Interfacial processes synthesis

Catalysis at interfaces between two immiscible liquid media is a rather wide topic extensively studied in various fields such as organic synthesis, bioenergetics, and environmental chemistry. One of the most common catalytic processes discussed in the literature involves the transfer of a reactant from one phase to another assisted by ionic species referred to as phase-transfer catalyst (PTC). It is generally assumed that the reaction process proceeds via formation of an ion-pair complex between the reactant and the catalyst, allowing the former to transfer to the adjacent phase in order to carry out a reaction homogeneously [179]. However, detailed comparisons between interfacial processes taking place at externally biased and open-circuit junctions have produced new insights into the role of PTC [86,180]. 

Phosgenation of ethylene diamine type compounds is a well established method for the preparation of 2-imidazo-lidones (cyclic five membered ureas). The utility of this method is illustrated by the synthesis of a valuable intermediate (I) for D-biotine manufacture. We have developed an improved interfacial process which affords (I) in good yield and high purity as shown in scheme 213. 

This short presentation of the general concept and some new applications of the two-phase systems in organic synthesis and also some specific features of the interfacial processes is hoped to promote better understanding and wider applications of this approach to many synthetic problems. 

Aromatic polycarbonates are prepared from various bisphenols, the most widely used being bisphenol A. The synthesis of aromatic polycarbonates is based on the reaction of bisphenol with carbonic acid derivatives such as phosgene, diphosgene, carbonic acid esters and chloroformic acid esters. The most important process for production of aromatic polycarbonate is the so-called interfacial process , first developed by Bayer. In this process, bisphenol A is phosgenated in the presence of methylene chloride in controlled conditions. 

The ITIES with an adsorbed monolayer of surfactant has been studied as a model system of the interface between microphases in a bicontinuous microemulsion [39]. This latter system has important applications in electrochemical synthesis and catalysis [88-92]. Quantitative measurements of the kinetics of electrochemical processes in microemulsions are difficult to perform directly, due to uncertainties in the area over which the organic and aqueous reactants contact. The SECM feedback mode allowed the rate of catalytic reduction of tra 5-l,2-dibromocyclohexane in benzonitrile by the Co(I) form of vitamin B12, generated electrochemically in an aqueous phase to be measured as a function of interfacial potential drop and adsorbed surfactants [39]. It was found that the reaction at the ITIES could not be interpreted as a simple second-order process. In the absence of surfactant at the ITIES the overall rate of the interfacial reaction was virtually independent of the potential drop across the interface and a similar rate constant was obtained when a cationic surfactant (didodecyldimethylammonium bromide) was adsorbed at the ITIES. In contrast a threefold decrease in the rate constant was observed when an anionic surfactant (dihexadecyl phosphate) was used. 

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