Micellar-catalyzed alkaline hydrolysis of 2,4-dinitrochlorobenzene in a cationic gemini surfactant

Micellar-catalyzed alkaline hydrolysis of 2,4-dinitrochlorobenzene (DNCB) in the presence of a conventional cationic surfactant CTAB or a cationic gemini surfactant 1,2-ethane bis(dimethyldodecylammonium bromide) (12-2-12) were studied spectrophotometrically at 25 °C. It was found that both CTAB and 12-2-12 micelles accelerated the alkaline hydrolysis of DNCB, and the binding constant of the substrate to the micelle, K_S, for 12-2-12 (K_S = 310 M⁻¹) was larger than that for CTAB (85 M⁻¹), which suggested that DNCB molecules bound with gemini micelles more easily than with CTAB. However, the second-order rate constant in micellar pseudophase (k_M = 1.22 × 10⁻³ s⁻¹) for 12-2-12 was lower than k_M for CTAB (4.01 × 10⁻³ s⁻¹) because the substrate may enter the interior of the 12-2-12 micelles. It was found also that 12-2-12 had a similar catalysis mechanism to CTAB when the concentration of 12-2-12 was relatively low (ca. <5 mM). However, above this concentration, higher microviscosity and significant increases in aggregation number and micelle size with increased surfactant concentration may remarkably influence the hydrolysis reaction.     

Influence of pyridine oximate and quaternized pyridinium oximate ions on the hydrolysis of phosphate esters in cationic microemulsions

Kinetic studies have been performed to understand the hydrolytic potencies of oximate (2- and 4-pyridinealdoxime) and its functionalized oximate (4-(hydroxyiminomethyl)-1-alkylpyridinium bromide) ions (alkyl?=?C₁₀H₂₁ (4-C₁₀PyOx^-); alkyl?=?C₁₂H₂₅ (4-C₁₂PyOx^-)) in the cleavage of phosphate esters, diethyl p-nitrophenylphosphate (Paraoxon) and p-nitrophenyl diphenyl phosphate (PNPDPP) in a cationic (O/W) microemulsion system (ME) over a pH range 7.5 to 11.0 at 300?K. The k_obs values for the reaction of paraoxon with oximate and its functionalized oximate were determined in different microemulsion composition and the kinetic rate data shows that k_obs values increases with increasing water content. The specificity of different chain length of alcohols (n-butanol, n-pentanol, n-hexanol and n-octanol) was also investigated in hydrolytic reactions of paraoxon for different microemulsion composition.     

Catalytic hydrolysis of phosphate esters in microemulsions

We have continued our kinetics investigation of the iodosobenzoate (IBA) catalysis of the hydrolysis of p-nitrophenyl diphenyl phosphate (PNDP), in microemulsion media composed of hexadecane in water stabilized by cetyltrimethylammonium bromide and 1-butanol over a range of water mass fractions. We have examined two iodosobenzoic acid derivatives (5-nitro-2-iodosobenzoic acid and 5-octyloxy-2-iodosobenzoic acid) as catalysts. In addition, we have determined by³¹P FT-NMR techniques that the major product of the hydrolysis of PNDP, both in IBA catalyzed and in uncatalyzed media, is diphenylphosphate.     

Surface properties and aggregate morphology of partially fluorinated carboxylate-type anionic gemini surfactants

Three anionic homologues of a novel partially fluorinated carboxylate-type anionic gemini surfactant, N,N′-di(3-perfluoroalkyl-2-hydroxypropyl)-N,N′-diacetic acid ethylenediamine (2 edda, where n represents the number of carbon atoms in the fluorocarbon chain (4, 6, and 8)) were synthesized. In these present gemini surfactants, the relatively small carboxylic acid moieties form hydrophilic head groups. The surface properties or structures of the aggregates of these surfactants are strongly influenced by the nonflexible fluorocarbons and small head groups; this is because these surfactants have a closely packed molecular structure. The equilibrium surface tension properties of these surfactants were measured at 298.2 K for various fluorocarbon chain lengths. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain lengths for 2 edda (n = 4, 6, and 8) showed a minimum for n = 6. Furthermore, the lowest surface tension of 2 edda at the cmc was 16.4 mN m⁻¹. Such unique behavior has not been observed even in the other fluorinated surfactants. Changes in the shapes and sizes of these surfactant aggregate with concentration were investigated by dynamic light scattering and transmission electron microscopy (TEM). The TEM micrographs showed that in an aqueous alkali solution, 2 edda mainly formed aggregates with stringlike (n = 4), cagelike (n = 6), and distorted bilayer structures (n = 8). The morphological changes in the aggregates were affected by the molecular structure composed of nonflexible fluorocarbon chains and flexible hydrocarbon chains.     

Synthesis and unusual properties of novel alkylbenzene sulfonate gemini surfactants

Seven new dialkyldibenzene disulfonate gemini surfactants have been synthesised. The physico-chemical properties such as their surface tensions, krafft temperatures and melting temperatures have been measured. It was found that the anionic gemini surfactants showed some aberrant properties. The results determined by drop-volume method indicated that surfactants Id, Ie at 25 °C and IIb at 50 °C showed no cmc and lowered surface tension of water hardly despite their seemingly favorable amphiphilic components. However, the three surfactants showed a sharp cmc and good surface activity with the increment of temperature. Surfactant Ie with two longer chains had a higher cmc than that for shorter chain surfactant Id. Furthermore, for this class of anionic gemini surfactants, the spacer carbon number had more important effects than the alkyl chain carbon number on their krafft temperatures and melting temperatures.     

萘(苯)双十四烷基双磺酸钠Gemini表面活性剂合成及性能研究

Gemini表面活性剂因其特殊的分子结构,使它在降低表面张力的效率与效能,以及起泡性、乳化力、润湿性等方面的性能大大优于传统表面活性剂。由此,Gemini表面活性剂成为近年日用化工及胶体与界面化学领域研究的热点课题之一。目前,Gemini表面活性剂优良的表化性能已被广泛认识,相应的理论研究趋于成熟,但Gemini表面活性剂在实际生产中的应用却不多见,究其原因主要是Gemini表面活性剂大都合成路线长,产品价格高,从而限制了它们的使用。本文拟以α-十四烯烃磺酸为原料,采用“一步法”合成萘（苯）双十四烷基双磺酸钠Gemini表面活性剂,其合成路线和反应条件均与现在生产α-烯烃磺酸钠相似,但成本却低于后者,有望实现高的性能价格比。     

Aqueous two-phase system of an anionic gemini surfactant and a cationic conventional surfactant mixture

The aqueous two-phase system formed by the mixture of dodecyltrimethylammonium bromide (DTAB) with a gemini surfactant O,O′-bis(sodium 2-lauricate)-p-benzenediol (C₁₁pPHCNa) has been studied. Two two-phase regions were observed, one was a wide region in the cationic surfactant-rich side and the other in the vicinity of R = 1:1, where R is the mixing mole ratio of DTAB to C₁₁pPHCNa in global solution. Multi-lamellar vesicles are formed in the concentrated upper phase of cationic surfactant-rich systems and spherical aggregates in the concentrated bottom phase at R = 1:1. The microstructure of the solution and the phase behavior of the aqueous two-phase system strongly depended on the total concentration and the composition of the system.     

Strong effect of NaBr on self-assembly of quaternary ammonium gemini surfactants at air/water interface and in aqueous solution studied by surface tension and fluorescence techniques

The effects of NaBr on the adsorption of alkanediyl-bis-(dimethyl dodecyl- ammonium bromide) (referred to as C₁₂-s-C₁₂ 2Br) at the air/water interface and on the micellization in the solution have been investigated by surface tension and fluorescence techniques. The results showed that the addition of NaBr greatly enhances their efficiency and effectiveness in surface tension reduction as well as the ability of micellization, even induces strong premicellar aggregation before the cmc. These were attributed to the unique molecular structure of gemini surfactant, where the flexible polymethylene chain was the spacer linking the two quaternary ammonium heads. By a short spacer, the charges of the two quaternary ammonium head groups are concentrated. Even for a long spacer (s = 12), since it is bent toward the alkyl tails, the similar effect is also produced. This results in the high sensitivity of their ionic head groups to salt. Besides, the addition of salt also effectively promotes the hydrophobic interaction between the alkyl tails of gemini surfactants. The addition of NaBr strongly promotes the adsorption of quaternary ammonium gemini surfactants C₁₂-s-C₁₂ 2Br at the air/water interface and the micellization in the solution.     

Micellization of monomeric and dimeric (gemini) surfactants in polar nonaqueous-water-mixed solvents

Dimeric or gemini surfactants are novel surfactants that are finding a great deal of discussion in the academic and industrial arena. They consist of two hydrophobic chains and two polar head groups covalently linked by a spacer. Data on critical micelle concentration (cmc) and degree of counterion dissociation (α) are reported on bis-cationic C₁₆H₃₃N⁺(CH₃)₂–(CH₂)_s–N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻, referred to as 16-s-16, for spacer lengths s=4, 5, 6 in aqueous and in polar nonaqueous (1-propanol, 2-methoxyethanol or methyl cellosolve, dimethyl sulfoxide, acetonitrile)-water-mixed solvents. The behavior is compared with conventional monomeric surfactant cetyltrimethylammonium bromide (CTAB). Thermodynamic parameters are obtained from the temperature dependence of the cmc values. It is observed that micellization tendency of the surfactants decreases in the presence of polar nonaqueous solvents. However, detailed studies with dimethylsulfoxide (DMSO) show that the geminis nearly outclass the micellization-arresting property of this solvent. Also, within geminis, higher spacer length is found suitable for showing micellization even with high DMSO content (50% v/v). The implications of these results of gemini micellization may be useful in micellar catalysis in polar nonaqueous solvents.     

Micellar effects of a triazole-based cationic gemini surfactant on the rate of a nucleophilic aromatic substitution reaction

The reaction between 2,4-dinitrochlorobenzene (DNCB) and hydroxide ion was studied spectrophotometrically at 25 °C in micelles of a triazole-based cationic gemini surfactant 18-triazole-18 or micelles of the conventional cationic surfactant CTAB. Both CTAB and 18-triazole-18 accelerated this nucleophilic aromatic substitution reaction. The binding constant of the substrate to the micelle, K _S, for 18-triazole-18 (K _S=335 M⁻¹) was found to be much larger than that for CTAB (85 M⁻¹) by fitting the kinetic results with pseudophase ion-exchange (PIE) model, which suggests that DNCB binds with gemini micelles more easily than it does with CTAB micelles. It was also found that 18-triazole-18 catalytic system was in accordance with PIE model at surfactant concentrations below ca. 0.5 mM, above which the increase of viscosity and the change of micelle size with increased surfactant concentration may remarkably influence the reaction. This was quite different from the reaction catalyzed by micelles of the conventional surfactant CTAB.     

Rheological and thermo-responsive characteristics of the mixed aqueous solution of gemini cationic surfactant and hydroxyl naphthalene carboxylic acid sodium

The new thermo-switchable wormlike micellar systems were developed by mixing the gemini cationic surfactant, 2-hydroxypropyl-1,3-bis (dimethylmyristylammonium chloride) (14-3(OH)-14(2Cl) and sodium 1-hydroxynaphthalene-2-carboxylate (1SHNC) and sodium 2-hydroxynaphthalene- 3-carboxylate (2SHNC) in a certain concentration range. Their viscoelastic and thermos-responsive behaviors as a function of the salts concentration or temperature were investigated via rheological and cryo-TEM investigations. The results demonstrated that the zero-shear viscosity (η₀) significantly increased while raising salt concentrations above a threshold concentration (C_S*) until reaching maximum and then decreased. For the mixed solutions before the maximum, the zero-shear viscosity linearly decreased with increasing temperature and conformed to the Arrhenius law. However, for those mixed systems displaying thermo-responsive characteristic after the summit, the curve of η₀ as a function of temperature exhibited a maximum over the whole temperature range, namely, the systems showed thermo-thickening and thermo-thinning behaviors at low and high temperatures. The abovementioned phenomena were explained by the formation of hydrogen bond in 14-3(OH)-14(2Cl) molecules and the different solubility of SHNC under different temperatures, and the transition mechanisms of the aggregates were analyzed accordingly.     

Mixed micellization of an anionic gemini surfactant (GA) with conventional polyethoxylated nonionic surfactants in brine solution at pH 5 and 298 K

The micellization behavior of an anionic gemini surfactant, GA with nonionic surfactants C₁₂E₈ and C₁₂E₅ in presence of 0.1 M NaCl at 298 K temperature, has been studied tensiometrically in pure and mixed states, and the related physicochemical parameters (cmc, γ _cmc, pC ₂₀, Γ _max, and A _min) have been evaluated. Tensiometric profile (γ vs log [surfactant]), for conventional surfactants, generally consists of a single point of intersection; a gradually decreasing line (normally linear, or with slight curvature) ultimately saturates in γ at a particular [surfactant], corresponding to complete monolayer saturation. The gemini, in this report, led to two unequivocal breaks in the tensiometric isotherm. An attempt to the interpretation of the two breaks from molecular point of view is provided, depending solely on the chemical structure of the surfactant. The gemini, even in mixed state with the conventional nonionic surfactants C₁₂E₅ and C₁₂E₈, manifested the dual breaks; of course, the dominance of the feature decreases with increasing mole fraction of the nonionics in the mixture. Theories of Clint, Rosen, Rubingh, Motomura, Georgiev, Maeda, and Nagarajan have been used to determine the interaction between surfactants at the interface and micellar state of aggregation, the composition of the aggregates, the theoretical cmc in pure and mixed states, and the structural parameters according to Tanford and Israelachvili. Several thermodynamic parameters have also been predicted from those theories.     

Synthesis and monolayer film of a series of new twin-tailed gemini cationic surfactants at the air/water interface

A series of new dimeric surfactants, twin-tailed gemini surfactants, 2(12)-s-2(12), were successfully prepared and characterized, and their monolayer films investigated by the measurement of surface pressure-area (π-A) and surface pressure-time (π-t) isotherms at the air/water interface by a Langmuir film balance. Compared to their monomeric counterparts, their collapse pressure (γ_collapse) is smaller, whilst all the molecular area parameters are larger. The limited area (A_limited) and the initial area (A_initial) of these twin-tailed gemini surfactants change with increasing spacer length s, and the surface pressure decreases with increasing time. It was also found that the higher the initial surface pressure, the larger the attenuation.      

Effect of aging time and salt on the viscosity behaviour of a Gemini cationic surfactant

Rheological properties of micellar solutions of a cationic Gemini surfactant, 2-hydroxypropyl-1,3-bis (dodecyldimethylammonium chloride), are studied as a function of aging time and salt addition. The results show that the self-aggregating behaviour in solution changes as a factor of time, probably due to intermolecular hydrogen bonds. The viscosity of the solution undergoes a series of visible changes so that the solution changes from a flow state to highly viscoelastic state, and finally, to a transparent solid, with a corresponding 4–6-fold increase in zero shear state viscosity. Rheology and freeze fracture transmission electron microscopy (FF-TEM) measurements show rod-like micelles at the beginning, which then change to wormlike micelles, and eventually to a quasi-gel-like network. Addition of an inorganic salt (NaCl) induces salting out, while the addition of an organic salt (NaSal) promotes micellar growth. At a fixed NaSal-to-surfactant molar ratio of 3:5, all solutions show Maxwell fluid behaviour and maximum zero-shear-rate viscosity; these trends can be attributed to the formation of a network structure between the cationic ions of the surfactant and Sal^– as the surfactant concentration increases. Crystal analysis further confirms the presence of structures linked by intermolecular hydrogen bonds.     

Small-angle neutron-scattering study and micellar model of the gemini (phenylenedimethylene)bis(n-octylammonium)dibromide surfactant micelles in water

The microstructure of the micelles formed in aqueous solution by gemini surfactants with aromatic spacers, [Br(CH₃)₂N⁺(C _m H_{2 m +1})-(Ph)-(C _m H_{2 m +1})N⁺(CH₃)₂Br, m=8 and Ph = o-, m- or p-phenylenedimethylene] has been examined by small-angle neutron scattering. Aggregation of the gemini surfactants with an o-phenylenedimethylene spacer brings about formation of premicelles and small micelles at concentrations below the second critical micelle concentration, while above this concentration marked micellar growth and variation in shape occurs. It is suggested that the minimum aggregate formed at this critical micelle concentration may be the trimer or tetramer and that this result supports the mechanism of “gemini → submicelle → assembly” for micellar growth. Received: 8 September 1998 Accepted in revised form: 27 November 1998     

Charge transfer photochemistry of Ru(bpz)3 with carboxylic acids and carboxylate ions

Ru(bpz)₃²⁺ (bpz = 2,2′-bipyrazine) has six peripheral uncoordinated nitrogen atoms potentially available for protonation in presence of acids. The emission from ^*Ru(bpz)₃²⁺ is efficiently quenched by organic acids and the observed quenching rate constants are explained in terms of proton transfer from acids to ^*Ru(bpz)₃²⁺. The absorption and emission intensity of Ru(bpz)₃²⁺ increases with increasing concentration of carboxylate ion suggesting the complex formation between the two reactants in the ground state. From these studies, the formation constant (K_f) have been evaluated by Benesi–Hildebrand method. The K_f values indicate that generally the ion pair association constants estimated from absorption and emission techniques are comparable and these values are sensitive to the structure of the carboxylate ions.     

On the hydrophobic chains effect on critical micelle concentration of cationic gemini surfactants using molecular connectivity indices

Monatshefte für Chemie - Chemical Monthly - The influence of the structure of hydrophobic tail chains on the critical micelle concentration of cationic gemini surfactants, using only the...     

Effect of imidazolium-based ionic liquids on the aggregation behavior of twin-tailed cationic gemini surfactant in aqueous solution

Micellization behavior of the twin-tailed surfactants can be modulated by the addition of various modifiers. Ionic liquids (ILs) are one of them and are documented here. The beauty of these environmentally benign neoteric molecules lies in their structural versatility. Here, we have investigated the effect of three ILs: 1-butyl-3-methylimidazolium bromide ([C₄mim][Br]), 1-hexyl-3-methylimidazolium bromide ([C₆mim][Br]), and 1-octyl-3-methylimidazolium bromide ([C₈mim][Br]) on the aggregation and surface adsorption behavior of cationic gemini surfactant, bis(hexadecyldimethyl ammonium)propane dibromide (16-3-16) through experimentally measured electrical conductivities, surface tensions, and by spectral methods (UV-vis absorbance and fluorescence measurements). The main focus of the study is to observe the effect of added ILs on the critical micelle concentration (cmc), various surface parameters, aggregation number, and size of the aggregates of gemini surfactant. The results show that the more hydrophobic ILs, that is, [C₆mim][Br] and [C₈mim][Br] behave as electrolyte at lower concentration and cosurfactant at higher concentration, whereas moderately hydrophobic IL [C₄mim][Br] acts as an electrolyte at all concentration ranges studied. The modulating effects of ILs were also compared with conventional electrolyte (NaBr) at similar conditions.     

Interaction between primary aliphatic amines and carboxylic acid esters in aqueous micellar solutions of cationic surfactants

The effects of cetylpyridinium bromide (CPB) on the acid-base equilibria of primary aliphatic amines and on the kinetics of reactions of the amines withp-nitrophenyl acetate (PNPA) andp-nitrophenyl caprylate (PNPC) were studied by potentiometric titration and UV spectroscopy. The values of apparent pK _a of the amines in the micellar phase, binding constants of their neutral forms, and the surface potentials of micelles were determined. Cetylpyridinium bromide accelerates the aminolysis of PNPA by factors of 3 to 8 by forming mixed micellar aggregates with the amines. The shift of pK _a values of the amines in micellar solutions is not the only factor that enhances their reactivity. The substrate specificity was found: in contrast to the reaction with PNPA, CPB accelerates (by factors of 15 to 65) or retards (by factors of 4 to 6) the aminolysis of PNPA depending on the hydrophobicity of the nucleophilic reagent. The binding constants of substrates, the rate constants in the micellar phase, and the critical concentrations of micellization were determined from the data obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1333–1338, July, 1998.     

钙离子对表面活性剂单层膜聚集结构的影响

采用分子动力学模拟研究了气液界面上钙离子对阴离子表面活性剂十二烷基苯磺酸钠单层膜聚集结构的影响.结果表明,单层膜结构与表面覆盖度及Ca2＋离子存在与否均有关系.Ca2＋离子能够压缩表面活性剂极性头使聚集结构排列更加紧密,均力势体现了Ca2＋离子与极性头之间的结合能力强弱,二者之间的相互作用与稳定的溶剂分离极小值有关,而Ca2＋离子需要克服一个溶剂能障才能与之发生相互作用,并引起极性头周围水分子结构的重排.模拟表明,分子动力学方法可以在分子水平上研究无机盐离子对表面活性剂单层膜水化结构的影响,解释无机盐离子在界面膜中的动力学行为.