Final answer:
Acid increases the rate of water addition to a carbonyl group by generating hydronium ions from an acid catalyst, which protonates the carbonyl group, enhancing its electrophilicity. High concentrations of water drive the reaction forward despite its weak nucleophilicity. In biological systems, enzymes like carbonic anhydrase demonstrate a similar mechanism, with a reactive Zn2+-bound hydroxide ion.
Step-by-step explanation:
Acid increases the rate of reaction for the addition of water to a carbonyl group through catalyst action and protonation, enhancing the electrophilicity of the carbonyl carbon. In acidic hydrolysis, water acts as a nucleophile that attacks the positively charged carbon atom of the carbonyl group. The presence of the acid catalyst generates a high concentration of hydronium ions (H3O+), which accelerates the reaction by protonating the carbonyl oxygen, making the carbon more susceptible to attack by the nucleophilic water molecule. Moreover, the conjugate base of the acid, such as the bisulfate ion HSO4- in the case of sulfuric acid, is a poor nucleophile compared to water. Therefore, despite water being a weak nucleophile, its high concentration leads to dominance in the addition reaction. Le Châtelier's principle highlights the shift in water autoionization equilibrium towards more hydronium ions in an acidic solution.
In biological systems, a similar process is illustrated by the enzyme carbonic anhydrase, which efficiently converts carbon dioxide to bicarbonate (HCO3-) and protons. The enzyme's active site contains a Zn2+ ion, which greatly lowers the pKa, creating a more reactive hydroxide ion. This accelerates the capture of carbon dioxide, preventing the build-up of CO2 pressure within tissues.