View
237
Download
5
Category
Preview:
Citation preview
10-1Chemistry 2060, Spring 2060, LSU
Chapter 10: AminesChapter 10: Amines
Sections 10.1-10.8Sections 10.1-10.8
10-2Chemistry 2060, Spring 2060, LSU
SectionsSectionsChapter 10: AminesChapter 10: Amines
1.1. IntroductionIntroduction2.2. Structure and classificationStructure and classification3.3. NomenclatureNomenclature4.4. Physical PropertiesPhysical Properties5.5. Basicity of aminesBasicity of amines6.6. Reaction with acidsReaction with acids7.7. Synthesis of arylamines: Reduction of –NO2 groupSynthesis of arylamines: Reduction of –NO2 group8.8. Reactions of primary amines with nitrous acidReactions of primary amines with nitrous acid
10-3Chemistry 2060, Spring 2060, LSU
Structure & ClassificationStructure & ClassificationClassificationClassification
• 1°, 2°, or , 3° amines1°, 2°, or , 3° amines: amines in which 1, 2, or 3 hydrogens of NH3 are replaced by alkyl or aryl groups
• 4° amines4° amines: ions in which nitrogen is bonded to four carbons and bears a positive charge
Methylamine(a 1° amine)
Trimethylamine(a 3° amine)
CH3
CH3
CH3-NH2 CH3-N
Tetramethylammonium bromide
(a 4° ammonium salt)
+CH3
CH3
CH3-N-CH3
Br-
10-4Chemistry 2060, Spring 2060, LSU
Structure & ClassificationStructure & ClassificationAmines are further divided into aliphatic, aromatic, Amines are further divided into aliphatic, aromatic,
and heterocyclic aminesand heterocyclic amines• aliphatic aminealiphatic amine: an amine in which nitrogen is bonded
only to alkyl groups• aromatic aminearomatic amine: an amine in which nitrogen is bonded
to one or more aryl groups
NH2 N-H
CH3
CH2-N-CH3
CH3
N-Methylaniline(a 2° aromatic
amine)
Benzyldimethylamine(a 3° aliphatic amine)
Aniline(a 1° aromatic
amine)
10-5Chemistry 2060, Spring 2060, LSU
Structure & ClassificationStructure & Classification• heterocyclic amineheterocyclic amine: an amine in which nitrogen is one
of the atoms of a ring
PyrrolePiperidinePyrrolidine Pyridine(heterocyclic
aliphatic amines)(heterocyclic
aromatic amines)
NN N N
HH H
10-6Chemistry 2060, Spring 2060, LSU
Structure & ClassificationStructure & ClassificationExample:Example: classify each amino group by type classify each amino group by type
(b)
(S)-(+)-Coniine
(a)
(S)-(-)-Nicotine
NNH
H N
CH3
H
N
O
O
OCH3
OH3C
Cocaine
(c)
10-7Chemistry 2060, Spring 2060, LSU
NomenclatureNomenclatureAliphatic amines: replace the suffix Aliphatic amines: replace the suffix -e-e of the parent of the parent
alkane by alkane by -amine-amine
The IUPAC system retains the common name The IUPAC system retains the common name anilineaniline
NH2
H2NNH2
C6H5
NH2
1,6-Hexanediamine(S)-1-Phenylethanamine2-Propanamine
NH2CH3
NH2
NO2
OCH3
NH2NH2
3-Methoxyaniline(m-Anisidine)
2-Methylaniline(o-Toluidine)
Aniline 4-Nitroaniline(p-Nitroaniline)
10-8Chemistry 2060, Spring 2060, LSU
NomenclatureNomenclatureAmong the various functional groups discussed in Among the various functional groups discussed in
the text, -NHthe text, -NH22 has one of the lowest priorities has one of the lowest priorities
H2NOH
COOH
NH2
2-Aminobenzoic acid(Anthranilic acid)
2-Aminoethanol
10-9Chemistry 2060, Spring 2060, LSU
NomenclatureNomenclatureCommon names for most aliphatic amines are Common names for most aliphatic amines are
derived by listing the alkyl groups bonded to derived by listing the alkyl groups bonded to nitrogen in one word ending with the suffix -nitrogen in one word ending with the suffix -amineamine
TriethylamineDicyclopentylamineMethylamine
N
H
CH3NH2
tert-Butylamine
NNH2
10-10Chemistry 2060, Spring 2060, LSU
Physical PropertiesPhysical PropertiesAmines are polar compounds, and both 1° and 2° Amines are polar compounds, and both 1° and 2°
amines form intermolecular hydrogen bondsamines form intermolecular hydrogen bonds• N-H- - - -N hydrogen bonds are weaker than O-H- - - -O
hydrogen bonds because the difference in electronegativity between N and H (3.0 - 2.1 = 0.9) is less than that between O and H (3.5 - 2.1 = 1.4)
CH3CH3 CH3NH2 CH3OH
-6.3 65.0-88.6
32.031.130.1molecular weight (g/mol)
boiling point (°C)
10-11Chemistry 2060, Spring 2060, LSU
BasicityBasicityAll amines are weak bases, and aqueous solutions All amines are weak bases, and aqueous solutions
of amines are basicof amines are basic
Kb = = = 4.37 x 10-4Keq[H2O][CH3NH3
+][OH
-]
[CH3NH2]
H
H
CH3-N: H-O-HH
H
CH3-N-H -:O-H
Methylammoniumhydroxide
Methylamine
++
10-12Chemistry 2060, Spring 2060, LSU
BasicityBasicityit is also common to discuss the basicity of amines it is also common to discuss the basicity of amines
by reference to the acid ionization constant of the by reference to the acid ionization constant of the corresponding conjugate acidcorresponding conjugate acid
• for any acid-conjugate base pair
pKa + pKb = 14.00
CH3NH3+
H2O
[CH3NH2][H3O+]
[CH3NH3+]
CH3NH2 H3O+++
2.29 x 10-11==Ka pKa = 10.64
10-13Chemistry 2060, Spring 2060, LSU
BasicityBasicityUsing values of pUsing values of pKKaa, we can predict the position of , we can predict the position of
equilibrium in acid-base reactionsequilibrium in acid-base reactions
• acetic acid is the stronger acid and, therefore, the position of this equilibrium lies to the right
CH3NH2 CH3COOH CH3NH3+ CH3COO-+ +
pKa 10.64pKa 4.76
(stronger acid)
(weaker acid)
(stronger base)
(weaker base)
10-14Chemistry 2060, Spring 2060, LSU
BasicityBasicity• aliphatic amines have about the same base strength,
pKb 3.0 - 4.0, and are slightly stronger bases than ammonia
CH3NH2
NH3
CH3CH2NH2
C6H11NH2
(CH3)2NH(CH3CH2)2NH
(CH3)3N
(CH3CH2)3N
Tertiary Aminesdiethylaminedimethylamine
cyclohexylamine
ethylaminemethylamine
Secondary Amines
Primary AminesAmmonia
pKaStructureAmine
trimethylaminetriethylamine
9.26
10.6410.81
10.66
10.7310.98
9.8110.75
pKb
4.74
3.363.19
3.34
3.273.02
4.193.25
10-15Chemistry 2060, Spring 2060, LSU
BasicityBasicity• aromatic amines are considerably weaker bases than
aliphatic amines
Cyclohexyl-amine
NH2
NH2
NH3+
NH3+
pKb 9.37
Aniline
OH-
OH-
pKb 3.34+ H2O
+ H2O
Cyclohexylammoniumhydroxide
Anilinium hydroxide
10-16Chemistry 2060, Spring 2060, LSU
BasicityBasicity• aromatic amines are weaker bases than aliphatic
amines because the resonance stabilization of the free base is lost on protonation
N N NH H H H
H NH HH +++
Interaction of the electron pair on nitrogen with the pi system of the aromatic ring
10-17Chemistry 2060, Spring 2060, LSU
BasicityBasicityElectron-withdrawing groups, such as halogen, Electron-withdrawing groups, such as halogen,
nitro, and carbonyl, decrease the basicity of nitro, and carbonyl, decrease the basicity of aromatic amines by decreasing the availability of aromatic amines by decreasing the availability of the electron pair on nitrogenthe electron pair on nitrogen
NH2 NH2O2N
Aniline(pKb 9.37)
4-Nitroaniline(pKb 15.0)
10-18Chemistry 2060, Spring 2060, LSU
BasicityBasicityExample:Example: select the stronger base in each pair of select the stronger base in each pair of
aminesamines
(D)(C)
(A) (B)
NH2CH3
CH2NH2
N
O
NH
(a)
(b)
or
or
10-19Chemistry 2060, Spring 2060, LSU
GuanidineGuanidineGuanidine, pGuanidine, pKKbb 0.4, is the strongest base among 0.4, is the strongest base among
neutral organic compoundsneutral organic compounds
• its basicity is due to the delocalization of the positive charge over the three nitrogen atoms
H2N-C-NH2
NH
H2OpKb 0.4
H2N-C-NH2
NH2+
OH-
++Guanidine Guanidinium ion
Three equivalent contributing structures
+ +
+
C
NH2
NH2H2N H2N C NH2
NH2
C
NH2
NH2H2N
10-20Chemistry 2060, Spring 2060, LSU
Reaction with AcidsReaction with AcidsAll amines, whether soluble or insoluble in water, All amines, whether soluble or insoluble in water,
react quantitatively with strong acids to form react quantitatively with strong acids to form water-soluble saltswater-soluble salts
NH2
HO
HO
OH
HClH2O
NH3+Cl
-
HO
HO
OH
(R)-Norepinephrine hydrochloride
(a water-soluble salt)
+
(R)-Norepinephrine(only slightly
soluble in water)
10-21Chemistry 2060, Spring 2060, LSU
Synthesis of 1° ArylaminesSynthesis of 1° ArylaminesMost are synthesized by nitration of an aromatic Most are synthesized by nitration of an aromatic
ring followed by catalytic reduction of the nitro ring followed by catalytic reduction of the nitro group to a primary aminegroup to a primary amine
COOH
NO2
3H2Ni
COOH
NH2
2H2O+(3 atm)
+
3-Nitrobenzoicacid
3-Aminobenzoicacid
10-22Chemistry 2060, Spring 2060, LSU
Reaction with Nitrous AcidReaction with Nitrous AcidNitrous acid is a weak acid, most commonly Nitrous acid is a weak acid, most commonly
prepared by treating an aqueous solution of prepared by treating an aqueous solution of NaNONaNO22 with H with H22SOSO44 or HCl or HCl
• nitrous acid reacts with amines of different types, depending on whether the amine is 1°, 2°, 3° and whether it is aliphatic or aromatic
• we concentrate on the reaction of nitrous acid with 1° aromatic amines because this reaction is useful in organic synthesis
HNO2 H2O H3O+ NO2
-+ Ka = 4.26 x 10-4
pKa = 3.37
+
10-23Chemistry 2060, Spring 2060, LSU
Reaction with Nitrous AcidReaction with Nitrous AcidTreating a 1° aromatic amine with HNOTreating a 1° aromatic amine with HNO22 gives a gives a
diazonium saltdiazonium salt
• warming the aqueous solution of the diazonium salt gives a phenol and N2 gas
NH2 NaNO2 HClH2O
N N Cl- H2O0°C
++
Benzenediazoniumchloride
+ +
Aniline(a 1° aromatic
amine)
Sodiumnitrite
N N Cl- H2O OH N2
Benzenediazoniumchloride
++
+
Phenol
Recommended