A 200 mL diethyl ether solution contains equimolar amounts of p-aminobenzoic acid (PABA
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 200 mL diethyl ether solution contains equimolar amounts of p-aminobenzoic acid (PABA, pKa of the –CO₂H group = 4.9; the –NH₂ group is basic, pKb = 4.8), phenol (pKa = 10.0), and anisole (methoxybenzene, non-ionizable under normal acid–base conditions). The laboratory has access only to water, diethyl ether, 6 M HCl, 1 M NaHCO₃, and 1 M NaOH. The goal is to isolate each compound in pure, neutral form while keeping total solvent use to a minimum.
(a) For each compound, identify which functional group(s) can be selectively protonated or deprotonated under the acidic or basic reagents available.
(b) Design a step-wise liquid–liquid extraction sequence that will separate the three compounds into distinct fractions using the fewest possible extraction operations. For every step specify: (i) the reagent added, (ii) which compound(s) will move into the aqueous phase, and (iii) which compound(s) remain in the organic phase.
(c) Write balanced chemical equation(s) for each proton-transfer process that drives the movement of a compound from one phase to the other in your proposed sequence.
(d) Describe how each compound can be regenerated in neutral, solid form from its final fraction, including any necessary pH adjustments, drying, or solvent removal steps.
(e) Justify how the order of steps chosen minimizes cross-contamination and overall solvent consumption, making explicit reference to relative acidity/basicity and the "like dissolves like" principle.