Effects of organic salts on the rate of intramolecular general base-catalyzed piperidinolysis of ionized phenyl salicylate in the presence of cationic micelles

摘要

The ion exchange between HOu0001 and Bru0001 was first detectednkinetically in the reactions of HOu0001 with neutral organicnsubstrates in the presence of cationic surfactants such as cetyltrimethylammoniumnbromide (CTABr). A pseudophase ionexchangen(PIE) model,1 which is the extension of the oldernpseudophase micellar (PM) model,2 has been developed tonexplain quantitatively such ion exchange. However, somenserious weaknesses in the PIE model have recently beennrealized.3 The use of the PIE model in micellar-mediated reactionnsystems containing two or more ion-exchange processes isnrare. To best of our knowledge, there are only a few reportsnwhere the PIE model has been used in reaction systems involvingntwo ion-exchange processes with relatively more restrictivenexperimental conditions (because of the conceptual andnmathematical complexity involved in formulating a practicallynworkable kinetic equation for data analysis) compared to thoseninvolving only one ion-exchange process.4 The effects of anninert inorganic salt (here, KBr) on the pseudo-first-order ratenconstants (kobs) for alkaline hydrolysis of moderately hydrophobicnanionic esters 5 and imides,6 in the presence of cationicnmicelles, have been explained in terms of the PIE modelncoupled with an empirical equation [eqn. (1)], where KS and KSn0nKS = KSn0 u0001 L[KBr] (1)nrepresent the micellar binding constant of a moderatelynhydrophobic anionic organic substrate in the presence andnabsence of KBr, respectively, and L is an empirical parameter,nthe measure of the ability of an ion (such as Bru0001) to expelnanother counterion (such as Su0001) from a micellar pseudophase tonthe aqueous pseudophase.nThe effects of [KBr] on the rate of methanolysis of ionizednphenyl salicylate (PSu0001) revealed the occurrence of eqn. (2),7nKS = KSn0/(1 u0002 KX/S[KBr]) (2)nwhere KX/S is an empirical parameter, the measure of the abilitynof an ion, Xu0001 (such as Bru0001) to expel another counterion, Su0001n(such as PSu0001) from a micellar pseudophase to the aqueousnpseudophase. The results of the effects of [C6H5COONa] on thenrate of reactions of PSu0001 with piperidine and n-butylamine supportednthe validity of eqn. (2).8 Spectrophotometric techniquesnhave been also used to determine KS (CTABr micellar bindingnconstant of PSu0001) at different [NaBr] and [C6H5COONa] in thenabsence of any amine and these data also support the validitynof eqn. (2).9 In the continuation of our work on testing thenvalidity of eqn. (2), the effects of a few organic salts on the ratenof piperidinolysis of PSu0001 in the presence of cationic micellesnhave been studied. The observed results and their probablenexplanation(s) are described in this paper.