nitrogen compounds ammonia derivatives. specification from ocr properties of primary amines...

Nitrogen CompoundsNitrogen Compounds

Ammonia derivativesAmmonia derivatives

Specification from OCRSpecification from OCR

Properties of primary aminesProperties of primary aminesAmino acids; peptide formationAmino acids; peptide formationHydrolysis of proteinsHydrolysis of proteins

AminesAmines

Amines are essentially molecules of ammoniaAmines are essentially molecules of ammonia One or more of the hydrogen atoms have been One or more of the hydrogen atoms have been

replaced with an alkyl group.replaced with an alkyl group.

HN

H H

AminesAmines

Replace one hydrogen atom with an alkyl Replace one hydrogen atom with an alkyl group = primary amine, replace 2 = secondary group = primary amine, replace 2 = secondary amine etc.amine etc.

R NH2Primary amine

RNH

R'Secondary amine

RN

R'R''

Tertiary amine

RN+

R''

R'''

R'

Quaternary ammonium salt

Reduction of nitrobenzene to Reduction of nitrobenzene to give phenylaminegive phenylamine

NO2

+ 6[H]i) conc. HCl/Sn

ii) NaOH(aq)

NH2

+ H2O

Conditions are reflux, this is important in the production of compounds called azo-dyes. The NaOH is essential to liberate the phenylamine rather than the salt.

Reactions of aminesReactions of amines

As basesAs bases As nucleophilesAs nucleophiles With nitrous acid With nitrous acid

R NH2

as bases

RNH3+Cl-

e.g. HCl

as

nucleophilesRNHR'

AliphaticAromatic

ROH

with HNO2

RN2+

Reactivity of AminesReactivity of Amines

The availability of the ‘lone pair’ of The availability of the ‘lone pair’ of electrons on the nitrogenelectrons on the nitrogen

Nitrogen is less electronegative than Nitrogen is less electronegative than oxygenoxygen

The lone pair is more available on nitrogen The lone pair is more available on nitrogen than it is with the alcoholsthan it is with the alcohols

Amines areAmines are

Quite good bases (donating a lone pair to Quite good bases (donating a lone pair to an Han H++ atom) atom)

Excellent ligands (in transition metal Excellent ligands (in transition metal chemistry)chemistry)

Good nucleophiles – able to attack the Good nucleophiles – able to attack the positive end of a polarised bond. positive end of a polarised bond.

Amines as basesAmines as bases

Bases are proton acceptors. Bases are proton acceptors. They don’t actually accept protons, they They don’t actually accept protons, they

donate a lone pair to the hydrogen atom to donate a lone pair to the hydrogen atom to form a dative bond. form a dative bond.

Ammonia and bases can do this with any Ammonia and bases can do this with any suitable acid to give a salt.suitable acid to give a salt.

H3N H Cl NH4+Cl-

Amines an basesAmines an bases An alkyl group is slightly electron donating.An alkyl group is slightly electron donating. This is because the electron pairs around the This is because the electron pairs around the

carbon repel the electron pair in the bond carbon repel the electron pair in the bond between the carbon and the functional group.between the carbon and the functional group.

C X

Replacing a hydrogen in ammonia Replacing a hydrogen in ammonia has the following effecthas the following effect

Causes increased electron donation in the Causes increased electron donation in the C-N bondC-N bond

Becomes polar, and nitrogen becomes Becomes polar, and nitrogen becomes slightly negativeslightly negative

Lone pair on nitrogen slightly repelledLone pair on nitrogen slightly repelledCan be donated to a proton more easilyCan be donated to a proton more easily1° amines are more basic than ammonia1° amines are more basic than ammonia

What about secondary and tertiary?What about secondary and tertiary?

So following the same argument, 2° So following the same argument, 2° amines will be more basic still, as the lone amines will be more basic still, as the lone pair will be repelled even more. pair will be repelled even more.

In phenylamine, the lone pair becomes In phenylamine, the lone pair becomes involved in the aromaticity, so it is less involved in the aromaticity, so it is less basic. The lone pair as part of the ring’s basic. The lone pair as part of the ring’s delocalised system, it is less readily delocalised system, it is less readily donated to a proton.donated to a proton.

A tertiary amine will be more basic still.A tertiary amine will be more basic still.

The relative basicity of some The relative basicity of some aminesamines

Name Type Structure pka pkb Ammonia NH3 9.25 4.75 Ethylamine Primary C2H5NH2 10.75 3.27 Diethylamine Secondary (C2H5)2NH 10.93 3.07 Triethylamine Tertiary (C2H5)N 10.64 3.36 Phenylamine Aromatic NH2

4.62 9.38

Reaction of amines with acidsReaction of amines with acids

A pretty standard Acid Base reaction.A pretty standard Acid Base reaction.

CH3CH2NH2 + HCl CH3CH2NH3+ + Cl-

Diazonium SaltsDiazonium Salts

Diazonium: there are 2 nitrogen atoms joined Diazonium: there are 2 nitrogen atoms joined together in the positive ion.together in the positive ion.

In French, nitrogen is still called by its old name In French, nitrogen is still called by its old name ‘azote’ which means unable to support life.‘azote’ which means unable to support life.

N N Cl

diazonium chloride

Diazonium SaltsDiazonium Salts

Notice the triple bond between the nitrogen Notice the triple bond between the nitrogen atomsatoms

The positive charge is on the nitrogen that is The positive charge is on the nitrogen that is attached to the benzene ringattached to the benzene ring

N N Cl

diazonium chloride

Why are they important? They Why are they important? They look pretty weird!look pretty weird!

They are essential in the dye industry. They are essential in the dye industry. A Diazonium salt is produced then reacted A Diazonium salt is produced then reacted

with a phenol. If the correct phenol is with a phenol. If the correct phenol is used, almost any colour can be produced.used, almost any colour can be produced.

OCR specify this as a reaction you need to OCR specify this as a reaction you need to know. know.

In the last CRS paper, this was a question In the last CRS paper, this was a question worth 6 marks! Very few students got worth 6 marks! Very few students got many marks at all.many marks at all.

Formation of the Diazonium salt.Formation of the Diazonium salt.

Formed by reacting phenylamine with Formed by reacting phenylamine with sodium nitrite and hydrochloric acid. sodium nitrite and hydrochloric acid.

These reagents form in situ nitrous acid These reagents form in situ nitrous acid HONO. HONO.


The Diazonium salt is unstable above 10°C, so The Diazonium salt is unstable above 10°C, so the reaction is normally carried out in ice.the reaction is normally carried out in ice.

An aliphatic Diazonium salt is very unstable, so An aliphatic Diazonium salt is very unstable, so only aromatics are used.only aromatics are used.

The lone pairs present in the salt can participate The lone pairs present in the salt can participate in the benzene ring, making it more stable. More in the benzene ring, making it more stable. More correctly this is due to overlap of p-orbitals in the correctly this is due to overlap of p-orbitals in the diazo group with the p-system in the ring.diazo group with the p-system in the ring.

So phenylamine would give benzenediazonium So phenylamine would give benzenediazonium chloride.chloride.


N N ClNH2

+ HONO(aq) + HCl(aq) + 2H2O(l)

Formation of the Diazonium salt. Formation of the Diazonium salt.

The conditions are 5°C and remember the The conditions are 5°C and remember the HONO (nitrous acid) is prepared in situ by HONO (nitrous acid) is prepared in situ by reacting sodium nitrite with hydrochloric reacting sodium nitrite with hydrochloric acid.acid.

The diazonium salt can ten do one of two The diazonium salt can ten do one of two things depending on the temperature things depending on the temperature

Reactions of aromatic diazonium Reactions of aromatic diazonium saltssalts

N N Cl

hydrolysisroom temperature

OH

Coupling reaction5 degrees Celciuswith phenol

N N

OH

HydrolysisHydrolysis

The following occurs if a solution of a The following occurs if a solution of a diazonium salt is warmed up:diazonium salt is warmed up:

C6H5N2+Cl-(aq) + H2O(l) → C6H5OH + N2(g) + HCl(aq)

Coupling reactionsCoupling reactions

The mechanism is for The mechanism is for interest only, you do interest only, you do not need to know it. not need to know it.

N N

O H

NN

OH

H

HO

H

NN

OH

General method for synthesis of General method for synthesis of azo dyesazo dyes

Add a cold aqueous solution of sodium nitrite Add a cold aqueous solution of sodium nitrite slowly (with cooling and stirring) to a cold slowly (with cooling and stirring) to a cold solution of the amine compound in excess solution of the amine compound in excess hydrochloric acidhydrochloric acid

The temperature must not rise above 5°C.The temperature must not rise above 5°C. This solution (still cold) should then be added This solution (still cold) should then be added

slowly with stirring to a solution of the coupling slowly with stirring to a solution of the coupling compound.compound.

This should be kept below 5°C the whole time.This should be kept below 5°C the whole time.

Amino AcidsAmino Acids

These are bi-functional compounds. The These are bi-functional compounds. The contain 2 functions groups:contain 2 functions groups:

A primary amine (in most cases) –NHA primary amine (in most cases) –NH22

The carboxylic acid group –COOHThe carboxylic acid group –COOHAn amino acid must contain at least both An amino acid must contain at least both

of these functional groups.of these functional groups.


The simplest amino acid is glycine.The simplest amino acid is glycine.

C CN

H

H

H

H

O

O H


All the amino acids (the twenty vitally important All the amino acids (the twenty vitally important ones biologically) are 2-amino acids. ones biologically) are 2-amino acids.

The amine and acid groups are both attached to The amine and acid groups are both attached to the same carbon.the same carbon.

All can be names systematically, but in most All can be names systematically, but in most cases the old names are used. cases the old names are used.

Alanine is also known as 2-aminopropanoic acid, Alanine is also known as 2-aminopropanoic acid, but alanine is the acceptable name to use.but alanine is the acceptable name to use.

AlanineAlanine

C CN

HH

H

O

O HC

H

H H

General FormulaGeneral Formula

C CNH

H

O

O H

H

R

Physical Properties Physical Properties

White solidsWhite solidsWith relatively high melting points glycine With relatively high melting points glycine

(the simplest) has a melting point of (the simplest) has a melting point of 235°C.235°C.

Normally readily soluble in waterNormally readily soluble in waterAlmost totally insoluble in non-polar Almost totally insoluble in non-polar

solventssolvents

Acid – Base PropertiesAcid – Base Properties

They are very largely ionic compounds. They are very largely ionic compounds. The carboxyl group can lose a protonThe carboxyl group can lose a protonThe amine group can gain a protonThe amine group can gain a protonThe result is a ZWITTERION. From the The result is a ZWITTERION. From the

German for hermaphrodite, hybrid or German for hermaphrodite, hybrid or mongrel!mongrel!

ZwitterionsZwitterions

Glycine mainly exists Glycine mainly exists as.as.

H3N+ CH2 COO-


The strong attractions in the crystal cause The strong attractions in the crystal cause the high melting pointthe high melting point

In aqueous solution depending on the pH, In aqueous solution depending on the pH, they form either the neutral form, or the they form either the neutral form, or the carboxylate will lose a proton, or the amino carboxylate will lose a proton, or the amino group will gain a proton.group will gain a proton.


C CNH

H

O

O H

H

H

+ H+ in strong acidC CO

O H

H

H

H3N+ -H+ in strong alkali C CNH

H

OH

H O-

Isoelectric PointIsoelectric Point

For each amino acid there is a definite pH For each amino acid there is a definite pH – the – the isoelectric point isoelectric point at which the acid at which the acid and basic ionisations are equal.and basic ionisations are equal.

The molecule is effectively neutral – it The molecule is effectively neutral – it carries equal and opposite chargescarries equal and opposite charges

This is rarely near pH 7 because the This is rarely near pH 7 because the molecule ionisation tendencies are molecule ionisation tendencies are affected by the other groups in the affected by the other groups in the molecule.molecule.

Isoelectric PointIsoelectric Point

Aspartic acid – which has 2 –COOH Aspartic acid – which has 2 –COOH groups – is acid in aqueous solution. groups – is acid in aqueous solution.

Lysine with more amino than carboxyl Lysine with more amino than carboxyl groups is alkaline.groups is alkaline.

Due to this dual functionality, they are able Due to this dual functionality, they are able to act as buffer solutions (able to maintain to act as buffer solutions (able to maintain a reasonably constant pH with small a reasonably constant pH with small additions of acid or alkali). additions of acid or alkali).

They also have optical activity.They also have optical activity.

How amino acids join togetherHow amino acids join together

Amino acids join together in specific ways to Amino acids join together in specific ways to form specific proteins.form specific proteins.

One amino acid can join to another to form a One amino acid can join to another to form a substituted amide.substituted amide.

H

C COOH

R'

H2N +

H

C COOHH2N

R''

H2N C

H

R'

C

O

N

H

C

H

R''

COOH + H2O


This kind of bond between 2 amino acids is This kind of bond between 2 amino acids is called a peptide bond or a peptide link. called a peptide bond or a peptide link.

CO

N

H


N CH

H

H

R'

CO

OHN C

H

H

H

R'

CO

OH

+

N C

H

R'

CO

OHC

R'

H

H

HCN

O

H


Two joined amino acids = dipeptideTwo joined amino acids = dipeptideThree = tripeptideThree = tripeptideMany = polypeptideMany = polypeptideAt some point a polypeptide becomes a At some point a polypeptide becomes a

protein. This can be put at 40 amino acids.protein. This can be put at 40 amino acids.

Acid Hydrolysis of proteinsAcid Hydrolysis of proteins

Proteins and peptides can be hydrolysed Proteins and peptides can be hydrolysed with hot concentrated (6 mol dm-3). with hot concentrated (6 mol dm-3).

The protein is refluxed for about 24 hours.The protein is refluxed for about 24 hours.This hydrolysis is the exact reverse of the This hydrolysis is the exact reverse of the

formation of the peptide bond. formation of the peptide bond. A molecule of water is in effect added A molecule of water is in effect added

across the linkage to regenerate the across the linkage to regenerate the original amino acid and carboxyl groups.original amino acid and carboxyl groups.

Acid Hydrolysis of proteinsAcid Hydrolysis of proteins

C

O

N CH

H

C

R O

NCH

H

R'

CO

NH + H2O C

O

N CH

H

C

R O

OHN

CH

H

R'

CO

NHH

+

nitrogen compounds ammonia derivatives. specification from ocr properties of primary amines...

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