Given the data in Problem 47:
b. 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

1. Identify the chemical properties of the functional groups involved: Carboxylic acids are acidic and can donate a proton (H⁺), while amines are basic and can accept a proton. This means their solubility can be manipulated by adjusting the pH of the solution.
2. Understand the solubility behavior: Carboxylic acids are more soluble in water when deprotonated (forming the carboxylate anion, RCOO⁻), which occurs at a pH above their pKa. Amines are more soluble in water when protonated (forming the ammonium ion, RNH₃⁺), which occurs at a pH below their pKa.
3. Determine the pKa values: Look up or use the provided pKa values for the carboxylic acid and the amine in the problem. These values will help you decide the pH range needed to selectively dissolve each compound in the desired layer.
4. Adjust the pH for selective solubility: To dissolve the carboxylic acid in the water layer, increase the pH above its pKa so it forms the carboxylate anion. To dissolve the amine in the ether layer, decrease the pH below its pKa so it remains neutral and nonpolar.
5. Verify the separation: After adjusting the pH, confirm that the carboxylic acid is in the water layer as the carboxylate anion and the amine is in the ether layer as the neutral compound. This ensures effective separation based on their solubility properties.

Key Concepts

Carboxylic Acids and pH

Carboxylic acids are weak acids that can donate a proton (H+) in solution. The pH of a solution affects the ionization of these acids; at lower pH values, they remain mostly in their protonated form, while at higher pH values, they can deprotonate to form carboxylate ions. To dissolve a carboxylic acid in water, the pH must 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 levels, amines are protonated and more soluble in water, while at higher pH levels, they remain unprotonated and are more soluble in organic solvents. Understanding this behavior is crucial for separating amines from aqueous solutions.

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 choice of pH can selectively alter the solubility of compounds, allowing for the separation of acids and bases. By adjusting the pH, one can manipulate the distribution of the carboxylic acid and amine between the water and ether layers.