Oxidative emulsion catalysis

Lu, H. Gao, J. Jiang, Z. Yang, Y. Song, B. Li, C. (2007). Oxidative desulfurization of dibenzothiophene with molecular oxygen using emulsion catalysis. Chem. Commun., 150-152, ISSN 1364-548X. 

Polymer-stabilized metal emulsion catalysis has also been used in oxidation reactions. The catalytic oxidation of ethylene to ethylene oxide by Ag catalysts. 

Ingold (6) did not review ascorbic acid per se, but did present a chapter on metal catalysis including the metal content of vegetable oils and the eflFect of valence state of the metals on oxidation of fats and oils. He reports cobalt, manganese, copper, iron, and zinc at the higher valences acted catalytically to oxidize many substrates. The author discussed the antioxidant activity of ascorbic acid in radiation-induced free radicals, fats in emulsions, fluid milk, and frozen fish. He also discussed the quandary of metal reactions vs. valence state. 

Hydrogenation of polymers results in better thermal and oxidative stability, and several attempts were made to employ homogeneous catalysis for this purpose. An ABS copolymer was reduced in the form of an aqueous emulsion with neutral and cationic Rh(I) complexes. The slightly water-soluble cationic complex was more efficiently built into the micelles of the anionic detergents used for polymer solubilization and this resulted in better conversions, e.g., 70% in contrast to 20% with [RhCl(PPh3)3] [76],... 

Oct5iphenol reacts with ethjiene oxide under base catalysis and the resulting ethoxylates are used in many of the same appHcations as the 4-non5iphenol-based surfactants. The consumption of 4-/ l -octylphenol-based surfactants in the United States is in excess of 22,700 t/yr. A major use area for ethoxjiates based on 4-/< oct5iphenol is as a surfactant in the emulsion polymerization of acryUc and vinyl monomers (52). The 4-/ l -octylphenol ethoxjiate aids in the dispersion of the monomers in the aqueous medium and stabilizes the latex formed as a result of polymerization. 

Fluid-fluid systems are widely used in chemical, petroleum, pharmaceutical, hydrometaflurgical, and food industries. Commercially important examples of gas-liquid mass transfer with or without reaction include gas purification, oxidation, halogenations, hydrogenation, and hydroformylation to name but a few. Important liquid-liquid reactions include nitration, phase transfer catalysis (PTC), cyclization, emulsion polymerization, homogenous catalyst screening, enzymatic reactions, extraction, precipitation, crystallization, and cell separation. 

An important question to consider is where does metal catalysis takes place in multiphase systems In bulk oils systems, the hydrophilic metals would be oriented in the air-oil interface to catalyse lipid oxidation (Figure 10.7). In emulsions and liposomes, the metals would be in solution in the aqueous phases and oriented in either the oil-water or phospholipid-water interfaces, where they may have an affinity for the hydrated layer around the droplets (Figure 10.4). 

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