1
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
Synthesis of Carboxylic Acids 1. From 1º Alcohols and Aldehydes: Oxidation (Section 11-2B and 18-20) O H2CrO4
R OH 1º Alcohol
•
R
O
H2CrO4
OH
R
H
No mechanism required for the reaction
2. From Alkenes: Oxidative Cleavage: (Section 8-15A and 9-10) H R2
R
O
KMnO4
R OH acid
R1
• • •
+
O R1 R2 ketone
No mechanism required for the reaction Where C=C begins, C=O ends. But where an attached H begins, an OH ends. RCH=CHR would give two acids; RCH=CH2 would give an acid and carbonic acid (H2CO3), etc..
3. From Aromatics: Oxidation of Alkylbenzenes (Section 17-14A) O KMnO4
• •
OH
No mechanism required for the reduction While toluenes (methylbenzenes) oxidize especially well, other alkyl benzenes can also be oxidized in this way.
4. From 1,3-Diesters: Via Hydrolysis/Decarboxylation: (Chapter 22) O RO
O
O
1. NaOR OR
•
2. R-X
O
RO
OR R
O
H3O+, heat
O
HO
O OH
HO
R
R
Mechanism: Deprotation/Alkylation covered previously. The hydrolysis of the esters to acids will be required (see reaction 8b)
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
2
5. From Grignard Reagents: Via Carboxylation: (Section 20-8B) 1. CO2 R-MgX
R-CO2H 2.
R
H+
Mg
X
Alkyl or Aryl Halide
ether
R
1. CO2
MgX
O R
2. H+
Grignard Reagent
-
O
Protonate R
O
OH
Access: Alkyl or Aryl Acids Alkyl group can be 1º, 2º, or 3º Mechanism required. (From Grignard on.)
• • •
6. From Nitriles: Hydrolysis (Section 20-8C) R C N
O
H+, H2O R
OH
Mechanism not required.
•
7. From Halides: Either via Formation and Carboxylation of Grignards (Reaction 5) or via Formation and Hydrolysis of Nitriles (Reaction 6)
R
Mg
X
Alkyl or Aryl Halide
ether
R
MgX
Grignard Reagent
1. CO2
O
2. H+
R
O
Protonate
O R
OH
NaCN If R-X is 1º alkyl halide
• • •
R C N
O
H+, H2O R
OH
Formation/Hydrolysis of Nitriles Requires a 1º Alkyl Halide to begin, since the formation of the nitrile proceeds via SN2 Reaction via the Grignard has no such limitation For 1º alkyl halides, the formation/hydrolysis of the nitrile is technically easier, since there is no need to handle air-sensitive Grignard reagents
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
3
8. From Acid Chlorides, Anhydrides, Esters, or Amides: Hydrolysis (Section 20-8C) a) “Downhill” hydrolysis: From acids or anhydrides with NEUTRAL WATER alone • mechanism required: addition-elimination-deprotonation O
O
H2O
R Cl Chloride ("Cl") O
O
R
+ H-Cl
OH
O
H2O
R O R' Anhydride ("A")
O
R
OH
+
HO
R'
b) “Lateral” hydrolysis: From esters with water and acid catalysis (ACID WATER) • mechanism required: protonation-addition-deprotonation (to hemiacetal intermediate) followed by protonation-elimination-deprotonation (hemiacetal to acid) • These reactions are under equilibrium control. With excess water, you go to the acid. With removal of water and/or excess alcohol, the equilibrium favors the ester O
H2O, H+
R OR1 Ester ("E")
O
ROH, H+
R
+ OH
OH R'OH
via
R
hemiacetal
OH OR1
c) “Basic” hydrolysis using NaOH (BASIC WATER) (always downhill) followed by H+ workup • mechanism required: addition-elimination-deprotonation (to carboxylate intermediate) followed by protonation • Since the reaction with NaOH is always downhill, all of these reactions work O R Cl Chloride ("Cl") O
O
1. NaOH
O
2. H+ 1. NaOH
R O R' + Anhydride ("A") 2. H O R OR' Ester ("E") O R NHR Amide ("N")
R
OH
O R
2.
R
1. NaOH 2. H+
O
O OH
+
HO
R'
via
OH
R'OH
via
O OH
+
RNH 2
-
R O Carboxylate ("O")
O R
-
R O Carboxylate ("O") O
+
-
R O Carboxylate ("O")
O
1. NaOH H+
O via
+ H-Cl
via
-
R O Carboxylate ("O")
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
4
Reactions of Carboxylic Acids 9. Reaction as a proton Acid (Section 20-4, 20-5) O R
NaOH (or other bases, including amines)
O
OH
H-X (proton acid)
• • • • • • •
-
+
R O Na carboxylate salt (basic)
Mechanism: Required (deprotonation) Reverse Mechanism: Required (protonation) Carboxylic acids are completely converted to carboxylate salts by base Carboxylate salts are completely neutralized back to carboxylic acids by strong acid The resonanance stabilization makes carboxylates much more stable than hydroxide or alkoxide anions, which is why the parents are carboxylic “acids” Carboxylic acids are more acidic than ammonium salts Patterns in acid strength: Reflect stabilization/destabilization factors on the carboxylate o Electron donors destabilize the carboxylate anion, so make the parent acid less acidic o Electron withdrawers stabilize the carboxylate anion, so make the parent acid more acidic
10. Conversion to Acid Chlorides (Section 20-11, 21-5) O R
OH
• • •
O
SOCl2 R
O Cl
R
O
SOCl2 ONa
R
Cl
Mechanism: Not Required Easy (but smelly) reaction. Side products HCl and SO2 are gases, so can just evaporate away leaving clean, useful product. So no workup is required, nice! Extremely useful because the acid chlorides are so reactive, and can be converted into esters, anhydrides, or amides.
11. Indirect Conversion to Anhydrides (Section 21-5) O R
OH
• • •
O
1. SOCl2 2. R'CO2H
R
O Cl
R
O O
R'
mechanism required for acid chloride to anhydride conversion: additionelimination-deprotonation Conversion of the acid chloride to the anhydride is a “downhill” reaction energetically. Conversion of the acid to the anhydride directly would be an “uphill” reaction
5
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 12. Direct Conversion to Esters (Sections 20-10-12, 21-5) O R
OH
• • • •
OH
R'OH, H+ H2O, H +
R
O
OH OR'
R
OR'
mechanism required: protonation-addition-deprotonation (to hemiacetal intermediate) followed by protonation-elimination-deprotonation (hemiacetal to ester) These reactions are under equilibrium control. With excess water, you go to the acid. With removal of water and/or excess alcohol, the equilibrium favors the ester This is a “lateral” reaction, neither uphill nor downhill energetically This is the exact reverse of reaction 8b
13. Indirect Conversion to Esters via Acid Chlorides (Sections 20-10-12, 21-5) O R
OH 2. R'OH
• •
O
1. SOCl2 R
O Cl
R
OR'
mechanism required for acid chloride to ester conversion: addition-eliminationdeprotonation Conversion of the acid chloride to the ester is a “downhill” reaction energetically.
14. Direct Conversion to Amides (Sections 20-11, 20-13, 21-5) O R
OH
• • •
O
RNH 2, heat R
NHR
mechanism not required This is a “downhill” reaction energetically, but is complicated and retarded by acid-base reactions. Normally the “indirect) conversion is more clean in the laboratory This reaction occurs routinely under biological conditions, in which enzymes catalyze the process rapidly even at mild biological temperatures.
15. Indirect Conversion to Amides (Sections 20-11, 20-13, 21-5) O R
OH
• •
O
1. SOCl2 2. RNH 2
R
O Cl
R
NHR
mechanism required for acid chloride to amide conversion: elimination-deprotonation This reaction sequence works very well in the laboratory
addition-
6
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 16. Reduction to Primary Alcohol (Sections 10-11, 20-14) O R
OH
1. LiAlH4 OH
•
R
2. H+
mechanism not required
17. Alkylation to Form Ketones (Section 18-19, 20-15) O
Ph OH 2. H+ acid
O
1. 2 RLi
Ph OH 2. H+ acid
•
O
1. 2 RLi
Ph R ketone
O Ph
OLi
carboxylate anion
mechanism not required
LiO
OLi
Ph
R
tetrahedral dianion
acid
HO
OH
Ph
R
tetrahedral "hydrate"
acid
O Ph R ketone
7
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 18. Interconversions of Acids and Acid Derivatives (Section 21-5 and many others) O Acid Chloride ("Cl")
O Anhydride (A") R
R
Cl
O O
SOCl2 R' SOCl2 O
Ester ("E") = Acid
O
R OR Ester
R OH Acid
O Amide ("N")
O Carboxylate ("O")
• • • •
•
R
R
NHR
-
O
“Cl-A-vE-N-O” Chlorides-Anhydrides-Esters (and Acids)-Amides-Carboxylates Any downhill step can be done directly Any “lateral” step (acid to ester or vice-versa) can be done with acid Any “uphill” sequence requires going up through the Acid Chloride, either directly (from an acid or a carboxylate) or indirectly (conversion to carboxylate; react with SOCl2 to get to the top; then go downhill from there.) Mechanism is required for any downhill conversion and is the same: protonationaddition-deprotonation (addition to produce the hemiacetal intermediate) followed by protonation-elimination-deprotonation (elimination)
8
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… Mechanisms A. Miscellaneous 5. From Grignard Reagents: Via Carboxylation:
-
O
O C O
R
R
H+
O
-
O
R
OH
exactly like any Grignard reaction
•
9. Reaction as a Proton Acid
-OH
O R
O
OH
-
O
R
B. Any “Downhill” Interconversions (8a, 8c, 11, 13, 15, 18): All Proceed by AdditionElimination-Deprotonation General O R
Examples Reaction 8a O R
Cl
Y
Add
-
HO-H Add
-
O
Z-H
O
+H
O R Cl H
R
+ Z H
Y
-
O
-Cl Elim
-
-Y Elim
+H
O H
R
O R
+ Z H
-
-
Deprot
O R
Z
O
Cl
Deprot
Y
OH
R
Reaction 8c (Note: Slightly different because hydroxide nucleophile is anionic, not neutral; and product carboxylate is anionic, not neutral)
-
O R
OH OMe
Add
O
R
MeO-H Cl
Add
Reaction 15 O R
MeNH-H Cl
Add
-
-MeO O H R Elim OMe
Reaction 13 O
-
O
-
+H
O R Cl Me
-
O R
-
-Cl Elim
O H + -Cl N H R Elim Cl Me
-
O H
O R
+H
O Me
O H + N H R Me
-OMe Deprot
O
-
O
Cl
Deprot
OMe
R
-
O
Cl
Deprot
-
O
R
R
NHMe
9
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
C. “Lateral” Interconversions (8b/12): Acid-Catalyzed conversion from Ester to Acid (8b) or From Acid to Ester (12): (ACID WATER) • General Mechanism: protonation-addition-deprotonation (acid-catalyzed addition to a carbonyl to produce the tetrahedral hemiacetal intermediate) followed by protonationelimination-deprotonation (acid catalyzed elimination) Examples Reaction 8b: Ester to Acid O
+
+
H
OH
R OR1 Protonate Ester
R
OH
HO-H OR1
R
Add
+H
O OR1 H
OH
+
-H
Deprotonate
R
OH OR1 hemiacetal
+
H
Protonate
R OH Acid
-H
Deprotonate
+
R OH Acid
+
H
OH
Protonate
R
+ OH
OH
Eliminate -R 1OH
R H
Reaction 12: Acid to Ester O
O H
+
O
R
OH
OH
R1OH R
Add
H
OH OR1
+
Deprotonate
+
OH
+
-H
OH OR1
R
OH OR1 hemiacetal
+
H
Protonate O R
OR1 Ester
O H
+
-H
Deprotonate
R
+ OR1
OH
Eliminate -R 1OH
R
+
OH OR1 2
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… Nomenclature (20.2) Formal: alkanoic acid (space in between) -highest priority of any functional group O H
OH O
H 3C
Common Formic acid
Ethanoic acid
Acetic acid
Benzoic acid
Benzoic acid
OH
O Ph
Formal Methanoic acid
OH O
Pentanoic acid
OH
O
(S)-2-aminobutanoic acid
OH H
NH2
1. Nomenclature. Provide names or structures for the following. O
a. 3-phenylbutanoic acid
OH
Cl
b. 2,2-dichloropropanoic acid
Cl
O OH
c. 2-hydroxy-3-propanoyl-4-ethoxy-5-amino-6-hydroxyheptanoic acid O
O
NH2
HO OH
O
OH
Physical Properties (Section 20.3) Boiling Points: (weight being equal): acid > alcohol > 1,2º amines > non-H-bonders • Acids boil about 20º higher than same-weight alcohols • First four acids are completely water soluble Water solubility (weight being equal): amines > acids ? ketones, alcohols, ethers >> alkanes • Basicity is more important than acidity 2. Circle the one with higher boiling point, and square the one with the greater solubility in water. O
O OH
OH
10
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
11
Acidity/Basicity Table 19.2: With both Neutral and Cationic Acids and both Neutral and Anionic Bases (Section 20-4) Class Strong Acids
Hydronium Carboxylic Acid
Structure
Ka
H-Cl, H2SO4
102
H3O+, ROH+ cationic
100
Most acidic
R
Cl
OH
R
H N
O HO S O O
,
Base Strength Least basic
H2O, HOR neutral
Cuz
R
O
10-10
People
O
10-12
R
Smell Awful! Humans
O
OH
R
Base
10-5
O
Phenol
Ammonium Ion (Charged)
Acid Strength
R
Against
R N
R
Neutral, but basic!
Charged, but only weakly acidic!
Water
HOH
10-16
Alcohol
ROH
10-17
Ketones and Aldehydes
O
10-20
Working
HO
Are
RO O
! H
Kingdoms !
Amine (N-H)
(iPr)2N-H
10-33
Alkane (C-H)
RCH3
10-50
Animal
(iPr)2N Li Least acidic
RCH2
Most basic
All
Quick Checklist of Acid/Base Factors 1. Charge 2. Electronegativity 3. Resonance/Conjugation 4. Hybridization 5. Impact of Electron Donors/Withdrawers 6. Amines/Ammoniums When comparing/ranking any two acids or bases, go through the above checklist to see which factors apply and might differentiate the two. When A neutral acid is involved, it’s often best to draw the conjugate anionic bases, and to think from the anion stability side.
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
12
Acidity (20-4) O R
O
-H OH
R
O O
R
O
Anion is stabilized by conjugation/resonance Charge dispersal Carboxylate is an anion, so is stabilized by electron withdrawing groups (increasing acidity) and destabilized by electron donating groups (decreasing acidity)
• • •
10-5
O
Carboxylic Acid
R
Ammonium Ion (Charged)
O
OH
R R
R
10-12
H N
R
R
10-17
ROH
R N
R
Neutral, but basic!
Charged, but only weakly acidic!
Alcohol
O
RO
Acids are a million times more acidic than average ammoniums (despite charge) Acids are trillions more acidic than alcohols
• •
Amino Acids: o Which way does the equilibrium lie? o Equilibrium always favors the weaker acid and weaker base? o What happens under acid conditions, and what happens under base conditions? O R
O OH H
H NH3 Both are in acid form at acidic pH
acid
R
stronger acid OH
Eq. favors H NH2 weaker acid stronger base and weaker base
O R
OH base
O H NH3 weaker base
weaker acid Both are in ionic form at neutral pH
O R
O H NH2 base base Both are in base form under basic conditions
3. Carboxylic Acids as Acids. Rank the acidity of the following groups, 1 being most acidic and 3 being least acidic. [Remember: the best guideline for acidity is the stability of the anion!] a.
acetic acid 1 Stability of conjugate anions b.
ethanol 3
phenol 2
propanoic acid CH3NH3Cl (CH3)3NHCl 1 2 3 1. carb acids beat ammoniums. 2. Alkyl donors stabilize ammoniums and reduce their acidity
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
13
Substituent Effects (20.4B) • Withdrawers stabilize anions, increase acidity • Donors destabilize anions, reduce acidity • Opposite from the effect of donors and withdrawers on amines and ammoniums 4. Carboxylic Acids as Acids. Rank the acidity of the following groups, 1 being most acidic and 3 being least acidic. [Remember: the best guideline for acidity is the stability of the anion!] a.
propanoc acid 3
3-Chloropropanoic acid 2
2-fluoropropanoic acid 1
Electron withdrawing groups stabilize carboxylate anion. The stronger and closer, the better. b.
benzoic acid 2
p-methylbenzoic acid 3
p-nitrobenzoic acid 1
Donor (methyl) destabilizes carboxylate. Withdrawer (nitro) stabilizes carboxylate. 5. For each of the following acid/base reactions, draw a circle around the weakest base, and draw an arrow to show whether the reaction would proceed from left to right, or from right to left. OH + NaOH
ONa + HOH
a.
Ph OH
+ NaOH
Ph ONa + HOH
Alkyl donor destabilizes the anion on the right side
Resonance stabilizes right side
b. O
O + NaOH
+ HOH
OH
Resonance stabilizes anion on right side
ONa
c. O OH Ka=10-5
d.
O + NaHCO3
ONa
+ H2CO3 Ka=10-7
The left acid is the stronger based on Ka. Equilibria always go from stronger to weaker. And the conjugate base of the stronger acid is always the weaker, more stable base. The reason bicarbonate is a stronger, less stable base than the carboxylate shown is because the extra oxygen on bicarbonate is an electron donor, and thus destabilizes the anion.
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
14
20.5 Carboxylate Salts RCO2H + NaOH RCO2Na + H2O • • • •
Produces weaker acid and base
Easy to make Ionic water soluble Acids are soluble in NaOH/water or NaHCO3/H2O Weak bases, react with HCl RCO2H Named: sodium alkanoate
Purification Schemes for Acids from other Organics Based on Acidity a. Dissolve acid and neutral organic in ether b. Treat with NaOH/water • Neutral stays neutral, goes in ether layer • Acid is deprotonated to RCO2Na, goes into water layer c. Concentrate ether layer pure neutral organic d. Add HCl to aqueous layer, results in: RCO2Na + HCl RCO2H e. Neutral RCO2H now has low solubility in water, so can be harvested by filtration (if solid) or by organic extraction 6. Design a solubility flow chart to separate benzoic acid ("A") from acetophenone PhC(O)CH3 ("B"). Make sure that your plan enables you to isolate both “A” and “B”. O
Dissolve A + B in ether
O OH
A
Add NaOH
B neutral
B
ether layer concentrate (boil off ether)
water layer
anion
A
Add excess HCl A neutral, insoluble in water Ether filter to get A, if it's a solid. Otherwise add ether to extract it, then boil off the ether layer to isolate pure A.
B
Soaps (20.6, 25.4) (not for test) RCO2Na with variable long alkyl chains Ex: C17H35CO2 Na Carboxylate head: hydrophilic water soluble Hydrocarbon tail: hydrophobic can dissolve grease and organic materials Form “micelles” in water The hydrophobic hydrocarbon tails (strings) self-aggregate, while the ionic heads (circles) keep the microdroplet soluble in water. Organic materials can be dissolved inside the organic center, and carried through the water. Thus grease gets dissolved, and dirt protected by grease is freed.
water
water organic water
water
15
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… B. Synthesis of Carboxylic Acids
Synthesis of Carboxylic Acids
Review (20.8) 1. From 1º Alcohols and Aldehydes: Oxidation (Section 11-2B and 18-20) O H2CrO4
R OH 1º Alcohol
•
R
O
H2CrO4
OH
R
H
No mechanism required for the reaction
2. From Alkenes: Oxidative Cleavage: (Section 8-15A and 9-10) H R2
R
O
KMnO4
R OH acid
R1
• • •
+
O R1 R2 ketone
No mechanism required for the reaction Where C=C begins, C=O ends. But where an attached H begins, an OH ends. RCH=CHR would give two acids; RCH=CH2 would give an acid and carbonic acid (H2CO3), etc..
3. From Aromatics: Oxidation of Alkylbenzenes (Section 17-14A) O KMnO4
• •
OH
No mechanism required for the reduction While toluenes (methylbenzenes) oxidize especially well, other alkyl benzenes can also be oxidized in this way.
4. From 1,3-Diesters: Via Hydrolysis/Decarboxylation: (Chapter 22) O RO
O
O
1. NaOR OR
•
2. R-X
O
RO
OR R
O
H3O+, heat
O
HO
O OH
HO
R
R
Mechanism: Deprotation/Alkylation covered previously. The hydrolysis of the esters to acids will be required (see reaction 8b)
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
16
New Routes 5. From Grignard Reagents: Via Carboxylation: (Section 20-8B) 1. CO2 R-MgX
R-CO2H 2.
R
H+
Mg
X
Alkyl or Aryl Halide
ether
R
1. CO2
MgX
O R
2. H+
Grignard Reagent
-
O
Protonate R
O
OH
Access: Alkyl or Aryl Acids Alkyl group can be 1º, 2º, or 3º Mechanism required. (From Grignard on.)
• • •
6. From Nitriles: Hydrolysis (Section 20-8C) R C N
O
H+, H2O R
OH
Mechanism not required.
•
7. From Halides: Either via Formation and Carboxylation of Grignards (Reaction 5) or via Formation and Hydrolysis of Nitriles (Reaction 6)
R
Mg
X
Alkyl or Aryl Halide
ether
R
MgX
Grignard Reagent
1. CO2
O
2. H+
R
O
Protonate
O R
OH
NaCN If R-X is 1º alkyl halide
• • •
R C N
O
H+, H2O R
OH
Formation/Hydrolysis of Nitriles Requires a 1º Alkyl Halide to begin, since the formation of the nitrile proceeds via SN2 Reaction via the Grignard has no such limitation For 1º alkyl halides, the formation/hydrolysis of the nitrile is technically easier, since there is no need to handle air-sensitive Grignard reagents
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… Problems 1. Preparation of Carboxylic Acids. Fill in the blanks for the following reactions. O
H2CrO4 OH
OH
(C3H8O)
a.
1. Mg 2. epoxide; H2O 3. H2CrO4
Bromobenzene
OH
O
b.
OH
1. KMnO4/NaOH/heat 2. H+
Ph
Ph
O
(+ carbonic acid)
c.
Benzene
Br2 FeBr3
Mg
Ph-Br
Ph-MgBr
1. CO2 2. H+
PhCO2H
d.
OH
1. 2.
O
PBr3 CN
OH
NaCN
e.
Ph
f.
Br
H3O+
1. NaCN 2. H3O+
OH Ph O
17
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
18
8. From Acid Chlorides, Anhydrides, Esters, or Amides: Hydrolysis (Section 20-8C) a) “Downhill” hydrolysis: From acids or anhydrides with NEUTRAL WATER alone • mechanism required: addition-elimination-deprotonation O
O
H2O
R Cl Chloride ("Cl") O
O
R
+ H-Cl
OH
O
H2O
R O R' Anhydride ("A")
O
R
OH
+
HO
R'
b) “Lateral” hydrolysis: From esters with water and acid catalysis (ACID WATER) • mechanism required: protonation-addition-deprotonation (to hemiacetal intermediate) followed by protonation-elimination-deprotonation (hemiacetal to acid) • These reactions are under equilibrium control. With excess water, you go to the acid. With removal of water and/or excess alcohol, the equilibrium favors the ester O
H2O, H+
R OR1 Ester ("E")
ROH, H+
O R
+ OH
OH R'OH
via
R
hemiacetal
OH OR1
c) “Basic” hydrolysis using NaOH (BASIC WATER) (always downhill) followed by H+ workup • mechanism required: addition-elimination-deprotonation (to carboxylate intermediate) followed by protonation • Since the reaction with NaOH is always downhill, all of these reactions work O R Cl Chloride ("Cl") O
O
2. H+
O
R
1. NaOH
R O R' + Anhydride ("A") 2. H
O
2. H+
O R
NHR 2. H+
O
O OH
+
HO
R'
via
R
OH
R'OH
via
O
R
OH
RNH 2
-
R O Carboxylate ("O")
O +
-
R O Carboxylate ("O") O
+
-
R O Carboxylate ("O")
O
1. NaOH
Amide ("N")
O via
+ H-Cl
OH
1. NaOH
R OR' Ester ("E")
R
O
1. NaOH
via
-
R O Carboxylate ("O")
19
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… Interconversions and Reactivity of Acids and Acid Derivatives (Section 21-5 and others) O Acid Chloride ("Cl") R
O
O O
SOCl2
H 2O
Anhydride (A") R
Cl
R' SOCl2
H2O O Ester ("E") = Acid
H2O, H
R OR Ester
O OH
R OH Acid
OH
H
O Amide ("N")
R
NHR
OH
OH O
Carboxylate ("O")
• • • •
•
R
-
O
“Cl-A-vE-N-O” Chlorides-Anhydrides-Esters (and Acids)-Amides-Carboxylates Any downhill step can be done directly Any “lateral” step (acid to ester or vice-versa) can be done with acid Any “uphill” sequence requires protonation or going up through the Acid Chloride, either directly (from an acid or a carboxylate) or indirectly (conversion to carboxylate; react with SOCl2 to get to the top; then go downhill from there.) Mechanism is required for any downhill conversion and is the same: protonationaddition-deprotonation (addition to produce the hemiacetal intermediate) followed by protonation-elimination-deprotonation (elimination)
“Cl-A-vE-N-O” applied to Hydrolysis 1. Chlorides and Anhydrides are “above” acids, so can be converted to acids by direct hydrolysis with neutral water 2. Esters are “lateral” to acids, so can be hydrolyzed to acids by acid-catalyzed hydrolysis 3. Chloride, anhydrides, esters, and amides can all be base-hydrolyzed (NaOH/water) to carboxylates. • Subsequent acid workup protonates the carboxylate and produces the acid • Base hydrolysis always works 4. For amides, basic hydrolysis is the only way to do it
20
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
2. For the following problems, draw the starting materials that would give the indicated hydrolysis products. • All of these are drawn as basic hydrolyses, but some could also be done using neutral water or acidic water. Mark which could proceed using neutral hydrolysis or acid-catalyzed hydrolysis in addition to via basic hydrolysis. O OMe
O
OH + MeOH
2. H3O+ O
1. NaOH, H2O NHMe
O
OH + MeNH2
2. H3O+ O
1. NaOH, H2O NH2
O
O
1. NaOH, H2O
2.
O
OH + NH3
H3O+ O
1. NaOH, H2O
OH + HO
Ph
O
2. H3
O+
Ph
O
2. H3
Ph
O
1. NaOH, H2O
O
O
OH + HO
O+
Ph
Mechanism: General Mechanism for Any “Downhill” Cl-A-vE-N-O Interconversions (8a, 8c, 11, 13, 15, 18): All Proceed by Addition-Elimination-Deprotonation General O R
-
O
Z-H Y
Add
R
+H
Z Y
-
O
-Y Elim
R
+ Z H
Y
-
Deprot
O Z
R
Base Case, Using Anionic Hydroxide: Slightly different because hydroxide nucleophile is anionic, not neutral; and product carboxylate is anionic, not neutral)
-
O R
OH OMe
Add
O
-
-
-MeO O H R Elim OMe
O R
O H
-OMe Deprot
O R
-
O
21
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
Acid-Catalyzed conversion from Ester to Acid (8b): (ACID WATER) • General Mechanism: protonation-addition-deprotonation (acid-catalyzed addition to a carbonyl to produce the tetrahedral hemiacetal intermediate) followed by protonationelimination-deprotonation (acid catalyzed elimination)
+
+
H
O
OH R
R OR1 Protonate Ester
OH
HO-H OR1
-H
O OR1 H
R
Add
OH
+
+H
Deprotonate
R
OH OR1 hemiacetal
+
H
Protonate O H
+
O
-H
R OH Acid
R
Deprotonate
+ OH
-R 1OH
O Ph
H+ workup
O
OMe 18
OH
Ph
O Ph
O
OH
+ HOMe 18 O
O Ph
Ph
OH OMe 18
The O
O H
O18 label
OMe 18
ends up in the product alcohol.
H2O Cl
O
-
O
HO-H Cl
O
HO
H2O O
+H
O Cl H
Add
-
O
-
+H
-Cl Elim
O H
OH
O
Cl
OH
Deprot
O
H2O
O
H
OH
H
OH H
-H
O
-H
H
OH OH2
HO
R H
Draw the Mechanisms for the following Hydrolyses +
OH
Eliminate
OH2 O
HO
OH OH
OH OH OH
OH OR1
+
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
22
C. Reactions of Carboxylic Acids 20.9, 21.5 Interconversions with Derivatives: Cl-A-vE-N-O
O Acid Chloride ("Cl")
O Anhydride (A") R
R
Cl
O O
SOCl2 R' SOCl2 O
Ester ("E") = Acid
O
R OR Ester
R OH Acid
O Amide ("N")
O Carboxylate ("O")
• • • • •
•
R
R
NHR
-
O
“Cl-A-vE-N-O” Chlorides-Anhydrides-Esters (and Acids)-Amides-Carboxylates All can be interconverted by substitution procedures: 1, 2, or 3 steps Any downhill step can be done directly Any “lateral” step (acid to ester or vice-versa) can be done with acid Any “uphill” sequence requires going up through the Acid Chloride, either directly (from an acid or a carboxylate) or indirectly (conversion to carboxylate; react with SOCl2 to get to the top; then go downhill from there.) Mechanism is required for any downhill conversion and is the same: protonationaddition-deprotonation (addition to produce the hemiacetal intermediate) followed by protonation-elimination-deprotonation (elimination)
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
23
Acid Chlorides: Preparation and Uses (Sections 20.11 and 21.5) 10. Conversion of acids or Carboxylates to Acid Chlorides (Section 20-11, 21-5) O R
OH
• •
•
O
SOCl2 R
O Cl
R
O
SOCl2 ONa
R
Cl
Mechanism: Not Required Easy (but smelly) reaction. o Side products HCl and SO2 are gases, so can just evaporate away leaving clean, useful product. So no workup is required, nice! Extremely useful because the acid chlorides are so reactive, and can be converted into esters, anhydrides, or amides.
11. Indirect Conversion to Anhydrides (Section 21-5) O R
OH
• • • •
O
1. SOCl2 R
2. R'CO2H
O Cl
R
O O
R'
mechanism required for acid chloride to anhydride conversion: additionelimination-deprotonation Conversion of the acid chloride to the anhydride is a “downhill” reaction energetically. Conversion of the acid to the anhydride directly would be an “uphill” reaction Base often present to absorb the HCl
13. Indirect Conversion to Esters via Acid Chlorides (Sections 20-10-12, 21-5) O R
OH 2. R'OH
• • •
O
1. SOCl2 R
O Cl
R
OR'
mechanism required for acid chloride to ester conversion: addition-eliminationdeprotonation Conversion of the acid chloride to the ester is a “downhill” reaction energetically. Base often present to absorb the HCl
15. Indirect Conversion to Amides (Sections 20-11, 20-13, 21-5) O R
OH
• • •
O
1. SOCl2 2. RNH 2
R
O Cl
R
NHR
mechanism required for acid chloride to amide conversion: elimination-deprotonation This reaction sequence works very well in the laboratory Base often present to absorb the HCl
addition-
24
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… Condensation/Hydrolysis: Interconversions between Acids and Esters (20.10, 13, 21.7) 12. Direct Conversion to Esters (Sections 20-10-12, 21-5) O R
OH
• •
• • •
OH
R'OH, H+ R
H2O, H +
O
OH OR'
R
OR'
mechanism required: protonation-addition-deprotonation (to hemiacetal intermediate) followed by protonation-elimination-deprotonation (hemiacetal to ester) These reactions are under equilibrium control. 1. With excess water, you go to the acid. 2. With removal of water and/or excess alcohol, the equilibrium favors the ester This is a “lateral” reaction, neither uphill nor downhill energetically This is the exact reverse of reaction 8b Under base conditions, the equilibrium always goes completely away from the ester and goes to the acid side 1. The base deprotonates the carboxylic acid, so LeChatellier’s principle says that the equilibrium keeps driving from ester towards acid to compensate
3. Draw the mechanism for the following reaction. O
OH
HOMe, H+
OMe OH Tetrahedral intermediate
Phase 1: addition
OH
O
+
+
H
O OH Acid
Phase 2: elimination
OH
Protonate
OH
OH
R1OH
OH OMe
Add
H
+
OMe
(+ H2O)
+
OH
-H
Deprotonate
OH OMe hemiacetal
+
H
Protonate O OMe Ester
+
-H
Deprotonate
O H
+ OMe
Eliminate
OH
-R1OH
OH OMe 2
+
14. Direct Conversion to Amides (Sections 20-11, 20-13, 21-5) O R
OH
• • •
O
RNH 2, heat R
NHR
mechanism not required This is a “downhill” reaction energetically, but is complicated and retarded by acid-base reactions. Normally the “indirect) conversion is more clean in the laboratory This reaction occurs routinely under biological conditions, in which enzymes catalyze the process rapidly even at mild biological temperatures.
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… Problems 4. Synthesis of Acid derivatives. Draw the products for the following reactions. O a. Ph
Ph
OH
O b.
Ph
OH
Ph
O Ph
2. 1-butanol
OH
Ph
O O
ethanol, H+
O d.
Cl
1. SOCl2
O c.
O
SOCl2
Ph
O
1. SOCl2 OH
O
2. cyclopentanol
Ph
O
O O e.
Ph
1. SOCl2 OH
Ph
O
2. 2-butanol
O
O
H+ f.
HO
OH H
O g.
Ph
OH
Ph
OH
Ph
Ph
2. diethylamine
Ph
2. NH3
N
O Ph
2. 2-butanamine
Ph
N H
O
diethylamine, heat OH
NH2
O
1. SOCl2 OH
O j.
O
1. SOCl2
O i.
H
Ph 1. SOCl2
O h.
O
Ph
NEt2
Ph
25
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 5. Draw the mechanism. O
O b.
Cl
+NH3
NH2 O b.
O +NH3
Cl
O
O
NH2
NH2 Cl H
6. Draw the products for the following reactions. O a.
Ph
H
1. LiAlH4 OH
O
Ph
2. H3O+
OH
2. H3O+
OH
O
1. MeLi (excess)
b. Ph
NH2
Ph
CH3
O
Ch. 21 Carboxylic Acid Derivatives: o Cl chloride o A anhydride o E ester o N amide o O: carboxylate 21.1,2 • • • •
General Alkanoyl chloride
Cl O
R
O O
R
O R
O
R'
Alkanoic Anhydride Alkyl Alkanoate
O R
X
Structure, Names, Notes all are subject to hydrolysis All hydrolyze to acids (actually, to carboxylate anion) upon treatment with NaOH/H2O Some (Cl and A) hydrolyze to acids under straight water treatment Esters hydrolyze to acids under acid catalysis
O R
R
Example Butanoyl chloride
O Cl O
O
R'
Alkanamide
High reactivity Named as if ionic
Propanoic anhydride
O O O
O
N R"
• •
N H
Ethyl Benzoate N-isopropyl pentanamide
Named as if ionic
26
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides…
27
7. Draw the structures for the following esters. a. propyl benzoate O O
b. methyl ethanoate O O
c. ethyl butanoate
O O
21.5 Interconversion of Acid Derivatives: Cl-A-vE-N-O O Acid Chloride ("Cl")
O Anhydride (A") R
R
Cl
O O
SOCl2 R' SOCl2 O
Ester ("E") = Acid
O
R OR Ester
R OH Acid
O Amide ("N")
O Carboxylate ("O")
• • • • •
•
R
R
NHR
-
O
“Cl-A-vE-N-O” Chlorides-Anhydrides-Esters (and Acids)-Amides-Carboxylates All can be interconverted by substitution procedures: 1, 2, or 3 steps Any downhill step can be done directly Any “lateral” step (acid to ester or vice-versa) can be done with acid Any “uphill” sequence requires going up through the Acid Chloride, either directly (from an acid or a carboxylate) or indirectly (conversion to carboxylate; react with SOCl2 to get to the top; then go downhill from there.) Mechanism is required for any downhill conversion and is the same: protonationaddition-deprotonation (addition to produce the hemiacetal intermediate) followed by protonation-elimination-deprotonation (elimination)
28
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 8. Rank the acidity of the following molecules, 1 being most acidic and 4 being least acidic. O H Cl
HOCH3
HO 2
1
NH2CH3
3
4
9. Rank the reactivity of the following toward hydrolysis. Do you see a similarity between your rankings for this question relative to your answers for question 8? O
O
O
O
O
Cl 1
O OCH3
2
NHCH3 4
3
The patterns are the same, because both reflect the stability of the anion. Acidity depends on the product anion; the reactivity in problem 14 also reflects the anion stability of the leaving group. O >
Cl
>
O
>
OCH3
NHCH3
Notes: • Any “downhill” reaction can be done in one laboratory step • Any “downhill” reaction involves a 3-step mechanism: addition-elimination-deprotonation O Add R
Y
-
Z-H r1
O R
Elim r-1
+H
Z Y
-
O
-Y Elim r2
+H
Y
Z
R
-
Deprot
O R
Z
•
The overall reactivity correlates the leaving ability of the Y for two reasons 1. This affects the kinetic r2/r-1 partion. If r2 is slow, the addition is simply reversible 2. The same factors that make Y a good leaving group also make the initial carbonyl more reactive toward addition (step 1, r1). 3. Thus good leaving groups have benefits at both r1 and r2
•
Memory o Think anion stability o Cliff Cl-A-vE-N-O
B. “Uphill” Reaction Sequences: 3-steps O R
1. NaOH, H2O Y
O R
2. SOCl2 3. HZ
Z
Ex: Ph
O
1. NaOH, H2O
O NH2
2. SOCl2 3. HOCH3
Ph
OCH3
Ph
+ NH3
O
O
SOCl2 O
OCH3 2. SOCl2 3. OH
HOCH3 NaOH
OH O
Ph
Ph
Cl
Ph
O
1. NaOH, H2O
O
Ph
+ HOCH3
O O HO NEt3 O
SOCl2 O
O
Ph
Cl
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 10. Which will proceed easily/directly? (“downhill”?) Add Appropriate Reactant(s) and Side Product. If it doesn’t go directly, give indirect route. O
O
a.
Ph
NH3
+ Cl
Cl
O
O
d.
Cl O E
HO E
O + H2O
+
Cl
+ H-Cl OCH3
E
Cl
OCH3
O
O
2. H+ 3. SOCl2
O
N
g.
h.
N
OCH3
NMe2
NMe2 2. H+ 3. SOCl2 4. HOMe
i.
E
O
O E
Cl
Yes, downhill
Yes, downhill
+ HOCH3
ONa
+ HNMe2
OMe
Yes, downhill
E
O
O
O O
No, uphill
HNMe2
OH
Cl
Cl
E
OMe
Indirect route, via hydrolysis then SOCl2
Note: direct H+ catalyzed conversion from acid to ester also fine.
O
O
+
HO
Cl
+ HOCH3
ONa
O
1. NaOH
OMe
NMe2
+ E
+
OH
E
O
HOMe
O
O
Indirect route, via hydrolysis then SOCl2
O O
O N
O
+ NaOH
+
O
O
O
+ NaOH
NMe2
No, Uphill
O
+ H-NMe2
E O
N O
Downhill, yes.
+ HOCH3
Cl
1. NaOH
OCH3
E O
H-Cl
E O
+ OH
f.
Downhill, yes.
HO
O
OH
O
e.
O +
A
O
c.
N
Downhill, yes.
H-Cl
NH2
O
+
O
b.
+ Ph
O
+ HOMe
No, uphill
A O
1. NaOH
O
OCH3 2. H+ 3. SOCl2
O
O
4. HO
O
E
O
O
O OH
Cl
Cl
A O
O
Indirect route, via hydrolysis then SOCl2
29
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 11. Draw the products for the following reactions. O a. Ph
OH
Ph
O b.
Ph
OH
Ph
2. Acetic acid, pyridine Ph
Ph
NHMe 2. SOCl2 3. MeOH, pyridine
Ph
O
O Ph
OMe
O
ethanol, pyridine
O
Ph 1. H3O+
OCH2CH3
O
Ph-CN
f.
O
NHPh
1. NaOH, H2O; H+
O
O
O
PhNH2
O
e.
O
OMe
d. Ph
Cl
1. SOCl2
O c.
O
SOCl2
2. MeOH, H+
Ph
OMe
12. Draw the mechanism for the following reaction. O O
O
O
O +
HO
OCH2CH3
O
O O
O O O H O
+
O HO
O +
O
O
O O H
(3 steps)
HO
+ O
HO
30
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 13. Provide reagents for the following transformations. O
a. Ph
OH O
b. Ph
Ph
OH
Ph
Ph
d.
Ph
OH
Ph
Ph
NH3 (E to N, downhill...) OMe
Ph
NH2
f.
Ph
Ph
OMe
g.
Ph
3. SOCl2 4. CH3OH
OMe
O Ph
3. SOCl2 4. O
O O
HO
1. H2CrO4 2. SOCl2
h.
NH2
O
1. NaOH 2. H+
O
NH2
O
1. NaOH 2. H+
O
NH2
Ph-CH2OH
3. CH3OH
or
(Method 1)
O
NH3, heat (E to N, downhill)
O
e.
O
OH
Ph
(Method 2)
OMe
1. SOCl2 2. NH3
O
(Method 1)
OMe O
1. SOCl2 2. CH3OH
O
c.
O
CH3OH, H+
1. H2CrO4 2. H+, CH3OH
O Ph
OMe
(Method 2)
31
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 14. Provide products for the following condensation or hydrolysis transformations. H+
O
a. Ph
OH
Ph
heat
OH + PhNH 2
b.
O
+ MeOH OMe
NHPh O
O
O O
O
H+
+ H 2O
c.
O Ph
1. NaOH N H
d.
Ph
+
Ph
2. HCl
OH
OH
OH
2. HCl
e.
O H OH
H
O
+
O H
OH
f.
O
O 1. NaOH
OH
2. HCl
g.
H 2N
O 1. NaOH
OMe
HO
O
O
O
+
OH
OH OMe
+
HO H
Ph
32
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 15. Cyclic Esters and Amides: Provide products or starting reactants for the following condensation or hydrolysis reactions involving cyclic esters or amides. O OH
O
H+
HO
a.
O
O
O 1. NaOH
OH
O
b.
2. H3
H Ph
O
H Ph
O
1. NaOH
N H
OH
OH
H
2. H3O+
Cl
c.
O+
N H
Cl
O
O HO NH2 H Me
d.
Heat
HN H Me
16. Rank the following as acids or bases. O F
O OH
a.
NH3
CH3NH3 OH
1
2
3
4
O
b.
(CH3)2NH2
PhNH3
3
c.
Et3N
2
2
1
EtNH2
3
H2O
OH
NH
4
1
PhMgBr
1
33
34
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 17. Provide reagents for the following transformations. There may be more than one solution.
1. PCC OH
N H
2. H+, NaBH3CN, H2N
a.
O Ph
1. Cl
b.
H2N
Ph
N H
2. LiAlH4
O 1. NH2
c.
O
or
Cl
O
, NaBH3CN, H+ N H
2. LiAlH4
H 2N
, NaBH3CN, H+
H N
d.
1. PBr3 OH
e.
2. NH3 (excess)
1. PBr3 OH
f.
2. KCN 3. LiAlH4
NH2
NH2
35
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 18. Provide reagents for the following transformations. There may be more than one solution.
O
1. NaOH OCH3
a.
OH
2. H+
O
(downhill, E to N)
NH(CH3)2
OCH3
b.
O
or H2O, H+
N(CH3)2
1. NaOH 2. H+
O
O
O
OCH3
O
3. SOCl2
HO
Ph
O
1. H2CrO4 OH
d.
Ph
O
4.
c.
O
Cl
2. SOCl2
1. PBr3 OH
OH
e.
2. KCN 3. H+, H2O
O
f. KMnO4
OH O
O
Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 19. Provide mechanism for the following reactions.
+
+
H
O
OH
OH
HO-H
-H
O OCH3H
OCH3 Add
OCH3 Protonate Ester
OH
+
+H
OH OCH3 hemiacetal
Deprotonate
+
H
Protonate O H
+
O
-H OH
Deprotonate
+ OH
Acid
a.
Eliminate
OH
-CH3OH
OH OCH3
H
+
O O O
1. NaOH, H2O
OH
2. H+
OH
OH H+ O HO
O
O
O
H
O
O O
b.
O Cl
H3C
NH2
+H
O Cl H
Add
c.
H 3C
-
O
HO-H
H 3C
Br
OH
-
N
H 3C
SN2
O
-Cl Elim
O H
H H
-
+H
O
Cl
OH
Deprot
OH
H3C
Deprotonate
NHCH3
SN2
H3C
d.
H3C
N
CH3 CH3
Br
CH3
SN2
H3C
OH N(CH3)2
Deprotonate
H 3C H3C
H3C
N
H CH3
Br
36