Abstract: The synthesis of tetraalkylammonium and tetraalkylphosphonium salts immobilized on a 2% cross-linked polysty- rene matrix is described. Under optimized reaction conditions, the catalytic activity of these salts is comparable with that of thebestsolublephase-transfercatalysts.Thefollowingfactorsaresignificant:(I) highlipophiliccharacterandatopologyen- suring enough separation between the anion and the cationic center; (2) a long spacer chain allowing the catalytic site to pro- trude into the reaction medium; (3) porosity of the resin; (4)highly efficient, turbulent stirring, in order to avoid diffusion con- trol. The relative importance of the latter depends on the amount of cross-linking.Reactions follow pseudo-first-orderkinetics, and ratesarelinearlydependentonmolarequivalentsofthepolymer-supportedcatalyst.Thekineticbehavior,thealmostex- clusive 0-alkylation of phenols, and the hydration numbers of halides bonded to quaternary groups strongly support the hy- pothesis that reactions occur in an organic shell surrounding the catalytic site. Some examples of applications of polymer-sup- ported phase-transfer catalysts to organic syntheses are also reported.
Polymer- Supported Phase-Transfer Catalysts. High Catalytic Activity of Ammonium and Phosphonium Salts Bonded to a Polystyrene matrix
MOLINARI, Henriette;
1979
Abstract
Abstract: The synthesis of tetraalkylammonium and tetraalkylphosphonium salts immobilized on a 2% cross-linked polysty- rene matrix is described. Under optimized reaction conditions, the catalytic activity of these salts is comparable with that of thebestsolublephase-transfercatalysts.Thefollowingfactorsaresignificant:(I) highlipophiliccharacterandatopologyen- suring enough separation between the anion and the cationic center; (2) a long spacer chain allowing the catalytic site to pro- trude into the reaction medium; (3) porosity of the resin; (4)highly efficient, turbulent stirring, in order to avoid diffusion con- trol. The relative importance of the latter depends on the amount of cross-linking.Reactions follow pseudo-first-orderkinetics, and ratesarelinearlydependentonmolarequivalentsofthepolymer-supportedcatalyst.Thekineticbehavior,thealmostex- clusive 0-alkylation of phenols, and the hydration numbers of halides bonded to quaternary groups strongly support the hy- pothesis that reactions occur in an organic shell surrounding the catalytic site. Some examples of applications of polymer-sup- ported phase-transfer catalysts to organic syntheses are also reported.
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