Phase-transfer method from organic

Extraction of protein from aqueous solution by surfactant-containing lipophilic organic solvent (phase transfer method, or equivalently, w/o-ME-based liquid-liquid extracting, LEE). 

The phase transfer method of protein solubihzation is fundamentally different from the other two methods. In this method, there are two bulk phases (aqueous and organic) which are brought to equihbrium. Under certain conditions, the protein molecules are transferred from the aqueous phase to the surfactant-containing organic phase. Unhke the dry-addition and injection methods, it is difficult to obtain a value for the maximum solubihzation using the phase-transfer method. Moreover, since this method is mainly used for protein extraction, it is desirable to use aqueous phase protein concentrations consistent with those in a typical fermentation broth. For the phase-transfer method, pH of the aqueous phase, the size and isoelectric point of the protein, and the surfactant type were shown to have a significant effect on protein solubilization [145]. 

A particularly attractive way of biphasing is to force the reactant from one phase into another where it can react with the reactant present in that phase. This is not exactly a method of protection but of forcing a reaction between components in two immiscible phases. It is always preferable to force ions into the organic phase than neutral molecules into the aqueous phase. This is best achieved by a technique known as phase-transfer catalysis. In view of the rapidly increasing importance of phase-transfer catalysis in organic technology/ synthesis, it is considered separately in the next chapter. 

The technique of phase transfer catalysis is now twenty-five years old and has come of age. It has been applied to many areas of organic synthesis, from small and simple molecules to large and complex polymers. Successful chiral catalysts are beginning to be reported [61], and industry is starting to embrace phase transfer methods [62]. Phase transfer catalysis clearly has an important role to play in a cleaner future. 

Recently, phase transfer catalysis has been effectively exploited in the field of synthetic organic chemistry.However, there are scant reports on the syntheses of condensation polymers by phase transfer methods. Five years ago, we started a broad investigation into the use of phase transfer catalysis (PTC) to effect polycondensation. Since then, we have successfully synthesized various types of condensation polymers with high molecular weights. For example, aromatic polysulfonate ni from aromatic disulfonyl chloride I and bisphenol II [Eq.(l)], / aromatic polyphosphonate V from phenyl-phosphonic dichloride IV and II [Eq.(2)], and aromatic polyether VII from activated aromatic dichloride VI and II [Eq.(3)]. ... 

Phase-transfer catalysis (Section 22.5) Method for increasing the rate of a chemical reaction by transporting an ionic reactant from an aqueous phase where it is solvated and less reactive to an organic phase where it is not solvated and is more reactive. Typically, the reactant is an anion that is carried to the organic phase as its quaternary ammonium salt. 

The oxidation methods described previously are heterogeneous in nature since they involve chemical reactions between substances located partly in an organic phase and partly in an aqueous phase. Such reactions are usually slow, suffer from mixing problems, and often result in inhomogeneous reaction mixtures. On the other hand, using polar, aprotic solvents to achieve homogeneous solutions increases both cost and procedural difficulties. Recently, a technique that is commonly referred to as phase-transfer catalysis has come into prominence. This technique provides a powerful alternative to the usual methods for conducting these kinds of reactions. 

In this method, a catalyst is used to carry the nucleophile from the aqueous into the organic phase. As an example, simply heating and stirring a two-phase mixture of 1-chlorooctane for several days with aqueous NaCN gives essentially no yield of 1-cyanooctane. But if a small amount of an appropriate quaternary ammonium salt is added, the product is quantitatively formed in about 2 h." There are two principal types of phase-transfer catalyst. Though the action of the two types is somewhat different, the effects are the same. Both get the anion into the organic phase and allow it to be relatively free to react with the substrate. 

Two phase reduction (Brust synthesis) This method is usually employed to make organic soluble quantum clusters [8]. This method consists of two steps. The first is the transfer of AuCLi from aqueous to the organic layer by a phase transfer reagent such as tetraoctyl ammonium bromide (TOABr). The next step is the subsequent reduction of AuCU in the presence of suitably selected ligands such as thiols, phosphines, etc. 

When a glass plate which is heated e.g. at 130°C is rubbed with a polytetrafluoroethylene (PTFE) briquette, a highly oriented thin film (2— 100 nm thick) of PTFE can be made on the plate such a film is termed a friction-transfer layer [24]. This method is applicable to make thin oriented layers of other polymers. Various kinds of organic compormds can be oriented on the PTFE friction-transfer layer from vapor phase, from solutions and from the melts [24]. 

There are three commonly used methods [145] to incorporate enzymes in RMs (i) injection of a concentrated aqueous solution, (ii) addition of dry lyophilized protein to a reverse miceUar solution, and (iii) phase transfer between bulk aqueous and surfactant-containing organic phases. Figure 3 shows schematically the three enzyme solubiHzation methods. The injection and dry addition techniques are commonly used in biocatalytic appHcations, the latter being well suited to hydrophobic proteins [146]. The phase transfer technique is the basis for extraction of proteins from aqueous solutions. 

Further examples of alkylation of imidazole derivatives were recently reported by Galous et a/.145 The nature and importance of significant factors in phase transfer alkylation of pyrazole was studied by Elguero et al.146 Their conclusions are equivalent to those of Dehmlow and Lissel.147 The optimization method used by Elguero et al. (several parameters at a time) is different from the conventional procedure (one parameter at a time) and will probably find applications in the future for optimization of organic syntheses. 

Apart from some aliphatic iodides, which have been oxidized directly to iodosyl derivatives with ozon or dimethyldioxirane [3], iodoarenes give directly iodylarenes with strong oxidants. From a synthetic point of view, potassium bro-mate in sulfuric acid has been used for the preparation of several members. The parent PhI02 can also be obtained by overoxidation of iodobenzene with peracetic acid, followed by hydrolysis as detailed in Organic Syntheses [36]. Another good method is oxidation of Arl by hypochlorite, at room temperature under phase transfer catalysis (Scheme 7) [37]. 

Procedures of the sample preparation are enough trivial now with the exception of producing of CgoFWS. This was produced without using of any solubilizers and chemical modification [4], The method is based on transferring of fullerene from organic solution into the aqueous phase with the help of ultrasonic treatment [6]. The highest concentration of the solution used in present experiments was 400 pM/1. 

The preparation of iodylbenzene has been described in Organic Syntheses from (dichloroiodo)benzene [24] an alternative simpler method involved the direct oxidation of iodobenzene using aqueous hypochlorite and phase transfer catalysis. 

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