Chapter 17 Carboxylic Acids, Anhydrides, Esters, and Amides Carboxylic Acids, Anhydrides, Esters,...
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Transcript of Chapter 17 Carboxylic Acids, Anhydrides, Esters, and Amides Carboxylic Acids, Anhydrides, Esters,...
Chapter 17
Carboxylic Acids, Carboxylic Acids, Anhydrides, Esters, Anhydrides, Esters, and Amidesand Amides
Introduction
Carboxylic acids, another carbonyl containing functional group also anhydrides, esters, and amides
loss of H2O is commonality here
RCOHO
RCOR'O
RCOCR'O O
RCNH2
O
RC-OHO
H-OCR'O
RC-OHO
H-OR' RC-OHO
H-NH2
A carboxylic acid An esterAn anhydride An amide
Carboxylic Acids
The functional group of a carboxylic acid is a carboxyl groupcarboxyl group, which can be represented in any one of three ways
CO2HCOOHC-OHO
Nomenclature
IUPAC namesFind the longest carbon chain that contains
the carboxyl group as the parent alkanedrop the final -ee and replace it by -oic acidoic acidcarboxyl group is carbon 1because the carboxyl carbon is understood
to be carbon 1, there is no need to give it a number
Nomenclature
in these examples, the common name is given in parentheses
an -OH substituent is indicated by the prefix hydroxy-; an -NH2 substituent by the prefix amino-
3-Methylbutanoic acid(Isovaleric acid)
Hexanoic acid(Caproic acid)
OH
O
OH
O1 1
63
OH
OOHH2N COOH
5-Hydroxyhexanoic acid
15
4-Aminobenzoic acid
Nomenclature
dicarboxylic acids have the suffix -dioic aciddioic acid and the parent contains both carboxyl groups
the numbers of the carboxyl carbons are not indicated
O
HOOH
O
Butanedioic acid(Succinic acid)
Ethanedioic acid(Oxalic acid)
Hexanedioic acid(Adipic acid)
Propanedioic acid(Malonic acid)
HO OH
O
OOH
O
OH
O
O
HO
O
HO
1 1
1 1
2 3
4 6OH
O
HO15
O
Pentanedioic acid(Glutaric acid)
CH3COOHHCOOH
CH3CH2COOHCH3(CH2)2COOHCH3(CH2)3COOHCH3(CH2)4COOHCH3(CH2)6COOHCH3(CH2)8COOHCH3(CH2)10COOHCH3(CH2)12COOHCH3(CH2)14COOHCH3(CH2)16COOHCH3(CH2)18COOH
DerivationCommon Name
IUPAC Name(acid)Structure
Greek: arachis, peanutGreek: stear, solid fatLatin: palma, palm treeGreek: myristikos, fragrantLatin: laurus, laurelLatin: caper, goatLatin: caper, goatLatin: caper, goatLatin: valere, to be strongLatin: butyrum, butterGreek: propion, first fatLatin: acetum, vinegarLatin: formica, ant
arachidicstearicpalmiticmyristiclauric
capriccapryliccaproicvalericbutyricpropionicaceticformic
eicosanoicoctadecanoichexadecanoictetradecanoicdodecanoicdecanoicoctanoichexanoicpentanoicbutanoicpropanoicethanoicmethanoic
Nomenclature
for common names, use, the Greek letters alpha (), beta (), gamma (), and so forth to locate substituents
C-C-C-C-OHO
OHH2N
O
OHOH
O
(-Aminobutyric acid; GABA)2-Hydroxypropanoic acid4-Aminobutanoic acid
4 3 2
1
4
1
2
(-Hydroxypropionic acid;lactic acid)
Physical Properties
The carboxyl group contains three polar covalent bonds; C=O, C-O, and O-H the polarity of these bonds determines the
major physical properties of carboxylic acids
Physical Properties
carboxylic acids have high boiling points these are a result of their polarity and the fact
that hydrogen bonding between two carboxyl groups creates a dimer that behaves as a higher-molecular-weight compound
H3C C
O
O
H
CH3C
O
O
H- +
+ -
hydrogen bondingbetween two molecules
Physical Properties
carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight
CH3COOHCH3CH2CH2OHCH3CH2CHO
CH3(CH2)2COOHCH3(CH2)3CH2OHCH3(CH2)3CHO
acetic acid
1-propanolpropanal
60.5
60.158.1
1189748
16388.1butanoic acid1-pentanol 88.1 137
103pentanal 86.1
Structure NameMolecularWeight
Boiling Point (°C)
Solubility(g/100 mL H2O)
infinite
infinite
16infinite
2.3slight
Acidity of RCOOHThe hydrogen on the oxygen is acidicsubstituents of high electronegativity,
especially -OH, -Cl, and -NH3+, near the
carboxyl group increase the acidity
CH3COOH ClCH2COOH Cl2CHCOOH Cl3CCOOHFormula:
pKa:
Name:
Increasing acid strength2.86
Chloroaceticacid
0.70
Trichloroaceticacid
1.48
Dichloroacetic acid
Acetic acid4.76
Reaction With Bases
All carboxylic acids react with NaOH, KOH, and other strong bases to form water-soluble salts
they also form water-soluble salts with ammonia and amines
COOH NaOHH2O
COO- Na
+H2O+ +
Benzoic acid(slightly soluble in water)
Sodium benzoate(60 g/100 mL water)
COOH NH3H2O
COO- NH4
++
Ammonium benzoate(20 g/100 mL water)
Benzoic acid(slightly soluble in water)
Ionization versus pH
The form in which a carboxylic acid exist in an aqueous solution depends on the solution’s pH
R-C-OHO OH-
H+ R-C-OHO
R-C-O-O
H+
OH-
R-C-O-O
at pH 2.0or lower
at pH 8.0or higher
+
at pH = pKa = 4.0 - 5.0both forms are present in
approximately equal amounts
Anhydrides
The anhydrideanhydride is two carbonyl groups bonded to the same oxygenThe most common are symmetrical but the
mixed anhydride may be made. to name an anhydride, drop the word "acidacid"
and add the word "anhydrideanhydride"
Acetic anhydrideCH3C-O-CCH3
O O
Esters
The esterester is a carbonyl group bonded to an -OR group esters names are derived from the names of the
parent carboxylic acids name the “R” first, followed by the name of the acid;
replace the suffix -icic acidacid by -ateate a cyclic ester is called a lactonelactone
CH3COCH2CH3
OO O
OO
O
O
A five-memberedlactone
Ethyl ethanoate(Ethyl acetate)
Diethyl pentanedioate(Diethyl glutarate)
Amides
The functional group of an amideamide is a carbonyl group bonded to a nitrogen atom to name an amide, drop the suffix -oic acidoic acid from the
IUPAC name of the parent acid, or -ic acidic acid from its common name, and add -amideamide
if the amide nitrogen is bonded to an alkyl or aryl group, name the group and show its location on nitrogen by N- ; two alkyl or aryl groups by N,N-di-
CH3CNH2
OCH3CNHCH3
OHCN(CH3)2
O
N-Methylacetamide(a 2° amide)
Acetamide(a 1° amide)
N,N-Dimethylformamide(a 3° amide)
Amidesa cyclic amide is called a lactamlactam
the penicillins are referred to as -lactam antibiotics
O
NH
O
NH
A four-membered lactam(a -lactam)
A seven-membered lactam
N
CH3
NH2
OHO
NHO
S
CH3
COOH
The penicillinsdiffer in the groupbonded to thecarbonyl carbon
The-lactam ring
Amoxicillin
Amides
the cephalosporins are also -lactam antibiotics
N
S
COOHO CH3
NHNH2
O
Cefalexin(a -lactam antibiotic)
The cephalosporinsdiffer in the groupbonded to the carbonylcarbon...
...and the group bonded to this carbon of the six-membered ring
Fischer Esterification
one of the most commonly used preparations of esterscarboxylic acid reacted with an alcohol in the
presence of an acid catalyst
reversible
CH3C-OHO
H-OCH2CH3
H2SO4CH3COCH2CH3
OH2O
Ethanoic acid(Acetic acid)
++
Ethyl ethanoate(Ethyl acetate)
Ethanol(Ethyl alcohol)
Preparation of Amides If a carboxylic acid and an amine are mixed, an
acid-base reaction to form an ammonium salt results if this salt is heated to a high enough temperature,
water is eliminated and an amide forms
H2OCH3C-NHCH2CH3
O
CH3C-O- H3NCH2CH3
OH2NCH2CH3CH3C-OH
O+
Aceticacid
Ethanamine(Ethylamine)
An ammonium salt
heat +
An amide
+
Preparation of Amides
it is much more common to prepare amides by treating an amine with an anhydride
CH3C-O-CCH3
O OH2NCH2CH3 CH3C-NHCH2CH3
OCH3COH
O+ +
Acetic anhdyride An amide
Hydrolysis of Anhydrides
carboxylic anhydrides, particularly the low-molecular- weight ones, react readily with water to give two carboxylic acids
CH3COCCH3
O OH2O CH3COH
OHOCCH3
O+ +
Acetic anhydride Acetic acid Acetic acid
Hydrolysis of Esters esters hydrolyze very slowly, even in boiling water hydrolysis becomes considerably more rapid,
however, when the ester is heated in aqueous acid or base
hydrolysis of esters in aqueous acid is the reverse of Fischer esterification
CH3COCH2CH3
O
H2OH+
CH3COHO
CH3CH2OH+ +
Ethyl acetate Acetic acid Ethanol
Hydrolysis of Esters hydrolysis of an ester using a hot aqueous base can
also work – but not a catalyst here! this reaction is often called saponificationsaponification, a
reference to its use in the manufacture of soaps the carboxylic acid formed reacts with hydroxide ion each mole of ester hydrolyzed requires one mole of
base
CH3COCH2CH3
ONaOH
H2OCH3CO-Na+
OCH3CH2OH
Sodiumhydroxide
+ +
Ethyl acetate Sodiumacetate
Ethanol
Hydrolysis of Amides amides require more vigorous conditions hydrolysis in hot aqueous acid is not catalytic hydrolysis is driven to completion by the acid-base
reaction between ammonia or the amine and the acid to form an ammonium ion
each mole of amide requires one mole of acid
CH3CH2CH2CNH2
OH2O HCl
H2OCH3CH2CH2COH
ONH4
+Cl-
Butanoic acidButanamide
++ +heat
Hydrolysis of Amides hydrolysis of an amide in aqueous base gives a
carboxylic acid salt and ammonia or an amine hydrolysis is driven to completion by the acid-base
reaction between the carboxylic acid and base to form a salt
each mole of amide requires one mole of base
CH3CNHO
NaOHH2O
CH3CO-Na+O
H2N
AnilineSodiumacetate
Acetanilide
++heat
Phosphoric Anhydrides the functional group of a phosphoric anhydridephosphoric anhydride is two
phosphoryl (P=O) groups bonded to the same oxygen atom
HO-P-O-P-OHOH OH
O O
O-
-O-P-O-P-O-O O
O-
OH OH
HO-P-O-P-O-P-OH
OH
O O O-O-P-O-P-O-P-O-
O O O
O- O- O-
Triphosphoric acid
Diphosphate ion(Pyrophosphate ion)
Diphosphoric acid(Pyrophosphoric acid)
Triphosphate ion
Phosphoric Esters phosphoric acid forms mono-, di-, and triphosphoric
esters it is common to name the organic molecule and then
indicate the presence of the phosphoric ester by either the word "phosphate" or the prefix phospho-
dihydroxyacetone phosphate and pyridoxal phosphate are shown as they are ionized at pH 7.4, the pH of blood plasma
CH3O-P-OHOCH3
O CCH2-O-P-O-
O O
O-
CH2OH
N
HO
H3C
CH2O-P-O-CHO O
O-
Dimethyl phosphate Dihydroxyacetonephosphate
Pyridoxal phosphate
Step-Growth Polymers
Step-growth polymersStep-growth polymers are formed by reaction between molecules containing two functional groups, with each new bond created in a separate step in this section, we discuss three types of
step-growth polymers; polyamides, polyesters, and polycarbonates
Polyamides Nylon-66Nylon-66 was the first purely synthetic fiber
it is synthesized from two six-carbon monomers
-H2O+
Hexanedioic acid(Adipic acid)
1,6-Hexanediamine(Hexamethylenediamine)
heat
n
Nylon-66(a polyamide)
O
HOOH
O
NN
ON
ON
H
HH
Hremove H2O
H
H
Polyamides the polyaromatic amide known as KevlarKevlar is also
made from aa aromatic dicarboxylic acid and an aromatic diamine
COHnHOCO O
N NH
HH
H
NHCNHCO O
-H2O
1,4-Benzenediamine(p-Phenylenediamine)
1,4-Benzenedicarboxylicacid
(Terephthalic acid)
nKevlar
(a polyaromatic amide)
+ heat
remove H2O
Polyesters the first polyester involved polymerization of this
diacid and ethylene glycol
OCH3
OCH3O
O HO
OH
O
O
OO
-CH3OH
Poly(ethylene terephthalate)(Dacron, Mylar)
heat
n
1,2-Ethanediol(Ethylene glycol)
Dimethyl terephthalate
+
remove CH3OH
Polycarbonates Lexan, the most familiar polycarbonatepolycarbonate, is formed by
reaction between the disodium salt of bisphenol A and phosgene
+Na-O
CH3
CH3
O-Na+ Cl Cl
O
OCH3
CH3
O
O
-NaCl
Phosgene
+
Disodium salt of Bisphenol A
Lexan(a polycarbonate)
n
remove Na+Cl-
End End Chapter 18Chapter 18
Chapter 18