
CH3CH2CH2CH2NH2 + H2O
+ H2O
RCOOH + H2O � RCOO- + H3O+
Acidity increase from CH3COOH < CH2ClCOOH < CHCl2COOH
Cl is electorn withdrawing group / caused negative inductive effect / Greater
number of Cl will increase the inductive effect, causing more acidic [1]
[H3O+] = pH = 1.9100.00014.0][ 3 ×=×
+OHorcK a
pKa = - lg Ka ; pKa = 1.3
alkene / C=C
hydroxyl group / -OH
Aldehyde / -CHO
KMnO4 / H+ cold , dilute
oxidation
Chlorine gas under UV
NaOH reflux
X
Effervescences occur, which turn lime water chalky
CH3COOH + NaHCO3 � CH3COO-Na+ + H2O + CO3
Y
Silver mirror is observed
CH2(OH)CHO + 2Ag+ + 3OH-� CH2(OH)COO- + 2H2O + 2 Ag
Acidic trend increase from 1 < 2 < 3 [1]
This is due to, when number of Cl increase, the negative inductive effect increase
gradually[1], which increase the acidity
Acid 2 is stronger than Acid 4 [1]
This is due to, inductive effect is stronger if Cl is closer to the π-bond of COOH
group [1]
[H3O+] =
pH = 3.5010.01026.1][ 5
3 ××=×−+
OHorcK a
ester
Dilute HCl under reflux
CH3OH catalysed by H2SO4 under reflux
CH2(Br)CH(Br)CH2(Br)
COOHCOCOOH
890g of triglyceride produces 3 × 298 = 894 g of biodiesel [1]
∴ 500kg produces 500 × 894/890 = 502 kg biodiesel [1]
C17H35CO2CH3 + 27 ½ O2 → 19 CO2 + 19 H2O
Mass of CO2 produced = 10 × 44 × 19/298
= 28 kg.
• economic argument (NOT just “cheaper”) – e.g. oil will become increasingly more expensive
as it runs out
• ref to CO2 cycle (e.g. no net increase in CO2, i.e. “carbon neutral”) or less global warming (due
to a smaller carbon “footprint”)
• renewable/sustainable
• the effect of biofuel cultivation on world food prices