Micellar effects on acid-base equilibria

Discussion of acid-base equilibria may seem out of place in a chapter devoted to reactivity, but micellar effects upon indicator equilibria played a key role in the development of ideas regarding micellar effects upon reactivity, so a brief discussion is in order (Hartley, 1948, Fendler and Fendler, 1975). 

Hartley showed that micellar effects upon acid-base indicator equilibria could be related to the ability of anionic micelles to attract, and cationic micelles to repel, hydrogen ions. More recently attempts have been made to quantify these ideas in terms of the behavior of a micelle as a submicroscopic solvent, together with an effect due to its surface potential (Fernandez and Fromherz, 1977). 

An alternative approach to this problem is to assume that deprotonation of a weak acid in the micellar pseudophase will be related to the concentration of bound OH which should follow the ion-exchange model (Section 5). As a result much of the work has been based on the use of very weak acids which are deprotonated only at high pH. 

The pH of the aqueous pseudophase, but not that at the micellar surface, can be controlled by buffers, although then it may be necessary to allow for exchange of buffer anions between water and micelles (Romsted, 1984). This approach has been used by some workers who have developed equations which include terms for exchange of all ionic species between water and micelles (Quina et al., 1980). 

A conceptually simpler approach is to avoid the use of buffers by using 

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