Carboxylic acids and their derivatives

HideShow resource information
  • Created by: hinna_k
  • Created on: 24-03-14 17:00
View mindmap
  • Carboxylic acids and their derivatives
    • Contain the group: C=O(X)
      • X could be 1) O-H; Carboxylic acid
      • 2) O-R; Ester
      • 3) Cl; Acid Chloride
      • or 4) NH2; Amide
    • Carboxylic Acids
      • Physical Properties
        • All acids in the homologous series Cn H2n+1 COOH are liquids up to n=9
        • All have strong smells
        • Hydrogen bonding with water allows carboxylic acids with few carbon atoms to dissolve in water. Solubility decreases with increased hydrocarbon chain lengths as these are hydrophobic.
        • Solubility in lipids increases with chain length
      • Preparation
        • - Oxidation of a primary alcohol under reflux with acidified potassium dichromate (vi)
          • - Oxidation of an aldehyde under same conditions as primary alcohol
        • - Oxidation of an aldehyde under same conditions as primary alcohol
        • - Hydrolysis of an ester
        • - Hydrolysis of a nitrile (and hydroxynitrile)
          • - Heated under reflux with aqueous alkali forms salt of the carboxylic acid
            • - Then addition of strong acid protonates the carboxylate ion forming carboxylic acid
        • - Iodoform reaction of a methyl ketone or a secondary alcohol
          • - On addition of soln of Iodine in NaOH(aq) to a methyl ketone, the salt of the acid with one fewer carbon atoms is produced. The free carboxylic acid is formed by adding excess strong acid to the mixture
      • Chemical Reactions
        • - Reacts reversibly with water. -OH group in carboxylic acid is more acidic than the -OH group in alcohols
        • - React with bases to form salts. The conc of an acid can be found by titrating it with a strong base
        • - React with carbonates and hydrogen-carbonates producing water, carbon dioxide and salt
        • Esterification
          • Carboxylic acids do not react readily with nucleophiles but they will react with alcohols in the presence of conc sulfuric acid (catalyst)
            • Acid + Alcohol Ester + Water
              • The acid acts by protonating the acid which then loses a water molecule
                • The lone pair of electrons on the oxygen of the alcohol bonds to the positive carbon atom of the protonated ion and then an H+ is removed thus reforming the catalyst
        • Reduction
          • Carboxylic acids are reduced by LiAlH4 in dry ether. The H- ion in the AlH4- is a strong nucleophile. It adds on to the delta+ carbon atom in the COOH group. A series of reactions take place and the final product has to be hydrolysed by a dilute acid.
          • CARBOXYLIC ACIDS ARE NOT REDUCED BY H2/Pt
        • Formation of Acid Chloride
          • - Ethanoic acid can be converted to ethanoyl chloride by adding solid phosphorus pentachloride to the dry acid:
            • CH3COOH + PCl5 ? CH3COCl + POCl3 + HCl
        • Formation of halogenoacid
          • If chlorine is bubbled into a boiling carboxylic acid in the presence of UV light, a chlorine atom replaces one of the hydrogen atoms in the alkyl chain:
            • CH3COOH + Cl2 ? CH2ClCOOH + HCl
              • = Free Radical Substitution
                • If chlorine is bubbled into a boiling carboxylic acid in the presence of UV light, a chlorine atom replaces one of the hydrogen atoms in the alkyl chain:
                  • CH3COOH + Cl2 ? CH2ClCOOH + HCl
                    • = Free Radical Substitution
      • Esters
        • Physical Properties
          • Most esters are liquid at room temp
          • All esters are insoluble in water even though they are polar. This is because they cannot form hydrogen bonds with water molecules due to there not being any delta+ Hydrogen atoms. Also the delta- Oxygen atoms are sterically hindered, preventing close approach by water molecules.
        • Preparation
          • By warming an alcohol and a carboxylic acid under reflux with a few drops of conc H2SO4 (reversible reaction)
            • A higher yield is obtained if the alcohol is reacted with an acid chloride at room temp because the reaction is NOT reversible
              • Preparation
                • By warming an alcohol and a carboxylic acid under reflux with a few drops of conc H2SO4 (reversible reaction)
                  • A higher yield is obtained if the alcohol is reacted with an acid chloride at room temp because the reaction is NOT reversible
          • Chemical Reactions
            • Hydrolysis
              • Hydrolysed when heated under reflux with either aqueous acid or alkali.
                • With Acid: Acid acts as catalyst and reaction is reversible so yield of acid and alcohol is low
                  • CH3COOC2H5 + H2O  CH3COOH + C2H5OH
                • With Alkali: Not reversible so there is a good yield of the salt of the carboxylic acid and the alcohol.
                  • CH3COOC2H5 + NaOH -> CH3COONa + C2H5OH
                    • If the organic acid is required then the soln is cooled and excess dilute strong acid is added
                      • CH3COONa + HCl -> CH3COOH + NaCl
              • Soaps are produced by hydrolysis of natural esters such as veg oils and animal fats
            • Trans-esterification
              • Reaction with another organic acid
                • The acid part of the ester is replaced by the acid reactant. Simplest example is the reaction between ethyl ethanoate and methanoic acid in the presence of an acid catalyst. The products are ethyl methanoate and ethanoic acid.
                  • CH3COOC2H5 + HCOOH HCOOC2H5 + CH3COOH
                  • This type of reaction is used in the manufacture of low-fat margarine where the incoming acid is saturated and the product acid is unsaturated
              • Reaction with another alcohol
                • The alcohol part of the ester is replaced by the alcohol reactant. E.g. reacn between ethyl ethanoate and methanol in the presence of an acid catalyst. The products are methyl ethanoate and ethanol
                  • CH3COO2H5 + CH3OH CH3COOCH3 + C2H5OH
                  • This type of reaction is used in the manufacture of biodiesel where the reactant alcohol is methanol or ethanol and the product alcohol is propane-1,2,3-triol
          • Uses
            • Perfumes and flavourings
            • Solvents
            • Anaesthetics
            • Biofuels
        • Acid Chlorides
          • Physical Properties
            • Most acid chlorides are volatile liquids at room temp
            • They are soluble in several organic solvents, but react water
          • Preparation
            • Acid chlorides are prepared from carboxylic acids. The -OH group is replaced by a chlorine atom. The reagents that can be used are PCl5, phosphorus trichloride or thionyl chloride.
              • CH3COOH + PCl5 -> CH3COCl + POCl3 + HCl
              • 3CH3COOH + PCl3 -> 3CH3COCl + H3PO3
              • CH3COOH + SOCl2 -> CH3COCl + SO2 + HCl
              • The organic product is ethanoyl chloride
          • Chemical Reactions
            • Reaction with water
              • Ethanoyl chloride reacts vigorously with water, forming ethanoic acid and clouds of hydrogen chloride gas
                • CH3COCl + H2O -> CH3COOH + HCl
              • All reagents and glassware must be dry when using ethanoyl chloride as a reactant
            • Reaction with alcohol
              • Ethanoyl chloride reacts rapidly in a non-reversible reaction with alcohols. The products are an ester and misty fumes of HCl vapour
                • CH3COCl + CH3OH -> CH3COOCH3 + HCl
              • Non-reversible with a good yield so is more efficient way of making ester than reacting alcohol with carboxylic acid
            • Reaction with ammonia
              • The N:- atom in NH3 is used in a nucleophilic attack on the C=O group. The product is an amide
                • CH3COCl + NH3 -> CH3CONH2 + HCl
            • Reaction with Amines
              • Have a lone pair of electrons on the nitrogen atom so react in the same way as ammonia
                • The N:- atom in NH3 is used in a nucleophilic attack on the C=O group. The product is an amide
                  • CH3COCl + NH3 -> CH3CONH2 + HCl
                • Product is an N-Substituted amide
            • Reaction with LiAlH4
              • Reduced in dry ether to form primary alcohol
            • Reaction with aromatic compounds
              • Ethanoyl chloride reacts with benzene and with phenol
      • The -OH group is replaced by a Cl atom and clouds of misty fumes of HCl are given off
        • - Ethanoic acid can be converted to ethanoyl chloride by adding solid phosphorus pentachloride to the dry acid:
          • CH3COOH + PCl5 ? CH3COCl + POCl3 + HCl
      • All esters are insoluble in water even though they are polar. This is because they cannot form hydrogen bonds with water molecules due to there not being any delta+ Hydrogen atoms. Also the delta- Oxygen atoms are sterically hindered, preventing close approach by water molecules.

      Comments

      No comments have yet been made

      Similar Chemistry resources:

      See all Chemistry resources »See all Reactions resources »