Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

3. Acids and Bases

Acid Base Equilibrium

Organic Chemistry

3. Acids and Bases

Acid Base Equilibrium

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6:30 minutes

Problem 48a

Textbook Question

Given the data in Problem 47:
a. What pH would you make the water layer to cause the carboxylic acid to dissolve in the water layer and the amine to dissolve in the ether layer?

Verified step by step guidance

Identify the functional groups in the compounds: A carboxylic acid contains a -COOH group, which can lose a proton (H⁺) to form a carboxylate anion (-COO⁻) in a basic environment. An amine contains a -NH₂ group, which can gain a proton to form an ammonium cation (-NH₃⁺) in an acidic environment.

Understand the solubility behavior: The carboxylate anion (-COO⁻) is water-soluble due to its ionic nature, while the neutral carboxylic acid is more soluble in organic solvents like ether. Similarly, the ammonium cation (-NH₃⁺) is water-soluble, while the neutral amine is more soluble in ether.

Determine the pH conditions for the carboxylic acid: To deprotonate the carboxylic acid and form the water-soluble carboxylate anion, the pH of the water layer should be made basic. This can be achieved by adding a base, such as NaOH, to raise the pH above the pKa of the carboxylic acid (typically around 4-5).

Determine the pH conditions for the amine: To keep the amine in its neutral form (which is ether-soluble), the pH of the water layer should not be too acidic. If the pH is below the pKa of the amine (typically around 9-11), the amine will protonate to form the water-soluble ammonium cation.

Adjust the pH accordingly: To achieve the desired separation, set the pH of the water layer to a value above the pKa of the carboxylic acid (e.g., pH > 5) but below the pKa of the amine (e.g., pH < 9). This ensures the carboxylic acid dissolves in the water layer as the carboxylate anion, while the amine remains in the ether layer in its neutral form.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Carboxylic Acids and pH

Carboxylic acids are weak acids that can donate protons (H+) in solution. The pH of a solution affects the ionization of these acids; at lower pH (more acidic), they remain mostly in their non-ionized form, while at higher pH, they can deprotonate to form carboxylate ions. To dissolve a carboxylic acid in water, the pH should be adjusted to a level that favors its ionization.

Amine Solubility in Organic Solvents

Amines are basic compounds that can accept protons, and their solubility in organic solvents like ether is influenced by their protonation state. At lower pH, amines are protonated and more soluble in water, while at higher pH, they are neutral and more soluble in organic solvents. Understanding this behavior is crucial for manipulating the solubility of amines in extraction processes.

Liquid-Liquid Extraction

Liquid-liquid extraction is a technique used to separate compounds based on their solubility in two different immiscible liquids, typically water and an organic solvent. The distribution of compounds between the two layers depends on their polarity and the pH of the aqueous layer. By adjusting the pH, one can selectively dissolve either the carboxylic acid in water or the amine in the organic layer, facilitating their separation.

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Related Practice

Textbook Question

Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH₃) has a pK_a value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with

b. ⁻NH₂.

c. Which would be a better base to use if you wanted to remove a proton from ethyne, HO⁻ or ^-NH₂?

Textbook Question

For each of the acid–base reactions in [Section 2.3], compare the pK_a values of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

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2. <IMAGE>

Textbook Question

For each of the acid–base reactions in [Section 2.3], compare the pK_avalues of the acids on either side of the equilibrium arrows to prove that the equilibrium lies in the direction indicated.

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4. <IMAGE>

Textbook Question

Ethyne (HC≡CH) has a pK_a value of 25, water has a pK_a value of 15.7, and ammonia (NH3) has a pKa value of 36. Draw the equation, showing equilibrium arrows that indicate whether reactants or products are favored, for the acid–base reaction of ethyne with

a. HO^-.

Textbook Question

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pKa values, but if you need a hint, you can consult Appendix 4.

j. CF₃CH₂O^– + FCH₂CH₂OH

Textbook Question

Complete the following acid–base reactions. In each case, indicate whether the equilibrium favors the reactants or the products, and explain your reasoning.

(g) KOH + CH₃CH₂OH ⇌

Textbook Question

Complete the following acid–base reactions. In each case, indicate whether the equilibrium favors the reactants or the products, and explain your reasoning.

(f) (CH₃)₃C–O^– + H₂O ⇌

Textbook Question

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pK_a values, but if you need a hint, you can consult Appendix 4.

g. NaOCH₂CH₃ + Cl₂CHCH₂OH

h. H₂Se + NaNH₂

i. CH₃CHFCOOH + FCH₂CH₂COO^–

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