The key difference between general and specific acid base catalysis is that general acid-base catalysis occurs at constant pH but different buffer concentrations, whereas specific acid base catalysis does not depend on the concentration of the buffer and is dependent on the hydronium ion content.
Catalysis can be described as a process where the rate and the outcome of the reaction can be influenced by the presence of a substance that does not get consumed during the reaction. Subsequently, this substance is removed from the reaction mixture. There are two kinds of acid-base catalysis, known as general catalysis and specific catalysis.
CONTENTS
1. Overview and Key Difference
2. What is General Acid Base Catalysis
3. What is Specific Acid Base Catalysis
4. General vs Specific Acid Base Catalysis in Tabular Form
5. Summary – General vs Specific Acid Base Catalysis
What is General Acid Base Catalysis?
General acid-base catalysis is a type of catalysis that occurs when acidic or basic residue at the active site is useful in facilitating proton transfers in the reaction. This type of catalysis is important for specificity and rate enhancement. The general acid or base refers to an amino acid residue in a glycoside hydrolase or a related enzyme that can participate in the mechanism of hydrolysis via removing or adding a proton. This mechanism is either a retaining or inverting mechanism.
What is Specific Acid Base Catalysis?
Specific acid-base catalysis is a process in which the reaction rate depends on the specific base and not on the other bases in the solution. In other words, the catalysis takes place by a hydronium or hydroxide ion, and it can be determined only by the pH, not the buffer concentration.
For example, the hydrolysis of ethyl acetate is a specific acid-base reaction. This is an exceedingly slow reaction at neutral pH since both nucleophiles and electrophiles are unreactive. Moreover, the reaction rate can be accelerated, or the reactivity of either the nucleophile or the electrophile can be enhanced. Since the increase in pH can increase the concentration of hydroxide ions (hydroxide ion is a better nucleophile compared to water), the rate of hydrolysis at a pH can increase. On the other hand, decreasing pH can increase the hydronium ion concentration that is able to protonate the ester carbonyl, which in turn can increase the electrophilicity, thereby increasing the hydrolysis rate.
What is the Difference Between General and Specific Acid Base Catalysis?
The key difference between general and specific acid base catalysis is that general acid-base catalysis occurs at constant pH but different buffer concentrations, whereas specific acid base catalysis does not depend on the concentration of the buffer and is dependent on the hydronium ion content. Moreover, in the general acid base catalysis, the solvent does not act as the acid or base, whereas in specific acid base catalysis, the solvent acts as the acid or base.
The following table summarizes the difference between general and specific acid base catalysis.
Summary – General vs Specific Acid Base Catalysis
General acid-base catalysis is a type of catalysis that occurs when acidic or basic residue at the active site is useful in facilitating proton transfers in the reaction. Specific acid-base catalysis is a process in which the reaction rate depends on the specific base and not on the other bases in the solution. The key difference between general and specific acid base catalysis is that general acid-base catalysis occurs at constant pH but different buffer concentrations, whereas specific acid base catalysis does not depend on the concentration of the buffer and is dependent on the hydronium ion content.
Reference:
1. “A1. General Acid and Base Catalysis.” Chemistry LibreTexts, Libretexts, 11 Aug. 2020.
Image Courtesy:
1. “Acid Base Catalysis” By Noxwei – Own work (CC BY-SA 3.0) via Commons Wikimedia