Phase transfer reactions, aqueous organic solvents

Phase transfer catalysis (PTC) has been utilized in organic synthesis to perform reactions in organic solvents when some of reactants are present in the aqueous phase (e.g., the substitution reaction involving alkylchlorides RCl),... 

Probably the most important group of phase transfer reactions, and certainly the commonest, are those in which an anion is transferred from the aqueous phase into the organic solvent, where nucleophilic substitution occurs. These would once have been performed in a dipolar aprotic solvent such as DMF. A good example is the reaction between an alkyl halide (such as 1-chlorooctane), and aqueous sodium cyanide, shown in Scheme 5.5. Without PTC, the biphasic mixture can be stirred and heated together for 2 weeks and the only observable reaction will be hydrolysis of the cyanide group. Addition of a catalytic amount of a quaternary onium salt, or a crown ether, however, will lead to the quantitative conversion to the nitrile within 2 h. 

Ion transfer at liquid-liquid interfaces — A single ion transfer between the aqueous phase (w) and the organic solvent phase (o) can be described by the reaction scheme... 

A modern version of dichromate oxidation in aqueous media is a phase-transfer reaction carried out in a two-phase system. Alkaline di-chromate is converted into tetraalkylammonium dichromate, which is soluble in organic solvents such as dichloromethane, chloroform, or benzene ( orange benzene ). The treatment of alcohols with a solution of potassium dichromate in acetic acid in the presence of Adogen 464 (Aldrich s trade name for methyltrialkyl [Cg-Cio] ammonium chloride) and benzene gives aldehydes at 55 °C [651. Similar results are obtained with a chloroform solution of tetrabutylammonium chromate at 60 °C [618]. ... 

While phase-transfer catalysis (PTC) is a well established method with diverse applications in organic synthesis, conventional catalysts suffer several drawbacks including hygroscopicity, low thermal stability and difficulty in separation and recovery. Ironically, the high solubilities of conventional catalysts are a drawback to recovery and a problem to product purification. The concept of triphase catalysis, whereby the catalyst is immobilised onto a support material and the resulting supported PTC is then used in a biphasic aqueous-organic solvent reaction mixture is recognised as a viable solution to many of these problems.144-146... 

This notion of a reactive electrode is used much more widely In modern science. For instance it can be found in phase transfer chemistry or in the study of liquid-liquid interfaces. Figure 2.7 represents the phase transfer reaction between a potassium chloride aqueous solution and a solution of a crown-ether (denoted by L) in an organic solvent . ... 

Now let us take the example of the phase transfer reaction between an aqueous solution containing potassium chloride and a solution containing crown ether L (a complexing agent of IC ions) in an organic solvent, as shown in figure 3.7... 

Water is compatible with a lot of major organic reactions, including most of the known Pd-catalyzed reactions. The only problem is negligible solubility of a majority of organic compounds in water. This is addressed by using (i) aqueous organic solvents, (ii) phase transfer, and (iii) solubilization. On the other hand, the immiscibility of organic... 

Synthesis. The particles were synthesized using a phase-transfer reaction (72). Gold salt (HAUCI4) was dissolved in water (30 ml, 0.030 M). Normally, the resulting AuC anion would be insoluble in organic solvents (75). However, when the aqueous solution is stirred for one hour with a toluene solution (80 ml, 0.050 M) of the phase-transfer catalyst, tetraoctylammonium bromide (N[CgH,7]4Br,) the gold species is transferred into the toluene. 

The dibasic acid can also be converted into diacid chloride and then condensed with diol. There are basically two methods the first one is interfacial polymerization either at low or high temperature. The aromatic diol is converted to phenolate ion in aqueous alkali solution phase. In organic medium aromatic diacid chloride is taken. Under high stirring the reaction takes place at the interface between phenolate and acid chloride [39]. Phase transfer catalyst can also be used for carrying out the reaction in organic solvent. The reaction rate is much faster than the first method. 

Phase-tiansfei catalysis (PTC) is a technique by which leactions between substances located in diffeient phases aie biought about oi accelerated. Typically, one OI more of the reactants are organic Hquids or soHds dissolved in a nonpolar organic solvent and the coreactants are salts or alkah metal hydroxides in aqueous solution. Without a catalyst such reactions are often slow or do not occur at ah the phase-transfer catalyst, however, makes such conversions fast and efficient. Catalysts used most extensively are quaternary ammonium or phosphonium salts, and crown ethers and cryptates. Although isolated examples of PTC can be found in the early Hterature, it is only since the middle of the 1960s that the method has developed extensively. 

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