AMINES

Derivatives of ammonia…

Properties Central N atom - sp3 hybridized

RNR bond angle < 109028’

because of lone pair bond pair

repulsion

Shape of the molecule-pyramidal

Basic in nature , bearing one lone

pair on N. Forms salts with acids

e- donating group

Can form single, double & triple

bond with C

NR

R

R

Classification

NH3 NH2R NHR2 NR3

NHRR' NRR'R''

ammonia 10 - amines 20 - amines 30 - amines

Simple amines

Mixed amines

20 - amines 30 - amines

R = alkyl/ aryl group

Nomenclature Common name IUPAC name

Rule : alkyl + amine = alkylamine Rule : alkane + amines = alkanamines

CH3NH2 Methylamine Methanamine

Isopropylamine Propan-2-amine

NH2-(CH2)6-NH2 Hexamethylenedimine Hexane-1,6-diamine (e –retained)

Trimethylamine N,N-Dimethylmethanamine

N,N-Dimethylethylamine N,N-Dimethylethanamine (one with more number of C atoms is given preference)

Allylamine Prop-2-en-1-amine (not prop-2-ene-1-amine)

Aniline Benzenamine

P-Bromoaniline 4-Bromobenzenamine

H2N

N

N

H2N

NH2

NH2Br

Physical properties

N-H bond is polar, because, electronegativity of N > H

Amines are comparable with alcohols in their physical properties

Since the electronegativity of N < O -----> N-H bond is less polar compared to O-H bond, implying amines are less polar compared to alcohols

So, amines are less effective in forming H-bond than alcohols.

So, boiling point (BP) of amines are less then alcohols

Methylamine Methanol

BP of amines < BP of alcohols

Comparing Between Amines

NR H

H

N RH

H

N

R

H

H N

H

H

R

10 - amines

NR H

R

N

R

R

H N

H

R

R

20 - amines

NR R

R

30 - amines

(no H-bond)

Extent of H-bonding

10 > 20 > 30

Boiling Point

n-butylamine

diethylamine

dimethylethylamine

2-methylbutane butanol

HONNH

H2N

BP

< < < <

Basic character of amines

Basic and nucleophilic because of the presence of lone pair on N

As it is basic, Amines + Acids ------> salts. This property can be used to purify amines

CH3 NH2Separate

NH3 ClCH3

HCl in H2O

soluble in water

insoluble in water

Separating funnel water layer containsamines

NH2

H2OOHR NH3R +

Kb pKb ==NH3R OH

NH2R- log Kb

pKb

strength of base

Structure-Basicity relationship of amines

A. Alkanamines >< ammonia

More basic an amine means,

More easily it denotes the lone pair / formed ammonium ion is more stabilized in the environment

NH2R NH3RH++

ease of donation of stability

N

R

H

H

10 - amines

N

R

H

H

20 - amines

NR H

R

30 - amines

Inductive effect

NH3 < 10 < 20 < 30

Basic character

HaminesH+

R

R

>

>

> >

> >

ingas

phase

N

H

H

HH

ammonia

N

R

H

H

10 - amines

N

R

H

H

20 - amines

NR H

R

30 - amines

Inductive effect

10 < 20 < 30

Basic character

H

amines

H+/H2O

R

R

>

>

> >

>

>

in aqueous phase

OH2

OH2

H2O

OH2

OH2 OH2

Extent of H-bonding

10 > 20 > 30

stability of ammonium ion& basic character

contradicting +steric effect depending on the

size of R, allowing H+ to reach

lone pair

Above three factors together decide the basic character of amines.Whatever dominates, will decide the property of an amine

(C2H5)2NH > (C2H5)3N > C2H5NH2 > NH3(CH3)2NH > CH3NH2 > (CH3)3N > NH3

+

B. Arylamines >< ammonia

H+

NH2 NH2 NH2 NH2 NH2

NH3 NH3

> 5 resonance structures, more stabilized

2 resonance structures, less stabilized

stab

i litydec

reas

es

* So, pKb value for aniline is high

* Means, aniline is less basic

* observed that it is less basic

than ammonia

> lone pair on N is less available becauseof delocalization into the ring

NH2 NH2 NH2 NH2

NO2

OCH3

arrange in the increasingorder of basic character

1 2 3 4

NH2

NO2

NH2 NH2NH2

OCH3

< < <

3. From nitriles

4. From amides

C NR

H+ or OH-

H2Oacid or basehydrolysis

Preparation of Amines

CNH2R

OH2

CNH2R

H2C

NH2H3CC

NH2H3C

O

C NH3COR

10-Amines

nitro compd1. Fromnitro compd

NO2NH2 NO2

H2/Pd (Ni, Pt)

Ethanol

Sn/HCl

Fe/HCl

FeCl2

hydrolysed

Fe(OH)3

or

(Regeneration of catalyst)

10-Amines

5. Gabriel phthalimide synthesis

O

O

N

O

O

NK

O

O

N

O

O

H R

ONa

ONa+R-NH2

KOH RX

NaOH(aq)

10-Amines

phthalimide

6. Hof fmann bromamide degradation reaction

CNH2R

O

RCONH2 + Br2 + 4NaOH RNH2 + Na2CO3 + 2NaBr + 2H2O

Br2 OH-

-Br-

RNH2Na2CO3

CNH

R

O

Br-HBr CNR

O

Br CNR

O

Br-H+

O C N R

H2O+

R'OHCNH

R'

O

R Ex:(CH3CONH2 ------> CH3NH2)

Ex:

10-Amines

2. From alkyl halides

H3N NH3XR X R NaOH NH2R+ + H2O

Cleavage of R-X bond brought about by NH3 -----> Ammonolysis

+ NaX

RNH2 R2NH R3N R4NRX RX RX

10 20 30 ammonium salt

** Excess of NH3 gives 10 - amine as major product

** or else ammonolysis gives mixture of products

** RI > RBr > RCl order of reactivity

LiAlH4 or H2/Ni

1.LiAlH4

2. H2O

From nitriles

CNH2H3C

C NH3C

Hof fmann bromamide degradation

O

NH2H3C

H2

C NH2H3C

(2)

(1)

(2)

(2)

(no. of C atoms)(no. of C atoms)Reactants

(no. of C atoms)

>

>(3)

(2)

(3)

(3)NH2

O

NH2

NH2N

Hof fmann bromamide degradation to reduce the length of amine chain by 1 carbon

Reactions of Amines

benzenesulphonyl chloride/Hinsberg's reagent

with benzoyl chloride(not benzyl chloride)CH3

CH2

N HH CCl

O

S Cl

O

O

R C Cl

O

+ +

+

S

O

O

CH3

H2C

HN C

O

H3CH2C

HN

R C

O

CH3

H2C

HN

Base

N-Ethylbenzenesulphonamide N-Ethylbenzamide

-HCl

-HCl

-HCl

N-Ethylalkanamide

Base

Base

(acidic proton of e-

withdrawing groups)

+

acet

ican

hydr

ide

C CH3

O

C

H3C

OO

H2C CH3

C

H3C

ONH

H3C

COH

O

N-E

thyl

etha

nam

ide

** base used in the above reactions should be stronger than amines

** similarly, secondary amines react

** tertiary amines can not react in this f ashion as it does not have replaceble proton

** both aliphatic and aromatic amines reacts with the above set of reactants

+CH

Cl3

3KOH

+

H3CH2C N C

3H2O

3KCl+

isocyanides orcarbylamines

H+

NH2NH2 NH2 NH2

NH3NH3

ANILINIUM ION

** e--donating to the ring

** ortho, para directing for

the incoming E+

** e-- withdrawing from the ring

** meta directing for the

incoming E+

electrophile - E+

electrophile - E+

NH2

NH3

E

E

NH2

E

NH2

E

EE

(trisubstitution is because of the

high reactivity of NH2 for E+)

OOO

pyridine

HN

electrophile - E+

O

activity

reduction x

acetanilide

HN

O

HN

O

E

NH2

E

Electrophilic substitution on Aniline

Electrophilic substitution on Aniline

NH2HN

O + 3Br2

NH2

BrBr

Br

HN

O

Br

+ H2OBr2CH3CO2H

NH2

Br

H+ or

OH-

HN

O

NO2

H2N

NO2

H+ or

OH-

HNO 3, H 2

SO 4

288K

HNO3 , H

2 SO4288K

NH2

NO2

NH2 NH2

NO2

NO2

+ +

(51%) (47%)(2%)

H2SO4

NH3 HSO4 NH2 NH3

SO3H SO3

Zwitter ion

Friede

l-Cra

ftsre

actio

n

AlC

l 3

X

NH2

AlCl3

Lewis acid + base

Diazonium Salts Ar N N X

N N N N N N N N

diazonium salts formed by aliphatic primary amines are not stable and that of

aromatic primary amines are stable below 50 C because of the resonance structure

NaNO2 HCl+

HNO2

NH2

+

Cl

(0-50C)

Reactions

N N X

CuCl/HCl

CuBr/HBr

CuCN/KCN

PhCl

PhBr

PhCN

+ N2

N2

N2

+

+

Sandmeyer reaction

Gatterman reaction

Cu/HCl

Cu/HBr

PhCl

PhBr

+ N2

N2+

+

+

CuX

CuX

PhI

PhF

+ N2

N2+PhN NBF4-

KI

HBF4

H3PO2 + H2O

CH3CH2OH

PhH + N2 + H3PO3 + HCl

PhH + N2 + CH3CHO + HCl

H2O PhOH + N2 + HCl

NaNO2

Cu,NO2

involving displacement of N2involving retention of diazo group

OH

NH2

OH-

OH-

N N NH2

N N OH

Yellow dye

Orange dye