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Transcript of Asam Karboksilat Dan Turunannya
Asam Karboksilat dan Turunannya
Ayik Rosita P., M.Farm., Apt
Bagian Kimia Farmasi
Universitas Jember
Asam KarboksilatSenyawa yang memiliki satu gugus karbonil
yang berikatan dengan 1 gugus hidroksil
R C
O
O H
Karbonil
Hidroksil
Karbonil + Hidroksil gugus “Karboksil”
O
OH
O
O
aspirin
3
• The C—O single bond of a carboxylic acid is shorter than the C—O bond of an alcohol.
• This can be explained by looking at the hybridization of the respective carbon atoms.
Structure and Bonding
• Because oxygen is more electronegative than either carbon or hydrogen, the C—O and O—H bonds are polar.
Tata Nama IUPACMengganti akhiran –a dari alkana induk
dengan imbuhan asam –oatKarbon karboksil diberi no. 1Jika memiliki 2 gugus karboksilat, penamaan
diberi akhiran -dioat
C
O
OH
H C
O
OH
H3C
C
O
OH
HC
H2C C
O
OH
H2CC
Br
O
HO
Asam metanoat Asam etanoat
Asam 2-bromobutanoat
H3C
Asam propanadioat
5
• Compounds containing two carboxy groups are called diacids. Diacids are named using the suffix –dioic acid.
• Metal salts of carboxylate anions are formed from carboxylic acids in many reactions. To name the metal salt of a carboxylate anion, put three parts together:
H3C CO2H
CO2H
CO2H
CO2HH2C CHCO2H
asam p-toluat asam o-ftalat
asam sikloheksanakarboksilat
asam akrilat
Penamaan IUPAC, Struktur cincin mgd gugus karboksil‘Asam (struktur cincin)karboksilat’
IUPAC
Tata Nama TrivialTanpa sistematika4 asam karboksilat pertama, sering dinamai
dengan nama trivial
Banyaknya atom C Struktur Nama Trivial Penurunan nama
1 HCOOH Asam format semut
2 CH3CO2H Asam asetat cuka
3 CH3CH2CO2H Asam propionat susu, keju
4 CH3(CH2)2CO2H Asam butirat mentega
5 CH3(CH2)3CO2H Asam valerat akar valeria
6 CH3(CH2)4CO2H Asam kaproat kambing
7 CH3(CH2)5CO2H Asam enantat anggur
8 CH3(CH2)6CO2H Asam kaprilat kambing
Chapter 20 8
Common Names
Many aliphatic acids have historical names.Positions of substituents on the chain are
labeled with Greek letters.
CH3CH2CHC
Cl
OH
O
-chlorobutyric acid
CH3CH2CH2CHCH2COOH
Ph
-phenylcaproic acid
=>
Chapter 20 9
Naming Cyclic Acids
Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids.
Aromatic acids are named as benzoic acids.
COOH
CH(CH3)2
2-isopropylcyclopentanecarboxylic acid
COOH
OH
o-hydroxybenzoic acid(salicylic acid)
=>
10
Give the IUPAC and common names:
A. CH3—COOH
CH3
|B. CH3—CH—COOH
C.
Learning Check
COOH
Br
11
A. CH3—COOH ethanoic acid (acetic acid) CH3
|B. CH3—CH—COOH 2-methylpropanoic acid
(-methylpropionic acid)
C. 2-bromobenzoic acid(o-bromobenzoic acid)
Solution
COOH
Br
Sifat Fisika KimiaAsam karboksilat memiliki 3 ikatan kovalen
polar senyawa polar
H3C
C
O
O
H
Asam karboksilat mampu membentuk ikatan H dg Sesamanya atau dengan air dijumpai dlm bentuk dimer (bahkan dalam fase uap)
H3C C
O
O H
H O
C CH3
O
H3C C
O
O H
H
O H
Sifat Fisika KimiaKarena ikatan H asam karboksilat > alkohol
m.p & b.p lebih tinggi dari alkohol dg mw ekivalen
Karena As. Karboksilat mampu membentuk ikatan H dengan air mudah larut air
H3CH2C C
OH
O
H3CH2C
H2C OH
m.p -220Cb.p 1410C
m.p -1260Cb.p 97,20C
H3CH2C C
OH
OGugus polar
Rantai C non polar
Physical Properties
Highest bp of compounds studied so far!
Alcohols
Alkyl halidesAlkanes
Incr
easi
ng B
P
Ethers/Aldehydes/Ketones
Carboxylic acids
Solubility of Organics
One electronegative group per four carbons will make a compound dissolve in water
Fatty AcidsLong un-branched carboxylic acidsMost have between 12 and 20 carbonsDerived from the hydrolysis of fatsMost have an even number of C’s If unsaturated, the cis isomer predominatesUnsaturated have lower melt points than saturated
Melting PointsSaturated have higher melting points than
unsaturated fatty acids
Soap
Soap is made by adding NaOH to a fatThis reaction is called soponificationThis cleaves each of the fatty acids
producing the solid fatty acid salt (soap)The other product is glycerol
C
C
C
O C
O
O C
O
O C
O
H
H
H
H
H
+ NaOH3
C
O
ONa+
3
+H
H OH
OHH
OHH
Hfat or oil
glycerol
soap
Soap
C
O
ONa+
soap
polar non polar
Soap Micelles
O
O
OO O
O O O
OO
O
O
O
O
O
O
Modern Detergents
Dodecylbenzene Sodium
4dodecylbenzenesulfonate
CH2(CH2)10CH2
H2SO4
NaOHCH2(CH2)10CH2 SO3-Na+
Keasaman Asam Karboksilat
Mrpk sifat kimia yang paling menonjolAsam karboksilat terionisasi dalam air mbtk larutan
yang bersifat sedikit asamKeasaman < dari asam anorganik……. Karena bersifat
asam lemahDibanding alkohol, pKa as. Karboksilat lebih kecil
karena asam karboksilat dapat beresonansi terstabilkan & meningkatkan Ka
H3C C
O
O- H3C C
O-
O
Acidic Properties
It is the release of the hydrogen ion (proton) to the water molecule
This forms the acid particles H+ or H3O+
Reactions due to the acidic nature of carboxylic acidsThis release of protons when in water
gives the solution a pH of less than 7. The usual reactions of acids are present. The conditions for all these reactions is
room temperature.
Acids as Proton Doners
The carboxylate anion helps in the understanding of the carboxyl group to release a proton.
The extra negative charge can be on either oxygen. It is partially delocalised and adds to the stability of the anion
This extra stability increased the chances of it being formed.
CH3 CO
O-CH3 C
O-
O
26
Carboxylic Acids—Strong Organic BrØnsted-Lowry Acids
• Carboxylic acids are strong organic acids, and as such, readily react with BrØnsted-Lowry bases to form carboxylate anions.
27
• An acid can be deprotonated by a base that has a conjugate acid with a higher pKa.
• Because the pKa values of many carboxylic acids are ~5, bases that have conjugate acids with pKa values higher than 5 are strong enough to deprotonate them.
28
29
• Carboxylic acids are relatively strong acids because deprotonation forms a resonance-stabilized conjugate base—a carboxylate anion.
• The acetate anion has two C—O bonds of equal length (1.27 Å) and intermediate between the length of a C—O single bond (1.36 Å) and C=O (1.21 Å).
30
• Resonance stabilization accounts for why carboxylic acids are more acidic than other compounds with O—H bonds—namely alcohols and phenols.
• To understand the relative acidity of ethanol, phenol and acetic acid, we must compare the stability of their conjugate bases and use the following rule:
- Anything that stabilizes a conjugate base A:¯ makes the starting acid H—A more acidic.
31
• Ethoxide, the conjugate base of ethanol, bears a negative charge on the O atom, but there are no additional factors to further stabilize the anion. Because ethoxide is less stable than acetate, ethanol is a weaker acid than acetic acid.
• Phenoxide, the conjugate base of phenol, is more stable than ethoxide, but less stable than acetate because acetate has two electronegative O atoms upon which to delocalize the negative charge, whereas phenoxide has only one.
32
• Note that although resonance stabilization of the conjugate base is important in determining acidity, the absolute number of resonance structures alone is not what is important!
Figure 19.7Summary: The relationship
between acidity and conjugatebase stability for acetic acid,
phenol, and ethanol
33
The Inductive Effect in Aliphatic Carboxylic Acids
34
35
Substituted Benzoic Acids
Recall that substituents on a benzene ring either donate or withdraw electron density, depending on the balance of their inductive and resonance effects. These same effects also determine the acidity of substituted benzoic acids.
[1] Electron-donor groups destabilize a conjugate base, making an acid less acidic—The conjugate base is destabilized because electron density is being donated to a negatively charged carboxylate anion.
36
[2] Electron-withdrawing groups stabilize a conjugate base, making an acid more acidic. The conjugate base is stabilized because electron density is removed from the negatively charged carboxylate anion.
37
Figure 19.8How common substituents
affect the reactivity of abenzene ring towards
electrophiles and the acidity ofsubstituted benzoic acids
38
Sulfonic Acids
• Sulfonic acids have the general structure RSO3H.
• The most widely used sulfonic acid is p-toluenesulfonic acid.
• Sulfonic acids are very strong acids because their conjugate bases (sulfonate anions) are resonance stabilized, and all the resonance structures delocalize negative charge on oxygen.
Pembuatan Asam Karboksilat
1. Hidrolisis derivat asam karboksilatDerivat diserang air / OH- pada C karbonilex derivat : ester, amida, anhidrida, dll
RC OR' + H2O
O
RCO2H + R'OH
RC X + H2O
O
RCO2H + X-
2. Reaksi Grignard Reagen Grignard (1o, 2o, 3o,vinil, aril) dan gas CO2
kering
- Terjadi pemanjangan rantai (1 C lebih banyak)
RX RMgX RCO2HMg
Eter kering
1. CO2
2. H2O, H+
RX RCN RCO2HCN- H2O, H+
SN2
MgBr CO2H
fenilmagnesium bromida asam benzoat (85%)
Ex:
3. Reaksi Oksidasi
Oksidasi alkohol primer dan aldehida
H2C OH + K2Cr2O7
H+H2CH3C C
H2CH3C
O
OHH2C OH + KMnO4
H2C
H2CH3C
H+
CH2C
H2C
O
OH
H3C
Oksidator kuat
C + Ag(NH3)2+
H2CH3C
O
H
NH4OHC
H2CH3C
O
OHOksidator lemah
3. Reaksi OksidasiOksidasi alkena
H3C
C
H3C
CH
H2C CH3
OKsidator
Kuat
H3C
C
H3C
O CH2C CH3
O
H
+
OKsidator
KuatCO2H
CO2H
sikloheksena asam adipat
Derivat Asam Karboksilat
Senyawa yang menghasilkan asam karboksilat bila direx dg air
C
R X
O
Halida asam(asil halida)
C
R O
O
Anhidrida asam
C
O
R'
C
R O
O
R'
Ester
C
R N
O
Amida
R C N
Nitril
Halida Asam
Acyl halides are compounds that have a halogen atom in place of the OH group of a carboxylic acid. The most common acyl halides are acyl chlorides and acyl bromides.
C
R X
O
Halida asam(asil halida)
F, Cl, Br, I
Tata Nama Klorida/Bromida Asam Nama As. Karboksilat induk, dengan
mengubah imbuhan asam –at menjadi –il klorida/bromida
C
H3C Cl
O
Etanoil kloridaasetil klorida
CCH2
Br
O
CH
CH3
H2CH3C
3-metilpentanoil bromida-metilvaleril bromida
C
O
Cl
siklopentanakarbonil kloridaIUPACTrivial
46
Nomenclature of Acid Halides
IUPAC: alkanoic acid alkanoyl halide Common: alkanic acid alkanyl halide
C
O
Cl
CH2
NH2
CH2 C
O
Cl
I: 3-aminopropanoyl chloride
c: -aminopropionyl chloride
I: benzenecarbonyl bromide
c: benzoyl bromide
Rings: (IUPAC only): ringcarbonyl halide
I: 3-cylcopentenecarbonyl chloride
CH2 C
O
ClC
O
Cl 4
I: hexanedioyl chloride
c: adipoyl chloride
C
O
Br
CH
NO2
CH2 CH2H3C C
O
Cl
I: 4-nitropentanoyl chloride
c: -nitrovaleryl chloride
R C
O
Cl
: :
:....
Chapter 21 47
ReactivityReactivity decreases as leaving group
becomes more basic.
=>
Chapter 21 48
Interconversion of Derivatives
More reactive derivatives can be converted to less reactive derivatives.
=>
Chapter 21 49
Hydrolysis of Acid Chlorides and Anhydrides
Hydrolysis occurs quickly, even in moist air with no acid or base catalyst.
Reagents must be protected from moisture.
+CH3 C
O
Cl HOH CH3 C
O
OH + HCl
=>
Pembuatan Klorida AsamKlorida asam didapat dari asam karboksilat
induk melalui reaksi dengan tionil klorida (SOCl2) / zat penghalogen aktif lain (ex PCl3)
R
C
O
OH
+ SOCl2
R
C
O
Cl
+ SO2 + HCl
R
C
O
OH
+ PCl3
R
C
O
Cl
+ H3PO3
H3C
C
O
OH H3C
C
O
Cl
+ H3PO3+ PCl3
contoh
Asam asetatAsetil klorida
Anhidrida Asam
Loss of water from two molecules of a carboxylic acid results in an acid anhydride.
“Anhydride” means “without water.”
Tatanama Anhidrida asam
If the two carboxylic acid molecules forming the acid anhydride are the same, the anhydride is a symmetrical anhydride.
If the two carboxylic acid molecules are different, the anhydride is a mixed anhydride.
Symmetrical anhydrides are named by using the acid name and replacing “acid” with “anhydride.”
Mixed anhydrides are named by stating the names of both acids in alphabetical order, followed by “anhydride.”
tatanama indonesia Anhidrida ditempatkan di awal
The word acid is replaced with anhydride.For a mixed anhydride, name both acids.Diacids may form anhydrides if a 5- or 6-membered ring
is the product.
O
O
O
1,2-benzenedicarboxylic anhydridephthalic anhydride
54
Nomenclature of Acid Anhydrides
Acid anhydrides are prepared by dehydrating carboxylic acids
CH3 C
O
OH H O C
O
CH3+
CH3 C
O
O C
O
CH3- H2O
acetic acid acetic anhydrideethanoic anhydrideethanoic acid
R RC
O
O C
O: : : :....
CH3 C
O
O C
O
HC
O
O C
O
H
C
O
O C
O
C CO OO
I: benzenecarboxylic anhydride
c: benzoic andhydride
I: butanedioic acid
c: succinic acid
I: benzoic methanoic anhydride
c: benzoic formic anhydride
C C
O
OH
O
HOC C
O OO
- H2O
I: butanedioic anhydride
c: succinic anhydride
I: cis-butenedioic anhydride
c: maleic anhydride
Some unsymmetrical anhydrides
I: ethanoic methanoic anhydride
c: acetic formic anhydride
Pembuatan Anhidrida
Umumnya, anhidrida asam tidak dapat dibentuk langsung dari as. Karboksilat induk harus dibuat bentuk derivat yang reaktif (klorida asam)
R
C
O
Cl
+
R
C
O
O
OC
O
R'
klorida asam ion karboksilat
C
O
R'
anhidrida
56
Conversion of Carboxylic Acids to Acid Anhydrides
• High temperature dehydration of carboxylic acids results in two molecules of the acid combining and eliminating one molecule of water.
CH3 C
O
OH H O C
O
CH3+
CH3 C
O
O C
O
CH3- H2O
acetic acid acetic anhydrideethanoic anhydrideethanoic acid
• Cyclic anhydrides with 5 or 6-membered rings are prepared by dehydration of diacids.
2HC
2HCC
OH
OHC
O
O
2HC
2HCC
O
C
O
O
H2O-
I: butanedioic acid
c: succinic acid
I: butanedioic anhydride
c: succinic anhydride
• Draw a reaction showing the preparation of cyclohexanecarboxylic anhydride.
C
O
OC
O
H2O-C
O
O H2
Ester
An ester is a compound that has an OR’ group in place of the OH group of a carboxylic acid
Siklik ester lakton
C
R O
O
R'
Ester
Tatanama Ester
Nama suatu ester tdd 2 kataKata pertama gugus Alkil yang terikat
pada O karboksilKata kedua dari nama asam karboksilat
dengan membuatng kata asam
(inggris –ic acid -ate)
Naming of Esters
Esters are named from the acid and alcohol stem.
CH3 CO
O C2H5
Alcohol Stem
Acid Stem
Naming of Esters
the alcohol stem comes at the start of the ester name
the acid stem provides the second part of the name
the name of the ester usually ends with –anoate.
The previous ester is ethyl ethanoate.
61
Nomenclature of Esters
CH3 O C
O
CH3
alkyl
I: alkanoatec: alkanate
R C
O
OH
: :
..
..R RC
O
O....
: :
+H2O-
carboxylicacid
alcohol esterH+
H O R....
O C
O
H
• Esters occur when carboxylic acids react with alcohols
I: methyl ethanoate
c: methyl acetate
C
O
O CH(CH3)2 O C CH(CH3)2
O
C O C(CH3)3
O
CH3 O C
O
C
O
O CH3
I: phenyl methanoate
c: phenyl formateI: t-butyl benzenecarboxylate
c: t-butyl benzoate
I: isobutyl cyclobutanecarboxylate
c: noneI: cyclobutyl 2-methylpropanoate
c: cyclobutyl -methylpropionate
I: dimethyl ethanedioate
c: dimethyl oxalate
Uses of Esters
Esters can be used as AdhesivesPerfumesFlavouringspainkillers.
63
Ester Products
Aspirin Is used to relieve pain and
reduce inflammation. Is an ester of salicylic acid
and acetic acid.
Oil of wintergreen Is used to soothe sore
muscles. Is an ester of salicylic acid
and methanol.
CH3
O
CO
OH
O
C
OH
CH3O
O
C
64
Esters in Plants
Esters give flowers andfruits theirpleasant fragrances and flavors.
TABLE 16.4
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
Some Esters and usesEthyl 2-methylbutanoate CH3CH2CH(CH3)COOCH2CH3 Apple flavour 3-Methylbutyl ethanoate CH3COOCH2CH2CH(CH3)2 Pear flavour 1-Methylpropyl ethanoate CH3COOCH(CH3)CH2CH3 Banana flavour Ethyl methanoate HCOOCH2CH3 Raspberry flavour Butyl butanoate CH3CH2CH2COOCH2CH2CH2CH3 Pineapple flavour Phenylmethyl ethanoate CH3COOCH2C6H5 Oil of Jasmine 2-Ethanoyloxybenzoic acid (acetylsalicylic acid)
OCOCH3
COOH
Aspirin
Methyl 2-hydroxybenzoate (methyl salicylate)
OH
COOCH3
Muscle rub
Ethyl ethanoate CH3COOCH2CH3 Glue solvent Methyl 2-cyanopropenoate CH2=C(CN)COOCH3 Superglue Ethenyl ethanoate CH3COOCH=CH2 PVA glue
Pembuatan Ester Dari asam karboksilat dan alkohol
CH2CH2CH2COH
O
asam 4-fenilbutanoat
+ CH3CH2OH CH2CH2CH2COCH2CH3
O
etanol etil 4-fenilbutanoat (85%)
Dari suatu karboksilat dan alkil halida yang reaktif
CH2Cl
benzil klorida
CH2OCCH3
O
Benzil asetat (93 %)
+ OC
O
R'
ion karboksilat
Cyclic esters are called lactones. In systematic nomenclature, they are named as “2-oxacycloalkanones.”
four-membered ring lactones are β-lactones (the carboxyl oxygen is on the β-carbon),
five-membered ring lactones are γ-lactones and six-membered ring lactones are δ-lactones
68
CH2
CH2 CH2
OH
C
O
OHH+
H2O-
CH2
CH2 CH2
O
C
O
OC
O
OO
I: 4-hydroxybutanoic acid
c: -hydroxybutyric acid
I: 4-hydroxybutanoic acid lactone
c: -butyrolactone
O
O
O
H3C
O
O
CH3
O
Nomenclature of Cyclic Esters, “Lactones”
Cyclic esters, “lactones”, form when an open chain hydroxyacid reacts intramolecularly. 5 to 7-membered rings are most stable.
‘lactone’ is added to the end of the IUPAC acid name. ‘olactone’ replaces the ‘ic acid’ of the common name and ‘hydroxy’ is dropped but its
locant must be included.
I: 4-hydroxypentanoic acid lactone
c: -valerolactone
I: 6-hydroxy-3-methylhexanoic acid lactone
c: -methyl--caprolactone
I: 5-hydroxypentanoic acid lactone
c: -valerolactone
I: 3-hydroxypentanoic acid lactone
c: -valerolactone
Chapter 21 69
Lactones
Formation favored for five- and six-membered rings.
O
OCOOH
OH H+
H2O+
• For larger rings, remove water to shift equilibrium toward products
H+
H2O+O
O
OH
COOH
=>
70
• Esters react like acid halides and anhydrides but are less reactive toward nucleophiles because the carbonyl C is less electrophilic. Both acyclic esters and cyclic esters (lactones) react similarly. Esters are hydrolyzed by HOH to carboxylic acids, react with amines to amides, are reduced by hydrides to aldehydes, then to 1alcohols, and react with Grignards to 3 alcohols.
Reactions of Esters
R C
O
OH
: :..
H2O
R C
O
NH2
: :..
NH3
R C
O
H
: :
[H]
RCH2OH[H]
R':- MgBr+
R C
O
R'
R C
OH
R'
R'
R':- MgBr+
3º alcohol
1º alcohols
amide
acid
ketone
aldehyde
R C
O
O
: :..
R'..
+R'OH
H+
71
• Esters are hydrolyzed (broken down by water) to carboxylic acids or carboxylates by heating in acidic or basic media, respectively.
• Base-promoted ester hydrolysis is called saponification (Latin ‘soap-making’). Boiling animal fat (which contains ester groups) in an aqueous solution of a strong base (NaOH, KOH, etc.) makes soap. A soap is long hydrocarbon chain with an ionic end group.
Base Hydrolysis of Esters
• The mechanism of base hydrolysis is nucleophilic acyl substitution in which OH - adds to the ester carbonyl group producing a tetrahedral intermediate. The carbonyl group reforms as the alkoxide ion leaves, yielding a carboxylate.
CH3(CH2)10C
O
O CH3
K+OH-
CH3(CH2)10C
O
O H
OCH3-
-
c: potassium laurate
CH3(CH2)10C
O
O - K+ + CH3OH
liquid soap
• The leaving group, methoxide (OCH3-), like all alkoxides, is a strong base (pKb = -2).
It will deprotonate the carboxylic acid intermediate converting it to a carboxylate. The alkoxide, when neutralized, becomes an alcohol.
c: sodium laurate
I: sodium dodecanoateC
O
O- Na+
bar soap
Hydrolysis of Esters
Hydrolysis means the break-up of a molecule using water.
Esters can be hydrolysed by both acids and alkalis.
CH3 CO
O C2H5
+ H2Oreflux CH3 C
O
O H+ C2H5OH
Hydrolysis of Esters
Alkali hydrolysis gives the carboxylate salt.Acid hydrolysis leads to equilibrium, the yield
of products is never 100%Alkaline hydrolysis breaks up the ester
completely.
CH3 CO
O C2H5
+ H2O CH3 CO
O-+ C2H5OH
alkali
74
Base hydrolysis (also called saponification) Is the reaction of an ester with a strong base. Produces the salt of the carboxylic acid and an alcohol. O ||
CH3—C—O—CH2—CH3 + NaOH O
CH3—C—O– Na+ + HO—CH2—CH3
salt of carboxylic acid alcohol
Base Hydrolysis (Saponification)
R OCH3
O
RO
CH3
O
HO
addition elimination
R O
O
Ester
O-HNa+
Na+
O-CH3H
Na+
R O
OO-CH3
Na+
Hsodium saltof carboxylicacid
75
Cleaning Action of Soap
A soap Contains a nonpolar end
that dissolves in nonpolar fats and oils, and a polar end that dissolves in water.
Forms groups of soap molecules called micelles that dissolve in water and are washed away.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
76
C
O
OCH3
H
OHH
+
• Acidic hydrolysis of an ester yields a carboxylic acid (and an alcohol). The mechanism of acidic ester hydrolysis is the reverse of Fischer esterification. The ester is protonated by acid then attacked by the nucleophile HOH. Transfer of a proton and elimination of ROH yields the carboxylic acid. The reaction is not favorable. It requires at least 30 minutes of refluxing.
• Draw the complete mechanism of acid hydrolysis of methyl cyclopentanecarboxylate.
Acid Hydrolysis of Esters
C
O
OCH3
H+
H2O
H2O
C
O
OCH3
H
+
..
C
O
OCH3
H
OH
H+
..
C
O
OH + +H3O+ CH3OH
• Acid hydrolysis of an ester can be reversed by adding excess alcohol. The reverse reaction is called Fischer Esterification. Explain why base hydrolysis of an ester is not reversible.
77
In acid hydrolysis An ester reacts with water to produce a carboxylic acid and an alcohol. An acid catalyst is required.
O O H+ H—C—O—CH2—CH3 + H2O H—C—OH + H—O—CH2—CH3
Acid Hydrolysis of Esters
78
+H+
R RC
O
O....
: :
ester alcohol
H O R'....
R R'C
O
O....
: :
ester
+
alcohol
H O R....
• Nucleophilic acyl substitution of an ester with an alcohol produces a different ester. The mechanism is the same as acid hydrolysis of esters except that that the nucleophile is an alcohol rather than water. A dry acid catalyst must be used, e.g., HCl(g) or H2SO4. If water is present, it will compete with the alcohol as the nucleophile producing some carboxylic acid in place of the ester product.
• The process is also called Ester Exchange or Transesterification
Alcoholysis of Esters
CH3CH2OH2H2SO4
C
O
OC
O
O
C
O
OCH2CH3C
O
CH3CH2O + OH2
dicyclobutyl terephthalate
dicyclobutyl 1,4-benzenedicarboxylate
diethyl terephthalate
diethyl 1,4-benzenedicarboxylate
cyclobutanol
79
CH C
O
OCH3
H3C
H3CNH3
• Amines can react with esters via nucleophilic acyl substitution yielding amides but the reaction is difficult, requiring a long reflux period. Aminolysis of acid chlorides is preferred.
• Draw the mechanism aminolysis of methyl isobutyroxide with ammonia.
Aminolysis of Esters
CH C
O
NH3C
H3CH
H
H- OCH3-
+
CH C
O
NH3C
H3CH
H+ CH3OH
c: -methylpropionamide
I: 2-methylpropanamide
• Write an equation showing how the following amide can be prepared from an ester.
C
O
N(CH3)2C
O
(CH3)2N C
O
OCH3C
O
CH3O + 2 NH(CH3)2
• Note that the amide intermediate must deprotonate to form a stable, neutral amide. Thus the amine must have at least one H. NH3, 1° and 2° amines will work but not 3°.
80
• Esters are easily reduced with LiAlH4 to yield 1 alcohols. The mechanism is similar to that of acid chloride reduction. A hydride ion first adds to the carbonyl carbon temporarily forming a tetrahedral alkoxide intermediate. Loss of the –OR group reforms the carbonyl creating an aldehyde and an OR - ion. Further addition of H: - to aldehyde gives the 1 alcohol. Draw the mechanism and show all products.
Hydride Reduction of Esters
• The hydride intermediate can be isolated if DIBAH is used as a reducing agent instead of LiAlH4. 1 equivalent of DIBAH is used at very low temp. (-78 C).
1.
2. H3O+
excessLiAlH4
O
O• Draw and name the products.
1 equiv.1.
2. H3O+
78°C-
DIBAHO
O
CH3
O
CH3
H
OH
CH2OHOH
c: -butyrolactone
I: 4-hydroxybutanoic acid lactonec: none
I: 1,4-butanediol
c: -valerolactone
I: 4-hydroxypentanoic acid lactoneI: 4-hydroxypentanal
c: -hydroxyvaleraldehyde
R C
O
O R'LiAlH4
R C
O
H- OR'-
LiAlH4R C
O
H
H
-
R C
O
H
H
H
+ R'OHH3O+
81
• Esters and lactones react with 2 equivalents of Grignard reagent to yield 3 alcohols in which the 2 substituents are identical. The reaction occurs by the usual nucleophilic substitution mechanism to give an intermediate ketone, which reacts further with the Grignard to yield a 3 alcohol.
Grignard Reduction of Esters
C
O
OCH3
MgBr
C
O
- OCH3-
MgBr
C
O-
C
O
H
+ CH3OH
H3O+
O -
O
CH3
CH3 MgBr
O -CH3
CH3O -
H3O+
OH
CH3
CH3OH
I: 4-hydroxybutanoic acid lactone
methyl benzoate benzophenone
triphenylmethanol
triphenylmethoxide
c: -butyrolactone
4-methyl-1,4-pentanediol
CH3 MgBr
O
O
Amida
Senyawa yang mempunyai satu Nitrogen trivalen yang terikat pada suatu gugus karbonil
An amide has an NH2,NHR, NR2 or group in place of the OH group of a carboxylic acid.
C
R N
O
Amida
Tatanama AmidaAmides are named by using the acid
name, replacing “oic acid” or “ic acid” with“amide.”
For acids ending with “carboxylic acid,” “ylic acid” is replaced with “amide.”
84
R C
O
NH
H
R C
O
NH
R R C
O
NR
R
CH3CH2CH2 C
O
NH
HC
O
NH
H
Cl
CH3CH
CH3
C
O
NCH3
HC
O
NH
H3CC
O
NCH3
CH2CH3
Nomenclature of Amides
1° amide2° amideN-substituted amide
3° amideN,N-disubstituted amide
1° amides: ‘alkanoic acid’ + amide ‘’alkanamide’ a ring is named ‘ringcarboxamide’
I: butanamide
c: butyramideI: 3-chlorocyclopentanecarboxamide
c: none
I: p-nitrobenzenecarboxamide
c: p-nitrobenzamide
C
O
NH
HNO2
2° and 3° amides are N-substituted amides
I: N,2-dimethylpropanamide
c: N,-dimethylpropionamide
I: N-phenylethanamide
c: N-phenylacetamide
I: N-ethyl-N-methylcyclobutanecarboxamide
c: none
c: acetanilide
NO
H2N
nicotinamideO
N
N
NN
O
caffeine
• Cyclic amides are called lactams. •Their nomenclature is similar to that of lactones.•They are named as “2-azacycloalkanones” in systematic nomenclature
(“aza” is used to designate the nitrogen atom).
86
Nomenclature of Cyclic Amides, “Lactams”
CH2
CH2 CH2
NH
C
O
OH
H H2O-
CH2
CH2 CH2
NH
C
O
NH
O
NH
OBr
Cyclic amides, “lactams”, form when an open chain aminoacid reacts intramolecularly. 5 to 7-membered rings are most stable.
I: 4-aminobutanoic acid
c: -aminobutyric acid
I: 4-aminobutanoic acid lactam
c: -butyrolactam
‘lactam’ is added to the end of the IUPAC acid name. ‘olactam’ replaces the ‘ic acid’ of the common name and ‘amino’ is dropped but its
locant must be included.
I: 5-aminohexanoic acid lactam
c: -caprolactam
I: 3-amino-2-bromopropanoic acid lactam
c: -bromo--propionolactam
I: 4-amino-3-methylbutanoic acid lactam
c: -methyl--butyrolactam
NH
O
H3C
NH
O
CH3
Pembuatan AmidaDisintesis dari derivat asam karboksilat dan
amonia atau amina yang sesuai
C
R
O
Cl
C
R
O
O
C
R
O
O
C
R'
O
R'
R'2NH
R'2NH
R'2NH
C
R
O
NR'2
89
CH3 C N CN CH2CH2CH2 I
CH3O CN
CNHS
R C
O
NH
H H2O-
POCl3R C N
Nomenclature of Nitriles
Nitriles are produced when 1° amides are dehydrated with reagents like POCl3
• IUPAC: alkane + nitrile ‘alkanenitrile’• IUPAC rings: ‘ringcarbonitrile’• Common: alkanic acid + ‘onitrile’ ‘alkanonitrile’
I: ethanenitrilec: acetonitrile
I: 4-iodobutanenitrile
c: -iodobutyronitrile
I: 3-methoxycyclohexanecarbonitrile
c: none
I: p-thiobenzenecarbonitrile
c: p-mercaptobenzonitrile
COOH
CN
I: 2-cyanocyclopentanecarboxylic acid
c: none
Chapter 21 90
Thioesters
More reactive than esters because:-S-R is a better leaving group than -O-RResonance overlap is not as effective.
=>
Chapter 21 91
Carbonic Acid Esters
CO2 in water contains some H2CO3.
Diesters are stable.Synthesized from phosgene.
+C
O
ClCl CH3CH2OCOCH2CH3
O
2 CH3CH2OH
diethyl carbonate
=>
Chapter 21 92
Urea and Urethanes
Urea is the diamide of carbonic acid.Urethanes are esters of a monoamide
of carbonic acid.
+C
O
ClCl C
O
NH2H2N2 NH3urea
N C O
H2ONH C OH
O
a carbamic acid
ROHNH C OR
O
a urethane =>
Chapter 21 93
Polymers
Polycarbonates are long-chain esters of carbonic acid.
Polyurethanes are formed when a diol reacts with a diisocyanate.
N C ONCO
CH3
HOCH2CH2OH
NH CHN
CH3
C
O
OCH2CH2O
O
n
=>