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CARBOXYLIC ACIDS

CARBOXYLIC ACIDS. CARBOXYLIC ACIDS and their derivatives. Carboxylic acid anhydride. Carboxylic acid ester. Carboxylic acid R = alkyl cycloalkyl alkenyl alkynyl aromatic ring. Carboxylic acid chloride. Carboxylic acid amide. Nitrile.

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CARBOXYLIC ACIDS

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  1. CARBOXYLIC ACIDS

  2. CARBOXYLIC ACIDS and their derivatives Carboxylic acid anhydride Carboxylic acid ester Carboxylic acid R = alkyl cycloalkyl alkenyl alkynyl aromatic ring Carboxylic acid chloride Carboxylic acid amide Nitrile

  3. CARBOXYLIC GROUP ELECTRONIC STRUCTURE Lone-pair electrons Acidic hydrogen π-bond Lone-pair electrons Hydrocarbon framework

  4. CARBOXYLIC GROUP THREE-DIMENSIONAL SHAPE sp2 sp3 Acetic acid - model sp3 sp2 C-C 1.52 ÅC=O 1.25 ÅC-OH 1.31 Å

  5. CARBOXYLIC ACIDS – various sites of reactivity Lewis basicity (greater) (nucleophilic centre) Lewis basicity (lesser) (nucleophilic centre) α-hydrogen chemistry Brőnsted acidity Lewis acidity (electrophilic centre)

  6. COMMON CARBOXYLIC ACIDS Aliphatic acids formicacid butyricacid aceticacid valericacid pivalicacid propionicacid

  7. COMMON CARBOXYLIC ACIDS Unsaturated acids acrylicacid propiolicacid crotonicacid fumaricacid trans maleicacid methacrylicacid cis

  8. COMMON CARBOXYLIC ACIDS Dicarboxylic acids oxalicacid glutaricacid malonicacid adipicacid succinicacid

  9. COMMON CARBOXYLIC ACIDS Aromatic acids benzoicacid phthalicacid benzoicacid

  10. Physical constants of some CARBOXYLIC ACIDS

  11. Carboxylic acids form dimers by strong Hydrogen Bonding Hence they have high boiling points

  12. Dissociation of carboxylic acid vs alcohol Equivalent resonance structures: negative charge always on O Unstabilizedalkoxide anion

  13. Dissociation of carboxylic acid vs alcohol ENERGY Alkoxide anion Resonance stabilization Carboxylate anion alcohol acid REACTION PROGRESS

  14. Acidity of carboxylic proton vs-proton in ketone Carboxylic group Which will be more acidic? Ketone

  15. Both anions are resonance stabilized

  16. Acidity of carboxylic proton vs-proton in ketone Carboxylic acids:equivalent resonance structures: negative charge always on O Ketones:notequivalentresonance structures: negative charge on O or on C!

  17. Compare acetic acid, pKa = 4.75, with acetone, pKa = 19.3!!!

  18. EVIDENCE FOR RESONANCE OF CARBOXYLATE ANION 1.27 Å 1.20 Å 1.34 Å 1.27 Å formic acid sodium formate

  19. ACIDITY OF SOME CARBOXYLIC ACIDS Structure Name pKa HCl hydrochloric acid -7 F3CCOOH trifluoroacetic acid (TFA) 0.23 Cl3CCOOH trichloroacetic acid 0.64 Cl2CHCOOH dichloroacetic acid 1.26 FCH2COOH fluoroacetic acid2.59 ClCH2COOH chloroacetic acid 2.85 BrCH2COOH bromoacetic acid 2.89 ICH2COOH iodoacetic acid 3.12 HCOOH formic acid 3.75 HOCH2COOH glycolic acid3.83 ClCH2CH2COOH 3-chloropropanoic acid 3.98 C6H5COOH benzoic acid 4.19 H2C=CHCOOH acrylic acid 4.25 C6H5CH2COOH phenylacetic acid 4.31 CH3COOH acetic acid4.72 CH3CH2COOH propanoic acid4.87 CH3CH2OH ethanol16 Stronger acid Weaker acid

  20. SUBSTITUENT EFFECT ON ACIDITY acetic acid chloroacetic acid dichloroacetic acid trichloroacetic acid pKa = 4.72 pKa = 2.85 pKa = 1.26 pKa = 0.64 Weaker acid Stronger acid

  21. SUBSTITUENT EFFECT ON ACIDITY Electron Withdrawing Group stabilizes carboxylate anion and strenghtens acidity Electron Donating Group destabilizes carboxylate anion and weakens acidity

  22. SUBSTITUENT EFFECTS ON ACIDITY Explain the difference in pKa values. The greater the distance (number of bonds) between an electron-withdrawing group (here chlorine) and the point of ionization, the less effect an electron-withdrawing group has.

  23. SUBSTITUENT EFFECT ON ACIDITY Dicarboxylic acids pKa1pKa2 Oxalic acid1.24.2 Succinic acid 4.25.6 Adipic acid 4.4 4.4

  24. SUBSTITUENT EFFECT ON ACIDITY Para-substituted benzoic acids pKa = 4.46 pKa = 4.19 pKa = 3.41 EDG – destabilizes carboxylate anion, decreases acidity EWG– stabilizes carboxylate anion, increases acidity Weaker acid Stronger acid

  25. SUBSTITUENT EFFECT ON ACIDITY Para-substituted benzoic acids Y pKa -OH 4.55 -OCH3 4.46 -CH3 4.34 -H 4.19 -Br 3.96 -Cl 3.96 -CHO 3.75 -CN 3.55 -NO2 3.41 EDG (activating ring in electrophilic substitution) EWG (deactivating ring in electrophilic substitution) Acidity

  26. Preparation of carboxylic acids (Industrial methods)

  27. Preparation of carboxylic acids Laboratory methods 1. Oxidation of alkylbenzenes, primary alcohols, aldehydes 88% yield 93% yield

  28. 85% yield

  29. 2. Hydrolysis of nitriles 3. Carboxylation of Grignard reagents 73% yield

  30. General reactions of carboxylic acids Deprotonation Decarboxylation Reduction α-Substitution Nucleophilic acyl substitution

  31. Decarboxylation Hunsdiecker reaction 93% yield 100% yield

  32. Deprotonation Salt formation in alkaline solutions: Na2CO3 can also be used

  33. Deprotonation Salt formation with ammonia (NH3) or amines (RNH2, R2NH, R3N): Proton transfer from carboxyl oxygen to amine nitrogen

  34. Reduction 87% yield 94% yield

  35. -Substitution -Halogenation of carboxylic acids – Hell, Volhard, Zelinskii reaction 90% yield

  36. Mechanism of -Halogenation

  37. Nucleophilic acyl substitution Net effect – replacing of hydroxyl group with nuclephile -OH is called leaving group

  38. Fischer esterification as nucleophilic acyl substitution Alcohol reactivity order: primary > secondary > tertiary R E A C T I V I T Y

  39. Fischer esterification as nucleophilic acyl substitution (mechanism) The full mechanism for Fischer esterification as well as for the reverse reaction, acid-catalyzed hydrolysis of an ester to a carboxylic acid.

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