Phase transfer catalysis interfacial mechanism

The effect of ultrasound on liquid-liquid interfaces between immiscible fluids is emulsification. This is one of the major industrial uses of ultrasound (74-76) and a variety of apparatus have been devised which will generate micrometer-sized emulsions (9). The mechanism of ultrasonic emulsification lies in the shearing stresses and deformations created by the sound field of larger droplets. When these stresses become greater than the interfacial surface tension, the droplet will burst (77,78). The chemical effects of emulsification lie principally in the greatly increased surface area of contact between the two immiscible liquids. Results not unlike phase transfer catalysis may be expected. 

With regards to the mechanism of the generation of onium anion, the Starks extraction mechanism and interfacial mechanism (Brandstrom-Montanari modification) are suggested (Scheme 1.7). As in the above-described case, the interfacial mechanism seems to be operative in the asymmetric phase-transfer catalysis. 

Mathias, L.J. and Vaidya, R.A. (1986) Inverse phase transfer catalysis. First report of a new class of interfacial reactions./. Am. Chem. Soc., 108, 1093. Fife, W.K. and Xin, Y. (1987) Inverse phase-transfer catalysis probing its mechanism with competitive transacylation. J. Am. Chem. Soc., 109, 1278. 

Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis Hung-Ming Yang and Ho-Shing Wu... 

Menger and Elrington found these principles to be valid too in the case of mustard detoxification [34]. Their oil-in-water (o/w)-type microemulsion was formed by 3 wt % cyclohexane, 82 wt % water, 5 wt % SDS, and 10 wt % butanol. The addition of O.lSmL half-mustard, a nontoxic substance and chemically similar to mustard, and 5 wt % aqueous hypochlorite to 15 mL microemulsion initiates a fast reaction to sulfoxides, which was finished within 15 s. Figure 14.7 shows the proposed mechanism for the oxidation. An alkyl hypochlorite is assumed to be formed at the oil-water interface and the oxidation of half-mustard to sulfoxide only takes place close to the interfacial region or inside the oil phase. This interfacial reaction is orders of tnagnimde faster than a sulfide oxidation in a two-phase phase transfer catalysis system [41],... 

The electrical double layer (edl) at the oil-water interface is a heterogeneous interfacial region that separates two bulk phases of polarized media and maintains a spatial separation of charges. EDLs at such interfaces determine the kinetics of charge transfer across phase boundaries, stability and electrokinetic properties of lyophobic colloids, mechanisms of phase transfer or interfacial catalysis, charge separation in natural and artificial photosynthesis, and heterogeneous enzymatic catalysis [1-5]. 

From thermodynamie and kinetic principles the interface between two immiscible liquids can have catalytic properties for interfacial charge-transfer reactions [1-10]. It is also possible to shift the redox potential scale in a desired direction by selecting appropriate solvents, thereby permitting reactions to occur that are highly unfavorable in a homogeneous phase [1,11-15]. The kinetic mechanism underlying the catalytic properties of the liquid/liquid interface was discussed first by Kharkats and Volkov [4-7] as they introduced a new term interfacial catalysis. ... 

The majority of research on catalysis by anion-exchange resins is devoted to the use of resins in interfacial catalysis reactions [38-43]. In this connection, quaternary ammonium or phosphonium, onium salts have been commonly obtained [44]. Crown-ethers, cryptands and linear polyesters supported on polymers also catalyze similar reactions dealing with the interfacial transfer of reagents. In the simplest case, the mechanism of interfacial catalysis represents a substitution reaction of Sf 2 type typical for the interaction of the nucleophile, T , present in the aqueous solution with the alkyl halogenide, RX, in the organic phase ... 

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