CHAPTER 14: Unit 5. Chemical reactions

Chemical reactions

Learning Objectives

1. Name the typical reactions that take place with carboxylic acids.
2. Describe how carboxylic acids react with basic compounds.

1. Carboxylic Acid Salts: Carboxylic acids are neutralized by bases to produce carboxylic acid salts. Such salts are usually more soluble in water than are the acids from which they were derived. Carboxylic acid salts are named by changing the -ic ending of the acid to -oate.
   Sodium butanoate
2. Carboxylic Acid produces gas when reacting with NaHCO3.
   

Example

Write an equation for each reaction.

1. the ionization of propionic acid in water (H₂O)
2. the neutralization of propionic acid with aqueous sodium hydroxide (NaOH)

Solution

Propionic acid has three carbon atoms, so its formula is CH₂CH₂COOH.

1. Propionic acid ionizes in water to form a propionate ion and a hydronium (H₃O⁺) ion.CH₃CH₂COOH(aq) + H₂O(ℓ) → CH₃CH₂COO⁻(aq) + H₃O⁺(aq)
2. Propionic acid reacts with NaOH(aq) to form sodium propionate and water.CH₃CH₂COOH(aq) + NaOH(aq) → CH₃CH₂COO⁻Na⁺(aq) + H₂O(ℓ)
3.  Esters: esters are formed by the reaction of an acid with an alcohol. Esters have the general formula RCOOR′, where R may be a hydrogen atom, an alkyl group, or an aryl group, and R′ may be an alkyl group or an aryl group but not a hydrogen atom. In such reactions, the -OR’ group from the alcohol replaces the -OH group in the carboxylic acid. Esters are polar compounds but they cannot form hydrogen bonds to each other. Therefore, their boiling points are lower than those of alcohols and acids of similar molecular mass.Because ester molecules can engage in hydrogen bonding with water molecules, however, esters of low molar mass are somewhat soluble in water. Borderline solubility occurs in those molecules that have three to five carbon atoms.
    Many low molecular weight esters have very pleasant smells and characteristic odor. These include  ethyl butanoate ( mangoes), pentyl butanoate ( banana) and methyl salicylate ( oil of wintergreen).

Esters are also present in some important drugs like Benzocaine, melatonin etc.Most common drug is aspirin,Example: Aspirin

Acetyl salicylic Acid

Preparation of Esters

Learning Objective

1. Identify and describe the substances from which most esters are prepared.

Some esters can be prepared by esterification, a reaction in which a carboxylic acid and an alcohol, heated in the presence of a mineral acid catalyst, form an ester and water:

The reaction is reversible. As a specific example of an esterification reaction, butyl acetate can be made from acetic acid and 1-butanol.

A Closer Look: Condensation Polymers

4.  Decarboxylation: A decarboxylation reaction is a chemical reaction in which a carboxylic acid is converted into smaller organic molecule and a molecule of carbon di oxide.

Within the human body, decarboxylation most often involves polyfunctional carboxylic acids with additional functional group located within two carbons of the carboxyl carbon rather than simple carboxylic acids. For example:

5. Reduction: Carboxylic acid is reduced to primary alcohol by strong reducing agent like LiAlH₄ in ether medium.

1. 

   IN CLASS PRACTICE PROBLEMS
   What is the reagent required in this process?

   HOMEWORK EXERCISE

   1. Write the equation for the ionization of CH₃CH₂CH₂COOH in water.
   2. Write the equation for the neutralization of CH₃CH₂CH₂COOH with sodium hydroxide [NaOH(aq)].
   3. Write the equation for the reaction of CH₃COOH with sodium carbonate [Na₂CO₃(aq)].
   4. Write the equation for the reaction of CH₃CH₂COOH with sodium bicarbonate [NaHCO₃(aq)].
   5. Write the equation for the ionization of propionic acid in water.
   6. Write the equation for the ionization of γ-chloropentanoic acid in water.
   7. Write an equation for the reaction of butyric acid with each compound.a. aqueous NaOHb. aqueous NaHCO₃
   8. Write the condensed structural formula for each compound.
   a. potassium acetate
   b. calcium propanoate
   9. Name each compound.
   a. CH₃CH₂CH₂COO⁻Li⁺
   b. CH₃CH₂CH₂COO⁻NH₄⁺

   Answers
   1. CH₃CH₂CH₂COOH(aq) + H₂O(ℓ) → CH₃CH₂CH₂COO⁻(aq) + H₃O⁺(aq) 
   3. 2CH₃COOH + Na₂CO₃(aq) → 2CH₃COO⁻Na⁺(aq) + H₂O(ℓ) + CO₂(g) 
   5. CH₃CH₂COOH(aq) + H₂O(ℓ) → CH₃CH₂COO⁻(aq) + H₃O⁺(aq) 
   7.
   a. CH₃CH₂CH₂COOH(aq) + NaOH(aq) → CH₃CH₂CH₂COO⁻Na⁺(aq) + H₂O(ℓ)
   b. CH₃(CH₂)₂COOH + NaHCO₃(aq) → CH₃(CH₂)COO⁻Na⁺(aq) + H₂O(ℓ) + CO₂(g) 

   9.
   a. lithium butyrate (lithium butanoate)
   b. ammonium butanoate or ammonium butyrate