Organic phases

The first step in designing a precursor synthesis is to pick precursor molecules that, when combined in organic solvents, yield the bulk crystalline solid. For metals, a usual approach is to react metal salts with reducing agents to produce bulk metals. The main challenge is to find appropriate metal salts that are soluble in an organic phase. 

One prevalent strategy for this involves tire use of a phase transfer agent, such as tetraoctyl ammonium bromide, to bring gold and silver salts into an organic phase [12, and. Reduction of tire metal salts... 

As can be seen in Figure 5-17, some search fields (e.g., POW [= Power]) do not need any input in the search mask this means that all entries with any content of those Helds are retrieved. However, other fields always demand an input. In case the input is omitted (for example for the decadic logarithm of the partition coefficient), a corresponding error message results. Since the PCB are more soluble in the organic phase, the input of that Field is restricted to positive values. 

Pd can also be recovered as insoluble complexes such as the dimethylglyox-ime complex, or PdCUiPhiP) by treatment with HCl and PI13P. When water-soluble phosphines are used, the catalyst always remains in the aqueous phase and can be separated from a product in the organic phase, and is used repeatedly. 

Quaternary ammonium salts catalyze the reaction between an anion and an organic substrate by transfemng the anion from the aqueous phase where it cannot contact the substrate to the organic phase In the example just cited the first step occurs m the... 

Once m the organic phase cyanide ion is only weakly solvated and is far more reactive than It IS m water or ethanol where it is strongly solvated by hydrogen bonding Nude ophilic substitution takes place rapidly... 

Earlier we learned that the partitioning of a solute between two phases is described by a partition coefficient. If the solute is initially in an aqueous phase and is extracted into an organic phase ... 

A large value for Kd indicates that the extraction of the solute into the organic phase is favorable. 

Conservation of mass requires that the moles of solute initially present in one phase equal the combined moles of solute in the aqueous and organic phases after the extraction thus... 

The fraction of solute present in the organic phase is, therefore, 0.600. Extraction efficiency is the percentage of solute successfully transferred from its initial phase to the extracting phase. The extraction efficiency is, therefore, 60.0%. 

Since 40.0% of the solute remains in the aqueous phase, and 60.0% has been extracted into the organic phase, the moles of solute in the two phases after extraction are... 

The relevant equilibria for extracting a neutral metal-ligand complex from an aqueous solution into an organic phase are shown in the following diagram. 

Aqueous solutions buffered to a pH of 5.2 and containing known total concentrations of Zn + are prepared. A solution containing ammonium pyrrolidinecarbodithioate (APCD) is added along with methyl isobutyl ketone (MIBK). The mixture is shaken briefly and then placed on a rotary shaker table for 30 min. At the end of the extraction period the aqueous and organic phases are separated and the concentration of zinc in the aqueous layer determined by atomic absorption. The concentration of zinc in the organic phase is determined by difference and the equilibrium constant for the extraction calculated. 

Let s assume that the solute to be separated is present in an aqueous phase of 1 M HCl and that the organic phase is benzene. Because benzene has the smaller density, it is the upper phase, and 1 M HCl is the lower phase. To begin the countercurrent extraction the aqueous sample containing the solute is placed in tube 0 along with a portion of benzene. As shown in figure A6.1a, initially all the solute is present in phase Lq. After extracting (figure A6.1b), a fraction p of the solute is present in phase Uq, and a fraction q is in phase Lq. This completes step 0 of the countercurrent extraction. Thus far there is no difference between a simple liquid-liquid extraction and a countercurrent extraction. 

Cyclohexane, produced from the partial hydrogenation of benzene [71-43-2] also can be used as the feedstock for A manufacture. Such a process involves selective hydrogenation of benzene to cyclohexene, separation of the cyclohexene from unreacted benzene and cyclohexane (produced from over-hydrogenation of the benzene), and hydration of the cyclohexane to A. Asahi has obtained numerous patents on such a process and is in the process of commercialization (85,86). Indicated reaction conditions for the partial hydrogenation are 100—200°C and 1—10 kPa (0.1—1.5 psi) with a Ru or zinc-promoted Ru catalyst (87—90). The hydration reaction uses zeotites as catalyst in a two-phase system. Cyclohexene diffuses into an aqueous phase containing the zeotites and there is hydrated to A. The A then is extracted back into the organic phase. Reaction temperature is 90—150°C and reactor residence time is 30 min (91—94). 

In the organic phase the monomer is in equiUbrium with the dimer ... 

Two-Phase Aqueous Extraction. Liquid—Hquid extraction usually involves an aqueous phase and an organic phase, but systems having two or more aqueous phases can also be formed from solutions of mutually incompatible polymers such as poly(ethylene glycol) (PEG) or dextran. A system having as many as 18 aqueous phases in equiHbrium has been demonstrated (93). Two-phase aqueous extraction, particularly useful in purifying biological species such as proteins (qv) and enzymes, can also be carried out in combination with fermentation (qv) so that the fermentation product is extracted as it is formed (94). 

As metal extraction into a diluent—extractant solution proceeds, there is sometimes a tendency for formation of two organic phases in equiHbrium with the aqueous phase. A third phase is highly undesirable and its formation can be prevented by adding to the organic phase a few percent of a modifier which is typically a higher alcohol or tri- -butyl phosphate (TBP) (7). 

In these cases, the use of weaker acids such as acetic acid or ammonium chloride permits the recovery of the desired alcohol. After the hydrolysis step is complete, the aqueous phase is separated from the organic phase and the product is then isolated. 

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