Chapter 22 amines
Download
1 / 51

Chapter 22 Amines - PowerPoint PPT Presentation


  • 76 Views
  • Uploaded on

Chapter 22 Amines. 22.1 Amine Nomenclature. Classification of Amines. Alkylamine N attached to alkyl group Arylamine N attached to aryl group Primary, secondary, or tertiary determined by number of carbon atoms directly attached to nitrogen. Nomenclature of Primary Alkylamines (RNH 2 ).

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Chapter 22 Amines' - kelsie-chambers


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Chapter 22 amines
Chapter 22Amines


22 1 amine nomenclature
22.1Amine Nomenclature


Classification of amines
Classification of Amines

  • Alkylamine

    • N attached to alkyl group

  • Arylamine

    • N attached to aryl group

  • Primary, secondary, or tertiary

    • determined by number of carbon atoms directly attached to nitrogen


Nomenclature of primary alkylamines rnh 2
Nomenclature of Primary Alkylamines (RNH2)

  • Two IUPAC styles

  • 1) analogous to alcohols: replace -e ending by -amine

  • 2) name alkyl group and attach -amine as a suffix


Examples some primary alkylamines

NH2

CH3CHCH2CH2CH3

NH2

Examples: some primary alkylamines

(RNH2: one carbon directly attached to N)

ethylamine or ethanamine

CH3CH2NH2

cyclohexylamine orcyclohexanamine

1-methylbutylamine or2-pentanamine


Nomenclature of primary arylamines arnh 2

NH2

Br

CH2CH3

F

NH2

Nomenclature of Primary Arylamines (ArNH2)

  • Name as derivatives of aniline.

p-fluoroaniline

5-bromo-2-ethylaniline


Amino groups as substituents

O

HC

NH2

Amino groups as substituents

  • amino groups rank below OH groups and higher oxidation states of carbon

  • in such cases name the amino group as a substituent

HOCH2CH2NH2

2-aminoethanol

p-aminobenzaldehyde


Secondary and tertiary amines
Secondary and Tertiary Amines

  • Name as N-substituted derivatives of parent primary amine.

  • (N is a locant-it is not alphabetized, but is treated the same way as a numerical locant)

  • Parent amine is one with longest carbonchain.


Examples

NHCH2CH3

NO2

Cl

CH3

N

CH3

Examples

CH3NHCH2CH3

N-methylethylamine

4-chloro-N-ethyl-3-nitroaniline

N,N-dimethylcycloheptylamine


Ammonium salts

CH3

+

Cl

N

CF3CO2

CH2CH3

H

Ammonium Salts

  • A nitrogen with four substituents is positivelycharged and is named as a derivative of ammonium ion (NH4+).

+

CH3NH3

methylammoniumchloride

N-ethyl-N-methylcyclopentylammoniumtrifluoroacetate


Ammonium salts1

CH3

+

CH3

CH2

I

N

CH3

Ammonium Salts

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

benzyltrimethylammonium iodide


22 2 structure and bonding
22.2Structure and Bonding


Alkylamines
Alkylamines

147 pm

112°

106°


Alkylamines1
Alkylamines

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


Geometry at n
Geometry at N

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

  • Pyramidal geometry at sp3-hybridized N in methylamine.

  • Planar geometry at sp2-hybridized N in formamide.

H

H

H

sp3

sp2

NH2

C

NH2

C

O

H


Geometry at n1
Geometry at N

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

  • Pyramidal geometry at sp3-hybridized N in methylamine.

  • Planar geometry at sp2-hybridized N in formamide.

sp3

sp2


Geometry at n2
Geometry at N

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

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

sp3

sp2

180°

~125°


Geometry at n3
Geometry at N

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

sp3

sp2

180°

~125°

142.5°


Geometry at n4
Geometry at N

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

142.5°


Geometry at n5
Geometry at N

  • Hybridization of N in aniline lies between sp3 and sp2.

  • Lone pair of N can be delocalized into ring best if N is sp2 and lone pair is in a p orbital.

  • Lone pair bound most strongly by N if pair is in an sp3 orbital of N, rather than p.

  • Actual hybridization is a compromise that maximizesbinding of lone pair.

142.5°


Electrostatic potential maps of aniline
Electrostatic Potential Maps of Aniline

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

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


22 3 physical properties
22.3Physical Properties


Physical properties
Physical Properties

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

CH3CH2CH3

CH3CH2NH2

CH3CH2OH

dipolemoment ():

0 D

1.2 D

1.7 D

boiling point:

-42°C

17°C

78°C


Physical properties1
Physical Properties

CH3CH2CH2NH2

CH3CH2NHCH3

(CH3)3N

boilingpoint:

50°C

34°C

3°C

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

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


22 4 basicity of amines
22.4Basicity of Amines


Effect of structure on basicity
Effect of Structure on Basicity

  • 1. Alkylamines are slightly stronger bases than ammonia.


Table 22 1 page 920 basicity of amines in aqueous solution
Table 22.1 (page 920)Basicity of Amines in Aqueous Solution

  • Amine Conj. Acid pKa

  • NH3 NH4+ 9.3

  • CH3CH2NH2 CH3CH2NH3+ 10.8

CH3CH2NH3+ is a weaker acid than NH4+;therefore, CH3CH2NH2 is a stronger base than NH3.


Effect of structure on basicity1
Effect of Structure on Basicity

  • 1. Alkylamines are slightly stronger bases than ammonia.

  • 2. Alkylamines differ very little in basicity.


Table 22 1 page 920 basicity of amines in aqueous solution1
Table 22.1 (page 920)Basicity of Amines in Aqueous Solution

  • Amine Conj. Acid pKa

  • NH3 NH4+ 9.3

  • CH3CH2NH2 CH3CH2NH3+ 10.8

  • (CH3CH2)2NH (CH3CH2)2NH2+ 11.1

  • (CH3CH2)3N (CH3CH2)3NH+ 10.8

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


Effect of structure on basicity2
Effect of Structure on Basicity

  • 1. Alkylamines are slightly stronger bases than ammonia.

  • 2. Alkylamines differ very little in basicity.

  • 3. Arylamines are much weaker bases than ammonia.


Table 22 1 page 920 basicity of amines in aqueous solution2
Table 22.1 (page 920)Basicity of Amines in Aqueous Solution

  • Amine Conj. Acid pKa

  • NH3 NH4+ 9.3

  • CH3CH2NH2 CH3CH2NH3+ 10.8

  • (CH3CH2)2NH (CH3CH2)2NH2+ 11.1

  • (CH3CH2)3N (CH3CH2)3NH+ 10.8

  • C6H5NH2 C6H5NH3+ 4.6


Decreased basicity of arylamines

H

••

+

N

H

+

H2N

Strongeracid

Strongerbase

pKa = 4.6

H

+

H3N

••

+

NH2

Weakerbase

Weakeracid

pKa =10.6

Decreased basicity of arylamines


Decreased basicity of arylamines1

H

N

H

H

+

H3N

••

+

NH2

Decreased basicity of arylamines

••

+

+

H2N

Strongeracid

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

Weakeracid


Decreased basicity of arylamines2

H

N

H

Strongerbase

H

+

H3N

••

+

NH2

Weakerbase

Decreased basicity of arylamines

••

+

+

H2N

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


Decreased basicity of arylamines3

pKa of conjugate acid:

4.6

0.8

~-5

Decreased basicity of arylamines

  • Increasing delocalization makes diphenylamine a weaker base than aniline, and triphenylamine a weaker base than diphenylamine.

C6H5NH2

(C6H5)2NH

(C6H5)3N


Effect of substituents on basicity of arylamines

X

NH2

Effect of Substituents on Basicity of Arylamines

  • 1. Alkyl groups on the ring increase basicity, but only slightly (less than 1 pK unit).

X pKa of conjugate acid

H 4.6

CH3 5.3


Effect of substituents on basicity of arylamines1

X

NH2

Effect of Substituents on Basicity of Arylamines

  • 2. Electron withdrawing groups, especially ortho and/or para to amine group, decrease basicity and can have a large effect.

X pKa of conjugate acid

H 4.6

CF3 3.5O2N 1.0


P nitroaniline

••

••

O

O

••

••

••

+

+

+

••

N

NH2

N

NH2

O

O

••

••

••

••

••

••

p-Nitroaniline

  • Lone pair on amine nitrogen is conjugated with p-nitro group—more delocalized than in aniline itself. Delocalization lost on protonation.


Effect is cumulative
Effect is Cumulative

  • Aniline is 3800 times more basic thanp-nitroaniline.

  • Aniline is ~1,000,000,000 times more basic than 2,4-dinitroaniline.


Heterocyclic amines

••

N

N

••

H

piperidine

pyridine

pKa of conjugate acid:

11.2

pKa of conjugate acid:

5.2

(resembles anarylamine inbasicity)

(an alkylamine)

Heterocyclic Amines

is more basic than


Heterocyclic amines1

N

H

••

N

••

N

••

Heterocyclic Amines

is more basic than

imidazole

pyridine

pKa of conjugate acid:

7.0

pKa of conjugate acid:

5.2


Imidazole

N

H

••

N

••

+

H

H

N

H

N

••

N

N

••

H

Imidazole

  • Which nitrogen is protonated in imidazole?

H+

H+

+


Imidazole1

N

H

••

N

••

+

H

H

N

H

N

H

N

N

••

Imidazole

  • Protonation in the direction shown gives a stabilized ion.

H+

+

••


22 5 tetraalkylammonium salts as phase transfer catalysts
22.5Tetraalkylammonium Saltsas Phase-Transfer Catalysts


Phase transfer catalysis
Phase-Transfer Catalysis

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

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


Phase transfer catalysis1

CH2CH2CH2CH2CH2CH2CH2CH3

CH2CH2CH2CH2CH2CH2CH2CH3

H3C

N

CH2CH2CH2CH2CH2CH2CH2CH3

Phase-Transfer Catalysis

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

+

Cl–

Methyltrioctylammonium chloride


Phase transfer catalysis2

CH2CH3

+

CH2CH3

N

CH2CH3

Phase-Transfer Catalysis

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

Cl–

Benzyltriethylammonium chloride


Example
Example

The SN2 reaction of sodium cyanide with butylbromide occurs much faster when benzyl-triethylammonium chloride is present than whenit is not.

+

CH3CH2CH2CH2Br

NaCN

benzyltriethylammonium chloride

+

CH3CH2CH2CH2CN

NaBr


Mechanism

CH2CH3

+

CH2CH3

N

CH2CH3

CH2CH3

+

+

Cl–

CN–

CH2CH3

N

(aqueous)

CH2CH3

(aqueous)

Mechanism

+

CN–

Cl–

(aqueous)

(aqueous)


Mechanism1

CH2CH3

+

CH2CH3

CN–

N

CH2CH3

(in butyl bromide)

CH2CH3

+

CH2CH3

N

CH2CH3

Mechanism

CN–

(aqueous)


Mechanism2

CH2CH3

+

CH2CH3

N

CH2CH3

CH2CH3

+

+

Br–

CH2CH3

CH3CH2CH2CH2CN

N

CH2CH3

(in butyl bromide)

Mechanism

+

CH3CH2CH2CH2Br

CN–

(in butyl bromide)


ad