Chapter 4 carboxylic acid


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Chapter 4 carboxylic acid

  1. 1. Chapter 4 CARBOXYLIC ACID Norfazrin Mohd Hanif Faculty of Applied Science UiTM Negeri Sembilan
  2. 2. CHAPTER OUTLINE General formula : RCOOH OR ArCOOH Nomenclature –IUPAC and common Physical properties of aldehyde : Boiling points and solubility Acidity Preparation Oxidation of Primary Alcohols, Aldehydes, Alkenes And Alkyl Benzene Carboxylation of Grignard reagent Hydrolysis of nitrile Reactions Salt formation Reduction to alcohols  Formation of Acyl Chlorides  Formation of Esters  Formation of Acid Anhydrides  Formation of Amides
  3. 3.  The functional group of a carboxylic acid is a carboxyl group, which can be represented in any one of three ways: O , R-COOH, R-CO2H R C OH
  4. 4.    Carboxylic acids named by replacing –e of the corresponding alkane name with –oic acid –CO2H carbon atom is numbered C1 Compound containing multiple –COOH group, add di- or tri- to the suffix –oic acid
  5. 5.   Carboxylic acids containing two carboxyl groups are called dicarboxyl acids. Their systematic names have the suffix ‘dioic’. COOH COOH CH2 COOH COOH ethanedioic acid (oxalic acid) propanedioic acid (malonic acid) COOH (CH2)4 COOH hexanedioic acid (adipic acid)
  6. 6.   Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids. Aromatic acids are named as benzoic acids. O C OH COOH OH COOH 1 6 5 benzoic acid 2-hydroxybenzoic acid 2 3 4 NO2 3-nitrobenzoic acid
  7. 7.   All common names of acid end in –ic acid. Positions of substituents on the chain are labeled with Greek letters. Cl O Ph CH3CH2CHC OH CH3CH2CH2CHCH2COOH -chlorobutyric acid -phenylcaproic acid
  8. 8. Boiling point (BP)  Carboxylic Acids have higher BP than other organic molecules with comparable MW.
  9. 9. Higher boiling points than similar alcohols, due to dimer formation. Acetic acid, b.p. 118C
  10. 10.    In the presence of water, hydrogen bond are formed between water molecules & individual molecules of acid. Carboxylic acid with up to 4 Carbon completely miscible in water at room temperature. Water solubility decreases with the length of the carbon chain. δ+ δ-………… H O R C OH H O Hydrogen bond with water.
  11. 11.  More soluble in water than comparable alcohols, ethers, aldehydes, and ketones Structu re N ame CH3 COOH CH3 CH2 CH2 OH CH3 CH2 CHO acetic acid 1-prop anol prop anal Boilin g Solubility Molecular Poin t Weigh t (°C) (g/100 mL H 2O) 60.5 118 infinite 97 60.1 infinite 58.1 48 16 CH3 (CH2 ) 2 COOH butan oic acid CH3 (CH2 ) 3 CH2 OH 1-pentan ol pentan al CH3 (CH2 ) 3 CHO 88.1 88.1 86.1 163 137 103 infinite 2.3 slight
  12. 12.  Carboxylic acids are acidic because of the hydrogen in the -COOH group.  Recall that acids are compounds which yield H+ ions in solution.  Carboxylic acids in solution dissociate into the following ions: Carboxylate ion
  13. 13.     Carboxylic acids – stronger acids than ROH The pKa of ethanol is ~16, compared to ~5 for acetic acid Alkoxide ion (R-O-): negative charge is localized on O Carboxylate ion (COO-): negative charge is delocalized over two equivalent O atoms: Resonance stabilization
  14. 14. Oxidation of  Alkyl benzene  Alkene  Alcohol  Aldehyde Carboxylation of Grignard reagent Hydrolysis of nitrile
  15. 15. o General Formula: R o Example: KMnO4 ,H+ COOH
  16. 16. o General Formula: R CH CH R' KMnO4 ,H3O+ R + R C OH o Example: O O C OH
  17. 17. o General Formula: R CH2OH KMnO4 ,H3O+ O R C OH o Example:
  18. 18. o General Formula: O R KMnO4 ,H3O C H o Example: O + R C OH
  19. 19. o General Formula: RMgX CO2 H3O+ RCOOH R = alkyl, allyl, benzyl, aryl CO2 = dry ice or bubbling gaseous CO2 • nucleophilic addition - alkyl or aryl magnesium halide is added to a double bond C=O of CO2 to form carboxylate ion. • when treated with acid, carboxylic acid is formed O R MgX O C O R C O- MgX+ + H3O O R C OH
  20. 20. o Example: CH3CH2MgCl i) CO2 + ii) H3O CH3CH2COOH i) CO2 MgCl ii) H3O+ COOH
  21. 21.  Alkyl halides react with NaCN to form nitriles which in turn undergo hydrolysis in acidic solution to produce carboxylic acid. O R     X NaCN R CN H3O+ R C OH + NH4+ Formation of nitriles involves nucleophilic substitution. Primary alkyl halides (Cl, Br, I) – SN2 substitution Aromatic nitriles cannot be prepared through this method but still can hydrolysed to give aromatic carboxylic acids. The nitrile is reflux with a dilute acid such as H2SO4 or HCl to form carboxylic acid.
  22. 22. o General Formula: o Example: Br NaCN CN + H H2O COOH
  23. 23.  Salt formation - neutralisation - reactions with electropositive metals      Reduction to alcohols Formation of Acyl Chlorides Formation of Esters Formation of Acid Anhydrides Formation of Amides
  24. 24. 1) Neutralisation: - carboxylic acids undergo neutralisation reactions with strong bases or some weak base such as NaOH, NaHCO3, Na2CO3, NH3 and amines to form carboxylate salts of carboxylic acids and water. RCO2H + NaOH → RCO2-Na+ + H2O RCO2H + NaHCO3 → RCO2-Na+ + H2O + CO2 2RCO2H + Na2CO3 → 2RCO2-Na+ + H2O + CO2 RCO2H + NH3 → RCO2-NH4+ * carboxylate salts are soluble in water
  25. 25. Examples: CH3COOH (aq) + NaOH (aq) → CH3COONa (aq) + H2O (l) sodium ethanoate
  26. 26.   an aqueous solution of benzoic acid turns blue litmus paper to red. Benzoic acids dissolves readily in alkalis to form salts (benzoates) and water. COOH NaOH - COO Na + H2O sodium benzoate   Carboxylic acids react with carbonates and hydrogen carbonates to form CO2, water and salts of carboxylic acids. Examples: 2HCOOH (aq) + Na2CO3 (aq) → 2HCOONa (aq) + CO2 (g) + H2O (l) sodium methanoate CH3CH2COOH(aq) + NaHCO3(aq) → CH3CH2COONa (aq) + CO2(g)+ H2O(l) sodium propanoate
  27. 27. 2) Reaction with electropositive metals - reactive metals (i.e. metals that are very electropositive) react with carboxylic acids to form hydrogen gas and salts of carboxylic acids. - examples of metals: calcium, magnesium, zinc and iron. 2CH3COOH (aq) + Mg → (CH3COO)2Mg(aq) + H2 (g) magnesium ethanoate
  28. 28. 1) Reaction with active metals RCO2H + Na  RCO2-Na+ + H2(g) 2) Reaction with base RCO2H + NaOH  RCO2-Na+ + H2O 3) Reaction with carbonate RCO2H + NaHCO3  RCO2-Na+ + CO2 + H2O
  29. 29. o General reaction O R C OH LiAlH4 ,H3O+ R CH2 OH o Example O CH3C OH LiAlH4 ,H3O+ CH3 CH2 OH
  30. 30.   Carboxylic acids reacts with phosphorus (v) chloride (PCl5) or sulphur dichloride oxide (thionyl chloride) or phosphorus trichloride (PCl3) at room temperature to form acyl chloride. In the case of benzoic acid, the reaction mixture is heated. O R C OH O PCl5 R C Cl carboxylic acids HCl acid chlorides O POCl3 O R C OH SOCl2 carboxylic acids carboxylic acids SO2 HCl acid chlorides O 3 R C OH R C Cl O PCl3 3 R C Cl acid chlorides H3PO3
  31. 31. Examples: O O CH3 C OH SOCl2 O benzoic acid SO2 HCl ethanoyl chloride ethanoic acid C OH CH3 C Cl O SOCl2 C Cl benzoyl chloride SO2 HCl
  32. 32.    When a carboxylic acid is heated with an alcohol in the presence of a little concentrated sulphuric acid, an ester is formed. Known as Fischer esterification. Since the reaction is reversible, the mixture must be heated or reflux. O CH3 C OH ethanoic acid H OC2H5 benzoic acid H+ = H2SO4 CH3 C OC2H5 heat or reflux O C OH O H+ H+ H OC2H5 heat or reflux H2O ethyl ethanoate O C OC2H5 ethyl benzoate H2O
  33. 33.  Preparation of acid anhydrides: - reaction of carboxylic acid with an acid chloride in the presence of pyridine. - pyridine, C5H5N (base) is added to neutralize the HCl formed in the reaction to prevent unnessary side reaction (if any). O R C OH carboxylic acid O Cl C R' O O pyridine HCl R C O C R' acid chloride acid anhydrides examples O CH3 C OH acetic acid O Cl acetic acid CH3 C O C CH3 O Cl C benzoyl chloride HCl acetic anhydride ethanoyl chloride O CH3 C OH C CH3 O O pyridine pyridine O O CH3 C O C acetic benzoic anhydride HCl
  34. 34.  Symmetrical anhydride is formed when two carboxylic acid is heated with phosphorus pentoxide (P2O5) (dehydration reaction) or heating with ZnO. O O CH3 C OH HO C CH3 two molecules of acetic acids P2O5 or ZnO/heat O O CH3 C O C CH3 acetic anhydride H2O
  35. 35. Amides can be synthesised directly from carboxylic acids, but the yield is poor. A better method of synthesising amides is by using acid chlorides. When ammonium carboxylates are heated in the presence of the free acid, dehydration occurs to form the primary amide. Ammonium carboxylates are obtained by the reaction of carboxylic acids with ammonia (poor method).     RCOO-NH4+  Excess RCOOH Heat (100-200 °C) RCONH2 + H2O 1° amide For example: CH3COOH + NH3 → CH3COONH4 ammonium ethanoate heat CH3CONH2 + H2O ethanamide
  36. 36.  Secondary and tertiary amides can be synthesised by using primary amines and secondary amines respectively. O O H H R C OH H N R' o 1 amine examples: O CH3 C OH o O H H N CH3 O o heat (100-200 C) o 2 amine CH3 C N CH3 H2O N-methylethanamide O R" R" H N R' H2O 2 amide H methylamine R C OH R C N R' heat (100-200 oC) heat (100-200 oC) R C N R' o H2O 3 amide examples: O CH3 C OH H N CH3 O CH3 CH3 dimethylamine o heat (100-200 C) CH3 C N CH3 N,N-dimethylethanamide H2O
  37. 37.  Other method: reaction of acid chloride with ammonia or amines O O R C Cl 2NH3 ammonia O R C NH2 amide NH4+ Clammonium chloride O H R C Cl 2RNH2 amine O R C N R secondary amide RNH3+ Clammonium chloride O R R C Cl 2R2NH secondary amine R C N R tertiary amide R2NH2+ Clammonium chloride examples: O CH3 C Cl O 2NH3 NH4+ Cl- O CH3 O CH3 C Cl CH3 C NH2 2CH3NH2 CH3 C N H CH3NH3+ Cl-
  38. 38. Thank you…