Two-phase method

Solutions with low content of alcohol and alcohol ether sulfates cannot be analyzed by the two-phase method and specialized procedures have been developed. ISO method 7875/1 [267] is the standard method for analyzing sulfates and other anionic surfactants at very low concentrations, such as in waste-waters. The absorbance of the chloroform layer containing the surfactant-dye complex is spectrometrically measured at 650 nm and quantified using a calibration curve. Different improvements of this method have been developed [268,269]. 

A -(4-Toluenesulphonyl)sulphilimines, which are useful precursors in the synthesis of oxiranes and in alkylidene transfer reactions, have been prepared under solidiliquid phase-transfer catalytic conditions from Chloramine-T [2], Comparable yields are obtained irrespective of whether the reaction is catalysed by Adogen or by benzyltriethylammonium chloride (Table 4.31). The procedure is an improvement on the liquiddiquid two-phase method [3]. 

Strictly anhydrous conditions are not critical, in the opinion of some workers, as an excess of the reagent reacts with water and removes it. Weiss and Tambawala [412] reported that with a sufficient excess of the reagent even quantitative results could be obtained with samples containing up to 90% of water. Further elaboration of this idea led to the development of a two-phase method for the concentration of the sample [413] applied to the analysis of monosaccharides. The principle of this method consists in the use of a solvent for the silylation reaction in which the derivatives produced are hardly soluble (e.g., dimethylformamide, dimethyl sulphoxide). A separate phase is then isolated from the reaction mixture, into which TMS derivatives are transferred. It is supposed that this phase is hexamethyldisiloxane, produced by the decomposition of HMDS and TMCS with traces of water, as in the absence of these two silylating reagents the phase is not formed. 

A two-phase method for preparing up to 90% monoperoxy esters or carbonates using a 2 1 molar ratio of methyl isobutyl ketone peroxide and acid chloride, respectively, is described. Nonsymmetrical diperoxides were also prepared by reacting the monoperoxy esters or carbonates with a different second mole of acid chloride. 

The Au nanoparticles were synthesized by using the Brust two-phase method [1] as described in the previous study [2]. They were spherical with a diameter of approximately 6 0.5 nm. 

A homogeneous variation of this two-phase method has been proposed, with triflic acid (TFA) as the solvent (Krummeich et al., 1996). 

The separability of homogeneous catalysts has been improved in the last few years by using organometaUic complexes that are soluble in both organic and aqueous phases. These can readily be removed from the product stream at die reactor outlet by transferring them to the aqueous phase. This two-phase method has already been used successfully in large-scale industrial processes, for example ... 

As seen in this example, low-pressure pumping costs by the two-phase method are appreciably less than with the conventional diffusion pump system in some... 

The best known two-phase method is that of Cross [4]. By titrating at three different pHs, it permits a degree of classification of the analyte. It requires two buffer solutions and two anionic indicators. 

It is to be expected that other types of surfactant-sensitive electrodes can be used with equal or greater success, and it would not be surprising if the two-phase methods, e.g. that of Cross (section 7.1.3) could also be used, although the author is unaware of any published evidence. 

In (Figure 2) and (Figure 3) a comparison between the experimental data and the simulation results is shown. The operating conditions are mentioned in (Table 2). The equilibrium model as well as the nonequilibrium model described the experimental data with a good accuracy. As explained before, for the calculation of the transport values as mass transfer coefficients and interfacial areas usually customary two-phase methods are used. With this background, the results for the nonequilibrium model are remarkably. On the other hand it was elaborated, that in the case of three-phase distillation only a two-phase problem exists at every interface and the profiles illustrate the acceptability of this assumption. 

In the presentation the nonequilibrium model for the calculation of the three-phase distillation in a packed column is presented. The model considers the mass transfer between all three existing phases. A remarkable point is that by using normal two-phase methods mass transfer coefficients and interfacial areas can be calculate in a first step. The study is strongly influenced by the interaction between the development of the model and the experiments. The validation was carried out in a packed column of the institute on experiments at total and finite reflux. Two different heterogeneous azeotropic mixtures have been separated by distillation. The distillation run at finite reflux showed an unusual behaviour, which is based in the heterogeneity of the liquid phase. In this case a nonequilibrium model is needed. A comparison of the simulation results and the experimental specifications shows the performance of the developed... 

Olive oil is nowadays produced by either two or three-phase extraction systems. The three phase method in which a solid fraction (wet pomace or alperujo), a liquid residue ( alpechin ), and the olive oil are obtained. Two phase method in which a solid fraction, wet pomace and a liquid one, the olive oil, are obtained. The main advantage of the two-phase system is the reduction of the olive mill wastewater amoimts compared to that originated from the three phase technology, in which 0.6-1.31 water/kg olives are used at the centrifugation step, by eliminating the production of alpechin thus avoiding its consequences environmental... 

Disclosing the binding motif of multiblock RAFT polymers on AuNPs from citrate reduction raises the questimi of whether the polymer binding can vary for different types of AuNPs. It is known that AuNPs from the two-phase Brust-Schiffrin synthesis can assemble into spherical particle networks when treated with low molecular weight crosslinking agent [106, 107]. When tetraocty-lammonium bromide-capped AuNPs from this two-phase method are functionalized in toluene dispersion with multiblock RAFT polymers of styrene, the formation of spherical AuNP assemblies can be observed by TEM (Fig. 9) [108]. It can be concluded from these TEM images that the particle density inside... 

These compounds are readily titrated with anionic surfactants, either according to the two-phase method or to the potentiometric end point, as discussed in Chapter 16. Alcohol is added as necessary for solubility (19). Determination of the alkyl chain length distribution may be performed directly, by HPLC, or after liberation of the fatty acids, by GC. More information is given in Chapters 7 and 8. 

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