General and Specific Acid-Base Catalysis

Arrhenius and Ostwald played very important roles in the early studies on add-base catalysis, one century ago. Arrhenius contributed to the definition of acids and bases, and established the dependence between the rate constants and the temperature. Additionally, he also formulated an electrolytic theory of dissociation that ultimately led to him receiving the 1903 Nobel Prize in Chemistry. Ostwald proposed useful definitions of catalysis and classifications of catalysts, but he was unable to develop a satisfactory theory of these effects. This is not surprising, in view of the very limited knowledge of the mechanisms of catalysis at his time, and of the lack of understanding of how molecular properties can influence the rates of reactions. Nevertheless, his seminal work on catalysis was rewarded by him receiving the 1909 Nobel Prize in Chemistry. 

Ostwald recognised that a catalysed reaction proceeds by an alternative reaction pathway, made possible by the addition of a new species. For a process that in the absence of catalysts proceeds with a rate constant kg, the general acid-base catalysed reaction follows the rate expression  

25) indicates that the reaction is catalysed by an acid, HA, or a base, A, present in the solution, in addition to catalysis by H+ and OH . We refer to catalysis in the former 

In the general catalytic mechanism represented by (13.11) and (13.III), an add catalysis corresponds to replacing X by SH+, the catalyst C by the acid AH and Y by that catalyst without a proton. In the second step, SH transfers a proton to the species, W, for example a water molecule, and gives the product P 

This example, where W is a solvent molecule, corresponds to a protolytic transfer. When W is the conjugate base of the catalyst, W=A , the mechanism is called prototropic. Table 13.1 presents the four possible combinations for acid and base catalysis that correspond to the possible identities of species involved in the general catalytic mechanism. 

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Kosonen, M., Lonnberg, H. General and specific acid/base catalysis of the hydrolysis and interconversion of ribonucleoside 2- and 3-phosphotriesters kinetics and mechanisms of the reactions of 5-O-pivaloyluridine 2- and 3-dimethylphosphates. J. Chem. Soc. Perkin Trans. 2. 1995, 1203-1209. 

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