Reactions in Two Phase Systems

For instance, we study here the influence of the surrounding media on the behavior of two enzymatic reactions in two-phase systems ... 

Quaternary ammonium salts are also known to promote nucleophilic substitution reactions in two-phase systems through the formation of micelles [15], but there is no evidence for micellar formation by bulky ammonium salts, such as tetra-n-buty-lammonium bromide, under liquidrliquid two-phase conditions [16]. 

Most reactions in two-phase systems occur in a liquid phase following the transfer of a reactant across an interface these are commonly known as extractive reactions. If the transfer is facilitated by a catalyst, it is known as phase-transfer catalysis [2]. Unusually, reactions may actually occur at an interface (interfacial reactions) examples include solvolysis and nucleophilic substitution reactions of aliphatic acid chlorides [3 ] and the extraction of cupric ion from aqueous solution using oxime ligands insoluble in water [4], see Section 5.2.1.3(ii). 

The study of electron transfer (ET) at the polarized oil (0)/water (W) (or liquid/ liquid) interface is useful for understanding not only certain catal)rtic reactions in two-phase systems (e.g., liquid membranes, microemulsions, micelles, etc.) but also energy conversion processes occurring at biomembranes. In 1979, Samec etal. [1,2] reported, as the first example, an ET between ferrocene (Fc) in nitrobenzene (NB) and Fe(CN)6 in W ... 

In our discussion of surface reactions in Chapter 11 we assumed that each point in the interior of the entire catalyst surface was accessible to the same reactant concentration. However, where the reactants diffuse into the pores within the catalyst pellet, the concentration at the pore mouth will be higher than that inside the pore, and we see that the entire catalytic surface is not accessible to the same concentration. To account for variations in concentration throughout the pellet, we introduce a parameter known as the effectiveness factor. In this chapter we will develop models for diffusion and reaction in two-phase systems, which include catalyst pellets and CVD reactors. The types of reactors discussed in this chapter will include packed beds, bubbling fluidized beds, slurry reactors, and trickle beds. After studying this chapter you will be able to describe diffusion and reaction in two- and three-phase systems, determine when internal pore diffusion limits the overall rate of reaction, describe how to go about eliminating this limitation, and develop models for systems in which both diffusion and reaction play a role (e.g., CVD). 

Several quaternary ammonium compounds are used in organic chemistry as phase-transfer catalysts. The mechanism of the catalytic process can be represented by a combination of phase-transfer and ion-exchange equilibria. In the case of substitution reactions in two-phase systems, the negatively charged nucleophile is extracted by the positive ammonium ion from the aqueous phase into the organic phase where substitution takes place (Makosza and rafin, 1965, Makosza, 1969, Dockx, 1973). 

In a similar line of research, Forssten et al. [91] investigated the formation of 2-hydroxy-3-methylbutyric acid (ROH) from 2-bromo-3-methylbutyric acid (RBr) at a waterjDCE interface. This 8, 2 reaction in two-phase systems can be represented as... 

So far, nearly aU the reported reactions in two-phase systems suffer similarly to their homogeneous counterparts from low catalyst efGciency. Thus it was predicted for the future that careful design of water-soluble catalyst sytems will make it possible to overcome these problems, and indeed some recent protocols describe the formation of phenylacetic acid or ibuprofen on a semi-technological scale [5,12],... 

As these mechanisms show, the formation of amides from acid chlorides and amines is accompanied by production of one equivalent of HCI, which needs to be neutralized by a second equivalent of amine. An alternative method for making amides is to carry out the reaction in the presence of another base, such as NaOH, which then does the job of neutralizing the HCI. The trouble is, OH- also attacks acyl chlorides to give carboxylic acids. Schotten and Baumann, in the late nineteenth century, published a way round this problem by carrying out these reactions in two-phase systems of immiscible water and dichloromethane.The organic amine (not necessarily ammonia) and the acyl chloride remain in the (lower) dichloromethane layer, while the base (NaOH) remains in the (upper) aqueous layer. Dichloromethane and chloroform are two common organic solvents that are heavier (more dense) than water. The acyl chloride reacts only with the amine, but the HCI produced can dissolve in, and be neutralized by, the aqueous solution of NaOH. 

Schumpe, A. and W.-D. Deckwer. Paper presented at Int. Symp. on "Mass Transfer with Chemical Reaction in Two-Phase Systems ACS meeting, March 29 - April 3, 1981, Atlanta, USA... 

Vasudevan,T.V. and M.M.Sharma. Some aspects of process design of liquid-liquid reactor. (Int. Sympo-siuir. on Mass Transfer with Chemical Reaction in Two-Phase Systems", ACS-Meeting, Atlanta, 1981). 

As shown earlier, the structural versatility of ILs and the derived ILBSs results in concomitant variation in the properties of the solvent proper or the micellar solution of ILBS these are important for applications. Examples that are worth mentioning include solvents for organic, organometallic, and inorganic compounds [71] and biopolymers [25] nonaqueous, polar solvents whose miscibility with water and organic solvents can be employed for carrying out reactions in two-phase systems [72] and templates for specific nanostructure [24,26,27]. 

Simultaneous diffusion and reaction in two-phase systems 5.4.1. The general problem... 

Note that eq. (5.37) can be applied to rapid reactions in two-phase systems. 

This case is basically similar to mass transfer and reaction in two phase systems which is well described in the literature. 

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