Chapter 17  Amines
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Chapter 17 Amines ( 胺 ). 17.1 Amine Nomenclature 17.2 Structures of amines 17.3 Basicity of amines 17.4 Preparation of amines 17.4.1 Preparation of amines by alkylation of ammonia 17.4.2 The Gabriel synthesis of primary amines

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Chapter 17 Amines ( 胺 )

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Chapter 17 amines

Chapter 17 Amines (胺)

17.1 Amine Nomenclature

17.2 Structures of amines

17.3 Basicity of amines

17.4 Preparation of amines

17.4.1 Preparation of amines

by alkylation of ammonia

17.4.2 The Gabriel synthesis of primary

amines

17.4.3 Preparation of amines by reduction

17.5 Reactions of amines

17.5.1 Alkylation of amines

17.5.2 Acylation of amines

17.5.3 The Hofmann Elimination


Chapter 17 amines

17.5.4 Reactions of amines with nitrous acid

(A) Reactions of primary aliphatic

amines with nitrous acid

(B) Reactions of primary arylamines

with nitrous acid

(C) Reactions of secondary amines

with nitrous acid

(D) Reactions of tertiary amines

with nitrous acid

17.5.5 Synthetic transformations of aryl

diazonium salt

(A) Replacement of the diazonium

group by -OH


Chapter 17 amines

(B) Replacement of the diazonium group

by -X, -CN

(c) Replacement of the diazonium group

by -H

17.5.6 Azo coupling

17.6 Spectroscopic analysis of amines


Chapter 17 amines

17.1 Amine Nomenclature

P380

Organic derivatives of ammonia

Alkylamines

Arylamines

Primary amines(伯胺):

Aniline

(苯胺)

Methylamine

(甲胺)

Isobutylamine

(异丁胺)

2-Methylpropylamine

(2-甲基丙胺)

Benzylamine

(苄胺)


Chapter 17 amines

Cyclohexylamine

(环己胺)

Secondary amines:

(仲胺)

Ethylmethylamine

(甲乙胺)

N-Methylethylamine

(N-甲基乙胺)

Diethylamine

(二乙胺)

Tertiary amines:

(叔胺)

Trimethylamine

N,N-Dimethylmethylamine

(三甲胺)

(N,N-二甲基甲胺)

N,N-Dimethyl-

aniline

(N,N-二甲基苯胺)


Chapter 17 amines

N-Ethyl-N-methylcyclohexylamine

(N-甲基-N-乙基环己胺)

Diamines:

1,2-Ethyldiamine

(1,2-乙二胺)

Ammonium ions

(铵离子)

Aminium salts

(铵盐)

Anilinium chloride

(盐酸苯胺)

Quaternary

ammonium

salts

(季铵盐)

2-Aminoethanol

(2-氨基乙醇)


Chapter 17 amines

Pyridine

(吡啶)

Pyrrole

(吡咯)

Quinoline

(喹啉)

Indole

(吲哚)

Pyrrolidine

(吡咯烷)

(四氢吡咯)

Piperidine

( 哌啶)

Heterocyclic amine:

(杂环胺)


Chapter 17 amines

sp3-sp3 hybridized

orbitals overlap

C-N:

sp3hybridized -1s

orbitals overlap

N-H:

17.2 Structures of amines

P383,

12.2

N: 1s22s22px12py12pz1

sp3-hybrid

Pyramid(棱锥型)

Tertiary amines with 3 different groups:

Interconversion of amine enantiomers


Chapter 17 amines

Quarternary ammonium salt:

17.3 Basicity of amines

P384,

12.3

Weak bases


Chapter 17 amines

pKb

Amines

4.7

3.4

3.3

4.3

9.4

13

8.7

NH3

CH3NH2

(CH3)2NH

(CH3)3N

Table 1 Basic strength of some amines

P385,

Table

12.1


Chapter 17 amines

2.

1. All amines are weak bases:

H2O < RNH2 < < OH-

P384,

12.3

Alkylamines are slightly stronger bases

than ammonia; Arylamines are much weaker

bases than ammonia and alkylamines.

p -πconjugation

+I

Delocalization of

nitrogen lone-pair

electrons

Decreasing the

electron density

at nitrogen.


Chapter 17 amines

pKa = -logKa

pKa + pKb = 14

Weaker base:Smaller pKa for ammonium ion

Stronger base: Larger pKa for ammonium ion


Chapter 17 amines

3. R2NH > RNH2 > R3N >NH3

Poorer solvation

Anilinium ion

Separation of amines from neutral organic

compounds

P384,

12.3

17.4 Preparation of amines

17.4.1 Preparation of amines by alkylation

of ammonia


Chapter 17 amines

17.4.2 The Gabriel synthesis of primary

amines

Primary alkyl halide, SN2

Potassium salt of

Phthalimide

(邻苯二甲酰胺钾盐)

Reagent:

Ch.P436

Imide

(酰亚胺)


Chapter 17 amines

ArX

17.4.3 Preparation of amines by reduction

Reduction of nitriles to amines

LiAlH4


Chapter 17 amines

Siegmund Gabriel was born

in Berlin,Germany,and

received his Ph.D. in1874

at the University of Berlin,

working with August von

Hofmann. After further

work with Robert Bunsen,

he became Professor of

Chemistry at the Univ. of

Berlin.

Robert Wilhelm

Bunsen

1811-1899

poohbah.cem.msu.edu/

Portraits/

Siegmund Gabriel

(1851-1924)


Chapter 17 amines

Gabriel Synthesis.

Gabriel, Ber. 20, 2224(1887).

M. S. Gibson, R. W. Bradshaw, Angew. Chem. Int. Ed.

7, 919 (1968); B. Dietrich et al.,J. Am. Chem. Soc. 103,

1282 (1981); O. Mitsunobu, Comp. Org. Syn. 6, 79-85 (1991).

Modified conditions: S. E. Sen, S. L. Roach, Synthesis 1994,

756; M. N. Khan, J. Org. Chem. 61, 8063 (1996).

Stereoselectivity: A. Kubo et al.,Tetrahedron Letters 37,

4957 (1996).


Chapter 17 amines

Reduction of nitro compounds to arylamines

P389

H2, cat

Reduction of amides to amines:


Chapter 17 amines

Reductive amination:

Imine

(亚胺)

Ch.P435


Chapter 17 amines

+ H X

+

17.5 Reactions of amines

Unshared electron pair

of nitrogen:

Basicity:

Nucleophilicity:

17.5.1 Alkylation of amines


Chapter 17 amines

(cyclohexylmethyl)-

trimethyl-

ammonium iodide

(99%)

(Cyclohexyl-

methyl)-

amine

Methyl

iodide

17.5.2 Acylation of amines

Acylating agents: acyl chlorides, carboxylic

acid anhydrides

Synthesis of Paracetamol (扑热息痛):


Chapter 17 amines

Hexylamine

Hexyltrimethylammonium iodide

Decreasing the activity of aryl ring or

Protecting amino groups :

17.5.3 The Hofmann Elimination

Methylation of an amine by excess CH3I:


Chapter 17 amines

Quaternary ammonium hydroxides

(氢氧化季铵碱)can be prepared from

Quaternary ammonium halides:

Quaternary ammonium hydroxides

to form alkenes

and an amine

heat

β- Elimination

Methylenecyclohexane

(亚甲基环己烷)

(69%)

Ch.P448

(六)


Chapter 17 amines

Transition state

E2 Reaction

Anti relationship

The base attacks the most

acidic hydrogen or least

hinder hydrogen.

Regioselectivity of Hofmann elimination:

To give a less substituted alkene.


Chapter 17 amines

C1–C2

C2–C3

Hofmann rule is opposed to the Zaitsev rule.


Chapter 17 amines

August Wilhelm von , 1818–1892,

German organic chemist. He was

Professor at the Univ. of Berlin

from 1865 and was a founder

(1868) of the German Chemical

Society. He studied the constitu-

tion of aniline and was the first

to prepare rosaniline and its

derivatives, thereby laying the

basis for the aniline dye industry.

He also discovered a reaction for

deriving amines from amides and

developed the Hofmann method

of finding the vapor densities, and

from these the molecular weights,

of liquids. He also helped to

popularize the concept of valence

(the word comes from his term

quantivalence

August Wilhelm von

1818–1892


Chapter 17 amines

17.5.4 Reactions of amines with

nitrous acid (Nitrosation亚硝化反应)

(A) Reactions of primary aliphatic amines

with nitrous acid

Nitrosating agent:

Primary aliphatic amines

Nitrous acid

to yield unstable aliphatic diazonium salt

(重氮盐)

Diazotization (重氮化反应)

Aliphatic diazonium salts decompose to form

carbocations and nitrogen:


Chapter 17 amines

Alkene, alcohol, alkyl halide

(B) Reactions of primary arylamines

with nitrous acid

P390

Primary arylamines form diazonium salt on

nitrosation:

Aryl diazoniumsalts are stable below 5℃


Chapter 17 amines

(C) Reactions of secondary amines

with nitrous acid

Secondary amines: both aryl amines and

alkyl amines react with nitrous acid to yield

N-nitrosoamines(亚硝胺)

N-nitrosoamines are usually separated from

the reaction mixture as oily yellow liquids

(D) Reactions of tertiary amines

with nitrous acid


Chapter 17 amines

Tertiary aryl amines react with nitrous acid

to form C-nitroso aromatic compounds:

Electrophilic aromatic substitution

()

17.5.5 Synthetic transformations of aryl

diazonium salt

The diazonium group (重氮基)may be replaced by other atomes or groups: -X, -OH, -CN and -H.

P391


Chapter 17 amines

p-Isopropylaniline

p-Isopropylphenol

(73%)

Aryl diazonium salts can be prepared

from arene:

(A) Replacement of the diazonium

group by -OH

Aryl diazonium ion is converted to phenols(酚)

Hydrolysis

:Electron-withdrawing group

Sulfuric acid is usually used instead of

hydrochloric acid

Question: Design a synsthesis of


Chapter 17 amines

(B) Replacement of the diazonium

group by -X, -CN

The preparation of aryl iodides

(81%)

The preparation of aryl fluorides:

Treating the diazonium salt with fluoboric

acid (HBF4)

(69%)


Chapter 17 amines

The Sandmeyer reaction:

Aryl diazonium salts react with cuprous

chloride, cuprous bromide, cuprous cyanide

(70% overall)

(65% overall)


Chapter 17 amines

Born inWettingen near Zurich, and lived in the

Zurich area for nearly all of his life. He trained

as a precision instrument-maker, but became

interested in chemistry. Self-educated in

chemistry, he carried out chemical

experiments in his kitchen. In 1881, he became

a lecture assistant to Victor Meyer

(1848-1897). He followed Meyer to

Göttingen in 1886, but soon returned to

Zurich and worked for Arthur Hantzsch

(1857-1935). Sandmeyer joined Geigy as

a research scientist in 1888, and eventually

became a director of the firm. He discovered

the decomposition of aryl diazonium

Chlorides to chloroarenes in the presence of

copper (I) chloride in 1884. He also worked

on the triphenylmethane dyes and the synthesis

of isatin. Many years before, he had suggested

to Victor Meyer an impurity in commerical

benzene was responsible for the isatin reaction

with sulphuric acid, thereby paving the way

for Meyer's discovery of thiophen.

Traugott Sandmeyer

(1854-1922).


Chapter 17 amines

(C) Replacement of the diazonium

group by -H

Aryl diazonium salts react with

hypophosphorous acid (H3PO2) (次磷酸)

or ethanol to yield the product:

P392

Deamination

(脱氨基作用)

(85%)


Chapter 17 amines

1,3,5-Tribromo-

Benzene(74-77%)

Aniline

2,4,6-Tribromoaniline

(100%)

  • The value of diazonium salts in synthesis:

  • Substituents that are otherwise accessible

  • only with difficulty, such as -F, -I,

  • -CN, -OH, may be introduced onto

  • a benzene ring.

  • Compounds that have substitution patterns

  • not directly available by electrophilic

  • aromatic substitution can be prepared


Chapter 17 amines

17.5.6 Azo coupling (偶氮偶合反应)

Aryl diazonium salts are weak electrophiles,

they react with highly reactive aromatic

compounds, to yield azo compounds

Alkaline solution

Azo dyes (偶氮染料)

Orange II:

P393


Chapter 17 amines

17. 6 Spectroscopic analysis of amines

Ch.P437(四)

IR:

3000-3500 cm-1

two peaks

Streching

vibration

Primary amine

3280 cm-1

one peak

Secondary amines

Tertiary amines

No peak

Aliphatic

amines

Streching

vibration

1020-1220 cm-1

Aromatic

amines

1250-1360 cm-1


Chapter 17 amines

N–H Stretchingvibration

C–N

Stretching

vibration

Infrared spectrum of isobutylamine


Chapter 17 amines

苯环

伸缩

N-H伸缩

C-N伸缩

N-甲基苯胺的红外光谱


Chapter 17 amines

1H NMR

N - H

δ:0. 6 ~ 5 ppm

δ:2.2 ~ 2.8 ppm


Chapter 17 amines

Problems to Chapter 17

12.41

12.42

12.48

12.51

12.52

P402

12.21 (a), (d),(e)

12.22 (a), (c),(f)

12.24酶斯卡灵,一种

高效的致幻剂。从

仙人掌中得来。

12.27(b), (d),

12.29(b), (c)

12.30 (a)

12.31(b), (c)

12.37

12.39


Chapter 17 amines

Additional Problems to Chapter 17

  • What are the major products you would

  • expect from Hofmann elimination of the

  • following amines? Show the reactions.

1

  • N-Methylcyclopentylamine

  • (c)

2. Predict the product(s) of the following

reactions.Give the major product.


Chapter 17 amines

(3) How would you prepare the following

compounds from toluene? A diaonio

(重氮盐)replacement reaction is needed

in some instances.

(4) Ch.P464

(十六), (十七)


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