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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
The number of COOH is
equal to the number of
NH2
The number of COOH is
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