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 CnH2n+1COOH or sometimes CnH2nO2.
The naming of carboxylic acid end with –oic acid. Name Structure

Methanoic Ethanoic Propanoic Butanoic acid acid acid acid HCOOH

Pentanoic Hexanoic acid acid

CH3COOH C2H5COOH C3H7COOH C4H9COOH C5H11COOH

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

2-methylbutanoic acid

6-chloro4,4-dimethylhexanoic acid

3,5-dibromobenzoic acid

2-phenylbutanoic acid

3-methylbutanoic acid

3-ethyl-3methylpentanoic acid CH2CH3

2-ethyl-3methylpentanoic acid

Propanedioic acid or malonic acid

But-2-enedioic acid

Pentandioic acid 2,3,4trimetylpentanoic acid HOOCCH2CH2CH2COOH CH3 CH3

H3C CH2CCH2COOH CH3CHCHCHCOOH CH3

3-hydroxy-3methylpentanoic acid

CH3




Practice : Draw all isomers for carboxylic acid with formula C3H7COOH

O CH3CH2CH2C

OH

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

Boiling point increase Explanation : 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 Compound

propanol (C3H7OH)

CH3COOH

Butane (C4H10)

Chloroethane (C2H5Cl)

RMM

60

60

58

64.5

Boiling 78 117 4.4 21 point (oC) 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

[ RCOO − ][ H 3O + ] Ka = [ RCOOH ]

pK a = − lg K a

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 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- + 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

p-methylbenzoic 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. 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

Oxidation of 10 alcohol

Acidified KMnO4 or acidified K2Cr2O7 + heat

Propan-1-ol

Acidified KMnO4 or acidified K2Cr2O7 + heat

Propanal

Oxidation of aldehyde

Hydrolysis of nitrile

Equation

propanoic acid

Dilute sulphuric acid H2SO4 + H2O under reflux 2-methylbutylnitrile

Hydrolysis of ester

propanoic acid

Dilute HCl / NaOH with heat

2-methylbutanoic acid

7.3.2

Chemical reaction of carboxylic acid

Name of reaction

Reagent used and condition Alkali, NaOH or Na2O

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

Equation

Name of reaction

Reagent used and condition

Esterification

Alcohol catalysed by concentrated sulphuric acid

Phosphorous pentachloride(P Cl5) Formation of acyl chloride @ Thionyl chloride (SOCl2) Lithium Reduction – aluminium Formation of hydride ; alcohol LiAlH4 with dry ether

Equation

(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

CH3COOH

NaOH

CH3CH2COOH

K2O

CH3CH2CH2COOH

Mg(OH)2

Salt

Water

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 hydrogen gas is released. liberated, indicating ………… Salt

Hydroge n

Carboxylic Acid

Metal

CH3COOH

Zn

Zn(CH3COO)2

H2

CH3CH2COOH

Mg

Mg(CH3CH2COO)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 carbon dioxide gas is released. chalky, indicating ………..……… Carboxylic Acid

Metal carbonate

CH3CH(CH3)COOH

K2CO3

CH3CH2COOH

ZnCO3

Salt

Carbon Water dioxide

CH(CH3)2COO–K+

CO2

H2O

Zn(CH3CH2COO)2

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

Carboxylic Acid

Alcohol

Carboxylate ion

Alkyl

ester Name of ester : Alkyl carboxylate

Carboxylic Acid

Alcohol

Ester

Water

CH3COOH

CH3CH2OH

H2O

CH3CH(CH3)COOH

CH3CH2CH2OH

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

CH3CH2COOH

PCl5

CH3CH2COCl

CH3CH(CH3)COOH

SOCl2

CH3CH(CH3)CH2COOH

HCl

PCl5

Side product

Hydrogen chloride

+ POCl3

+ HCl

CH3CH(CH3)COCl

+ SO2

+ HCl

CH3CH(CH3)CH2COCl

+ H 2O

Acyl chloride

+ 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 dry ether → CH3CH2CH2OH + H2O CH3CH2COOH + LiAlH4   dry ether → CH3CH(CH3)CH2OH + H2O CH3CH(CH3)COOH + LiAlH4  

dry ether → C(CH3)3CH2OH + H2O CH3C(CH3)2COOH + LiAlH4  

+ LiAlH4 dry ether  →

7.3.3 Simple test for carboxylic acid Differentiate Chemical test

Sodium carbonate, Na2CO3 Carboxylic acid with other organic compound

Observation & Equation 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

Positive test : Carboxylic acid Dark red solution is obtained when FeCl3 is added to carboxylic acid. Equation : CH3COO- + FeCl3  Fe(CH3COO)3 + 3 ClIron (III) red solution chloride, FeCl3 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

Observation : White precipitate is 1st formed and eventually turn to silver Silver nitrate, Equation : HCOONa + AgNO3  AgNO3 HCOOAg (white ppt) + NaNO3 2 HCOOAg  2 Ag (silver) + CO2 Due to the presence of aldehyde as functioning group, it give positive test to Tollen reagent (silver complex) Tollen’s Test 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 : When heated with conc. H2SO4, methanoic acid dehydrated reaction with and produce carbon monoxide and water conc. conc. H SO4 sulphuric Equation : HCOOH 2 → CO + H2O acid, H2SO4 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

Unlike other carboxylic acid, when react with phosphorous Phosphorous pentachloride, it will not form acyl chloride pentachloride , PCl5 Equation : HCOOH + PCl5  CO + 2 HCl + POCl3

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

 → ∆ 2 HCOONa

Step 2 : add with sulphuric acid

 →

Na2C2O4 + H2

Na2C2O4 + H2SO4 ∆ H2C2O4 + Na2SO4




Reaction with ethanedioic acid Reaction with

Observation, Equation and explanation The purple colour of potassium manganate (VII) is reduced to Mn2+ which is pink colour according to the equation

Acidified potassium manganate (VII), Equation : 5 C2O42- + 2 MnO4- + 16 H+  2 Mn2+ + 8 H2O + + KMnO4 / H 10 CO2 Concentrated sulphuric acid, H2SO4

Calcium chloride, CaCl2

Similar to methanoic acid, dehydration occur when added to conc. H2SO4 Equation : H2C2O4 + conc. H2SO4  CO2 + CO + H2O 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 7.7.1


→

esters

→

amides

Physical properties of carboxylic acid derivatives

The boiling point of a few organic compounds are shown below Name Ethanoyl chloride Ethyl methanoate Butanal Butanone Propanamide

Molecular structure CH-3COCl CH3COOCH3 CH3CH2CH2COH CH3COCH2CH3 CH3CH2CONH2

Molecular mass 78 74 72 72 73

Boil point (0C) 51 57 76 80 213

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 reactive compound Ethanoyl chloride
CH3COCl Propanoyl chloride
CH3CH2COCl 2-methylpropanoyl chloride
CH3CH(CH3)COCl 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

Hydrolysis

Water

Esterification

Alcohol

Equation

propanoyl chloride

water

propanoyl chloride

ethanol

propanoic acid

ethyl propanoate

Formation of Ammonia of amide 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

CH3COOH

HCl

CH3CH(CH3)COCl

+ H2O

+ H2O

CH3CH(CH3)COOH

HCl

HCl

(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

CH3COCl

CH3CH2OH

CH3COOCH2CH3

HCl

CH3CH2CH2COCl

CH3CH2CH2OH

CH3CH2CH2COOCH2CH2CH3

HCl

CH3C(CH3)2COCl

CH3OH

CH3C(CH3)2COOCH3

HCl




Ester

HCl

When phenol react with benzoyl chloride, NaOH is used. HCl

(C)


Formation of amide

Acyl chloride form amides when reacted with ammonia, primary and secondary amine Acyl chloride

Ammonia / amine

CH3CH2COCl

NH3

CH3COCl

CH3CH2CH2COCl

Amide

HCl

CH3CH2CONH2

HCl

CH3CH2NH2

CH3CONHCH2CH3

HCl

CH3NH(CH3)

CH3CH2CH2CON(CH3)2

HCl

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 Methyl propanoate Ethyl butanoate Propyl benzoate Phenyl benzoate







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.

7.9.1 Preparation of ester Name of reaction

Reagent used and condition

Esterification by carboxylic acid with alcohol

Alcohol catalysed by concentrated sulphuric acid

Esterification by acyl chloride with alcohol

Equation

propanoyl chloride

ethanol

Alcohol

ethyl propanoate

7.9.2 Chemical reaction of ester Name of reaction

Reagent used and condition

Diluted acidic solution

Hydrolysis of ester Sodium hydroxide (NaOH)

Equation

Name of reaction

Reagent used and condition

ethyl propanoate Reaction Concentrated with NH3 ammonia

Equation

ammonia

propylamide

Lithium Reduction tetrahydrido- ethyl propanoate of ester aluminate (LiAlH4)

propan-1-ol

ethanol

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

+ H2O/ CH3CH2CH2COOH H+

+ H2O/ H+

+ H2O/ H+

Alcohol

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

+ NH3

Amide

CH3CH2CONH2

+ NH3

+ NH3

Alcohol

CH3CH2OH

CH3OH

CH3CH2CONH2

(C) Reduction of ester
When reduced using strong reducing agent such as LiAlH4, ester will formed alcohol as products Ester

LiAlH4

Alcohol

LiAlH4 / H+

CH3CH2CH2OH

LiAlH4 / H+

LiAlH4 / H+

CH2OH

CH3CH2CH2OH

Alcohol

CH3CH2OH

CH3OH

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 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 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 N-propylethanamide

N-phenylpropanamide

30 amide N-ethyl-N-methylbutanamide

N,N-dimethylbenzamide

7.11

Preparation of amide

Name of reaction

Reagent used and condition Acyl chloride with ammonia

Equation

propanoyl chloride

ammonia

propylamide

Reaction with amine Acyl chloride Ethanoyl chloride with amine

Heating ammonium salt with ester

propylamine

Ammonium salt with ester ammonia

ethanamide

Name of reaction

Reagent used and condition

Hydrolysis of amide

Diluted HCl under reflux

Distilled over Dehydration phosphorous of amide pentoxide, P2O5

Reaction with nitrous acid, HNO2

Nitrous acid, HNO2

Equation

ethanamide

ethanoic acid

Propanamide

Propanamide

propanitrile

nitrous acid

propanoic acid

Name of reaction

Reagent used and condition

Hoffmann degradation

Bromine in sodium hydroxide, NaOH

Equation

propanamide

ethylamine

Reduction of amide

Lithium tetrahydridoaluminate, 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

Overall :

Step 1 : Formation of ammonium salt

Step 2 : Formation of carboxylate salt Under alkaline medium (way of distinguish between amine and amide)

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

2O5 P →

LiAlH 4 →

P2 O 5

 →

H 2O , H +

  →

2O5 P →

LiAlH 4 →

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)




cold →

HNO2 + NaCl

When nitrous acid, HNO2, react with amide, carboxylic acid, nitrogen and water is produced Amide

Nitrous acid

Carboxylic acid

Side product

HNO2

+ H2O + N2

HNO2

+ H2O + N2

HNO2

+ 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)

Amide

Bromine in sodium hydroxide Br2 + 4 NaOH

Br2 + 4 NaOH

Br2 + 4 NaOH

Amine

Side products

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 Amide

Strong reducing agent

LiAlH4

LiAlH4

LiAlH4

Amine

Side products

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+] =

K a × c or [ H 3O + ] = 0.0014 × 0.100

pKa = - lg Ka ; pKa = 1.3

pH = 1.9

alkene / C=C

hydroxyl group / -OH

Aldehyde / -CHO

O CH2 O-

C

C

CH2

OH

KMnO4 / H+

cold , dilute oxidation

Chlorine gas NaOH

under UV reflux

H

H C

HO

C OH

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+] =K a × c or [ H 3 O + ] = pH = 3.5

1 . 26 × 10 − 5 × 0 . 010

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