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Carboxylic acids and their Derivatives (chapter 36)

Carboxylic acids and their Derivatives (chapter 36). O. -I effect. O-H. R. C. Structure. Two functional groups adjacent to each other. C=O and –OH groups modify each other and shows different properties. Formation of RCOOH. Halides  nitriles  acids

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Carboxylic acids and their Derivatives (chapter 36)

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  1. Carboxylic acids and their Derivatives(chapter 36)

  2. O -I effect O-H R C Structure Two functional groups adjacent to each other C=O and –OH groups modify each other and shows different properties.

  3. Formation of RCOOH • Halides  nitriles  acids • Oxidation of 1o R-OH and R-CHO • Oxidation of Alkylbenzene • Iodoform reaction

  4. Carbonyl group property Acidic property O R C H O Alkanolic property Decarboxylation Possible reactions

  5. O R C H O Acidity Greater polarization of this bond extra +ve Polarization of this bond is increased, O-H bond is weakened. (Acidic)

  6. .. O O- R C R C .. O- O Acidity -ve charge is spreaded over the –C=O group and stabilize the anion RCOO-

  7. Acid strength RCOOH  RCOO- + H+ Acid pKa HCOOH 3.8 CH3COOH 4.8 CH3CH2COOH 4.9 CH3CH3CH2COOH 4.8 All are weak acids, <1% ionized in water

  8. Question • Explain the following order of acid strength • a. RCOOH > C6H5OH > R-OH • b. CCl3COOH > CHCl2COOH > CH2ClCOOH • > CH3COOH

  9. Formation of salts • Formation of salts by reacting with • Metals • Carbonates • Hydroxides

  10. H2/Ni NaBH4 No reaction No reaction Reaction of the C=O group 1. LiAlH4/ether 2. H3O+ RCH2OH RCOOH

  11. H O R C R C O H O H H R C O- R C OH H+ H H Reduction mechanism H:- H:-

  12. Nucleophilic substitution • Nucleophilic substitution • C-OH bond as attractor of Nu: (HBr, PBr3, SOCl2) • C=O play background role in enhancing the • reactivity of C-OH bond by attracting Nu:

  13. O O O R C R R C C Cl H R’ O O Ester O O O Acid Chloride R C NH2 R C O C R Amide Acid Anhydride Acid Derivatives

  14. Conversion to Acid Derivatives • To Acyl chlorides • PCl5/SOCl2 • RCOOH  RCOCl • To Ester • H+ • R’COOH + ROH  R’COOR + H2O

  15. Conversion to Acid Derivatives • To acid anhydride • RCOOH + R’COCl RCOOCOR’ + HCl • To amide • RCOOH + NH3 RCOO-NH4+ • excess RCOOH •  RCONH2 + H2O • reflux • (excess RCOOH is used to repress the hydrolysis of amide)

  16. O O O R C O C R R C + - Cl + - Reactions of acyl halides and acid anhydrides C=O provides extra polarity to activate the C-X, C-O bonds

  17. O O:- R C Z C BH+ R HB: Z -Z- O O C BH+ R -H+ C B R Reactions of acyl halides and acid anhydrides pKa HCl -2.2 RCOOH 4~5 ROH 16~19 NH3 34 Reactivity: -Cl > -OCOR > -OR > -NH2 (base strength: NH2->OR->OCOR->Cl-)

  18. O O O H2O: RCOOH + HCl 2 RCOOH R C O C R R C Cl H2O: Reaction with water

  19. COOH + (CH3CO)2O OH COOH + CH3COOH OCOCH3 (Aspirin) Reaction with R-OH CH3COCl + R-OH  CH3COOR + HCl

  20. Reaction with ammonia and amine CH3COCl + 2NH3 CH3CONH2 + NH4Cl CH3COCl + NH(CH3)2 CH3CON(CH3)2 + HCl (CH3CO)2O + 2NH3 CH3CONH2 + NH4+CH3COO- (CH3CO)2O + 2RNH2 CH3CONHR + RNH3+CH3COO-

  21. Reactions of esters • Hydrolysis • H3O+, reflux • RCOOR’ + H2O  RCOOH + R’OH • OH- • RCOOR’ + H2O  RCOO- + R’OH • Reduction with LiAlH4 • 1. LiAlH4/ether • RCOOR’  RCH2OH + R’OH • 2. H3O+

  22. O O AlH3- AlH4- O R R C C H OR’ R C OR’ H + R’O-AlH3- LiAlH4 H3O+ RCH2O-AlH3- R’OH H3O+ RCH2OH Mechanism of reduction

  23. Reactions of amides • Hydrolysis • reflux • RCONH2 + H3O+ RCOOH + NH4+ • reflux • RCONH2 + OH- RCOO- + NH3 • Dehydration • P2O5, heat • C6H5CONH2 C6H5CN + H2O

  24. Reactions of amides • Hofmann degradation • CH3CH2CONH2 + 4KOH + Br2 •  CH3CH2NH2 + K2CO3 + 2KBr + 2H2O • (one carbon atom less) • Reduction (LiAlH4) • LiAlH4 H3O+ • RCONH2  RCH2NH2

  25. O O O + Br- + H2O Br2 R R R + C C C N NH2 NH + OH- Br H O OH- -Br- R C N- Br Br R-N=C=O O R-NH-C-OH RNH2 + CO2 R-N=C=O + H2O Mechanism (Hofmann)

  26. O O- Li+ R C NH2 R C NH2 :H- H :H- LiAlH4 RCH2NH2 + Li2O Mechanism (reduction)

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