The Physical and Chemical Properties, and Reactions of Amines
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Transcript of The Physical and Chemical Properties, and Reactions of Amines
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The Physical and Chemical
Properties, and Reactions of
Amines
Chem-261
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IntroductionOq.
04/19/23Dr Seemal Jelani 2 =>
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Classes of Amines
OPrimary (1): one C-N bond, 2 N-H bonds.
OSecondary (2): two C-N bonds, 1 N-H bond.
OTertiary (3): three C-N bonds, no N-H bond.
OQuaternary (4): four C-N bonds, nitrogen has a + formal charge. 04/19/23Dr Seemal Jelani 3
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Classify:
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N
H
CH3 C
CH3
CH3
NH2
NCH3
CH3
CH3CH2 N
CH3
CH2CH3+
Br_
=>
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Common NamesName the alkyl or aryl groups bonded to
nitrogen, then add suffix -amine.
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(CH3CH2)2NCH3
NHCH3
NH
diethylmethylamine
cyclopentylmethylamine
Diphenylamine =>
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Amine as SubstituentOOn a molecule with a higher priority
functional group the amine is named as a substituent.
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NH2CH2CH2CH2COOH
NHCH3
OH
-aminobutyric acid or4-aminobutanoic acid
2-methylaminophenol =>
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IUPAC NamesO Name is based on longest carbon chain.O -e of alkane is replaced with -amine.O Substituents on nitrogen have N- prefix.
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NH2CH2CH2CHCH2CH3
BrCH3CH2CHCH2CH2CH3
N(CH3)2
3-bromo-1-pentanamine N,N-dimethyl-3-hexanamine
=>
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Aromatic AminesAmino group is bonded to a benzene ring. Parent compound is called aniline.
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NH2
aniline
NCH3
CH3
N,N-dimethylaniline
=>
NH2
H3C
4-methylanilineor p-toluidine
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Heterocyclic AminesThe nitrogen is assigned the
number 1.
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N
H
N
H
N
HN N CH3
aziridinePyrrole
PyrrolidinePyridine
2-methylpyridine
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Structure of AminesNitrogen is sp3 hybridized with a lone pair of
electrons in an sp3 orbital.
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Chirality of AminesNitrogen may have 3 different groups and a lone pair, but enantiomers cannot be isolated due to inversion around N.
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Boiling PointsO N-H less polar than O-H.O Weaker hydrogen bonding.O Tertiary amines cannot hydrogen bond.
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Solubility and Odor
OSmall amines (<6 C) soluble in water.OAll amines accept hydrogen bonds from
water and alcohol.OBranching increases solubility.OMost amines smell like rotting fish.
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NH2CH2CH2CH2CH2CH2NH2
1,5-pentanediamine or cadaverine=>
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Basicity of AminesOLone pair of electrons on nitrogen can
accept a proton from an acidOAqueous solutions are basic to litmus.OAmmonia pKb = 4.74
OAlkyl amines are usually stronger bases than ammonia
O Increasing the number of alkyl groups decreases solvation of ion, so 2 and 3 amines are similar to 1 amines in basicity. 04/19/23Dr Seemal Jelani 14
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OAlkyl Amine is more basic than ammonia because of the +I effect of the Alkyl group present
O It donates its electron cloud to the nitrogen group therefore nitrogen has a greater tendency to donate it lone pair of electrons
O This makes it more basic than ammonia where such a positive inductive effect is absent.
Why is alkyl amine more basic than ammonia?
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Resonance EffectsAny delocalization of the electron pair weakens
the base.
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Amine Salts
OIonic solids with high melting points OSoluble in water ONo fishy odor
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Reactions of AminesChem-261
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Reaction of AminesO Amines are BASES!
O React with acids and accept a proton (H+) to Form alkyl ammonium salts
methylamine
NH2H3C + HCl
methylammonium chlorideNH3
+ Cl-H3C
diethylamine
NH CH2 CH3CH2CH3 + HCl
diethylammonium chloride
NH2CH2 CH3CH2CH3+
Cl-
N,N-dimethylaniline
N CH3CH3
+ HCl
NH CH3CH3
N,N-dimethylanilinium chloride
+Cl-
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Reaction of AminesO Amines are BASES!
?
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Electrophilic Substitution of Aniline
O-NH2 is strong activator, o-,p-directing.
OMay trisubstituted with excess reagent.OH+ changes -NH2 to -NH3
+, a meta-directing deactivator.
OAttempt to nitrate aniline may explode.
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Aniline Substitution
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Electrophilic Substitution of Pyridine
OStrongly deactivated by electronegative N.OSubstitutes in the 3-position.OElectrons on N react with electrophile.
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N
fuming H2SO4
HgSO4, 230oC
N
SO3H
=>
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Alkylation of Alkylation of AmmoniaAmmonia
Desired reaction is:Desired reaction is:
2 NH2 NH33 ++ R—XR—X R—NHR—NH22++ NHNH44XX
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Alkylation of Alkylation of AmmoniaAmmonia
Desired reaction is:Desired reaction is:
2 NH2 NH33 ++ R—XR—X R—NHR—NH22++ NHNH44XX
via:via:
HH33NN ••••••••
••••RR XX••••
HH33NN RR++ ••••
••••XX••••
••••––
++ ++
then:then:
HH33NN •••• ++
HH NN
HH
HH
RR++
HH33NN HH++
++ NN
HH
HH
RR••••
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Alkylation of Alkylation of AmmoniaAmmonia
But the method doesn't work well in practice.But the method doesn't work well in practice.Usually gives a mixture of primary, secondary,Usually gives a mixture of primary, secondary,and tertiary amines, plus the quaternary salt. and tertiary amines, plus the quaternary salt.
NNHH33
RRXXRRNNHH22
RRXXRR22NNHH
RRXX
RR33NNRRXX
RR44NN++
XX––
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ExampleExample
CHCH33(CH(CH22))66CHCH22BrBrNHNH33
CHCH33(CH(CH22))66CHCH22NHNH22
(45%)(45%)
++
CHCH33(CH(CH22))66CHCH22NHNHCHCH22(CH(CH22))66CHCH33
(43%)(43%)
OAs octylamine is formed, it competes with ammonia for the remaining 1-bromooctane. Reaction of octylamine with 1-bromooctane gives N,N-dioctylamine.
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Ogives primary amines without formation ofsecondary, etc. amines as byproducts
Ouses an SN2 reaction on an alkyl halide to formthe C—N bond
Othe nitrogen-containing nucleophileis N- potassiophthalimide
Gabriel SynthesisGabriel Synthesis
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Othe pKa of phthalimide is 8.3
ON- potassiophthalimide is easily prepared by
the reaction of phthalimide with KOH
N-PotassiophthalimideN-Potassiophthalimide OO
OO
NN•••• ••••––
KK++
OO
OO
NNHH••••KOHKOH
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N-Potassiophthalimide as a N-Potassiophthalimide as a nucleophilenucleophile OO
OO
NN•••• ••••–– ••••
••••RR XX••••
++
OO
OO
NN RR••••
+ + ••••
••••XX••••
••••––
SSNN22
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Cleavage of Alkylated Cleavage of Alkylated PhthalimidePhthalimide
OO
OO
NN RR•••• ++ HH22OO
HH22NN RR++
COCO22HH
COCO22HH
acid or baseacid or base
Oimide hydrolysis is imide hydrolysis is nucleophilic acyl nucleophilic acyl substitutionsubstitution
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Formation of Sulfonamides
OPrimary or secondary amines react with sulfonyl chloride.
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R NH2 S
O
O
R' Cl S
O
O
R' NH R
H
+Cl
_base S
O
O
R' NH R
• Sulfa drugs are sulfonamides that are antibacterial agents.
NH2
S OO
NH2=>
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Oxidation of AminesOAmines are easily oxidized, even in air.OCommon oxidizing agents: H2O2 , MCPBA.OMeta chloroperoxybenzoic acidO2 Amines oxidize to hydroxylamine (-NOH)O3 Amines oxidize to amine oxide (-N+-O-)
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Reduction
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CH3 C
O
ClNH3
CH3 C
O
NH2
LiAlH4
H2O
1)
2)CH3 CH2 NH2
primary amine
LiAlH4
H2O
1)
2)C
O
ClHN(CH3)2
C
O
N(CH3)2CH2 N(CH3)2
tertiary amine =>
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Reduction of Nitro Compounds (1)
O -NO2 is reduced to -NH2 by catalytic hydrogenation, or active metal with acid.
O Commonly used to synthesize anilines.
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CH3
NO2
Zn, HCl
CH3CH2OH
CH3
NH2
=>
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Hofmann Rearrangement of
Amides (1)In the presence of a strong base, primary amides react with chlorine or bromine to form amines with one less C.
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C
O
NH2H2O
Br2, OH_
NH2
=>