The rate constants for reactions of OH with 2,4-dinitrochlorobenzene (DNCB), 2,4-dinitrochloronaphthalene (DNCN), and p-nitrophenyl diphenyl phosphate (pNPDPP) in micellized cetyltrimethylammonium hydroxide (CTAOH) do not conform to the pseudophase ion-exchange model. The rate constants do not become constant when substrates are fully micellar bound and increase on addition of NaOH. However, with the more hydrophobic substrates DNCN and pNPDPP we appear to reach limiting rate constants at high [CTAOH] or high [NaOH]. These observations can be explained on the assumption that the charge on a CTAOH micelle decreases on addition of OH-, i.e., the concentration of OH- in the micelle increases with increasing [OH-] in the aqueous pseudophase. The rate-surfactant profiles for reactions of DNCN and pNPDPP can be interpreted quantitatively in these terms. For reactions of DNCB the rate data can be interpreted if we assume that added OH- also increases binding of DNCB to the micelle.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry