Formamides, surfactants

The diastereoselection of the Diels Alder reaction of methyl acrylate with cyclopentadiene was investigated [74] in microemulsions prepared with isooctane oil, CTAB as surfactant and 1-butanol as cosurfactant, and the results were compared with those found in pure solvents and water (Table 6.12). In emulsions rich in 1-butanol and formamide (entries 1 and 4) the reaction was slow (72 h) and the diastereoselectivity was practically the same as that... 

By dynamic light scattering it was found that, in surfactant stabilized dispersions of nonaqueous polar solvents (glycerol, ethylene glycol, formamide) in iso-octane, the interactions between reversed micelles are more attractive than the ones observed in w/o microemulsions, Evidence of intermicellar clusters was obtained in all of these systems [262], Attractive intermicellar interactions become larger by increasing the urea concentration in water/AOT/ -hexane microemulsions at/ = 10 [263],... 

A new family of hexagonal mesoporous all-germanium semiconductors was prepared by the surfactant-assisted cross-linking polymerization reaction of Zintl [Geg]" anions (Scheme 1) with Ge(lV) bridges in formamide/ethylenediamine solution (1) [43]. 

Recently, we demonstrated that the Zintl clusters [Geg]" react with chalcogen atoms (S, Se, and Te) in the presence of surfactant templates to form ordered mesoporous Ge-rich chalcogenides [74]. The mesostructured frameworks grow through a coupling reaction of (Ge9)-clusters with chalcogens in formamide/ethy-lenediamine mixture solution in an unusual reaction that seems to be a redox process (5). 

Experiments on the stability of the HIPEs indicated that one of the most important factors was the solubility of the emulsifier in the continuous (formamide) phase. Thus, the higher the surfactant solubility, the more stable the emulsion. The emulsifier concentration was also important stability increased to a maximum, then decreased, with increasing surfactant concentration. Surprisingly, the HLB number did not appear to have much effect on the stability of the emulsions, over the range studied (11 to 14). This was attributed to the high concentration of emulsifier in the continuous phase, although the narrow HLB value range is probably also a factor. 

Different kinds of nonelectrolytes were also examined for their effect on the CP (Pandya et al., 1993). The effect of different amides on the CP is Lrst considered. Amides such as urea, thiourea, acetamide, and formamide were used each showed an increase in CP (Figure 13.16). The increasing CP effect of ureas and other amides on solutions of nonionic surfactants has been examined before (Han et al., 1989 Briganti et al., 1991). These amides decrease the water structure and thus favor hydration of PEO chain, resulting in an increase in the CP. 

It was shown that the principle of aqueous miniemulsions could be transferred to non-aqueous media [45]. Here, polar solvents, such as formamide or glycol, replace water as the continuous phase, and hydrophobic monomers are miniemulsified with a hydrophobic agent, which stabilizes the droplets against molecular diffusion processes. It turned out that steric nonionic surfactants based on poly(ethylene oxide) tails are far more efficient than ionic stabilizers,... 

Non-aqueous synthetic methods have recently been used to assemble mesoporous transition metal oxides and sulfides. This approach may afford greater control over the condensation-polymerization chemistry of precursor species and lead to enhanced surface area materials and well ordered structures [38, 39], For the first time, a rational synthesis of mesostructured metal germanium sulfides from the co-assembly of adamantanoid [Ge4S ()]4 cluster precursors was reported [38], Formamide was used as a solvent to co-assemble surfactant and adamantanoid clusters, while M2+/1+ transition metal ions were used to link the clusters (see Fig. 2.2). This produced exceptionally well-ordered mesostructured metal germanium sulfide materials, which could find application in detoxification of heavy metals, sensing of sulfurous vapors and the formation of semiconductor quantum anti-dot devices. 

In addition to divalent metal cations, trivalent and tetravalent cations (i.e. ln +, Ga +, Sb +, and Sn +) were also effective as linking agents to organize [Ge4Sio]" clusters to form hexagonally ordered mesostractures. In this case, cetylpyridinium bromide was nsed as the surfactant, and formamide served as the solvent. The mesophases made with Ga + and Sb + showed intense visible photoluminescence at77K. 

Ge4Sio]" and [Fe4S4CLi] clusters was synthesized from a formamide solution containing the surfactant cetylpyridinium bromide. ... 

Due to solubility difficulties and the use of highly polar solvents such as dimethyl formamide (DMF) or dimethyl sulfoxide (DMSO) we had some difficulty in obtaining reproducible results. For all biological tests great care had to be taken to ensure that homogeneous testing solutions were used. As an extra precaution, we usually tested the reference compounds and standards using the same solvents and surfactants. 

Rico, I. and Lattes, A. (1986). Krafft temperatures and micelle formation of ionic surfactants in formamide. Journal of Physical Chemistry, 90, 5870-2. 

Micellization has been studied in a large number of nonaqueous polar solvents, such as different alcohols, formamide, fused salts [19-26], hydrazine, hydrogen fluoride [27], and IV-methylsydnone [28,29], However, most of the early investigations used indirect methods such as surface tension measurements or conductimetry for the detection of surfactant aggregation. More recently, direct methods have been used to prove the existence of aggregates in the solution phase of polar solvent other than water. For example, PGSE-NMR [17], fluorescence spectroscopy [30], and SANS [31] have proven to be powerful methods for probing micelle formation in aqueous and nonaqueous systems. 

The aggregation of fluorinated surfactants in nonaqueous solvents has also been studied. These surfactants form aggregates at lower concentrations than ordinary hydrogenated surfactants in water. Chrisment et al. have studied nonionic fluoro-alkyllipopeptides in DMSO and found progressive and very limited aggregation in this solvent as expected from the low polarity of the solvent [65], In addition, the lithium salt of nonadecafluorodecanoic acid has been studied with 19F NMR in formamide, A-methylformamide, and ethylene glycol [66],... 

E-, I-, and D-phases have been observed in the SDS-formamide system. In other solvents, ethylene glycol, glycerol, A-methylformamide, only a D-phase is formed at high surfactant concentrations with SDS [94],... 

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