- The Effects of Zwitterionic Surfactant Systems upon Aromatic Nucleophilic Substitution
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Reactions of OH(-) with 4-chloro-3,5-dinitrobenzoic acid (1) and 2-chloro-3,5-dinitrobenzoic acid (2) have been examined in solutions of N,N-dimethyl-N-tetradecylglycine (DTG) and N,N-dimethyl-N-hexadecylglycine (DHG).DTG and DHG ihibit hydroxydehalogenation of (1) and kinetic profiles for this reaction tend towards a plateau which assumes different values depending on the pH; hence the inhibition does not stop the reaction.Reactions of (2) with OH(-) in the presence of DTG and DHG exhibit a 'non-effect'.The important factor underlying this difference of behaviour between (1) and (2) in the presence of zwitterionic surfactants is probably the orientation of the substrates within the microaggregates.
- Cipiciani, Antonio,Primieri, Stefania
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p. 1365 - 1367
(2007/10/02)
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- Micellar Effects upon the Reaction of Betaine Esters with Hydroxide Ion
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The reaction of hydroxide ion with methyl N,N,N-trimethylglycinate (1a) is inhibited by cationic micelles of C14H29NMe3Cl and C16H33NMe3Cl (MTACl and CTACl) besause the substrate is largely in the aqueous pseudophase which is depleted in OH- by the cationic micelles.Added Cl- displaces OH- from the micelles and decreases micellar inhibition.The corresponding reaction of methyl N-dodecyl-N,N-dimethylglycinate (1b) is catalyzed by both MTACl and CTACl which bind both reactants, but this catalysis is reduced by NaCl.Self-micellization of methyl N-hexadecyl-N,N-dimethylglycinate (1c) speeds reaction with OH-, and the rate constants reach plateau values with increasing substrate concentration and are independent of OH-.But addition of either CTACl or NaCl slows reaction because Cl- displaces OH- from the micelle.These diverse rate effents can be accounted for quantitatively in terms of the pseudophase ion-exchange model, which considers reactions in both the aqueous and micellar pseudophases and the distribution of both reactants between the pseudophases.
- Al-Lohedan, Hamad,Bunton, Clifford A.,Romsted, Laurence S.
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p. 2123 - 2129
(2007/10/02)
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