Chemistry Form 6 Sem 3 07

CHEMISTRY UPPER 6

ORGANIC 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 C

H

COOH or

sometimes

C

H

O

.

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 C

.

2. Identify the group that attached to the parent chain and name them

accordingly

3. Give the numbering of the group that attached accordingly

2-methylbutanoic acid 6-chloro-4,4-dimethylhexanoic acid 2-ethyl-3-methylpentanoic acid 3-hydroxy-3-methylpentanoic acid 3-methylbutanoic acid 3-ethyl-3-methylpentanoic acid 2,3,4-trimetylpentanoic acid Pentandioic acid

3,5-dibromobenzoic acid 2-phenylbutanoic acid _{Propanedioic acid} or malonic acid But-2-enedioic acid CH₂CCH₂COOH CH₃ CH₂CH₃ H₃C CH₃CHCHCHCOOH CH₃ CH₃ CH₃ HOOCCH2CH2CH2COOH

Practice : Draw all isomers for carboxylic acid with formula C₃H₇COOH

CH

CH

CH

C

O

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. increase the weak Van Der Waals forces causing boiling point increase.

Boiling point of different functioning group

Compound propanol

(C₃H₇OH) CH3COOH Butane (C4H10)

Chloroethane (C₂H₅Cl) RMM 60 60 58 64.5 Boiling point (o_C) 78 117 4.4 21 point ( C)

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 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 pK

value. It undergoes partial dissociation

a a a

pK

K

RCOOH

O

H

RCOO

K

lg

]

[

]

][

[

−

=

=

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

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)

position of donate proton)

Similar to alcohol, carboxylic attached to an alkyl has lower

acidity compare 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- _{+ H}

3O+

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- _{+ H}

3O+

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 condition Equation

Oxidation of 10 _alcohol

Acidified KMnO₄ or acidified

K₂Cr₂O₇ + heat _{Propan-1-ol propanoic acid}

Oxidation of Acidified KMnO4 or acidified aldehyde or acidified

K₂Cr₂O₇ + heat _{Propanal propanoic acid}

Hydrolysis of nitrile

Dilute sulphuric acid H₂SO₄ + H₂O under reflux

2-methylbutylnitrile 2-methylbutanoic acid

Hydrolysis of ester

Dilute HCl / NaOH with heat

Name of reaction Reagent used and condition Equation Properties of an acid Alkali, NaOH or Na₂O

7.3.2 Chemical reaction of carboxylic acid

of an acid ---Reaction with alkali, metal and metal carbonate Sodium, Na Sodium carbonate, Na₂CO₃

Name of reaction

Reagent used

and condition Equation

Esterification Alcohol catalysed by concentrated sulphuric acid Formation of acyl chloride Phosphorous pentachloride(P Cl₅) @ acyl chloride @ Thionyl chloride (SOCl₂) Reduction – Formation of alcohol Lithium aluminium hydride ; LiAlH₄ with dry

(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 CH CH COOH K O CH₃COO–_Na+ _H 2O CH₃CH₂COO–_K+ _{H O} CH₃CH₂COOH K₂O CH₃CH₂CH₂COOH Mg(OH)₂ CH₃CH₂COO–_K+ _H 2O 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 Salt Hydroge

n CH₃COOH Zn _Zn(CH 3COO)2 H₂ hydrogen CH₃CH₂COOH Mg _Mg(CH 3CH2COO)2 H2

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 Salt Carbon Water

carbon dioxide

Carboxylic Acid Metal carbonate Salt Carbon

dioxide Water CH₃CH(CH₃)COOH K₂CO₃ CH₃CH₂COOH ZnCO₃ CO₂ H₂O Zn(CH₃CH₂COO)₂ CH(CH₃)₂COO–_K+ 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 alcohol ester

Carboxylic Acid Carboxylate ion Alcohol Alkyl Name of ester : Alkyl carboxylate

Carboxylic Acid Alcohol Ester Water CH₃COOH CH₃CH₂OH CH₃CH(CH₃)COOH CH₃CH₂CH₂OH H₂O H₂O CH₃C(CH₃)₂COOH CH₃CH(CH₃)OH 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 acid Chlorine

Compound Acyl 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 tetrahyd

rid

oluminate

(LiAlH

), carboxylic acid is readily to reduce to become alcohol.

Reagent : Lithium tetrahydridoaluminate (LiAlH

) under dry ether

CH

CH

COOH + LiAlH

CH

CH(CH

)COOH + LiAlH







→









→



CH

C(CH

)

COOH + LiAlH

+ LiAlH







→









→



7.3.3 Simple test for carboxylic acid

Differentiate Chemical test Observation & Equation

Carboxylic acid with other Sodium carbonate, Na₂CO₃

Positive test : Carboxylic acid

Effervescence occurs. Gas released turn lime

water chalky indicating carbon dioxide is released. Eq. : R–COOH + Na₂CO_{3 }

R–COO-_Na+ _{+ CO}

2 + H2O

Positive test : Carboxylic acid

Dark red solution is obtained when FeCl₃ is added to carboxylic acid.

other organic

compound _{Iron (III)} chloride, FeCl₃ to carboxylic acid. Equation : CH₃COO- _{+ FeCl} 3  Fe(CH3COO)3 + 3 Cl -red solution

When boiled, the red solution turns to brown precipitate.

Fe(CH₃COO)₃ + 2 H_{2O }

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 + AgNO_{3 }

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 Tollen’s Test

Observation : a silver mirror is observed Equation : HCOOH + Ag_{2O }

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 HgCl_{2  Hg2}Cl₂ + CO₂ + 2 HCl Under excess methanoic acid, a black precipitate of mercury is observed

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

As discussed earlier, when methanoic acid dissolved in

KMnO₄ / H+_{, the purple colour of potassium manganate (VII) is}









→



KMnO₄ / H+_{, the purple colour of potassium manganate (VII) is}

decolourised while carbon dioxide and water is formed Equation : HCOOH + KMnO₄ / H+ _{ CO}

2 + H2O

Phosphorous pentachloride

, PCl₅

Unlike other carboxylic acid, when react with phosphorous pentachloride, it will not form acyl chloride

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



→

→



→



→



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 MnO} 4- + 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. H₂SO_{4  CO2} + CO + H₂O

Calcium chloride, CaCl₂

White precipitate is observed when reacted

Equation : Ca2+ _{+ C}

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

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 (0_C)

Ethanoyl chloride CH_-3COCl 78 51

Ethyl methanoate CH₃COOCH₃ 74 57

Butanal CH CH CH COH 72 76

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 C_nH_2n+1COCl.

The ending of alkyl group attached to COCl = ~noyl chloride

Acyl chlorides are colourless liquids with pungent smell. They are very

reactive compound
CH₃COCl
CH₃CH₂COCl
CH₃CH(CH₃)COCl C H COCl Ethanoyl chloride Propanoyl chloride 2-methylpropanoyl chloride Benzoyl chloride
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 nucleophilic attack

Name of reaction Reagent used and condition Equation Hydrolysis Water

propanoyl chloride water propanoic acid

Esterification Alcohol propanoyl chloride ethanol

ethyl propanoate

Formation of amide

Ammonia of amine

(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

CH COCl + H O CH COOH 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.

Acyl chloride Alcohol Ester HCl

CH₃COCl CH₃CH₂OH CH₃COOCH₂CH₃ HCl

When phenol react with benzoyl chloride, NaOH is used.

CH₃CH₂CH₂COCl CH₃CH₂CH₂OH HCl

CH₃C(CH₃)₂COCl CH₃OH HCl

CH₃CH₂CH₂COOCH₂CH₂CH₃ CH₃C(CH₃)₂COOCH₃

(C) Formation of amide

Acyl chloride form amides when reacted with ammonia, primary and

secondary amine

Acyl chloride Ammonia /

amine Amide HCl CH₃CH₂COCl NH₃ CH3CH2CONH2 HCl CH₃COCl CH₃CH₂NH₂ HCl CH₃CH₂CH₂COCl CH₃NH(CH₃) HCl 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 C_nH_2nO₂. In naming ester, the alkyl attached to alcohol is named where the carboxylic acid is named as its anion. Examples

Methyl propanoate Ethyl butanoate

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.

Propyl benzoate

7.9.1 Preparation of ester

Name of reaction

Reagent used

and condition Equation

Esterification by carboxylic acid with alcohol Alcohol catalysed by concentrated sulphuric acid Esterification by acyl chloride with alcohol Alcohol

propanoyl chloride ethanol

7.9.2 Chemical reaction of ester

Name of reaction

Reagent used

and condition Equation

Hydrolysis Diluted acidic solution Hydrolysis of ester Sodium hydroxide (NaOH)

Name of reaction

Reagent used

and condition Equation

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+ CH₃CH₂CH₂COOH CH₃CH₂CH₂OH + H₂O/ H+ + H₂O/ H+ 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.

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

+ NH_{3 CH3CH2CONH2} CH₃CH₂OH

+ NH₃

+ NH₃

CH₃OH

(C)

Reduction of ester

When reduced using strong reducing agent such as LiAlH

, ester will

formed alcohol as products

Ester LiAlH₄ Alcohol Alcohol

LiAlH₄ / H+ CH₃CH₂CH₂OH CH3CH2OH LiAlH₄ / H+ LiAlH₄ / H+ CH₂OH _CH 3OH 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.

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

Polyunsaturated Monounsaturated Fats / oil Saturated fat Polyunsaturated

fat Monounsaturated 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
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

C

H

CONH

. Amides are formed by replacing hydroxyl (–OH)

with amine (–NH

) group.

Naming of amide end with suffix “amide”. Examples of amides are

ethanamide

propanamide propanamide

butanamide

2

_amide

3

_amide

3

_amide

7.11

Preparation of amide

propanoyl chloride ammonia propylamide

Acyl chloride

with amine Ethanoyl chloride propylamine

Heating ammonium salt with ester Ammonium salt with ester ammonia ethanamide

Name of reaction

Reagent used

and condition Equation

Hydrolysis of amide

Diluted HCl

under reflux _{ethanamide ethanoic acid}

Dehydration of amide Distilled over phosphorous pentoxide, P₂O_{5 Propanamide propanitrile} Reaction with nitrous acid, HNO₂ Nitrous acid,

HNO₂ Propanamide nitrous acid

Name of reaction Reagent used and condition Equation 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

Step 1 : Formation of ammonium salt

Step 2 : Formation of carboxylic acid

Under acidic medium

Step 2 : Formation of carboxylic acid

Under alkaline medium

(way of

Step 1 : Formation of ammonium salt

Step 2 : Formation of carboxylate salt

(way of distinguish between amine

and amide)

(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



 →



 →









→









→



 →











→



 →



_

_

_

_→

(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

+ H

O

+ H

O

+ N

+ H

O

+ N

+ H

O

+ N

(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)

Amide

Bromine in sodium hydroxide

Amine Side products

hydroxide Br₂ + 4 NaOH Br₂ + 4 NaOH Br₂ + 4 NaOH

CH

CH

NH

CH

CH

CH

NH

(E)Reduction of amide

Amide can be reduced to become an amine using strong reducing

agent such as LiAlH

(lithium tetrahydridoaluminate) under dry ether.

The number of carbon after reduction remains the same

Amide Strong reducing

agent Amine Side products LiAlH₄ CH₃CH₂CH₂NH₂ + H₂O LiAlH₄ LiAlH₄ 3 2 2 2 2 CH₃CH₂CH₂CH₂NH₂ + H₂O + H₂O

RCOOH + H_{2O  RCOO}- _{+ H} 3O+

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+_{] = [ ] 0.0014 0.100 pH = 1.9}

3 = ×

× _{c or H O}+ K_a

alkene / C=C

hydroxyl group / -OH hydroxyl group / -OH

O CH₂ C C

KMnO₄ / H+ _{cold , dilute} oxidation

Chlorine gas under UV

C C H OH H HO X

Effervescences occur, which turn lime water chalky Effervescences occur, which turn lime water chalky CH₃COOH + NaHCO_{3  CH3}COO-Na+ _{+ H}

2O + CO3 Y

Silver mirror is observed

CH₂(OH)CHO + 2Ag+ _{+ 3OH-  CH}

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

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 = 3.5 010 . 0 10 26 . 1 ] [ ₃ = × 5 × × _{c or H O} + − K _a

ester

Dilute HCl under reflux

CH₃OH catalysed by H₂SO₄ under reflux CH2(Br)CH(Br)CH2(Br)

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 CO produced = 10 × 44 × 19/298 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