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Diterbitkan olehLeonardo Puttraa Telah diubah "9 tahun yang lalu
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AMINA Senyawa yang mengandung gugus NH2 Strukrur : RNH2
Jenis : Amina primer (1o) Amina sekunder (2o) Amina tersier (3o)
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Tata Nama Amina alifatik sederhana dinamakan dengan gugus alkil yang terikat pada atom N dan diberi akhiran amin.
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Sistem IUPAC, gugus NH2 dinamakan gugus amino
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Tata Nama : Jika atom N mengikat 4 gugus hidrokarbon akan bermuatan positif dam dikenal sebagai ion ammonium kuartener
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Tata Nama : Senyawa yang mengandung gugus –NH2 pada cincin benzena dinamakan sebagai derivat anilin.
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Tata Nama : Senyawa siklis dimana satu atom C atau lebih diganti dengan atom nitrogen, diberi nama khusus sebagai heterosiklik amin.
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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
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Contoh Senyawa Heterosiklis
Klorofil berwarna hijau adalah kompleks Mg dengan porfirin yang termodifikasi.
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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
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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 6
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Basicity Constant (Kb) and pKb
Kb is the equilibrium constant for the reaction: R3N + H H OH •• – • • OH •• R3N • • + + [R3NH+][HO–] Kb = [R3N] and pKb = - log Kb 2
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Ka and pKa of Conjugate Acid
Ka is the equilibrium constant for the dissociation of the conjugate acid of the amine: R3N • • + H H+ [R3N][H+] Ka = [R3NH+] and pKa = - log Ka 3
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Relationships between acidity and basicity constants
Ka Kb = pKa + pKb = 14 3
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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….
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Acid -Base Chemistry (Physical Properties)
m.p. 98 oC b.p. (very volatile > 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?
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“Regular” Cocaine Conjugate Acid of Cocaine (Physical Properties)
m.p. >195 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?
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Acid -Base Reactions
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Acid Base Reactions
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Basicity of Amines in Aqueous Solution
Amine Conj. Acid pKa NH3 NH4+ 9.3 CH3CH2NH2 CH3CH2NH CH3CH2NH3+ is a weaker acid than NH4+; therefore, CH3CH2NH2 is a stronger base than NH3. 6
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Effect of Structure on Basicity
1. Alkylamines are slightly stronger bases than ammonia. 2. Alkylamines differ very little in basicity. 5
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Basicity of Amines in Aqueous Solution
Amine Conj. Acid pKa NH3 NH4+ 9.3 CH3CH2NH2 CH3CH2NH (CH3CH2)2NH (CH3CH2)2NH (CH3CH2)3N (CH3CH2)3NH+ 10.8 Notice that the difference separating a primary, secondary, and tertiary amine is only 0.3 pK units. 6
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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. 5
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Basicity of Amines in Aqueous Solution
Amine Conj. Acid pKa NH3 NH4+ 9.3 CH3CH2NH2 CH3CH2NH (CH3CH2)2NH (CH3CH2)2NH (CH3CH2)3N (CH3CH2)3NH+ 10.8 C6H5NH2 C6H5NH3+ 4.6 6
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Decreased basicity of arylamines
NH2 •• H OH •• + Aniline (reactant) is stabilized by conjugation of nitrogen lone pair with ring p system. This stabilization is lost on protonation. NH3 + – • • OH •• + 2
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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 Kb 3.8 x 10-10 6 x 10-14 ~10-19 2
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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. 5
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Basicity of Arylamines
X NH2 X NH3+ X pKb pKa H CH CF O2N 7
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p-Nitroaniline NH2 O N – + O N – NH2 + +
•• • • + O N – •• • • NH2 + + Lone pair on amine nitrogen is conjugated with p-nitro group—more delocalized than in aniline itself. Delocalization lost on protonation. 2
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Aniline is 3800 times more basic than p-nitroaniline.
Effect is Cumulative Aniline is 3800 times more basic than p-nitroaniline. Aniline is ~1,000,000,000 times more basic than 2,4-dinitroaniline. 2
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(resembles an arylamine in basicity)
Heterocyclic Amines N •• N H •• is more basic than piperidine pyridine Kb = 1.6 x 10-3 Kb = 1.4 x 10-9 (an alkylamine) (resembles an arylamine in basicity) 9
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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 3
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Synthesis of Amines via Reductive Amination
In reductive amination, an aldehyde or ketone is subjected to catalytic hydrogenation in the presence of ammonia or an amine. O C R R' fast NH C R R' + NH3 + H2O The aldehyde or ketone equilibrates with the imine faster than hydrogenation occurs. 12
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Synthesis of Amines via Reductive Amination
The imine undergoes hydrogenation faster than the aldehyde or ketone. An amine is the product. O C R R' fast NH C R R' + NH3 + H2O NH2 R R' C H H2, Ni 12
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Example: Ammonia gives a primary amine.
H2, Ni O H NH2 + NH3 ethanol (80%) NH via: 18
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Example: Primary amines give secondary amines
CH3(CH2)5CH O + H2N H2, Ni ethanol CH3(CH2)5CH2NH (65%) 18
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Example: Primary amines give secondary amines
CH3(CH2)5CH O + H2N H2, Ni ethanol CH3(CH2)5CH2NH (65%) N CH3(CH2)5CH via: 18
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Example: Secondary amines give tertiary amines
H CH3CH2CH2CH O + H2, Ni, ethanol N CH2CH2CH2CH3 (93%) 18
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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
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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
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Curtius Rearrangement
Heating an acyl azide prepared from substitution an acid chloride Migration of R from C=O 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
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Cope Elimination Reaction
Amine Oxides Undergo a Cope Elimination Reaction
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COPE EXAMPLE Mild conditions
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Reactions of Amines Alkylation and acylation have already been presented
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Arylamines Are Not Useful for Friedel-Crafts Reactions
The amino group forms a Lewis acid–base complex with the AlCl3 catalyst, preventing further reaction Therefore we use the corresponding amide
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Diazonium Salts: The Sandmeyer Reaction
Primary arylamines react with HNO2, yielding stable arenediazonium salts NaNO HCl HONO
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Uses of Arenediazonium Salts
The N2 group can be replaced by a nucleophile
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Diverse Reactions of Arenediazonium Salts
Sequence of (1) nitration, (2) reduction, (3) diazotization, and (4) nucleophilic substitution leads to many different products
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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
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Aryl Nitriles and Carboxylic Acids
An arenediazonium salt and CuCN yield the nitrile, ArCN, which can be hydrolyzed to ArCOOH
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Formation of Phenols (ArOH)
From reaction of the arenediazonium salt with copper(I) oxide in an aqueous solution of copper(II) nitrate
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Reduction to a Hydrocarbon
By treatment of a diazonium salt with hypophosphorous acid, H3PO2
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Mechanism of Diazonium Replacement
Through radical (rather than polar or ionic) pathways
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Diazonium Coupling Reactions
Arenediazonium salts undergo a coupling reaction with activated aromatic rings, such as phenols and arylamines, to yield brightly colored azo compounds, ArN=NAr
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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
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Azo Dyes Azo-coupled products have extended conjugation that lead to low energy electronic transitions that occur in visible light (dyes)
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