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- W1971297943 abstract "Phase-transfer catalysis have been immobilized on polystyrene matrices [1] and on silica gel [2]; the phosphonium salts supported on silica gel ( 1, 2, 3 and 4 ) are different from those immobilized on polystyrene matrices because the catalyzed reaction occurs on the adsorbed substrate and in a microenvironment constituted by the water present on the inorganic matrix. Kinetic measurements on the reaction: are carried out. The accessibility of both organic and inorganic phase on such a system is facilitated by the peculiar structure of the silica gel functionalized phosphonium salts: the silica skeleton and the covering organic functions are permeable to both organic and aqueous phase. Nevetheless the anions exchange in the inner catalytic centers, without stirring, is the more difficult process. Our results (by Arrhenius plots, kinetics without or with different stirring speed, etc. ) well agree with a mechanism in which only a molar ratio (function of stirring speed and of the alkyl chain in the catalyst) of the catalytic centers catalyze full time the reaction; all the remainder is equal to the mechanism of the soluble onium salts. Because such systems are constituted by a polar domain (silica gel and onium salt) and by a hydrophobic one (organic chain), and, moreover, work via substrate adsorption, they are able to catalyse the reaction carried out in water, as the micelles do. In the decarboxylation of 6-nitrobenzixazole-3-carboxylate (test reaction for. micellar catalysis) catalytic amounts of 3 (0.05 molar equiv. with respect to the carboxylate) give 2-cyano-5-nitrophenolate with a k dec = 1.1 × 10 -4 s -1 in water at 30 °C; this value is higher or comparable with the other miceIlar agents as the cationic polysoaps [4] and the polycrown ethers [5]." @default.
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- W1971297943 date "1980-01-01" @default.
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- W1971297943 title "Phosphonium salts immobilized on silica gel: Phase-transfer catalysts in two phase systems and micellar Catalysts in water" @default.
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- W1971297943 doi "https://doi.org/10.1016/s0020-1693(00)92241-2" @default.
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