dr. wolf's chm 201 & 202 22-1 chapter 22 amines. dr. wolf's chm 201 & 202 22-2...

Dr. Wolf's CHM 201 & 202 22-1

Chapter 22Chapter 22AminesAmines

Dr. Wolf's CHM 201 & 202 22-2

22.122.1

Amine NomenclatureAmine Nomenclature

Dr. Wolf's CHM 201 & 202 22-3

AlkylamineAlkylamine

N attached to alkyl groupN attached to alkyl group

ArylamineArylamine

N attached to aryl groupN attached to aryl group

Primary, secondary, or tertiaryPrimary, secondary, or tertiary

determined by number of carbon atoms determined by number of carbon atoms directly attached to nitrogendirectly attached to nitrogen

Classification of AminesClassification of Amines

Dr. Wolf's CHM 201 & 202 22-4

Two IUPAC stylesTwo IUPAC styles

1)1) analogous to alcohols: replace -analogous to alcohols: replace -e e ending by -ending by -amineamine

2)2) name alkyl group and attach -name alkyl group and attach -amineamineas a suffixas a suffix

Nomenclature of Primary Alkylamines (RNHNomenclature of Primary Alkylamines (RNH22))

Dr. Wolf's CHM 201 & 202 22-5

Examples: some primary alkylaminesExamples: some primary alkylamines

CHCH33CHCHCHCH22CHCH22CHCH33

NNHH22

(RNH(RNH22: one carbon directly attached to N): one carbon directly attached to N)

CHCH33CHCH22NNHH22 NNHH22

ethylamineethylamine or or ethanamineethanamine

cyclohexylaminecyclohexylamine or orcyclohexanaminecyclohexanamine

1-methylbutylamine 1-methylbutylamine oror2-pentanamine2-pentanamine

Dr. Wolf's CHM 201 & 202 22-6

Name as derivatives of aniline.Name as derivatives of aniline.

Nomenclature of Primary Arylamines (ArNHNomenclature of Primary Arylamines (ArNH22))

pp-fluoroaniline-fluoroaniline 5-bromo-2-ethylaniline5-bromo-2-ethylaniline

NNHH22FF

NNHH22

BrBr CHCH22CHCH33

Dr. Wolf's CHM 201 & 202 22-7

Amino groups as substituentsAmino groups as substituents

pp-aminobenzaldehyde-aminobenzaldehyde

amino groups rank below OH groups and higher amino groups rank below OH groups and higher

oxidation states of carbonoxidation states of carbon

in such cases name the amino group as a in such cases name the amino group as a

substituentsubstituent NNHH22HHCC

OO

HHOOCHCH22CHCH22NNHH22

2-aminoethanol2-aminoethanol

Dr. Wolf's CHM 201 & 202 22-8

Name as Name as NN-substituted derivatives of parent -substituted derivatives of parent primary amine.primary amine.

(N is a locant-it is not alphabetized, but(N is a locant-it is not alphabetized, butis treated the same way as a numericalis treated the same way as a numericallocant)locant)

Parent amine is one with longest carbonParent amine is one with longest carbonchain.chain.

Secondary and Tertiary AminesSecondary and Tertiary Amines

Dr. Wolf's CHM 201 & 202 22-9

ExamplesExamples

CHCH33NNHCHHCH22CHCH33 NN-methylethylamine-methylethylamine NNHCHHCH22CHCH33

NONO22

ClCl

4-chloro-4-chloro-NN-ethyl-3-nitroaniline-ethyl-3-nitroaniline

CHCH33

NN

CHCH33

NN,,NN-dimethylcycloheptylamine-dimethylcycloheptylamine

Dr. Wolf's CHM 201 & 202 22-10

A nitrogen with four substituents is positivelyA nitrogen with four substituents is positivelycharged and is named as a derivative of charged and is named as a derivative of ammonium ammonium ion (NHion (NH44

++).).

Ammonium SaltsAmmonium Salts

CHCH33NHNH33

++ClCl

––

methylammoniummethylammonium

chloridechloride

NN

CHCH33

HH

CHCH22CHCH33

++CFCF33COCO22

––

NN-ethyl--ethyl-NN-methylcyclopentylammonium-methylcyclopentylammonium

trifluoroacetatetrifluoroacetate

Dr. Wolf's CHM 201 & 202 22-11

When all four atoms attached to N are carbon,When all four atoms attached to N are carbon,the ion is called a the ion is called a quaternary ammonium quaternary ammonium ion andion andsalts that contain it are called salts that contain it are called quaternaryquaternary ammoniumammonium salts. salts.

Ammonium SaltsAmmonium Salts

++

CHCH22 NN

CHCH33

CHCH33

CHCH33 II––

benzyltrimethylammonium iodidebenzyltrimethylammonium iodide

Dr. Wolf's CHM 201 & 202 22-12

22.222.2

Structure and BondingStructure and Bonding

Dr. Wolf's CHM 201 & 202 22-13

147 pm147 pm

106°106°112°112°

AlkylaminesAlkylamines

Dr. Wolf's CHM 201 & 202 22-14

Most prominent feature is high electrostaticMost prominent feature is high electrostaticpotential at nitrogen. Reactivity of nitrogen lonepotential at nitrogen. Reactivity of nitrogen lonepair dominates properties of amines. pair dominates properties of amines.

AlkylaminesAlkylamines

Dr. Wolf's CHM 201 & 202 22-15

Compare geometry at N of methylamine, aniline,Compare geometry at N of methylamine, aniline,and formamide.and formamide.

spsp33 spsp22

Geometry at NGeometry at N

Pyramidal geometry at Pyramidal geometry at spsp33-hybridized N in -hybridized N in

methylamine.methylamine.

Planar geometry at Planar geometry at spsp22-hybridized N in formamide.-hybridized N in formamide.

CCOO

NNHH22

HH

CC NNHH22

HH

HH

HH

Dr. Wolf's CHM 201 & 202 22-16

Compare geometry at N of methylamine, aniline,Compare geometry at N of methylamine, aniline,and formamide.and formamide.

spsp33 spsp22


Pyramidal geometry at Pyramidal geometry at spsp33-hybridized N in -hybridized N in

methylamine.methylamine.

Planar geometry at Planar geometry at spsp22-hybridized N in formamide.-hybridized N in formamide.

Dr. Wolf's CHM 201 & 202 22-17

Angle that the C—N bond makes with bisector ofAngle that the C—N bond makes with bisector ofH—N—H angle is a measure of geometry at N.H—N—H angle is a measure of geometry at N.

spsp33 spsp22


~125°~125°180°180°

Note: this is not the same as the H—N—H bond angleNote: this is not the same as the H—N—H bond angle

Dr. Wolf's CHM 201 & 202 22-18

Angle that the C—N bond makes with bisector ofAngle that the C—N bond makes with bisector ofH—N—H angle is a measure of geometry at N.H—N—H angle is a measure of geometry at N.

spsp33 spsp22


~125°~125°180°180°

142.5°142.5°

Dr. Wolf's CHM 201 & 202 22-19

Geometry at N in aniline is pyramidal; closer toGeometry at N in aniline is pyramidal; closer tomethylamine than to formamide.methylamine than to formamide.


142.5°142.5°

Dr. Wolf's CHM 201 & 202 22-20


142.5°142.5°

Hybridization of N in aniline lies between Hybridization of N in aniline lies between spsp33 and and spsp22..

Lone pair of N can be delocalized into ring best if N is Lone pair of N can be delocalized into ring best if N is

spsp22 and lone pair is in a and lone pair is in a pp orbital. orbital.

Lone pair bound most strongly by N if pair is in an Lone pair bound most strongly by N if pair is in an spsp33

orbital of N, rather than orbital of N, rather than pp..

Actual hybridization is a compromise that maximizesActual hybridization is a compromise that maximizes

binding of lone pair.binding of lone pair.

Dr. Wolf's CHM 201 & 202 22-21

Electrostatic Potential Maps of AnilineElectrostatic Potential Maps of Aniline

Nonplanar geometry at Nonplanar geometry at N. Region of highestN. Region of highestnegative potential is at N.negative potential is at N.

Planar geometry at N. Planar geometry at N. High negative potential High negative potential shared by N and ring.shared by N and ring.

Dr. Wolf's CHM 201 & 202 22-22

22.322.3

Physical PropertiesPhysical Properties

Dr. Wolf's CHM 201 & 202 22-23

Amines are more polar and have higher boiling Amines are more polar and have higher boiling points than alkanes; but are less polar andpoints than alkanes; but are less polar andhave lower boiling points than alcohols.have lower boiling points than alcohols.


CHCH33CHCH22CHCH33 CHCH33CHCH22NNHH22 CHCH33CHCH22OOHH

dipoledipolemoment (moment ():):

boiling point:boiling point:

0 D0 D 1.2 D1.2 D 1.7 D1.7 D

-42°C-42°C 17°C17°C 78°C78°C

Dr. Wolf's CHM 201 & 202 22-24

Boiling points of isomeric amines decrease inBoiling points of isomeric amines decrease ingoing from primary to secondary to tertiary amines.going from primary to secondary to tertiary amines.

Primary amines have two hydrogens on N capable Primary amines have two hydrogens on N capable of being involved in intermolecular hydrogen of being involved in intermolecular hydrogen bonding. Secondary amines have one. Tertiary bonding. Secondary amines have one. Tertiary amines cannot be involved in intermolecular amines cannot be involved in intermolecular hydrogen bonds.hydrogen bonds.


CHCH33CHCH22NNHCHHCH33CHCH33CHCH22CHCH22NNHH22 (CH(CH33))33NN

boilingboilingpoint:point:

50°C50°C 34°C34°C 3°C3°C

Dr. Wolf's CHM 201 & 202 22-25

22.422.4

Basicity of AminesBasicity of Amines

Dr. Wolf's CHM 201 & 202 22-26

Effect of Structure on BasicityEffect of Structure on Basicity

1. Alkylamines are slightly stronger bases than 1. Alkylamines are slightly stronger bases than ammonia.ammonia.

Dr. Wolf's CHM 201 & 202 22-27

AmineAmine Conj. AcidConj. Acid pKpKaa

NHNH33 NHNH44++ 9.39.3

CHCH33CHCH22NHNH22 CHCH33CHCH22NHNH33++ 10.810.8

Table 22.1 (page 920)Table 22.1 (page 920)Basicity of Amines in Aqueous SolutionBasicity of Amines in Aqueous Solution

CHCH33CHCH22NHNH33++ is a weaker acid than NH is a weaker acid than NH44

++;;therefore, CHtherefore, CH33CHCH22NHNH22 is a stronger base is a stronger base than NHthan NH33..

Dr. Wolf's CHM 201 & 202 22-28



2. Alkylamines differ very little in basicity.2. Alkylamines differ very little in basicity.

Dr. Wolf's CHM 201 & 202 22-29


NHNH33 NHNH44++ 9.39.3


(CH(CH33CHCH22))22NHNH (CH(CH33CHCH22))22NHNH22++ 11.111.1

(CH(CH33CHCH22))33NN (CH(CH33CHCH22))33NHNH++ 10.810.8


Notice that the difference separating a primary,Notice that the difference separating a primary,secondary, and tertiary amine is only 0.3 pK units.secondary, and tertiary amine is only 0.3 pK units.

Dr. Wolf's CHM 201 & 202 22-30



2. Alkylamines differ very little in basicity.2. Alkylamines differ very little in basicity.

3. Arylamines are much weaker bases than3. Arylamines are much weaker bases thanammonia.ammonia.

Dr. Wolf's CHM 201 & 202 22-31


NHNH33 NHNH44++ 9.39.3


(CH(CH33CHCH22))22NHNH (CH(CH33CHCH22))22NHNH22++ 11.111.1

(CH(CH33CHCH22))33NN (CH(CH33CHCH22))33NHNH++ 10.810.8

CC66HH55NHNH22 CC66HH55NHNH33++ 4.64.6


Dr. Wolf's CHM 201 & 202 22-32

HH22NN•••• Decreased basicity of arylaminesDecreased basicity of arylamines

++HH

NN

HH

HH

++ NNHH22 ++•••• ++

HH33NN

ppKKaa = 4.6 = 4.6

ppKKaa =10.6 =10.6

StrongerStrongeracidacid

WeakerWeakeracidacid

StrongerStrongerbasebase

WeakerWeakerbasebase

Dr. Wolf's CHM 201 & 202 22-33


++HH

NN

HH

HH

++ NNHH22 ++•••• ++

HH33NN

StrongerStrongeracidacid

WeakerWeakeracidacid

When anilinium ion loses a proton, theWhen anilinium ion loses a proton, theresulting lone pair is delocalized into the ring.resulting lone pair is delocalized into the ring.

Dr. Wolf's CHM 201 & 202 22-34


++HH

NN

HH

HH

++ NNHH22 ++•••• ++

HH33NN

Aniline is a weaker base because its Aniline is a weaker base because its lone pair is more strongly held.lone pair is more strongly held.

StrongerStrongerbasebase

WeakerWeakerbasebase

Dr. Wolf's CHM 201 & 202 22-35

Decreased basicity of arylaminesDecreased basicity of arylamines

CC66HH55NNHH22 (C(C66HH55))22NNHH (C(C66HH55))33NN

ppKKa a of conjugate acid:of conjugate acid:

4.64.6 0.80.8 ~-5~-5

Increasing delocalization makes diphenylamine a Increasing delocalization makes diphenylamine a

weaker base than aniline, and triphenylamine a weaker weaker base than aniline, and triphenylamine a weaker

base than diphenylamine.base than diphenylamine.

Dr. Wolf's CHM 201 & 202 22-36

Effect of Substituents on Basicity of ArylaminesEffect of Substituents on Basicity of Arylamines

1. Alkyl groups on the ring increase basicity, but1. Alkyl groups on the ring increase basicity, butonly slightly (less than 1 ponly slightly (less than 1 pKK unit). unit).

XX NHNH22

XX ppKKa a of conjugate acidof conjugate acid

HH 4.64.6CHCH33 5.35.3

Dr. Wolf's CHM 201 & 202 22-37

Effect of Substituents on Basicity of ArylaminesEffect of Substituents on Basicity of Arylamines

2. Electron withdrawing groups, especially ortho2. Electron withdrawing groups, especially orthoand/or para to amine group, decrease basicityand/or para to amine group, decrease basicityand can have a large effect.and can have a large effect.

XX NHNH22

XX ppKKa a of conjugate acidof conjugate acid

HH 4.64.6CFCF33 3.53.5

OO22NN 1.01.0

Dr. Wolf's CHM 201 & 202 22-38

p-Nitroanilinep-Nitroaniline NNHH22

OO

NN

OO

–– ••••••••••••

••••

++

••••

••••

OO

NN

OO

–– ••••••••••••

•••• ••••••••––

NNHH22

++ ++

Lone pair on amine nitrogen is conjugated with Lone pair on amine nitrogen is conjugated with

pp-nitro group—more delocalized than in aniline -nitro group—more delocalized than in aniline

itself. Delocalization lost on protonation.itself. Delocalization lost on protonation.

Dr. Wolf's CHM 201 & 202 22-39

Effect is CumulativeEffect is Cumulative

Aniline is 3800 times more basic thanAniline is 3800 times more basic than

pp-nitroaniline.-nitroaniline.

Aniline is ~1,000,000,000 times more basic than Aniline is ~1,000,000,000 times more basic than

2,4-dinitroaniline.2,4-dinitroaniline.

Dr. Wolf's CHM 201 & 202 22-40

Heterocyclic Amines Heterocyclic Amines NN

HH

••••

NN••••

is more basic thanis more basic than

piperidinepiperidine pyridinepyridineppKKaa of conjugate acid: of conjugate acid:

11.211.2

ppKKaa of conjugate acid: of conjugate acid:

5.25.2

(an alkylamine)(an alkylamine)(resembles an(resembles anarylamine inarylamine in

basicity)basicity)

Dr. Wolf's CHM 201 & 202 22-41

Heterocyclic Amines Heterocyclic Amines NN••••

is more basic thanis more basic than

imidazoleimidazole pyridinepyridineppKKaa of conjugate acid: of conjugate acid:

7.07.0

ppKKaa of conjugate acid: of conjugate acid:

5.25.2

NN HHNN•••• ••••

Dr. Wolf's CHM 201 & 202 22-42

ImidazoleImidazole NN HHNN•••• ••••

Which nitrogen is protonated in imidazole?Which nitrogen is protonated in imidazole?

HH++ HH++ NN HHNN ••••HH

++

NN HHNN••••

HH

++

Dr. Wolf's CHM 201 & 202 22-43

ImidazoleImidazole NN HHNN•••• ••••

Protonation in the direction shown gives a Protonation in the direction shown gives a

stabilized ion.stabilized ion.

HH++ NN HHNNHH

++ ••••

NN HHNNHH

••••++

Dr. Wolf's CHM 201 & 202 22-44

22.522.5

Tetraalkylammonium SaltsTetraalkylammonium Salts

as Phase-Transfer Catalystsas Phase-Transfer Catalysts

Dr. Wolf's CHM 201 & 202 22-45

Phase-Transfer CatalysisPhase-Transfer Catalysis

Phase-transfer agents promote the solubility ofPhase-transfer agents promote the solubility ofionic substances in nonpolar solvents. Theyionic substances in nonpolar solvents. Theytransfer the ionic substance from an aqueoustransfer the ionic substance from an aqueousphase to a non-aqueous one.phase to a non-aqueous one.

Phase-transfer agents increase the rates ofPhase-transfer agents increase the rates ofreactions involving anions. The anion is relativelyreactions involving anions. The anion is relativelyunsolvated and very reactive in nonpolar mediaunsolvated and very reactive in nonpolar mediacompared to water or alcohols.compared to water or alcohols.

Dr. Wolf's CHM 201 & 202 22-46


Quaternary ammonium salts are phase-transferQuaternary ammonium salts are phase-transfercatalysts. They are soluble in nonpolar solvents.catalysts. They are soluble in nonpolar solvents.

NNHH33CC

CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH33



++ClCl––

Methyltrioctylammonium chlorideMethyltrioctylammonium chloride

Dr. Wolf's CHM 201 & 202 22-47


Quaternary ammonium salts are phase-transferQuaternary ammonium salts are phase-transfercatalysts. They are soluble in nonpolar solvents.catalysts. They are soluble in nonpolar solvents.

ClCl––

Benzyltriethylammonium chlorideBenzyltriethylammonium chloride

NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

Dr. Wolf's CHM 201 & 202 22-48

ExampleExample

The SThe SNN2 reaction of sodium cyanide with butyl2 reaction of sodium cyanide with butyl

bromide occurs much faster when benzyl-bromide occurs much faster when benzyl-triethylammonium chloride is present than whentriethylammonium chloride is present than whenit is not.it is not.

CHCH33CHCH22CHCH22CHCH22BrBr ++ NaNaCNCN

CHCH33CHCH22CHCH22CHCH22CNCN ++ NaNaBrBr

benzyltriethylammonium chloridebenzyltriethylammonium chloride

Dr. Wolf's CHM 201 & 202 22-49

MechanismMechanismMechanismMechanism

ClCl––

(aqueous)(aqueous)

NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

(aqueous)(aqueous)

CNCN––++

ClCl––NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

++CNCN––

(aqueous)(aqueous)

(aqueous)(aqueous)

Dr. Wolf's CHM 201 & 202 22-50

NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

CNCN––

(aqueous)(aqueous)

(in butyl bromide)(in butyl bromide)

NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

CNCN––


Dr. Wolf's CHM 201 & 202 22-51


NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

CNCN––


CHCH33CHCH22CHCH22CHCH22BrBr++

NN

CHCH22CHCH33

CHCH22CHCH33

CHCH22CHCH33

++

BrBr––


CHCH33CHCH22CHCH22CHCH22CNCN++

dr. wolf's chm 201 & 202 22-1 chapter 22 amines. dr. wolf's chm 201 & 202 22-2...

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