Topic 7: Carboxylic Acids and its Derivativez

• Esters, a type of carboxylic acid derivative, are largely responsible for the flavors and fragrances of ripe fruits, such as pineapples
• Carboxyl group


  General structural representation

  
• Attachments to carboxyl group carbon atom

  • Hydrogen
  • Alkyl groups
  • Aryl group

  
• Carboxylic acid derivative


  Organic compound that can be synthesized from or converted into a carboxylic acid

  
• Carboxylic acid derivatives


  • Esters
  • Acid chlorides
  • Acid anhydrides
  • Amides

  
• Acyl group


  Part of a molecule with the general formula

  
• Monocarboxylic acid


  Carboxylic acid in which one carboxyl group is present

  
• Nomenclature rules for monocarboxylic acids

  • Select the longest carbon chain that includes the carbon atom of the carboxyl group as the parent chain
  • Name the parent chain by changing the -e ending of the corresponding alkane to -oic acid
  • Number the parent chain by assigning the number 1 to the carboxyl carbon atom, but omit this number from the name
  • Determine the identity and location of any substituents and append this information to the front of the parent chain name
  • If the carbonyl group is bonded to a carbon ring, name the ring and add the words carboxylic acid

  
• Dicarboxylic acid


  Carboxylic acid that contains two carboxyl groups, one at each end of a carbon chain

  
• Dicarboxylic acid examples


  • Pentanedioic acid
  • 3-Methylpentanedioic acid

  
• Benzoic acid


  Simplest aromatic carboxylic acid

  
• Ester


  Carboxylic acid derivative in which the -OH portion of the carboxyl group has been replaced with an -OR group

  
• Atoms that can be attached to the ester functional group

  • Hydrogen
  • Alkyl groups
  • Aromatic group

  
• Ester nomenclature rules


  • The name for the alkyl part of the ester appears first and is followed by a separate word giving the name for the acyl part of the ester
  • The name for the alkyl part of the ester is simply the name of the R group (alkyl, cycloalkyl, or aryl) present
  • The name for the acyl part of the ester is obtained by dropping the -ic acid ending for the acid's name and adding the suffix -ate

  
• Acid chloride


  Carboxylic acid derivative in which the -OH portion of the carboxyl group has been replaced with a -Cl atom

  
• Acid chloride nomenclature rules

  • Replace the -ic acid ending of the common name of the parent carboxylic acid with -yl chloride
  • Replace the -oic acid ending of the IUPAC name of the parent carboxylic acid with -oyl chloride
• Acid anhydride


  Carboxylic acid derivative in which the -OH portion of the carboxyl group has been replaced with a group

  
• Acid anhydride nomenclature rules

  • For symmetrical acid anhydrides (both R groups are the same), replace the acid ending of the parent carboxylic acid name with the word anhydride
  • For mixed acid anhydrides (different -R groups present), name the individual parent carboxylic acids (in alphabetic order) followed by the word anhydride
  • If an acid halide group is connected to a ring, the suffix, "carboxylic acid" can be replaced with "carbonyl halide"

  
• Carboxylic acids are abundant in nature, and found in a wide variety of synthetic pharmaceuticals

  
• The US produces over 2.5 million tons of acetic acid per year, which is primarily used to produce vinyl acetate

  
• Vinyl acetate is used in paints and adhesives
• Carboxylic acid derivatives such as vinyl acetate are very common and play a central role in organic chemistry

  
• Examples of common carboxylic acids

  • Formic acid
  • Acetic acid
  • Propionic acid
  • Butyric acid
  • Valeric acid
  • Caproic acid
  • Oxalic acid

  
• Structure and properties of carboxylic acids

  • Carbonyl has trigonal planar geometry
  • Acid moiety is capable of strong hydrogen bonding including H-bonding between acid pairs
  • Have higher boiling points than alcohols

  
• Carboxylate salt


  Carboxylic acids exist as a carboxylate salt in the presence of base

  
• Carboxylic acids


  Weak acids that only dissociate slightly in water
• pKa of carboxylic acids

  Between 4 and 5

  
• Compared to HCl or H2SO4, carboxylic acids are very weak acids
• Compared to an alcohol, carboxylic acids are relatively acidic

  
• Stability of carboxylate conjugate base

  Due to resonance

  
• At physiological pH (7.3) the ratio of a carboxylate ion and the corresponding carboxylic acid is 1000:1

  
• Pyruvic acid exists primarily as the pyruvate ion at physiological pH
• Effect of electron-withdrawing substituents on acidity


  The stronger and/or closer they are to the acidic proton, the stronger the acid
• Electron withdrawing substituents affect benzoic acid acidity as well
• Reactions that produce a carboxylic acid

  • Hydrolysis of nitriles
  • Carboxylation of a Grignard reagent with CO2

  
• Carboxylic acids can be reduced to a 1˚ alcohol with LAH

  
• LAH is a strong base, so it destroys carboxylic acids
• Electron withdrawing substituents


  • Affect benzoic acid as well
• Preparation of Carboxylic Acids

  1. Hydrolysis of nitriles

  2. Carboxylation of a Grignard reagent w/ CO2

  
• Reduction of a carboxylic acid with LAH

  1. Deprotonation of the carboxylic acid

  2. Reduction of the carboxylate to an aldehyde

  3. Reduction of the aldehyde to a 1° alcohol