Agent phase-transfer

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... 

Phase separation Phase structure Phase-transfer agents Phase-transfer catalysis... 

Pha.se-Tra.nsfer Ca.ta.lysts, Many quaternaries have been used as phase-transfer catalysts. A phase-transfer catalyst (PTC) increases the rate of reaction between reactants in different solvent phases. Usually, water is one phase and a water-iminiscible organic solvent is the other. An extensive amount has been pubHshed on the subject of phase-transfer catalysts (233). Both the industrial appHcations in commercial manufacturing processes (243) and their synthesis (244) have been reviewed. Common quaternaries employed as phase-transfer agents include benzyltriethylammonium chloride [56-37-17, tetrabutylammonium bromide [1643-19-2] tributylmethylammonium chloride [56375-79-2] and hexadecylpyridinium chloride [123-03-5]. 

The crown ethers and cryptates are able to complex the alkaU metals very strongly (38). AppHcations of these agents depend on the appreciable solubihty of the chelates in a wide range of solvents and the increase in activity of the co-anion in nonaqueous systems. For example, potassium hydroxide or permanganate can be solubiHzed in benzene [71 -43-2] hy dicyclohexano-[18]-crown-6 [16069-36-6]. In nonpolar solvents the anions are neither extensively solvated nor strongly paired with the complexed cation, and they behave as naked or bare anions with enhanced activity. Small amounts of the macrocycHc compounds can serve as phase-transfer agents, and they may be more effective than tetrabutylammonium ion for the purpose. The cost of these macrocycHc agents limits industrial use. 

Alkaline depolymerization of PET at 80° C in the presence of phase transfer agents resulted in the isolation of terephthalic acid in yields as high as 93%. 

A 500 mL round-bottom flask containing aqueous sodium hydroxide (25 or 50 wt%) and benzyltrimethylammonium bromide as the phase transfer agent (0.2 g, 0.0008 mole) was placed in a constant-temperature oil bath and heated to the reflux temperature of 165°C. Chopped nylon-4,6 fibers (6 g, 0.030 mol) were placed in the reaction flask. The reaction mixture was constantly stirred with a magnetic stirrer and the reaction was carried out at atmospheric pressure for a period of 24 or 36 h (see Table 10.3 for results). The aqueous sodium hydroxide solution containing products of depolymerization was concentrated by evaporation and 30 mL of 35% aqueous hydrochloric acid was added to the concentrate. The precipitate was filtered and washed with water. The product was dried in a vacuum oven at 120°C for 24 h. 

In 2003, Van der Fycken pubhshed a copper- and palladiirm-free microwave-assisted Sonogashira-type protocol in water with phenylacetylene as the alkyne (Scheme 51) [69]. The phase-transfer agent TBAB was used to facilitate... 

The same group also described the rapid cyanation of aryl iodides in water using CuCN (Scheme 72) [82]. The addition of the phase-transfer agent TBAB was crucial for the reactions otherwise, no reaction occurred. CuCN can also be generated in situ from NaCN and Cul (Scheme 72). While aryl iodides gave good results, the yield obtained with 3-pyridinyl iodide was poor. 

We developed and applied two oxidation methods to lycopene and p-carotene. The first chemical oxidation method was performed in biphasic medium using the potassium permanganate hydrophilic oxidant. Cetyltrimethylammoniumbromide was the phase transfer agent used to achieve contact of the hydrophilic oxidant with the lycopene lipophilic carotenoid dissolved in methylene chloride/toluene (50/50, v/v). 

Finally, the reaction of 19b with potassium fluoride in the presence of a crown-ether phase-transfer agent to yield the sulfonyl fluoride 67 and diphenylacetylene belongs to the same category in which a nucleophile (F in this case) attacks the electrophilic sulfur of the sulfone group (equation 19). 

Figure 3.56. Schematic representation of phase-transfer catalysis for the reaction RX -t Y -> RY + X Q is the phase-transfer agent.

In liquid-solid processes reaction takes place between a liquid reactant and an insoluble or sparingly soluble solid which must be finely divided to speed up the process. Another measure to accelerate the process is to use an aqueous solution of a phase-transfer agent (typically a quaternary ammonium salt). The solid can also be a catalyst for reactions between liquid components, e.g. in acylations, carried out both conventionally in the presence of metal chlorides (mostly AICI3) or catalysed by zeolites and Grignard reactions. 

Recently Carraher, Naoshima and coworkers effected the modification of polysaccharides employing organostannanes and bis(cyclopenta-dienyl)titanium dichloride, BCTD (20-25). Here we report the modification of dextran employing the interfacial condensation technique using various phase transfer agents utilizing BCTD and dibutyltin dichloride, DBTD. 

While the terms phase transfer catalyst and phase transfer agent... 

The complexes [PdCl2(133)2] catalyze the hydrogenolysis of 1-chloromethylnaphthalene with K[HCOO] or Na[HCOO]. Both the solid methanoates and their aqueous solutions could be used. Addition of [R4N]+X phase transfer agents significantly accelerated the hydrogenolysis of aryl halides with methanoates.347... 

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