MICELLAR EFFECTS UPON NUCLEOPHILIC AROMATIC AND ALIPHATIC SUBSTITUTION

The reaction between hydroxide ion and 2,4-dinitrochlorobenzene in water or aqueous alcohol is catalyzed by cationic micelles of cetyltrimethylammonium bromide (CTA) and retarded by anionic micelles of sodium lauryl sulfate (NaLS), but a nonionic micelle has no effect. The cationic micelles decrease the activation energy and the anionic micelles increase it. Added salts, especially arenesulfonates, inhibit the catalysis by CTA. The rate constant, in the presence of CTA, increases to a maximum, and then falls, and the kinetic form can be interpreted quantitatively in terms of incorporation of substrate and hydroxide ion into the cationic micelles. The binding constant between substrate and ionic micelles is 4600 for CTA and 2700 for NaLS in water at 25°. The kinetic effects of the ionic micelles are much larger in water than in ethanol-water 25:75 w/w or in t-butyl alcohol-water 18:82 w/w. The reaction between thiophenoxide ion and 2,4-dinitrochlorobenzene in ethanol-water 25:75 w/w is also assisted by cationic micelles of CTA, and inhibited by anionic micelles of NaLS. There is similar catalysis and retardation of the reaction between n-pentyl bromide and thiosulfate ion by CTA and NaLS in ethanol-water 25:75 w/w. However, these effects disappear in ethanol-water 44:56 w/w where CTA and NaLS display simple positive and negative kinetic salt effects. © 1968, American Chemical Society. All rights reserved.