Investigation on the Solubilization Locus of Aniline-HCl Salt in SDS Micelles with 1H NMR Spectroscopy
Investigation on the Solubilization Locus of Aniline-HCl Salt in SDS Micelles with 1H NMR Spectroscopy
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DOI：
10.1021/la0012889
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发表时间：
2001
期刊：
影响因子：
3.9
通讯作者：
B. Kim;S. Im;Seong-Geun Oh
中科院分区：
文献类型：
--
作者：
B. Kim;S. Im;Seong-Geun Oh
The presence of the hydrophobic (micellar core) and the hydrophilic interface in normal micellar solutions may induce orientation of reactants in micelles, which in turn affects the regioselectivity of the reaction and reaction kinetics. The conventional nitration of phenol in bulk aqueous media resulted in an approximate 2: 1 ratio of para to ortho isomer. When this reaction was performed in an AOT-based microemulsion, a selectivity for orthonitration in the order of 80% was obtained. The preference for nitration in the ortho position when the reaction was performed in microemulsion was probably due to accumulation of phenol at the oil/water interface, with the phenolic hydroxyl group oriented into the water phase and phenyl groups inserted into the hydrophobic region. Because the reacting nitronium ion resided entirely in the aqueous phase in solution, attack at the para position was less likely than at the ortho position. Thus, the loci and alignment of reactants in micelles significantly influenced reaction products. 1 In recent years, we reported studies on polymerization of aniline in surfactant micellar solutions. 2, 3 Location of aniline or anilinium ion in the reaction medium was a very important factor in understanding how overall reactions proceeded and where the initial reaction or nucleation occurred, consequently affecting the properties of the final product. In these reports, we proposed that anilinium cations were solubilized at the micellar surface with the phenyl group inserted into the hydrophobic part and with-NH3+ ions toward the aqueous phase, as shown in Figure 1. This proposal was based on the solubilization of phenol in a benzene/AOT/water microemulsion because phenol and anilinium cations are similar in their molecular structures, with the hydrophilic-OH group in phenol replaced by hydrophilic-NH3+ ions in anilinium cations. We analyzed the polymerization kinetics of polyaniline based on this proposed model. In this study, we confirm our proposed model for the loci and alignment of anilinium cations in sodium dodecyl sulfate (SDS) micelles by using 1H NMR spectroscopy. Among various NMR techniques, relaxation time measurement and the FT-PGSE method were used to investigate the microenvironment, partitioning behavior of the solute, and phase identification by measuring self-diffusion coefficients. 4 When solubilizate molecules have a phenyl group which interacts with surfactant protons, an upfield shift of surfactant protons in the 1H NMR spectra with an increase of solute concentration could be used to reveal the solubilization locus. 5 Many studies have reported on these phenomena with the solubilization loci of phenol and its derivatives, acetophenone and benzophenone. The chemical shifts linearly decreased as the solute concentration increased. 5, 6
