ORGANIC CHEMISTRY Chapter 18 - Xiamen...
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ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 18 18.8 Amides
Transcript of ORGANIC CHEMISTRY Chapter 18 - Xiamen...
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 18
18.8 Amides
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 18
18.8A Synthesis of AmidesAmides can be prepared in a variety ways, starting with acyl chlorides, acid anhydrides, esters, carboxylic acids, and carboxylic salts.All of these methods involve nucleophilic addition-elimination reactions by ammonia or an amine at an acyl carbon.
R C LO
+ NH3
R'NH2R'R"NH
R C NH2
O
NHR'NR'R"
L = OH,OR',O C R,O
Cl, O Na
ORGANIC CHEMISTRY
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Chapter 18
18.8B Amides from Acyl ChloridesPrimary amines, secondary amines, and ammonia all react rapidly with acid chlorides to form amides. An excess of ammonia or amine is used to neutralize the HCl that would be formed otherwise.
R C ClO
+ NH3 R C ClO
NH3
R C NH3
O
NH3 R C NH2
ONH4+
An amide
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Chapter 18
R C ClO
+ R'NH2 R C ClO
H2NR C NH2
O
R'NH2 R C NHR'O
R'NH3+An N-substituted amide
R'R'
R C ClO
+ R'R"NH2 R C ClO
NH
R C NH
O
R'R"NHR C NR'R"
OR'NH3+
An N,N-disubstituted amide
R'
R'
R"R"
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Two molar equivalents of amine are required in the reaction. One molecule of amine acts as a nucleophile, the second as a base.It is possible to use only one molar equivalent of amine in these reactions if some other base, such as NaOH, pyridine, is present in the reaction mixture.
C6H5 C ClO
HNNaOH
H2OC6H5 C N
O+
C ClO
HN ONaOH
H2OC NO
O+CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
Schotten-Baumann reaction
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Tertiary amines react with acyl chlorides to form acylammonium chloride (氯化酰基铵)：
R C ClO
+ R C NR3ClO
Acylammonium chloride3°AmineR3N
Acylammonium ion is not stable in the presence of water or any hydroxylic solvent.
R C NR3ClO
H2O
R'OH
R C OHO
R C OR'O
+ R3NHCl
+ R3NHCl
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18.8C Amides from Carboxylic Anhydrides
R C O NH4
O+ NH3 R C NH2
O
R'NH2
R'R"NH2 R C NR'R"O
(RCO)2O 2 +
+(RCO)2O 2 R C NHR'O
R C O NH3R'O
+
+(RCO)2O 2 R C O NH2R'R"O
+
O
O
O
+ NH32 O NH4
O
O
NH2 ∆NH
O
OPhthalimide
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18.8D Amides from Esters
R CO
OR'" R'R"NH+ R CO
NR'R" R'"OH+R' and/or R"
may be HAmmonolysis of esters
CH2 C CCH3
OOCH3 + NH3
H2OCH2 C C
CH3
ONH2 + CH3OH
FCH2COCH2CH3
O+ NH2 FCH2C
ONH + CH3CH2OH
∆
75%
61%
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Chapter 18
DCC-Protected amide Synthesis
CO
OHR N C N C6H11C6H11+ C O
OH
R N
CN C6H11
C6H11
C O
OH
R N
CN C6H11
C6H11
C O
O
R N
CHN C6H11
C6H11R'NH2
C OO
R
N
CHN C6H11
C6H11NH2R'O
N
CHN C6H11
C6H11
CRNH2R'
O+
O
HN
CHN C6H11
C6H11
CR NH2R'O
+
Dicyclohexylcarbodiimide(DCC)
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18.8E Amides from Carboxylic Acids and Ammonium Carboxylates
R CO
OH + R CO
O NH4
+R C NH2
O
NH3
R CO
O NH4 (solid)∆
H2O
CH3CH2CH2CO2HNH3(g)
185℃CH3CH2CH2CONH2
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CH3CO
OH NH3+ CH3CO
O NH4
CH3CO
NH2 HOH+100 °C
n HO2C(CH2)4CO2H + H2N(CH2)6NH2n 270℃10 atm
C(CH2)4CO
HN(CH2)6NH n + H2O
Nylon-66
O
ORGANIC CHEMISTRY
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18.8F Hydrolysis of Amides
+R C NH2
OH2O
H+R C OH
O+ NH4
+R C NH2
OH2O
OHR C O
O+ NH3
∆
∆
CH3CH2CHC6H5
C NH2
OCH3CH2CH
C6H5
C OHO
+ H2OH2SO4
∆ + NH4 HSO4
BrNHCCH3
O+ H2O
KOH∆
BrH2N CH3CO2K+
88 ~ 90%
95%
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MechanismMechanismMechanism
CO
NH2R COH
NH2ROH2
COH
NH2RH+ H2O
COH
NH3ROH
COH
OHR + NH3 CO
OHR + NH4
CO
NH2R CO
NH2ROH
OHCO
OHR + NH2
CO
OR + NH3
ORGANIC CHEMISTRY
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18.8G Nitriles from the Dehydration of Amides
Primary amides react with dehydrating agents, such as P4O10(P2O5), POCl3, SOCl2, and acetic anhydride, to form nitriles.
CO
NH2RP4O10 or (CH3CO)2O
∆H2O
C NR + H3PO4
CH3CO2Hor
CO
NH2(CH3)2CHP4O10
200°CC N(CH3)2CH
69 ~ 86%
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18.8H Hydrolysis of Nitriles
C NR H2O+H+
or OH− CO2HR
H+R C NH
+R C NH
+ R C
OH2
NH+
R C
OH
NH2+
R C NH2
OH2
OH
+
R C OHOH+
R C NH2O
H2OR C NH3
OH
OH
+
R C OHOH
−H+
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Basic hydrolysis of amides
R C N OH+ R C
OH
NOHH
R C
OH
NHOH
R C NH
OH
OHR C NH2
O
OHR C OH
O+ NH2
R C OO
+ NH3
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18.8I LactamsCyclic amides are called lactams.Just as amides are more stable than esters, lactams are are more stable than lactones.β-Lactams are highly reactive, their strained four-membered rings open easily in the presence of nucleophilic reagents
NH
O
R NH
OR NH O
A β-lactam A γ-lactam A δ-lactam
R NH
O
A ε-lactam
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β-Lactams are among the best known products of the pharmaceutical industry.The penicillin and cephalosporin (头孢菌素) antibiotic, which are so useful in treating bacterial infections, are β-lactams and are customarily referred to as β-lactams antibiotics.
NO
S
CO2HCH3
HNCO
CHC6H5NH2
NO
NHCO
C6H5CH2 S CH3
CH3CO2H
Penicillin G Cephalexin 头孢氨苄青霉素 G
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18.8J ImidesCompounds that have two acyl groups bonded to a single nitrogen are known as imides.
RCN
RCR'
O
O
NH
O
O
NH
O
OImide Succinimide Phthalimide
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NH
O
O
KOHN K
O
O
RXN
O
O
R
H3O
CO2H
CO2H
+ R NH2
NH
O
O
NK
O
O
NBr
O
O
KOH
Br2
NBS
pKa 8.3
pKa 9.6
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Chapter 18
R CO
OH
R CO
X
R CO
O2
R CO
OR' R CO
NH2
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Chapter 18
Hydrolysis of Acid Derivatives
CH3COCl
(CH3CO)2O
CH3CO2C2H5
CH3CONH2
+ H2O
+ H2O
+ H2O
+ H2O
CH3COOH + HCl
2CH3COOH
CH3COOH + C2H5OH
CH3COOH + NH3
H+
or OH-
H+
or OH-
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1 0.97 0.053 1.15Relative rateCH3 C2H5 CH(CH3)2 C(CH3)3R
CH3CO2R H2OH
CH3CO2H ROH+
CH3 C
O
OC(CH3)3 CH3 C
OH
OC(CH3)3
H+
CH3 C
OH
O
H2O
CH3 C
OH
OC(CH3)3 + C(CH3)3
(CH3)3C OH2H+
(CH3)3C OH
ORGANIC CHEMISTRY
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Alcoholysis of Acid Derivatives
CH3COCl
(CH3CO)2O
CH3CO2CH3
CH3COOC2H5 + HCl
CH3COOC2H5 + CH3CO2H
CH3COOC2H5 + CH3OHH+
or C2H5O-
+ C2H5OH
+ C2H5OH
+ C2H5OH
base
base
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Amonolysis of Acid Derivatives
+ NH3
+ NH3
CH3CONH2 + CH3CH2OH
CH3CON(C2H5)2 + CH3CO2H
CH3CONH2 + HCl
CH3CO2CH2CH3
(CH3CO)2O
CH3COCl
+ (C2H5)2NH
CH3CONH2 + CH3NH2 CH3CONHCH3 + NH3
base
base
ORGANIC CHEMISTRY
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Chapter 18
Nucleophilic addition-elimination reaction
CO
YR CO
NuR+ Nu + Y
CO
YR CO
NuR+ Nu + Y
CO
YR
CO
NuR
+ Nu
+ Y
CO
YRNu
ORGANIC CHEMISTRY
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Acid-catalyzed mechanism
CO
YR
COH
NuR
+
Nu YCOH
YRNu
H+ COH
YR
HCO
NuR
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Chapter 18
Other Reactions of CarboxylicAcid Derivatives
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Reaction with Organometallic Reagents
——RR’C=ORR’C=ORCN
——RR’2COHRR’2COHRCO2R’’
RR’C=ORR’2COHRR’2COHRCOX
R’2CuLiRLiR’MgX
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Chapter 18
The reaction of acid anhydrides with Grignard reagent
R CO
O CO
RR'MgX
R COMgX
O CO
RR'
R CO
R' R CO
OMgX+
MgX
CH3OO
O
O
+
CH3O
O CO2H
H2O
ORGANIC CHEMISTRY
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Chapter 18
The reaction of amides with Grignard reagent
R CO
NH22R'MgX
R CO
N(MgX)2
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Chapter 18
Reductions
RCH2OHNaBH4
RCH2NH2
RCH2NH2RCH2OHR’OH
RCH2OHRCH2OHLiAlH4
RCH2NH2
RCH2NH2slowRCH2OHB2H6
RCH2NH2
RCH2NH2RCH2OHR’OH
RCH2OHRCH2OHH2/cat.
RCNRCONH2RCO2R’(RCO)2ORCOX
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R CO
OR' RCH2OH + R'OHNaEtOH
Bouveault—Blank Reaction
R CO
OR' e R CO
OR' R CO
OR'
R CO
OR'H
e R CO
OR'H
RCHO
1 321 2
3
Na EtOH
Na
RCH2O RCH2OHH+
ORGANIC CHEMISTRY
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Chapter 18
R CO
OR'
R CO
OR' XyleneR C ONa
R C ONa
R C O
R C OH
Acyloin condensation偶姻缩合
Na H2O
(CH2)n
CO2R
CO2R
Xylene(CH2)n
C O
C O(CH2)n
C O
C OH
Na H2O
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Mechanism Mechanism
R CO
OR'
R CO
OR'
R C O
R C O
R CO
OR'
R CO
OR'
R CO
OR'
R CO
OR'
2RO R C O
R C O
R C O
R C O
R C OHR C OH
R C O
R CH OH
2Na
2Na
H2O
2 e
2 e
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Elimination of esters
CH3 CO
OCH2CH3400~500℃ CH3CO2H + CH2 CH2
C CO H
C OCH3
C CO H
C OCH3
α β
OC OH
CH3+ C C
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Chapter 18
C CC6H5 C6H5
H H
C6H5 CH CH2C6H5
O CO
CH3
C CC6H5 H
H C6H5+
(Major product)
500℃
(Minor product)
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Chapter 18
MechanismMechanism
C CH C6H5
C6H5 HO H
C OCH3
C CH C6H5
C6H5 HO H
C OCH3
α β
C CC6H5
H
H C6H5
ORGANIC CHEMISTRY
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Chapter 18
MechanismMechanism
C CH H
C6H5 C6H5
O HC O
CH3
C CH H
C6H5 C6H5
O HC O
CH3
α β
C CC6H5 C6H5
H H
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Chapter 18
Regioselectivity
CH3 CHO
CH2CH2CH3
CO
CH3
CH2 CH CH2CH2CH3 CH3 CH CHCH2CH357% 43%
+
500℃
CH3 C CH2CH3
CH3
OCOCH3
CH2 C CH2CH3
CH3
CH3 C CHCH3
CH3
+76% 24%
PhCH2 CHOCOCH3
CH3 PhCH CH CH3 PhCH2 CH CH2
75% 25%+
Hofmann’s rule
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Chapter 18
CH3 CH2 O CS
SCH3 C CO H
C SCH3S
C CO H
C SCH3S
α β
OC SH
CH3S+C C
O C SCH3SH +
170℃
ORGANIC CHEMISTRY
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Chapter 18
Ot-Bu
H
HCS
SCH3 170℃t-Bu H
H
OCS
SCH3
PhCH CHOC
CH3 PhC CH CH391%
CH3
SSCH3 CH3
90~96%
ORGANIC CHEMISTRY
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Chapter 18
18.9 α-Halo Acids: The Hell-Volhard-Zelinski Reaction
α-卤代酸
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Chapter 18
Hell-Volhard-Zelinski Reaction
Aliphatic carboxylic acids react with bromine or chlorine in the presence of phosphorus (or a phosphorus halide, acyl halides) to give α-halo acids.
RCH2CO2H RCHCO2HX
(1) X2, P
(2) H2Oα-Halo acid
Hell-Volhard-Zelinski (or HVZ) reaction
CH3(CH2)3CHCO2HCH3(CH2)3CH2CO2H(1) Cl2, P
(2) H2O Cl
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MechanismMechanismMechanism
RCH2CO2HPBr3
RCHCO2HBr
RCH2CO
Br
RCH COH
BrBr Br
RCH COH
BrBr
+
H+
RCH CO
BrBr
RCH2CO2H
RCH2CO
Br+
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Chapter 18
RCH2CClO
+
I2RCH2CClO
+HI
SOCl2RCHCCl
O
I
N
O
O
XHX
SOCl2RCHCCl
O
X
X = Br, Cl
+ N
O
O
H
ORGANIC CHEMISTRY
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Chapter 18
Reactions of α-Halo Acids
RCHCO2HBr
RCHCO2HOH
RCHCO2HNH2
RCHCO2HCN
NaOHH2O
NH3
H+
(1)NaHCO3
(2) NaCN
H3O+RCHCO2H
CO2H
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Chapter 18
RCHCH2CO2HBr
NaOH-H2OCHCO2NaRCH
H+CHCO2HRCH
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Chapter 18
18.10 Derivatives of Carbonic Acid
碳酸衍生物
HO C OHO
碳酸Carbonic acid
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Chapter 18
18.10A Alkyl Chloroformates and Carbamates (Urethanes)氯甲酸酯和氨基甲酸酯
Cl C ClO
Cl C ORO
H2N C ORO
RO C ORO
光气
氨基甲酸酯
碳酸二酯
ROH
NH3
ROHCarbonyl dichloride
Alkylchloroformate氯甲酸酯
A carbamate
Dialkyl carbonate
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Cl C ClO
Cl C NH2
O
光气
C NHO
C NHO
氰酸
异氰酸
H2N C NH2
O
脲(尿素)
C NRO异氰酸酯
RHN C NHRO
N,N'－二取代脲
RN C NR碳二亚胺
氨基甲酰氯
NH3 HCl
NH3
RNH2
RNH2 PhSO2ClEt3N
DialkylcarbodiimideN,N'-Disubstitutedurea
Cyanic acidCarbamic chloride(phosgene)
Carbonyl dichloride
Isocyanic acid
Alkyl isocyanate
Urea
ORGANIC CHEMISTRY
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Benzyloxycarbonyl group is used to protect amino groups of amino acids in the synthesis of peptides and proteins.
C6H5CH2O C ClO
R NH2+ C6H5CH2O C NHO
ROH
C6H5CH2O C NHO
R
H2, Pd
HBrCH3CO2H
R NH2
R NH3
+ CO2 + C6H5CH3
+ CO2 + C6H5CH2Br
ORGANIC CHEMISTRY
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Carbamates can also be synthesized by allowing an alcohol to react with an isocyanate.
C NC6H5O R OH+ RO C NHC6H5
O
C NCH3O
OH
+
OC N
H
OCH3
ORGANIC CHEMISTRY
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Chapter 18
Chloroformic acid, alkyl hydrogen carbonates, and carbamic acid are not stable, which decompose spontaneously to liberate carbon dioxide.
HO C ClO
HO C OEtO
HO C NH2
O
氯甲酸
碳酸单乙酯
氨基甲酸
CO2 + HCl
CO2 + EtOH
CO2 + NH3
Chloroformic acid
Ethyl hydrogen carbonate
Carbamic acid
Unstable compounds
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Chapter 18
18.11 Decarboxylation of Carboxylic Acids
羧酸的脱羧反应
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Chapter 18
The loss of a molecule of carbon dioxide (CO2) from a carboxylic acid is called a decarboxylation.
R CO2H R H CO2+
Carboxylic acid Alkane Carbon dioxide
Decarboxylation
Decarboxylation of simple carboxylic acids takes place with great difficulty and is rarely encountered.Special groups usually have to be present in the molecule for decarboxylation to be rapid enough to be synthetically useful.
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β-Keto acids decarboxylate readily when they are heated to 100–150°C.
CH2 CO2HCRO
100−150°CCH3CR
OCO2+
A β-keto acid
CH2 CO2HCCH3
OCH3CCH3
OCO2+
Acetoacetic acid(3-Oxobutanoic acid)
Acetone(Propanone)
CH2 CO2HCC6H5
OCH3CC6H5
OCO2+
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There are two reasons for this case of decarboxylation:1. When the carboxylate anion decarboxylates, it forms
a resonance-stabilized enolate anion:
CH2 CCRO O
OCO2
CH2CRO
CRO
CH2
Resonance-stabilizedanion
HA
CH3CRO
Much more stable thanRCH2¯
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2. When the acid itself decarboxylates, it can do so through a six-membered cyclic transition state:
R
O
O
O OH
O
R O
O
CH3R
OH
CH2R－CO2
HO
HO
R OCyclic transistion state
Enol Ketone
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Malonic acids also decarboxylate readily for similar reasons.
CH2 CCHOO
OHO
100−150°C OH
O
HO O
CH3CHOO
Manolic acid
Acetic acidCO2+
CO2H
CO2H
185°CCO2H CO2+
74%
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Chapter 18
Aromatic carboxylic acids can be decarboxylated by converting them to a cuprous salt and then heating the salt with quinoline in an inert atmosphere in the presence of cuprous oxide.
Ar CO2HCu2O
Ar CO2Cu NCu2O, N2, heat
Ar H CO2+
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Carboxylic acids whose have an electron-withdrawing group attached at α-carbon decarboxylate readily when they are heated.
CH2 CO2H CO2+A CH3Aheat
A = NO2,CN,CO2H, CR,O
CX3, ArElectron-withdrawing groups
O2NCH2CO2H O2NCH3 + CO2
NCCH2CO2H NCCH3 + CO2
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18.11A Decarboxylation of Carboxyl Radicals
Carboxyl radicals (RCO2·) decarboxylate by losing CO2 and producing alkyl radicals:
R CO2 R CO2+
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Koble ReactionKoble Reaction
CH3(CH2)12CO2NaCH3ONa, CH3OH
ElectrolysisCH3(CH2)24CH3 + 2CO2
Hunsdiecker ReactionHunsdiecker Reaction
CH3
CH2CO2Ag
Br2
CCl4
CH3
CH2Br+ CO2 AgBr+
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Cristol ReactionCristol Reaction
2RCO2H + HgO + 2Br2
CCl4
Reflux2RBr + 2CO2 + HgBr2 + H2O
Kochi ReactionKochi Reaction
CH3CH2 CCH3
CH3
CO2HPb(OAc)2 , LiCl
C6H6 , ∆CH3CH2 C
CH3
CH3
Cl + CO2
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Mechanism Mechanism
R CO
OAg R CO
OBrBr2
R CO
OBr R CO
O + Br
R CO
O R ＋ CO2
R R CO
OBr+ R CO
O + RBr
(1)
(2)
(3)R R
R
R R+
R CO
O + R CO
OR
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Chapter 18
18.12 Chemical Tests for Acyl Compounds
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Chapter 18
Water-soluble carboxylic acids → blue litmus paperWater-insoluble carboxylic acids
NaOH (aq.) → dissolvedNaHCO3 (aq.) → dissolved+ CO2↑ (distinguish from phenols)
Acyl chlorides
R CO
ClH2O
R CO
OH + ClAgNO3 AgCl
Acid anhydridesNaOH (aq.) , heat → dissolved
Esters and amides: NaOH (aq.) , heat (hydrolysis)Esters → RCO2Na + R’OHAmides → RCO2Na + NH3 (R’NH2, R’2NH)
