Brandstrom—Montanari modification

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. 

Starks Extraction Mechanism Brandstrom-Montanari Modification... 

FIG. 2 Brandstrom-Montanari modification of Starks extraction mechanism for simple phase-transfer-catalyzed displacement reaction. 

If the catalyst is highly organophilic, it can be present exclusively in the organic phase and still be a good PT catalyst. Brandstrom-Montanari (Brandstrom, 1977 Landini et al. 1977) modification to the extraction mechanism is more appropriate (Figure 16.2b). Here, ion exchange takes place at the interface of the two phases and not in the aqueous phase. Thus, partitioning of the quat between the two liquid phases is not a necessary condition for effective phase-transfer action in liquid-liquid systems. 

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