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20152015 SPECIFICATIONSSPECIFICATIONS

AN INTRODUCTION TOAN INTRODUCTION TO

THE CHEMISTRYTHE CHEMISTRYOF AMINESOF AMINES

INTRODUCTION

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AMINESAMINESKNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING

CONTENTS

• Prior knowledge

• Structure and classification

• Nomenclature

• Physical properties

• Basic properties

• Nucleophilic properties

• Amino acids

• Peptides and proteins

• Amides

• Check list

AMINESAMINES

Before you start it would be helpful to…

• know the functional groups found in organic chemistry

• know the arrangement of bonds around atoms

• recall and explain nucleophilic substitution reactions

AMINESAMINES

STRUCTURE & CLASSIFICATIONSTRUCTURE & CLASSIFICATION

Structure Contain the NH2 group

Classification

primary (1°) amines secondary (2°) amines

tertiary (3°) amines quarternary (4°) ammonium salts

Aliphatic methylamine, ethylamine, dimethylamine

Aromatic NH2 group is attached directly to the benzene ring (phenylamine)

R N:

H

H

R N:

R

H

R N:

R

R

R

+R N R

R

NOMENCLATURENOMENCLATURE

NomenclatureNamed after the groups surrounding the nitrogen + amine

C2H5NH2 ethylamine

(CH3)2NH dimethylamine

(CH3)3N trimethylamine

C6H5NH2 phenylamine (aniline)

PREPARATIONPREPARATION

Amines can be prepared from halogenoalkanes

Reagent Excess, alcoholic ammonia (WHY USE EXCESS?)

Conditions Reflux in excess, alcoholic solution under pressure

Product Amine (or its salt due to a reaction with the acid produced)

Nucleophile Ammonia (NH3)

Equation C2H5Br + NH3 (alc) ——> C2H5NH2 + HBr ( or C2H5NH3+Br¯ )

PREPARATIONPREPARATION

Amines can be prepared from halogenoalkanes

Reagent Excess, alcoholic ammonia (WHY USE EXCESS?)

Conditions Reflux in excess, alcoholic solution under pressure

Product Amine (or its salt due to a reaction with the acid produced)

Nucleophile Ammonia (NH3)

Equation C2H5Br + NH3 (alc) ——> C2H5NH2 + HBr ( or C2H5NH3+Br¯ )

WHY USE EXCESS AMMONIA?

Ammonia attacks halogenoalkanes because it has a lone pair and is a nucleophile.

The amine produced also has a lone pair C2H5NH2 so can also attack a halogenoalkane;

this leads to the formation of substituted amines. Using excess ammonia ensures that all the halogenoalkane molecules react with theammonia before having the chance to react with any amines produced.

PHYSICAL PROPERTIESPHYSICAL PROPERTIES

The LONE PAIR on the nitrogen atom in 1°, 2° and 3° amines makes them ...

LEWIS BASES - they can be lone pair donors

BRØNSTED-LOWRY BASES - they can be proton acceptors

RNH2 + H+ ——> RNH3+

NUCLEOPHILES - provide a lone pair to attack an electron deficient centre

PHYSICAL PROPERTIESPHYSICAL PROPERTIES

Boiling point Boiling points increase with molecular mass

Amines have higher boilingpoints than correspondingalkanes because of theirintermolecular hydrogen bonding

Quarternary ammonium

salts are ionic and exist as salts

Solubility Lower mass compounds aresoluble in water due to hydrogenbonding with the solvent.

Solubility decreases as themolecules get heavier.

Soluble in organic solvents.

BASIC PROPERTIESBASIC PROPERTIES

Bases The lone pair on the nitrogen atom makes amines basic;

RNH2 + H+ ——> RNH3+ a proton acceptor

Strength depends on the availability of the lone pair and its ability to pick up

protons

• the greater the electron density on the N, the better it can pick up

protons

• this is affected by the groups attached to the nitrogen

BASIC PROPERTIESBASIC PROPERTIES

Bases The lone pair on the nitrogen atom makes amines basic;

RNH2 + H+ ——> RNH3+ a proton acceptor

Strength depends on the availability of the lone pair and its ability to pick up

protons

• the greater the electron density on the N, the better it can pick up

protons

• this is affected by the groups attached to the nitrogen

electron withdrawing substituents (benzene rings)decrease basicity as the electron density on N islowered and the lone pair is less effective

C6H5 N:

H

H

BASIC PROPERTIESBASIC PROPERTIES

Bases The lone pair on the nitrogen atom makes amines basic;

RNH2 + H+ ——> RNH3+ a proton acceptor

Strength depends on the availability of the lone pair and its ability to pick up

protons

• the greater the electron density on the N, the better it can pick up

protons

• this is affected by the groups attached to the nitrogen

electron withdrawing substituents (benzene rings)decrease basicity as the electron density on N islowered and the lone pair is less effective

electron releasing substituents (CH3 groups)increase basicity as the electron density isincreased and the lone pair is more effective

CH3 N:

H

H

C6H5 N:

H

H

BASIC PROPERTIESBASIC PROPERTIES

Measurement the strength of a weak base is depicted by its pKb value

the smaller the pKb the stronger the base

the pKa value can also be used;

it is worked out by applying pKa + pKb = 14

the smaller the pKb, the larger the pKa.

Compound Formula pKb Comments

ammonia NH3 4.76

methylamine CH3NH2 3.36 methyl group is electron releasing

phenylamine C6H5NH2 9.38 electrons delocalised into the ring

strongest base methylamine > ammonia > phenylamine weakest base smallest pKb largest pKb

CHEMICAL REACTIONS - CHEMICAL REACTIONS - WEAK BASESWEAK BASES

Water Amines which dissolve in water produce weak alkaline solutions

CH3NH2(g) + H2O(l) CH3NH3+(aq) + OH¯(aq)

Acids Amines react with acids to produce salts.

C6H5NH2(l) + HCl(aq) ——> C6H5NH3+Cl¯(aq) phenylammonium

chloride

This reaction allows one to dissolve an amine in water as its salt.

Addition of aqueous sodium hydroxide liberates the free base from its salt

C6H5NH3+Cl¯(aq) + NaOH(aq) ——> C6H5NH2(l) + NaCl(aq) +

H2O(l)

CHEMICAL REACTIONS - CHEMICAL REACTIONS - NUCLEOPHILICNUCLEOPHILIC

Due to their lone pair, amines react as nucleophiles

Reagent Product Mechanism

haloalkanes substituted amines nucleophilic substitution

acyl chlorides N-substituted amides addition-elimination

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION

HALOALKANES

Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.

C2H5NH2 + C2H5Br ——> HBr + (C2H5)2NH diethylamine, 2° amine

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION

HALOALKANES

Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.

C2H5NH2 + C2H5Br ——> HBr + (C2H5)2NH diethylamine, 2° amine

(C2H5)2NH + C2H5Br ——> HBr + (C2H5)3N triethylamine, 3° amine

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION

HALOALKANES

Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.

C2H5NH2 + C2H5Br ——> HBr + (C2H5)2NH diethylamine, 2° amine

(C2H5)2NH + C2H5Br ——> HBr + (C2H5)3N triethylamine, 3° amine

(C2H5)3N + C2H5Br ——> (C2H5)4N+ Br¯ tetraethylammonium bromide

a quaternary (4°) salt

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION

HALOALKANES

Amines are also nucleophiles (lone pair on N) and can attack halogenoalkanes to produce a 2° amine. This too is a nucleophile and can react further producing a 3° amine and, eventually an ionic quarternary ammonium salt.

C2H5NH2 + C2H5Br ——> HBr + (C2H5)2NH diethylamine, 2° amine

(C2H5)2NH + C2H5Br ——> HBr + (C2H5)3N triethylamine, 3° amine

(C2H5)3N + C2H5Br ——> (C2H5)4N+ Br¯ tetraethylammonium bromide

a quaternary (4°) salt

Uses Quarternary ammonium salts with long chain alkyl groups are used as cationic surfactants in fabric softening e.g. [CH3(CH2)17]2N+(CH3)2 Cl¯

AMINO ACIDSAMINO ACIDS

Structure Amino acids contain 2 functional groups

amine NH2

carboxyl COOH

They all have a similar structure - the identity of R1 and R2 vary

H2N C COOH

H

H

H2N C COOH

CH3

H

H2N C COOH

R2

R1

AMINO ACIDS – AMINO ACIDS – OPTICAL ISOMERISMOPTICAL ISOMERISM

Amino acids can exist as optical isomersIf they have different R1 and R2 groups

Optical isomers exist when a moleculeContains an asymmetric carbon atom

Asymmetric carbon atoms have fourdifferent atoms or groups attached

Two isomers are formed - one rotates planepolarised light to the left, one rotates it to the right

Glycine doesn’t exhibit optical isomerism asthere are two H attached to the C atom

H2N C COOH

CH3

H

H2N C COOH

H

H

GLYCINE2-aminoethanoic acid

AMINO ACIDS - AMINO ACIDS - ZWITTERIONSZWITTERIONS

Zwitterion • a dipolar ion

• has a plus and a minus charge in its structure

• amino acids exist as zwitterions

• give increased inter-molecular forces

• melting and boiling points are higher

H3N+ C COO¯

R2

R1

• amino acids possess acidic and basic properties

• this is due to the two functional groups

• COOH gives acidic properties

• NH2 gives basic properties

• they form salts when treated with acids or alkalis.

H2N C COOH

R2

R1

AMINO ACIDS - AMINO ACIDS - ACID-BASE PROPERTIESACID-BASE PROPERTIES

AMINO ACIDS - AMINO ACIDS - ACID-BASE PROPERTIESACID-BASE PROPERTIES

Basic properties:

with H+ HOOCCH2NH2 + H+ ——> HOOCCH2NH3+

with HCl HOOCCH2NH2 + HCl ——> HOOCCH2NH3+ Cl¯

Acidic properties:

with OH¯ HOOCCH2NH2 + OH¯ ——> ¯OOCCH2NH2 + H2O

with NaOH HOOCCH2NH2 + NaOH ——> Na+ ¯OOCCH2NH2 + H2O

PEPTIDES - PEPTIDES - FORMATION & STRUCTUREFORMATION & STRUCTURE

Amino acids can join together to form peptides via an amide or peptide link

2 amino acids joined dipeptide

3 amino acids joined tripeptide

many amino acids joined polypeptide

a dipeptide

PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS

Peptides are broken down into their constituent amino acids by hydrolysis

• attack takes place at the slightly positive C of the C=O

• the C-N bond is broken

• hydrolysis with water is very slow

• hydrolysis in alkaline/acid conditions is quicker

• hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts

with HCl NH2 becomes NH3+Cl¯

H+ NH2 becomes NH3+

NaOH COOH becomes COO¯ Na+

OH¯ COOH becomes COO¯

PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS

Peptides are broken down into their constituent amino acids by hydrolysis

H2N C CO

CH3

H

NH C CO

H

H

NH C COOH

CH3

CH3

Which amino acids are formed?

PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS

Peptides are broken down into their constituent amino acids by hydrolysis

H2N C CO

CH3

H

NH C CO

H

H

NH C COOH

CH3

CH3

CH3

H

H2N C COOH

H

H

H2N C COOH

CH3

CH3

H2N C COOH++

H2N C CO

CH3

H

NH C CO

H

H

NH C COOH

H

CH3

PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS

Peptides are broken down into their constituent amino acids by hydrolysis

Which amino acids are formed?

H2N C CO

CH3

H

NH C CO

H

H

NH C COOH

H

CH3

PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS

Peptides are broken down into their constituent amino acids by hydrolysis

CH3

H

H2N C COOH

H

H

H2N C COOH2 x +

PROTEINSPROTEINS

• are polypeptides with high molecular masses • chains can be lined up with each other • the C=O and N-H bonds are polar due to a difference in electronegativity • hydrogen bonding exists between chains

dotted lines ---------- represent hydrogen bonding

AMIDESAMIDES

Structure derivatives of carboxylic acids

amide group is -CONH2

NomenclatureWhite crystalline solids named from the corresponding acid(remove oic acid, add amide)

CH3CONH2 ethanamide (acetamide)

C2H5CONHC6H5 N - phenyl propanamide - the N tells you the

substituent is on

the nitrogen

Nylons are examples of polyamides

Preparation Acyl chloride + ammonia

CH3COCl + NH3 ——> CH3CONH2 + HCl ethanoyl chloride ethanamide

AMIDES - AMIDES - CHEMICAL PROPERTIESCHEMICAL PROPERTIES

Hydrolysisgeneral reaction CH3CONH2 + H2O ——> CH3COOH + NH3

acidic soln. CH3CONH2 + H2O + HCl ——> CH3COOH + NH4Cl

alkaline soln. CH3CONH2 + NaOH ——> CH3COONa + NH3

Identification Warming an amide with dilute sodium hydroxide solution andtesting for the evolution of ammonia using moist red litmus

paperis used as a simple test for amides.

ReductionReduced to primary amines: CH3CONH2 + 4[H] ——> CH3CH2NH2 + H2O

© 2015 © 2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHINGJONATHAN HOPTON & KNOCKHARDY PUBLISHING

AN INTRODUCTION TOAN INTRODUCTION TO

THE CHEMISTRYTHE CHEMISTRYOF AMINESOF AMINES

THE ENDTHE END