Transcript Chapter 20: Carboxylic Acids and Nitriles

Chapter 21
Carboxylic Acid Derivatives:
Nucleophilic Acyl
Substitution Reactions
Why this Chapter?
Carboxylic acids are among the most widespread of
molecules.
A study of them and their primary reaction
“nucleophilic acyl substitution” is fundamental to
understanding organic chemistry
Carboxylic Compounds

Acyl group (C=O) bonded to X, an electronegative atom
or leaving group
X includes: halide (acid halides), acyloxy (anhydrides),
alkoxy (esters), amine (amides), thiolate (thioesters),
phosphate (acyl phosphates)
2
General Reaction Pattern

Nucleophilic acyl substitution
3
21.1 Naming Carboxylic Acid Derivatives

Acid Halides, RCOX
◦ Derived from the carboxylic acid name by replacing the
-ic acid ending with -yl or the
◦ -carboxylic acid ending with –carbonyl and
◦ specifying the halide
Acetic Acid

Benzoic Acid

Acetyl chloride
Benzoyl bromide
Cyclohexanecarboxylic
Acid

4
Cyclohexanecarbonyl
chloride
Naming Acid Anhydrides, RCO2COR'

If symmetrical replace “acid” with “anhydride” based on
the related carboxylic acid
Acetic anhydride

Benzoic anhydride
Succinic anhydride
Unsymmetrical anhydrides - cite the two acids alphabetically
Acetic benzoic anhydride
5
Naming Amides, RCONH2
With unsubstituted NH2 group. replace

◦ -oic acid or -ic acid with -amide, or by replacing the
◦ -carboxylic acid ending with –carboxamide
Acetamide

Cyclopentane
-carboxamide
Hexanamide
If the N is further substituted, identify the substituent
groups (preceded by “N”) and then the parent amide
N-Methylpropanamide
N,N-Diethylcyclohexanecarboxamide
6
Naming Esters, RCO2R’

Name R’ and then, after a space, the carboxylic
acid (RCOOH), replace“-ic acid” with “-ate”
Malonic acid

Dimethyl malonate
Acetic acid

Ethyl acetate
Cyclohexanecarboxylic acid

tert-Butyl cyclohexanecarboxylate
7
Naming Thioesters, RCOSR’

Name like an ester but:
For common names
add “thio” before the acid name “-ate”
Methyl acetate

Methyl thioacetate
For IUPAC names
Ethyl butanoate

Ethyl butanthioate
Methyl cyclohexanecarboxylate

Methyl cyclohexanecarbothioate
Replace “-oate” or “-carboyxlate” with “thioate” or “-carbothioate”
Naming Acyl Phosphates

Name Acyl group then add -phosphate:
Benzoyl phosphate
Acetyl adenosyl phosphate
If an alkyl group is attached to a phospate O name it
after the acyl group
Naming Summary:
Learning Check:
Name the following:
Solution:
Name the following:
4-methylpentanoyl chloride
Cyclohexylacetamide
Isopropyl 2-methylpropanoate
Learning Check:
Name the following:
Solution:
Name the following:
Benzoic anhydride
Isopropyl cyclopenanecarboxylate
Cyclopentyl 2-methylpropanoate
Learning Check:
Name the following:
Solution:
Name the following:
N-Methyl-4-pentenamide
(R)-2-Hydroxypropanoyl phosphate
Ethyl 2,3-dimethyl-2-butenethioate
21.2 Nucleophilic Acyl Substitution

Carboxylic acid
derivatives have an acyl
carbon bonded to a group
Y that can leave

A tetrahedral
intermediate is formed
and the leaving group is
expelled to generate a
new carbonyl compound,
leading to substitution
17
Nucleophilic Acyl Substitution
Relative Reactivity of Carboxylic Acid Derivatives
Nucleophiles
react more
readily with
unhindered
carbonyl groups

More electrophilic carbonyl groups are more reactive to addition
◦ (acyl halides are most reactive, amides are least)

The intermediate with the best leaving group decomposes fastest
19
Substitution in Synthesis
More
reactive
acid
derivatives
can be
readily
converted
into a less
reactive
one

Reactions in the opposite sense are possible but require more complex approaches
20
General Reactions of Carboxylic Acid
Derivatives
ammonia or an amine  an amide
alcohols  esters
water  carboxylic acid
hydride source  an aldehyde or an alcohol
Grignard reagent  a ketone or an alcohol
Learning Check:
Complete the following reaction:
Solution:
Complete the following reaction:
Learning Check:
Rank compounds in the following sets in order of reactivity
toward nucleophilic acyl substitution: (#1 = fastest)
Solution:
Rank compounds in the following sets in order of reactivity
toward nucleophilic acyl substitution: (#1 = fastest)
1
2
3
3
2
1
21.3 Reactions of Carboxylic Acids
Nucleophilic Acyl Substitution
Must enhance reactivity
 Convert OH into a better leaving group
 Specific reagents can produce acid chlorides,
anhydrides, esters, amides

26
Carboxylic Acids into Acid Chlorides

Reaction with thionyl chloride, SOCl2
27
Mechanism of Thionyl Chloride Reaction


Nucleophilic acyl substitution pathway
Carboxylic acid is converted into a chlorosulfite which
then reacts with chloride
28
Carboxylic Acids into Acid Anhydrides

Acid anhydrides can be derived from two molecules of
carboxylic acid by strong heating to remove water
29
Carboxylic Acids into Esters

Methods include reaction of a carboxylate anion with a
primary alkyl halide
30
Fischer Esterification

Heating a carboxylic acid in an alcohol solvent containing
a small amount of strong acid produces an ester from the
alcohol and acid
31
Mechanism of the Fischer Esterification

acid-catalyzed,
nucleophilic acyl
substitution of a
carboxylic acid
32
Mechanism of the Fischer Esterification
When 18O-labeled methanol reacts with benzoic acid, the methyl
benzoate produced is 18O-labeled but the water produced is unlabeled
Carboxylic Acids into Amides
Amides difficult
to prepare.
 Carboxylic acids
more easily react
with amines to
make salts.
 Reaction with
DCC makes
better leaving
group that will be
kicked out by an
amine.

34
Carboxylic Acids into Alcohols
Carboxylic Acids into Alcohols
•Preferred over LiAlH4 due to relative ease and safety.
•Selectively reduces Carboxylic acids in presence of
nitros
21.4 Chemistry of Acid Halides


Acid chlorides are prepared from carboxylic acids by
reaction with SOCl2
Reaction of a carboxylic acid with PBr3 yields the acid
bromide
37
Reactions of Acid Halides
Nucleophilic acyl substitutions
Halogen replaced by OH, by OR, or by NH2
Reduction yields a primary alcohol
Grignard reagent yields a tertiary alcohol
38
Hydrolysis: Acid Halides into Acids


Acid chlorides react with water to yield carboxylic acids
HCl is generated during the hydrolysis: a base is added to
remove the HCl
39
Acid Halides to Esters


Esters are produced in the reaction of acid chlorides with
alcohols in the presence of pyridine or NaOH. This is
called Alcoholysis
The reaction is better with less steric bulk
40
Aminolysis: Acid Halides into Amides

Amides result from the reaction of acid chlorides with
NH3, primary (RNH2) and secondary amines (R2NH)
HCl produced is neutralized by
the amine or an added base
The reaction with tertiary amines (R3N) gives an unstable species that cannot be isolated
41
Reduction: Acid Chlorides into Alcohols

LiAlH4 reduces acid chlorides to yield aldehydes and then
primary alcohols
42
Acid Chlorides with Organometallic Reagents

Grignard reagents react with acid chlorides to yield tertiary
alcohols in which two of the substituents are the same
43
Formation of Ketones from Acid Chlorides
Acid chloride with a lithium diorganocopper (Gilman) reagent, Li+ R2Cu
44
21.5 Chemistry of Acid Anhydrides

Prepared by nucleophilic acyl substitution of a
carboxylate with an acid chloride
45
Reactions of Acid Anhydrides

Similar to acid chlorides in reactivity
46
Acetylation

Acetic anhydride forms acetate esters from alcohols
and N-substituted acetamides from amines
47
21.6 Chemistry of Esters


Many esters are pleasant-smelling liquids: fragrant odors of
fruits and flowers
Also present in fats and vegetable oils
48
Preparation of Esters

Esters are usually prepared from carboxylic acids
49
Reactions of Esters

Less reactive toward nucleophiles than are acid
chlorides or anhydrides

Cyclic esters are called lactones and react
similarly to acyclic esters
Hydrolysis: Esters into Carboxylic Acids

An ester is hydrolyzed by aqueous base or aqueous acid
to yield a carboxylic acid plus an alcohol
51
Mechanism of Ester Hydrolysis:
Base catalysed

Hydroxide
catalysis via
an addition
intermediate
52
Mechanism of Ester Hydrolysis:
Acid catalysed
53
Aminolysis: Esters into Amides

Ammonia reacts with esters to form amides
54
Reduction: Esters into Alcohols

Reaction with LiAlH4 yields primary alcohols
55
Mechanism of Reduction of Esters
Hydride ion adds to the carbonyl group, followed by
elimination of alkoxide ion to yield an aldehyde
 Reduction of the aldehyde gives the primary alcohol


Use bulky DIBAH to stop at an aldehyde
56
Reaction of Esters with Grignard
Reagents

React with 2 equivalents of a Grignard reagent to yield a
tertiary alcohol
57
21.7 Chemistry of Amides

Amides are abundant in all living organisms…proteins, nucleic
acids, and other pharmaceuticals have amid functional groups
58
Preparation of Amides

Prepared by reaction of an acid chloride with ammonia,
monosubstituted amines, or disubstituted amines
59
Reactions of Amides
Heating in either aqueous acid or aqueous base produces
a carboxylic acid and amine
 Acidic hydrolysis by nucleophilic addition of water to the
protonated amide, followed by loss of ammonia

60
Basic Hydrolysis: Amides  Acids

Addition of hydroxide and loss of amide ion
61
Reduction: Amides into Amines


Reduced by LiAlH4 to an amine rather than an alcohol
Converts C=O  CH2
62
Mechanism of Reduction


Addition of hydride to carbonyl group
Loss of the oxygen as an aluminate anion to give an
iminium ion intermediate which is reduced to the amine
63
Uses of Reduction of Amides


Works with cyclic and acyclic
Good route to cyclic amines
64
21.8 Chemistry of Thioesters and Acyl Phosphates:
Biological Carboxylic Acid Derivatives


Nucleophilic
carboxyl
substitution in
nature often
involves a
thioester or acyl
phosphate
Acetyl CoA’s
are most
common
thioesters in
nature
65
21.9 Polyamides and Polyesters: StepGrowth Polymers



Reactions occur in distinct linear steps, not as chain reactions
Reaction of a diamine and a diacid chloride gives an ongoing
cycle that produces a polyamide
A diol with a diacid leads to a polyester
66
Polyamides (Nylons)


Heating a diamine with a diacid produces a polyamide called Nylon®
Nylon 66® is from adipic acid and hexamethylene-diamine at 280°C
67
Polyesters

The polyester from dimethyl terephthalate and ethylene
glycol is called Dacron® and Mylar® to make fibers
68
Biodegradable Polymers
21.10 Spectroscopy of Carboxylic Acid
Derivatives

Infrared Spectroscopy
◦ Acid chlorides absorb near 1800 cm1
◦ Acid anhydrides absorb at 1820 cm1 and also at 1760
cm1
◦ Esters absorb at 1735 cm1, higher than aldehydes or
ketones
◦ Amides absorb near the low end of the carbonyl
region
72
Nuclear Magnetic Resonance
Spectroscopy


Hydrogens on the carbon next to a C=O are near 2 in
the 1H NMR spectrum.
All acid derivatives absorb in the same range so NMR
does not distinguish them from each other
74
13C
NMR
 13C

NMR is useful for determining the presence or
absence of a carbonyl group in a molecule of unknown
structure
Carbonyl carbon atoms of the various acid derivatives
absorb from 160 to 180
75
Learning Check:
Which of the following is not an acyl derivative?
1.
2.
O
O
O
Cl
3.
H
N
O
4.
O
O
O
5.
O
O
Solution:
Which of the following is not an acyl derivative?
1.
2.
O
O
O
Cl
3.
H
N
O
4.
O
O
O
5.
O
O
Learning Check:
Which of the following is not an ester?
1.
2.
O
O
O
O
4.
3.
O
O
O
O
Solution:
Which of the following is not an ester?
1.
2.
O
O
O
O
4.
3.
O
O
O
O
Learning Check:
All lactams can be classified as amides and vice versa.
1.
2.
True
False
Solution:
All lactams can be classified as amides and vice versa.
1.
2.
True
False
Learning Check:
Name the following:
A.
O
B.
N
H
1.
2.
3.
4.
5.
ethyl-N-2-butylmethylamide
N-(2-methylbutyl)propanamide
N-methylbutylpropane amide
N-(2-methylbutyl)propane amide
N-(2-methylbutylethyl) amide
O
O
1.
2.
3.
4.
5.
3,4-dimethylphenyl pentanoate
3,4-dimethylpentyl benzenoate
3,4-dimethylpentyl benzoate
benzyl 3,4-dimethylpentanoate
phenyl 3,4-dimethylpentanoate
Solution:
Name the following:
A.
O
B.
N
H
1.
2.
3.
4.
5.
ethyl-N-2-butylmethylamide
N-(2-methylbutyl)propanamide
N-methylbutylpropane amide
N-(2-methylbutyl)propane amide
N-(2-methylbutylethyl) amide
O
O
1.
2.
3.
4.
5.
3,4-dimethylphenyl pentanoate
3,4-dimethylpentyl benzenoate
3,4-dimethylpentyl benzoate
benzyl 3,4-dimethylpentanoate
phenyl 3,4-dimethylpentanoate
Learning Check:
Name the following:
A.
Br
O
1.
2.
3.
4.
5.
3-ethyl-3-phenylpropanoyl bromide
3-phenyl-3-ethylpropanoyl bromide
1-ethyl-1-phenylpropanoyl bromide
1-phenyl-1-ethylpropanoyl bromide
3-phenylpentanoyl bromide
Solution:
Name the following:
A.
Br
O
1.
2.
3.
4.
5.
3-ethyl-3-phenylpropanoyl bromide
3-phenyl-3-ethylpropanoyl bromide
1-ethyl-1-phenylpropanoyl bromide
1-phenyl-1-ethylpropanoyl bromide
3-phenylpentanoyl bromide
Learning Check:
Which of the following is true concerning the
given two carboxylic acid derivatives?
O
O
NH
A
1.
2.
3.
4.
5.
O
B
Only molecule A can be hydrolyzed.
Only molecule B can be hydrolyzed.
Both molecules can be hydrolyzed, but A will react faster than B.
Both molecules can be hydrolyzed, but B will react faster than A.
A and B can be hydrolyzed at roughly the same rate.
Solution:
Which of the following is true concerning the
given two carboxylic acid derivatives?
O
O
NH
A
1.
2.
3.
4.
5.
O
B
Only molecule A can be hydrolyzed.
Only molecule B can be hydrolyzed.
Both molecules can be hydrolyzed, but A will react faster than B.
Both molecules can be hydrolyzed, but B will react faster than A.
A and B can be hydrolyzed at roughly the same rate.
Learning Check:
Determine the product of the following:
O
SOCl2
OH
2.
1.
O
OH
H
3.
O
Cl
4.
O
S
5.
OH
O
S OH
O
Solution:
Determine the product of the following:
O
SOCl2
OH
2.
1.
O
OH
H
3.
O
Cl
4.
O
S
5.
OH
O
S OH
O
Learning Check:
Which step occurs first in the mechanism of
Fischer esterification?
1.
2.
3.
4.
5.
attack of the nucleophile on the carbonyl carbon
protonation of the carbonyl oxygen
loss of water from the tetrahedral carbonyl addition
intermediate
protonation of the alcohol oxygen
formation of the tetrahedral carbonyl addition
intermediate
Solution:
Which step occurs first in the mechanism of
Fischer esterification?
1.
2.
3.
4.
5.
attack of the nucleophile on the carbonyl carbon
protonation of the carbonyl oxygen
loss of water from the tetrahedral carbonyl addition
intermediate
protonation of the alcohol oxygen
formation of the tetrahedral carbonyl addition
intermediate
Learning Check:
Which of the following is the tetrahedral intermediate that
appears in the Fischer esterification of ethanol and benzoic
acid?
2.
1.
HO
O
OH
OH
O
O
3.
HO
4.
OH
5.
O
O
O
O
HO
OH
O
Solution:
Which of the following is the tetrahedral intermediate that
appears in the Fischer esterification of ethanol and benzoic
acid?
2.
1.
HO
O
OH
OH
O
O
3.
HO
4.
OH
5.
O
O
O
O
HO
OH
O
Learning Check:
What is the expected product for the following reaction?
O
H2SO4
OH
HO
1.
2.
O
O
HO
HO
3.
O
HO
4.
OH
O
5.
O
O
Solution:
What is the expected product for the following reaction?
O
H2SO4
OH
HO
1.
2.
O
O
HO
HO
3.
O
HO
4.
OH
O
5.
O
O
Learning Check:
What sequence of reagents will accomplish the following?
OH
OH
O
1.+
H
2 PhMgBr
CH3OH
Et2O
2.
H3O+
2 PhMgBr
H3O+
Et2O
3.+
H
4.+
H
CH3OH
PhOH
2 PhOH
5.
SOCl2
2 PhOH
Solution:
What sequence of reagents will accomplish the following?
OH
OH
O
1.+
H
2 PhMgBr
CH3OH
Et2O
2.
H3O+
2 PhMgBr
H3O+
Et2O
3.+
H
4.+
H
CH3OH
PhOH
2 PhOH
5.
SOCl2
2 PhOH
Learning Check:
Predict the product of the following:
1) LiAlH4
O
NH2
2 ) H2O
1.
2.
OH
NH2
3.
HO
OH
NH2
4.
OH
NH2
OH
+
NH2
5.
none of these
Solution:
Predict the product of the following:
1) LiAlH4
O
NH2
2 ) H2O
1.
2.
OH
NH2
3.
HO
OH
NH2
4.
OH
NH2
OH
+
NH2
5.
none of these
Learning Check:
What sequence of reagents will accomplish the following?
O
O
NH2
Cl
1.
2.
HCl
SOCl2
H2O
3.
H2O
4.
+
H3O
SOCl2
HCl
5.
SOCl2
Solution:
What sequence of reagents will accomplish the following?
O
O
NH2
Cl
1.
2.
HCl
SOCl2
H2O
3.
H2O
4.
+
H3O
SOCl2
HCl
5.
SOCl2
Learning Check:
Predict the product of the following:
O
O
1) 2
MgBr, THF
2) H3O+
1.
2.
O
O
OH
OH
O
3.
O
O
5.
4.
OH
OH
OH
OH
Solution:
Predict the product of the following:
O
O
1) 2
MgBr, THF
2) H3O+
1.
2.
O
O
OH
OH
O
3.
O
O
5.
4.
OH
OH
OH
OH
Learning Check:
Identify the compound that will react fastest when heated
in aqueous NaOH.
1.
2.
O
O
N(CH3)2
O
3.
O
OCH3
4.
5.
O
O
O
O
Solution:
Identify the compound that will react fastest when heated
in aqueous NaOH.
1.
2.
O
O
N(CH3)2
O
3.
O
OCH3
4.
5.
O
O
O
O