chemistry form 6 sem 3 08

8/13/2019 Chemistry Form 6 Sem 3 08

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CHEMISTRY FORM 6

ORGANIC CHEMISTRYCHAPTER 8 : AMINE


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9.1 Introduction and nomenclature

Amines are organic compounds with functioning group NH2

(aminO)

The naming of amine depends on the classification of amine. Tablebelow shows different class of amine and their naming

Classificati

on Example

CH3CH2CH2NH2

Primary

amine

propylamine 2-methylpropylamine3-ethyl-1-methylpentylamine

cyclopentylamine4,4-dimethyl

cyclohexylaminePhenylamineor Aniline


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Secondary

amine

Tertiary

N-ethylpropylamineN-propylaniline

N-cyclopentylcyclohexylamine

amine

Quaternary

salt

N-ethyl-N-methylpropylamine

N,N-diphenylmethylamine

N,N-dipropylethylamine

Ammonium chloride Tetramethylammoniumbromide

Tetraethylammoniumhydroxide


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9.1 Physical properties of amine

Boiling point of increasing in homologous series

Amine CH3NH2 C2H5NH2 C3H7NH2 C4H9NH2 C5H11NH2Boiling point

oC4 17 52 83 106

Boiling pointtrend 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

Classification of

aminePrimary amine Secondary amine Tertiary amine

Example (same

RMM)CH3CH2CH2NH2 CH3CH2NHCH3 (CH3)3N

Boiling point (oC) 52 34 2

Explanation :

er aa s orces caus ng o ng po n ncrease.

Amine can form hydrogen bond between molecules. Straight chain molecule hasa larger total surface area compare to a branched chain molecule. Hence, greater the total

surface area exposed, greater the Van Der Waals forces, higher the boiling point. However,tertiary amine cannot form hydrogen bond, so their boiling point decrease significantly.


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Organic CH3CH2CH2CH3 CH3CH2CH2NH2 CH3CH2CH2OH CH3COOH

RMM 58 57 60 60

Boiling point oC 4 52 78 118

Boiling point of different organic compounds

Ethanoic acid has 2 hydrogen bond within their molecules, so their hydrogen bond

is the strongest. Both propylamine and propan1-ol has hydrogen bond, but propan-1-ol has a stronger hydrogen bond since O is more electronegative than N. Butaneis a non-polar molecule, which is held by weak Van DerWaals forces

Amine CH3NH2 C2H5NH2 C3H7NH2 C4H9NH2 C5H11NH2

Solubility trend

Solubility DEcreaseExplanation

o u y o am ne

methylamine, ethylamine and propylamine are completely miscible inwater as they can form hydrogen bond with water. However, the LONGER the ALKYLGROUPS ATTACHED, molecule become MORE HYDROPHOBIC. As a result,

HYDROGEN BOND BECOME LESS SIGNIFICANT and cause the solubility decrease.


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C) Basicity of amine

Amine is a weak base. When dissolve in water, it undergoes

partial dissociation where

bbb KpKOHRNH

K lg]][[ 3

==

+

The pKb of some amine is given in the table below2

Amine CH3NH2 C2H5NH2 C3H7NH2 CH3CH2NHCH3

pKb 3.42 3.27 3.03 2.88

(CH3)3N

2.64 9.41 9.58


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All alkyls are electron donating group, which donate electron

density to N in NH2, making N to be more readily to accept

proton. Hence, equilibrium shift more to right, increasing the

basicity. Longer the alkyl chain, greater the electron donatingeffect, greater the basicity.

Basicity increase from 10 amine < 20 amine < 30 amine. This is due to, the

more the alkyl group surrounding N, greater the electron donating effect,

where N has large electron density and are more readily to accept proton,

causing equilibrium to shift more to right, increasing the basicity of amine.


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phenylamine is a weaker base compare to alkyl amine, due

to the benzene ring is an electron withdrawing group. As a

result, N in amine has lesser electron density and is less

readily to accept proton (conversely more readily to donate

proton) which caused equilibrium shift more to left. This

results the basicity of phenylamine is lesser than alkyl

amine. When a ring activator is bonded to phenylamine, ita

activate further the ring and caused the ring to be morereadily to accept proton, hence increase the basicity.

Conversely, if a ring deactivator is bonded to phenylamine, it

deacticate the ring and caused benzene to be less readily

to accept proton, decreasing the basicity


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9.2 Preparation of amine

Name ofreaction

Reagent

used andcondition

Equation

Alkylation

ofhaloalkane

Concentrated

NH3 1-bromopropane conc. propylamine

Ammonia

Reductionof nitrile

aluminiumtetrahydride

LiAlH42-methylbutylnitrile 2-methylbutylamine

Reduction

of amide

Lithiumtetrahydrido-

aluminate,

LiAlH4propanamide propylamine


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9.2.1 Chemical reaction of amine

Name of

reaction

Reagent used

and condition Equation

Reaction

with mineral

acid

Mineral acid

such as HCl ;

H2SO4

NitrosationHNO2 under +CH3CH2CH2 NH2 O N OH

of amine

condition

Reaction

with acylchloride,

RCOCl

RCOCl,acyl chloride

CH3CH2CH2OH + H2O + N2


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(A) Reaction with mineral acids : Formation of salts

Amine dissolves in aqueous solution of mineral acid to form salt of

ammonium. Example

Class of amine Example Mineral acid Salt

CH3CH

2NH

2HCl CH

3CH

2NH

3

+Cl

(CH3CH2)2NH HCl

Primary amineSecondary amine

Tertiar amine

(CH3CH2)2NH2+Cl

+

The amine salt form is white crystalline solid dissolve readily in water

When dissolve in alkaline solution, amine is form back

CH3CH2NH3+Cl (aq) + OH (aq) CH3CH2NH2 (aq) + H2O (l)+ Cl (aq)


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(B) Reaction of amine with nitrous acid

Nitrous acid (or nitric (III) acid) is unstable. It can be prepared by reaction of sodium

nitrite and hydrochloric acid Equation : NaNO2 (s) + HCl (aq) NaCl (aq) + O=NOH (aq)

The organic products formed from the reaction between nitrous acid and amine

depend on 2 factors Class of amine used Condition of the reaction

When aliphatic primary amine reacts with nitrous acid, nitrogen is evolved rapidlyand alcohol is roduce as ma or roduct alon with some side roduct such as alkene

and in some case, ether. The reaction of nitrous acid follows the mechanism below


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Primary amine :

Amine act as nucleophile and attack nitrosyl cation, the following mechanism of

reaction take place.

diazonium ion The reaction after the formation of diazonium ion is complex. Depend on the

condition of the reaction, it form various organic compound such as alcohol oralkene. Exam le :

Secondary amine

Secondary amine reacts with nitrous acid (nitrosyl cation) under room condition toform nitrosoamine. Unlike primary amine, theres no nitrogen gas evolve. Example

Nnitrosoamine


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Tertiary amine

Tertiary amine dissolve readily in acidic solution of nitrous acid to form salt

according to the equation

(C) Reaction with acyl chloride (refer Chap 8.4)

When acyl chloride reacts with primary amine, it will form a secondary amide

When react acyl chloride with a secondary amine, it will form a tertiary amide

Acyl chloride will not be acylated as it does not has a hydrogen atom tobe substituted.


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9.3 Aromatic amine

The simplest form of aromatic amine is phenylamine, which is better known

as aniline

Some of the common naming of aromatic amines are shown below

HN

aniline p-nitroaniline o-methylaniline N-methylaniline

diphenylamine

N-ethyl-N-

methylaniline N,N-diethylaniline phenylmethylamine


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9.3.1 Preparation of aniline

Aniline can be prepare by using nitrobenzene. Reagent : conc. HCl catalysed

by tin, Sn.

9.3.2 Chemical reaction of aniline

1. Reaction with acid : the basic properties of aniline

Aniline is considerably weak acid as the pKb = 9.3

This is due to the electron withdrawing effect of the benzene, causes theelectron density of nitrogen decrease. When this occur, nitrogen are more

readily to donate proton rather than accept and equilibrium shift more to theleft (Kb decrease)

Though, aniline is able to react with acid by accepting the H+ from acid andform salt


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Aniline Acid Salt

HCl

H2SO4

H2SO4

HNO3

Salts of aniline are colourless, crystalline solid and mostly are soluble in water.When react with alkali, it give back the phenyl amine with salt and water


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2. Reaction of aniline with haloalkane

If aniline is reacted with iodomethane (CH3I) under ethanolic, a secondary amine is

first formed and eventually turns out to become salt

If excess haloalkane is used, the reaction will further to form a tertiary amine andquaternary salt.

3. Reaction of aniline with acyl chloride (Chapter 8.4)

This is one of the method use to prepare amide as discussed earlier. When acylchloride react with amine, a secondary amide is formed


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When a secondary amine reacts with acyl chloride, it will form a tertiary amide.

Tertiary amine will not react with acyl chloride as theres no H substitute out

4. Reaction of aniline with nitrous acid

Similar to the reaction of nitrous acid with alkyl amine, aniline react with theelectrophile nitrosyl cation where the formation of ion follow the mechanism below

When aniline attacks the electrophilic nitrosyl cation, it form benzenediazoniumion.


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Benzenediazonium chloride formed is unstable and tends to react with othersubstances. Diagram below shows the type of reaction that the benzenediazonium

can undergoes


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5. Formation of dyes by coupling reaction

The reaction of forming azo dye is via coupling reaction. Diazonium ion react with

benzene attached with strong ring activate group, under alkaline condition, to givebright colouration of azo dye. Strong ring activate group direct at ortho-paraposition.

Benzenediazonium chloride phenol 4-hydroxyphenylazobenzene

en react wit -nap t o , it orm a rig t scar et azo ye

When react with another aniline, it form an orange-red precipitate dye.


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9.4 Chemical tests for aniline

(1) Reaction with bromine

Similar to phenol, aniline is a strong ring activate group. So, when aniline isreacted with aqueous bromine solution, it forms a white precipitate.

2 Reaction with sodium chlorate I NaClO

When aniline is added to NaClO, a purple colouration is obtained

(3) Reaction with phenol under alkaline solution

As discuss earlier, when aniline is react phenol under NaOH, a yellow

precipitate is observed.


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10.1 Introduction

Amino acid has the general formula of NH2 CHR COOH.

From the general above, we can tell that there are 2functioning groups of NH2 (amine) and COOH

(carboxylic acid). There are 22 types of amino acids and almost all

naturally occurring amino acids are -amino acid

The terms - mean both NH2 and COOH areattached at the same C. Considering COOH act asthe functioning group, -amino acid has the generalnaming as 2-aminocarboxylic acid

The simplest form of amino acid is called glycine (2-aminoethanoic acid)

All amino acids are optical active (except glycine) asthey have 4 different functioning groups (chiral carbon

atom).


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Acidic amino acid Neutral amino acid Basic amino acid

H2N CH CCH2

OH

O

CH2

The number of COOH is

more than NH2


equal to the number of

NH2


less than NH2

C

OH

O


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Since amino acid has both acidic (COOH) and basic (NH2) fuctional

group, hence amino acid undergoes 3 types of chemical reaction : reactions characteristic of the amino group

reactions characteristic of the carboxylic group

reaction due to the presence of both group Because of both (COOH) and (NH2) group, it makes amino acid very

soluble in water. Neutral amino acid such as alanine and glycine are slightlym sc e on e ano an epoxye an.

This is due to amino acid exist as polar ion.amino acid exist as azwitterions, which carries both positive and negative charge in its

molecule. A zwitterions is formed when COOH donated its proton to

NH2, according to


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Condition Equation Charge

AcidicPositive

charge

Neutral Zwitterions

BasicNegative

charge


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Isoelectric point the pH at which amino acid has a net charge of zero.

Amino acids with one COOH and one NH2 have isoelectric points in thepH range 5.5 6.5

Acidic amino acid (eg : aspartic acid and glutamic acid) has lower isoelectric

point (lower pH value) while basic amino acids (eg : lysine and arginine) havehigher isoelectric point (higher pH value)


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10.2 Chemical Properties of Amino acid

10.2.1 Preparation of amino acid

Name of

reaction

Reagent used

and conditionEquation

Reaction of

ammonia with

-halo

Concentrated

ammonia


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10.2.2 Formation of peptide lingkage

The reaction which link 2 amino acids together is a condensation reaction wherewater is given off and formed a dipeptide. Peptide link is a secondary amide groupwhere the C- from one amino acid is linked to the N of another amino acid.

If 3 amino acids joined together, the product is .. When a lot ofamino acids join together, the product is a .. When the many chain ofpeptide formed ......


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10.2.3 Hydrolysis of Protein

Protein could be broken into its constituent amino acids by heating underreflux with aqueous NaOH or dilute H2SO4 via hydrolysis reaction.

Hydrolysis of protein can be completely or partially hydrolyse.

Complete hydrolysis of protein gives the number and relative amount ofamino acids, but does not provide the information of the order of how they

joined together (the sequence of R)


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10.3 Chemical Test for amino acid

Aminoethanoic acid (NH2CH2COOH) gives the following reactions : It liberates CO2 when treated with Na2CO3 and NaHCO3.

Form dark red solution when treated with neutral iron (III) chloride solution.

It gives a deep blue solution when treated with copper (II) solution due to thecopper (II) complex.

10.4 Function of Proteins

proteins are ma e up o ong c ains o amino aci s.

Each protein is determined by its amino acid sequence (which ranges from 44amino acids in the hormone insulin to giant molecules with more than 50,000amino acids).

Proteins are essential in living systems - animals, plants and micro-organisms. Proteins are responsible for growth, repair and maintenance of the body.


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Types of

proteins

Function

structuralproteins

provide the framework which defines the size andshape of cells

e.g. elastin (in ligament)

a -keratins (in skin, hair, nails)collagen (in connective tissue, tendon, cartilage)

produces mechanical force and movement,

e.g. actin and myosin

transportproteins

move metabolites around the cell or around the wholeorganism

e.g. haemoglobin which transports oxygen in blood

Somehormones

control the level and type of cell activity, e.g. insulin which regulates glucose metabolism

Enzymes catalyse metabolic processes which produce energy,

build up new cell structures and destroy old ones


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10.5 Protein Structures

The structure of proteins are categorised into four levels of complexity:> primary (1) structure > secondary (2) structure

> tertiary (3) structure > quaternary (4) structure

10.5.1 Primary (1) structure The primary (1) structure of a protein shows the order (or sequence) of amino

acids in a protein chain


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By convention, amino acid sequence is written with free NH2 on left &

free COOH on right. The primary structure includes any covalent cross-linkages, e.g. SS

bonds.

The primary structure determines -what the protein is, how it folds, and itsfunction.

The sequence of R groups determines whether the protein chain will

1. coil with hydrogen bonding between N-H and C=O groups withineach chain (helix), or

2. fold with hydrogen bonds formed between two protein chains (pleated sheet).


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Conc. HNO3

catalysed by H2SO

4under reflux

Conc. HCl under tin

C6H5NH2 + HCl C6H5NH3Cl

Phenylamine is a weaker base than ammonia

Phenyl is an electron withdrawing group, which decrease the electron density of N

Making N more readily to donate proton


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Sodium nitrite, NaNO2 + hydrochloric acid, HCl

0 5 0C

Sodium hydroxide


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Iodine in Sodium hydroxide

Yellow precipitate is formed

No changes occur

CH3CH(OH)COOH + I

2+ OH- -OOCCOO- + CHI

3+ 3 HI

J (chloropropanoic acid) is stronger acid than propanoic acid

Due to the inductive effect caused by Cl in the carboxylic acid

CH3CH(NH2)COOH + NaOH CH3CH(NH2)COONa + H2O


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peptide linkage / peptide bond / amide

C6H5COCl

HCl or H2SO4 or NaOH (aq) + heat/reflux


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Electrophilic aromatic substitution reaction

Conc. HNO3 catalysed by conc. H2SO4 under reflux

NO2+ + H

NO2H+


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reduction

Conc. HCl under tin

PCl5 under room temperature

amide


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amide

NH2 CH C

CH2

O

CH CH3CH3

NH CH C

CH2

OH

O

OH


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2 Ag+ + HOPhNH2 + 2 OH- O==O + H2O + NH3 + 2 Ag

Rodinol is a weaker base than ammonia, since rodinol has an electron

withdrawing benzene ring to reduce the basicity.


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HO NH2

BrBr

Br Br

Conc. HNO3 in conc. H2SO4 under reflux

reduction

Conc. HCl in tin


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Phenol and amide

CH3COCl


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Bromine water

amide


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NaNO2 in HCl under 0-50C

chemistry form 6 sem 3 08

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