Study of the reaction methyl 4‐nitrobenzene‐sulfonate + Cl⁻ in mixed hexadecyltrimethyl‐ammonium chloride‐triton X‐100 micellar solutions

Abstract

The reaction methyl 4-nitrobenzenesulfonate + Cl − was studied in hexadecyltrimethylammonium chloride (CTAC) in the absence and presence of 0.1 M NaCl, as well as in mixed CTAC/Triton X-100 (polyoxyethylene(9.5)octylphenyl ether) aqueous micellar solutions with CTAC molar fractions of 0.9, 0.8, 0.7, and 0.6. Conductivity measurements were used to obtain critical micellar concentrations and micellar ionization degrees of the various micellar reaction media. From these data, thermodynamic information on the cationic/nonionic mixed micellar solutions was obtained. Micellar effects on the observed rate constant were explained by pseudophase kinetic models. The estimated second-order rate constants in the micellar pseudophase of the different micellar reaction media showed that pure CTAC and mixed CTAC/Triton X-100 micelles, at the high cationic surfactant molar fractions studied, provide reaction sites of similar characteristics at the interfacial region. This was in agreement with previous structural studies carried out on mixed CTAC/Triton X-100 micellar solutions. C 2002

Effects of Surfactants on the Rate of Chemical Reactions

“…In the latter case, the interaction of anionic surfactants with neutral substrates increases the electronic repulsion between the resulted complex and hydroxide ions. On the other hand, the reaction rates of a number of nucleophiles (other than hydroxide ion) with neutral [71][72][73] and anionic [74][75][76][77][78][79] substrates are increased in the presence of cationic surfactants. It was observed that the increase in the chain length of cationic surfactants [75] and adding TX-100 [79] to the reaction media decreases the reaction rate.…”

“…On the other hand, the reaction rates of a number of nucleophiles (other than hydroxide ion) with neutral [71][72][73] and anionic [74][75][76][77][78][79] substrates are increased in the presence of cationic surfactants. It was observed that the increase in the chain length of cationic surfactants [75] and adding TX-100 [79] to the reaction media decreases the reaction rate. Also, results show that adding organic cosolvents [76][77][78] to the surfactant-contained media further decreases the reaction rate compared to that in the presence of surfactant only.…”

Microheterogeneous Catalysis

“…These mixtures produce micelles in which the surface charge density can be controlled by changing the proportion of the surfactants in the mixture. This topic has been studied by Moya et al [ 65 , 116 , 117 , 118 , 119 , 120 ] Thus, in reference [ 116 ] the authors studied the effects on the base hydrolysis of 1,1,1-trichloro-2,2-bis( p -chlorophenyl)ethane and 2-( p -nitrophenyl)ethyl bromide of mixed micelles of tetradecyltrimethylammonium bromide and penthanol. The presence of the alcohol produces a change in the ionization degree of the micelles as well as a change in the cmc.…”

“…The applicability of the Pseudophase Model in solutions containing mixtures of surfactants (CTACl and TX-100) has been shown by Moya et al . [ 119 ] using as a probe the reaction between methyl-4-nitrobenzenesulfonate and Cl - . In this mixture, according to the authors, the neutral surfactant has little influence on the characteristics of the interfacial region where the reaction takes place.…”

Kinetics of the reaction of methyl 4‐nitrobenzenesul‐fonate + Br− in ethanol amine based surfactants

“…The S N 2 reaction (Scheme ) of Br − with methyl 4‐nitrobenzenesulfonate (MNBS) in the presence of cationic surfactants has been studied extensively 2–7, and the mechanism of this process is well known. Most previous authors have used alkyltrimethylammonium bromides or chlorides.…”