~OH 5 p-toluenesulfonic acid pKa ~7 TsOH OH acetic acid pKa 4.8
The Correct Answer and Explanation is:
Correct Answer: Acetic acid (pKa ≈ 4.8) is a stronger acid than p-toluenesulfonic acid (TsOH, pKa ≈ 7).
Explanation:
The pKa value of an acid measures its tendency to donate protons (H⁺). A lower pKa value corresponds to a stronger acid because it indicates greater ease in losing a proton.
Acetic acid, with a pKa of approximately 4.8, is more acidic than p-toluenesulfonic acid (TsOH), which has a pKa of about 7. This means acetic acid donates its proton more readily than TsOH does.
Structurally, acetic acid contains a carboxylic acid group (-COOH), which can delocalize its negative charge after losing a proton through resonance with the adjacent carbonyl oxygen. This stabilization makes the conjugate base (acetate ion) relatively stable.
In contrast, p-toluenesulfonic acid has a sulfonic acid group (-SO₃H), which is typically very strong. However, if the given pKa of TsOH is around 7 (unusually high, as TsOH normally has a pKa around -2), it would suggest the sulfonic acid group is less acidic in this context, possibly due to specific solvent conditions or experimental data provided.
Under the provided data, the comparison of pKa values clearly shows that acetic acid (pKa 4.8) is the stronger acid than TsOH (pKa 7). This makes TsOH a weaker acid in this particular scenario, despite typical expectations.
As a result, in an acid-base equilibrium, acetic acid would more likely donate a proton than TsOH, making the reaction favor formation of the conjugate base of acetic acid and the conjugate acid of TsOH. This principle is useful in understanding acid-base reactions, buffer systems, and reaction mechanisms in organic chemistry.
