Ch 20-21 Answers (all) - Chem 360 Jasperse Ch 20 21 Notes...

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Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 1 Synthesis of Carboxylic Acids 1. From 1º Alcohols and Aldehydes: Oxidation (Section 11-2B and 18-20) R OH 1º Alcohol H 2 CrO 4 R OH O H 2 CrO 4 R H O No mechanism required for the reaction 2. From Alkenes: Oxidative Cleavage : (Section 8-15A and 9-10) KMnO 4 R R 2 H R 1 R OH O R 1 R 2 O + acid 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=CH 2 would give an acid and carbonic acid (H 2 CO 3 ), etc.. 3. From Aromatics : Oxidation of Alkylbenzenes (Section 17-14A) KMnO 4 OH O 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) RO O HO R O OR O RO O OR O R HO O OH O R 1. NaOR 2. R-X H 3 O + , heat Mechanism: Deprotation/Alkylation covered previously. The hydrolysis of the esters to acids will be required (see reaction 8b)
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Chem 360 Jasperse Ch. 20, 21 Notes + Answers. Carboxylic Acids, Esters, Amides… 2 5. From Grignard Reagents: Via Carboxylation : (Section 20-8B) R-MgX 1. CO 2 2. H + R-CO 2 H R X Alkyl or Aryl Halide Mg ether R MgX Grignard Reagent 1. CO 2 2. H + R O O R OH O - - Protonate 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 OH O C N R H + , H 2 O 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 X Alkyl or Aryl Halide Mg ether R MgX Grignard Reagent 1. CO 2 2. H + R O O R OH O - - Protonate C N R H + , H 2 O NaCN If R-X is 1º alkyl halide R OH O Formation/Hydrolysis of Nitriles Requires a 1º Alkyl Halide to begin, since the formation of the nitrile proceeds via S N 2 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
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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 R Cl O R OH O H 2 O R O O R' O R OH O + H-Cl + HO R' O H 2 O Chloride ("Cl") Anhydride ("A") 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 H 2 O, H + R OR 1 O R OH O + Ester ("E") R'OH ROH, H + R OH OH OR 1 via hemiacetal
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  • Fall '07
  • Baron
  • Carboxylic acid, anhydrides, Proton Acid, Aryl Acids Alkyl, Protonate Ester, carboxylates

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