AMINA

1
AMINA

• Senyawa yang mengandung gugus NH2
• Strukrur RNH2
• Jenis Amina primer (1o)
• Amina sekunder (2o)
• Amina tersier (3o)

2
Tata Nama

• Amina alifatik sederhana dinamakan dengan gugus
  alkil yang terikat pada atom N dan diberi akhiran
  amin.

3
Sistem IUPAC, gugus NH2 dinamakan gugus amino
4
Tata Nama

• Jika atom N mengikat 4 gugus hidrokarbon akan
  bermuatan positif dam dikenal sebagai ion
  ammonium kuartener

5
Tata Nama

• Senyawa yang mengandung gugus NH2 pada cincin
  benzena dinamakan sebagai derivat anilin.

6
Tata Nama

• Senyawa siklis dimana satu atom C atau lebih
  diganti dengan atom nitrogen, diberi nama khusus
  sebagai heterosiklik amin.

7
Beberapa Contoh Senyawa Heterosiklis Amin

• Alkaloid senyawa yang mengandung nitrogen yang
  bersifat basa dari tumbuhan dan hewan. Senyawa
  ini mempunyai struktur yang rumit dan sifat
  farmakologis (faali) yang nyata
• Nikotin dari tembakau
• Porfirin senyawa heterosiklis yang mengandung 4
  cicin pirol yang saling berikatan. Porfirin
  membentuk kompleks dengan ion logam. Apabila
  membentuk kompleks dengan Fe membentuk
  besi-porfirin yang menyebabkan warna darah merah
  pada darah arteri ? Hemoglobin

8
Contoh Senyawa Heterosiklis

• Klorofil berwarna hijau adalah kompleks Mg dengan
  porfirin yang termodifikasi.

9
Sifat-Sifat Fisik Amina

• Amina 1? dan 2? bersifat polar karena mampu
  membentuk ikatan hydrogen intermolekuler.
• Larut dalam air karena mampu membentuk ikatan
  hidrogen dengan air.
• Ikatan hidrogen

10
Measures of Basicity

• The basicity of amines may be measured by
• 1) Kb
• 2) pKb
• 3) Ka of conjugate acid
• 4) pKa of conjugate acid

11
Basicity Constant (Kb) and pKb

• Kb is the equilibrium constant for the reaction

R3NHHO
Kb
R3N
and
pKb
- log Kb
12
Ka and pKa of Conjugate Acid

• Ka is the equilibrium constant for the
  dissociation of the conjugate acid of the amine

R3NH
Ka
R3NH
and
pKa
- log Ka
13
Relationships between acidity and basicity
constants
Ka Kb 10-14
pKa pKb 14
14
The beverage reportedly produced using the
extract of leaves of Erythroxylon coca
The compound cocaine, it is an organic base
Merck Index, 2450, 11th ed. Caution May be
habit forming.
15
Acid -Base Chemistry(Physical Properties)

• m.p. 98 oC
• b.p. (very volatile gt 90 oC)
• Solubility
• Water 1.67 x 10-3 g/mL
• CHCl3 1.43 g/mL
• Ether 0.29 g/mL

What structural feature makes cocaine a base?
What simple compound can you relate it to?
16
Regular Cocaine Conjugate Acid of
Cocaine(Physical Properties)

• m.p. gt195 oC
• Solubility
• Water 2.5 g/mL
• CHCl3 0.08 g/mL
• Ether insoluble

What accounts for the differences in solubilities
of the base and conjugate acid?
17
Acid -Base Reactions
18
Acid Base Reactions
19
Basicity of Amines in Aqueous Solution

• Amine Conj. Acid pKa
• NH3 NH4 9.3
• CH3CH2NH2 CH3CH2NH3 10.8

CH3CH2NH3 is a weaker acid than NH4therefore,
CH3CH2NH2 is a stronger base than NH3.
20
Effect of Structure on Basicity

• 1. Alkylamines are slightly stronger bases than
  ammonia.
• 2. Alkylamines differ very little in basicity.

21
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.
22
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.

23
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

24
Decreased basicity of arylamines

• Aniline (reactant) is stabilized by conjugation
  of nitrogen lone pair with ring p system.
• This stabilization is lost on protonation.

25
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
3.8 x 10-10
6 x 10-14
10-19
Kb
26
Effect of Substituents on Basicity of Arylamines

• 1. Alkyl groups on the ring increase basicity,
  but only slightly (less than 1 pK unit).
• 2. Electron withdrawing groups, especially
  ortho and/or para to amine group, decrease
  basicity and can have a large effect.

27
Basicity of Arylamines

• X pKb pKa
• H 9.4 4.6
• CH3 8.7 5.3
• CF3 11.5 2.5
• O2N 13.0 1.0

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p-Nitroaniline

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

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Effect is Cumulative

• Aniline is 3800 times more basic
  thanp-nitroaniline.
• Aniline is 1,000,000,000 times more basic than
  2,4-dinitroaniline.

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Heterocyclic Amines
is more basic than
piperidine
pyridine
Kb 1.6 x 10-3
Kb 1.4 x 10-9
(an alkylamine)
(resembles anarylamine inbasicity)
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Preparation and Reactions of Amines
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The Gabriel Synthesis of Primary Amines
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Reductive Amination
34
Synthesis of Amines via Reductive Amination
In reductive amination, an aldehyde or ketoneis
subjected to catalytic hydrogenation in
thepresence of ammonia or an amine.
fast


NH3
H2O

• The aldehyde or ketone equilibrates with
  theimine faster than hydrogenation occurs.

35
Synthesis of Amines via Reductive Amination
The imine undergoes hydrogenation fasterthan the
aldehyde or ketone. An amine is the product.
fast


NH3
H2O
H2, Ni
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Example Ammonia gives a primary amine.
H2, Ni

NH3
ethanol
(80)
via
37
Example Primary amines give secondary amines
H2, Ni
ethanol
(65)
38
Example Primary amines give secondary amines
H2, Ni
ethanol
(65)
via
39
Example Secondary amines give tertiary amines

H2, Ni, ethanol
(93)
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Reductive Amination Is Versatile

• Ammonia, primary amines, and secondary amines
  yield primary, secondary, and tertiary amines,
  respectively

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Mechanism of Reductive Amination

• Imine is intermediate

42
Hofmann and Curtius Rearrangements

• Carboxylic acid derivatives can be converted into
  primary amines with loss of one carbon atom by
  both the Hofmann rearrangement and the Curtius
  rearrangement

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Hofmann Rearrangement

• RCONH2 reacts with Br2 and base
• Gives high yields of arylamines and alkylamines

44
Curtius Rearrangement

• Heating an acyl azide prepared from substitution
  an acid chloride
• Migration of ?R from CO to the neighboring
  nitrogen with simultaneous loss of a leaving group

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COPE REACTION
N-OXIDE
LESS HINDERED BETA HYDROGEN
SYN ELIMINATION
46
Amine Oxides Undergo a Cope Elimination Reaction
47
COPE EXAMPLE
Mild conditions
48
Reactions of Amines

• Alkylation and acylation have already been
  presented

49
Arylamines Are Not Useful for Friedel-Crafts
Reactions

• The amino group forms a Lewis acidbase complex
  with the AlCl3 catalyst, preventing further
  reaction
• Therefore we use the corresponding amide

50
Diazonium Salts The Sandmeyer Reaction

• Primary arylamines react with HNO2, yielding
  stable arenediazonium salts

NaNO2 HCl HONO
51
Uses of Arenediazonium Salts

• The N2 group can be replaced by a nucleophile

52
Diverse Reactions of Arenediazonium Salts

• Sequence of (1) nitration, (2) reduction, (3)
  diazotization, and (4) nucleophilic substitution
  leads to many different products

53
Preparation of Aryl Halides

• Reaction of an arenediazonium salt with CuCl or
  CuBr gives aryl halides (Sandmeyer Reaction)
• Aryl iodides form from reaction with NaI without
  a copper(I) salt

54
Aryl Nitriles and Carboxylic Acids

• An arenediazonium salt and CuCN yield the
  nitrile, ArCN, which can be hydrolyzed to ArCOOH

55
Formation of Phenols (ArOH)

• From reaction of the arenediazonium salt with
  copper(I) oxide in an aqueous solution of
  copper(II) nitrate

56
Reduction to a Hydrocarbon

• By treatment of a diazonium salt with
  hypophosphorous acid, H3PO2

57
Mechanism of Diazonium Replacement

• Through radical (rather than polar or ionic)
  pathways

58
Diazonium Coupling Reactions

• Arenediazonium salts undergo a coupling reaction
  with activated aromatic rings, such as phenols
  and arylamines, to yield brightly colored azo
  compounds, Ar?NN?Ar?

59
How Diazonium Coupling Occurs

• The electophilic diazonium ion reacts with the
  electron-rich ring of a phenol or arylamine
• Usually occurs at the para position but goes
  ortho if para is blocked

60
Azo Dyes

• Azo-coupled products have extended ? conjugation
  that lead to low energy electronic transitions
  that occur in visible light (dyes)