Carboxylic Acids (RCOOH)

• Contain the Carboxyl group = carbonyl + hydroxyl

• The carboxyl group is polar, but the carbon chain is not, so RCOOH of 4 or fewer carbons are completely soluble, but solubility decreases as the chain gets longer.

• Weak acids (meaning they dissociate slightly in aq solution).

• Capable of forming H bonds with water and between acid molecules.  The molecule pairs formed in this way are called dimers.  Because of this, RCOOH has a higher boiling point than other compounds we've studied.

  

• Fatty acids are straight chain carboxylic acids.  Unsaturated fatty acids contain C-C double bonds.

  • Larger Ka value = stronger acid

    • Also, electronegative atoms attached to the R group increase the acidity.

  • Long Chain RCOOH + alkali metal base yeilds soap + water (so soaps are the alkali metal salts of long chain fatty acids.)

    

    • The soap molecule has a long hydrocarbon chain that is non-polar and hydrophobic, and a charged carboxylate ion head that is polar and water soluble.

    • Forms micelles

    • In hard water soaps form insoluble salts.

  • Detergents do not form insoluble salts in hard water.

  • See Reactions handout for synthesis of Carboxylic acids.

• Carboxylic Acid Anhydrides

  • Formed by the loss of a molecule of water from 2 carboxylic acid molecules.

    

  • Named by adding word "anhydride" after the name of the parent acid.

  • Opposite of the reaction that forms anhydrides is Hydrolysis.

• Carboxylic Esters (RCOOR')

  • Derivatives of carboxylic acids in which the H of the carboxyl group is replaced by the alkyl or aryl group.

  • Can H bond to water (so esters of low molar mass are somewhat soluble).

  • Cannot H bond to self (so lower boiling point).

  • Named with R' group (from the alcohol) first as an alkyl group.  Then name the acid, replacing the -ic acid ending with -ate.

  • Esterification is the name of the reaction that forms esters (see Reactions handout).

• Phosphoric Acids, Esters and Anhydrides

  • H₃PO₄

  • Can be dehydrated to form phosphoric acid anhydrides.

  • Can react with alcohols to form phosphate esters.  Because it has three hydroxyl groups, it can form monoesters, diesters, and triesters.

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