Solvent systems insufficient separation

The ligands of Table 4 were investigated in the carboxytelomerization reaction using the solvents IPA and IPA/PF-hexane (Table 6). The hgand (P(et - Rf8)3). which showed the best separability, yielded the worst performance (entry 30). We also tested the reaction in the best solvent system of Table 5, the system IPA/PF-hexane. However, as shown in entry 31, the stability of Pd was improved but was still insufficient. The solvent system works quite well, but the main problem remains the activity of the ligand. 

A suitable solvent system is the key to successful separation with countercurrent chromatography. But for some solvent systems, the retention of stationary phase would become insufficient, possibly caused by low interfacial... 

In some cases, the chemistry within a given column can be insufficient to separate some analytes. It is possible to direct a series of unresolved peaks onto a second column with different physico-chemical (Chemical classification) properties. Since the mechanism of retention on this new solid support is different from the first dimensional separation, it can be possible to separate compounds that are indistinguishable by one-dimensional chromatography. The sample is spotted at one comer of a square plate,developed, air-dried, then rotated by 90° and usually redeveloped in a second solvent system. 

In this case, a moderately water-soluble amphiphilic N-vinylcaprolaclam (NVC1) played the role of a fl-unit, and a well-water-compatible N-vinyl-imidazole (NVIAz) served as a P-unil. The polymerization was carried out in a medium of 10% aqueous dimethylsulfoxide (DMSO). The addition of DMSO to the reaction solvent was necessary because of insufficient NVC1 solubility in pure water. It was also shown that in this solvent mixture, the NVCl-homopolymers and NVCl/NVIAz-copolymers retained their LCST-behaviour [26,28]. Hence, the DMSO in the reaction solvent did not significantly suppress the hydrophobic interactions of the NVC1 units. The polymerization was initiated by the redox system (N,N,N, N -tetramethylethylenediamine (TMEDA) + ammonium persulphate (APS)) and was carried out at 65 °C (1st step). This condition was very important, since admittedly the temperature was higher than the phase separation threshold of the reaction bulk when the polymeric products were formed that is, under these thermal conditions, hydrophobically-induced folding as the NVCl-blocks appear was ensured. After completion of the reaction, the... 

Homogeneous solutions are the preferred formulation systems for parenteral administration because they can be easily visually inspected for the absence of particulate matter. For this reason, cosolvent solubilization is the first choice for parenteral products once purely aqueous systems provide insufficient solvency. The compositions of three commercial, injectable products are given in Table 39.5. The first product (1) has a low percentage of cosolvent in the separate solvent ampoule. The drug substance is provided as a dry powder because of its limited stability in solution. The second one (2) is solubiUzed with two cosolvents amounting to 50% of the total volume, whereas in the third product the drug dose is dissolved in a water-free mixture of cosolvents. This draws the attention to a further point to consider when cosolvents are employed in formulations. The formulation has to be devised such that the effect of dilution of... 

Clearly, for two reactants simply to reach a contact distance is insufficient they must also retain this disposition. The longer the time that two atoms spend poised in a position to react, the greater the probability of thermal activation and the faster the rate. Because the hypothesis involves, therefore, a pair of fluents (time and distance), we have found it useful to ignore the time by examining only rigid intramolecular systems. Unfortunately, this situation may not always be possible or desirable. In such cases, a preassociation constant relating solvent-separated species with van der Waals... 

In Fig. 12.9-la a typical equilibrium diagram is shown where solute A is infinitely soluble in solvent C, which would occur in the system of soybean oil (/l)-soybean inert solid meal (B)-hexane solvent (C). The upper curve of N versus for the slurry underflow represents the separated solid under experimental conditions similar to the actual stage process.The bottom line of N versusx, where N = Oon the axis, represents the overflow liquid composition where all the solid has been removed. In some cases small amounts of solid may remain in the overflow. The tie lines are vertical, and on a yx diagram, the equilibrium line is y = on the 45° line. In Fig. 12.9-lb the tie lines are not vertical, which can result from insufficient contact time, so that all the solute is not dissolved adsorption of solute A on the solid or the solute being soluble in the solid B. 

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