carboxylic

• Carboxylic acids


  Another class of organic compounds containing the carbonyl group

  
• Carboxyl group


  The functional group of a carboxylic acid, can be represented in 3 ways

  
• IUPAC naming of acyclic carboxylic acids

  1. Take the longest carbon chain that contains the carboxyl group as the parent alkane

  2. Drop the final -e from the name of the parent alkane and replace it by -oic acid

  3. Number the chain beginning with the carbon of the carboxyl group

  
• IUPAC names of carboxylic acids


  • Acetic acid (ethanoic acid)
  • 3-Hydroxybutanoic acid (3-hydroxybutyric acid)
  • 4-Aminobutanoic acid (4-aminobutyric acid)

  
• Naming dicarboxylic acids


  Add the suffix -dioic acid to the name of the parent alkane that contains both carboxyl groups

  
• The numbers of the carboxyl carbons are not indicated in dicarboxylic acid names because they can be only at the ends of the chain

  
• Common names of carboxylic acids


  Use Greek letters alpha (a), beta (b), gamma (g), etc. to locate substituents

  
• Carboxyl group


  • Contains three polar covalent bonds: C=O, C-O, and O-H

  
• Polarity of carboxyl group bonds


  Determines the major physical properties of carboxylic acids

  
• Carboxylic acids have significantly higher boiling points than other types of organic compounds of comparable molecular weight
• Higher boiling points of carboxylic acids


  Result of their polarity and the fact that hydrogen bonding between two carboxyl groups creates a dimer that behaves as a higher-molecular-weight compound

  
• Carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight
• Fatty acids


  Long chain carboxylic acids derived from animal fats, vegetable oils, or phospholipids of biological membranes
• More than 500 fatty acids have been isolated from various cells and tissues
• Most fatty acids have between 12 and 20 carbons in an unbranched chain
• In most unsaturated fatty acids, the cis isomer predominates; trans isomers are rare
• The most abundant fatty acids


  • Palmitic acid
  • Stearic acid
  • Oleic acid
  • Linoleic acid
  • Arachidonic acid
• Unsaturated fatty acids generally have lower melting points than their saturated counterparts
• Saturated fatty acids


  Solids at room temperature due to the regular packing of their hydrocarbon chains
• Unsaturated fatty acids


  Liquids at room temperature because the cis double bonds interrupt the regular packing of their hydrocarbon chains
• Natural soaps


  Sodium or potassium salts of fatty acids
• Preparation of natural soaps


  1. Boiling triglycerides (triesters of glycerol) with NaOH (saponification)

  2. Boiling with KOH gives a potassium soap
• Soap micelles in water

  Spherical arrangement of molecules with hydrophobic parts shielded from the aqueous environment and hydrophilic parts in contact with the aqueous environment
• Soaps and dirt (grease, oil, fat stains) mixed in water


  The nonpolar hydrocarbon inner parts of the soap micelles "dissolve" the nonpolar substances
• Natural soaps form water-insoluble salts in hard water
• Detergents


  Molecules containing a sulfonate (-SO3-) group instead of a carboxylate (-CO2-) group to overcome the problem of precipitates in hard water
• Common additives to detergents are foam stabilizers, bleaches, and optical brighteners
• Carboxylic acids


  Weak acids with Ka values typically in the range 10-4 to 10-5 (pKa 4.0 - 5.0)
• Substituents near the carboxyl group


  Increase the acidity of carboxylic acids, especially -OH, -Cl, and -NH3+

  
• Dichloroacetic acid and trichloroacetic acid are stronger acids than H3PO4 (pKa 2.1)
• Form of carboxylic acid in aqueous solution


  Depends on the pH of the solution
• Reaction of carboxylic acids with bases

  1. Form water-soluble salts with NaOH, KOH, ammonia, and amines

  2. Also form water-soluble salts with sodium bicarbonate and sodium carbonate, evolving CO2
• Fischer esterification


  1. Reaction of a carboxylic acid with an alcohol in the presence of an acid catalyst to form an ester

  2. Reversible reaction, can be driven in either direction
• Mechanism of Fischer esterification


  Alcohol adds to the carbonyl group of the carboxylic acid to form a tetrahedral carbonyl addition intermediate, which then loses H2O to give an ester
• Decarboxylation


  Loss of CO2 from a carboxyl group
• Almost all carboxylic acids will undergo thermal decarboxylation at very high temperatures
• Most carboxylic acids are resistant to moderate heat and melt and even boil without undergoing decarboxylation
• Exception to decarboxylation resistance


  Any carboxylic acid that has a carbonyl group on the carbon β to the COOH group

  
• Mechanism of thermal decarboxylation of β-ketoacids


  Redistribution of electrons in a cyclic transition state followed by keto-enol tautomerism