Phosphonium ions polystyrenes

Polystyrene-supported quaternary phosphonium ions with spacer chains between the active site and the aromatic ring (5, 4, 17-19% RS)... 

Comparison of polystyrene-supported phosphonium ion catalysts 1 in the reaction of 1-bromooctane with iodide ion showed a 4.5 % CL catalyst to be only half as active as a 2% CL catalyst74 . Use of decane, toluene and o-dichlorobenzene as solvents gave rate constants that increased as the swelling ability of the solvent increased. Swelling ratios were measured at 90 °C, the reaction temperature. 

Recent evidence for rate limitation by intraparticle diffusion of ions was found in the effect of % RS on activity of polystyrene-bound phosphonium ions 1, 3, and 4 80). The rate constants for cyanide displacement on 1-bromooctane increased as % RS increased from 7-9 % to 17-19 % and decreased again with >30% RS (Fig. 7). 

No experiments with variation in particle size of the silica gel have been done to study intraparticle diffusion effects. In silica gel such diffusion would be only through the pores (analogous to the macropores of a polystyrene) since the active sites lie on the internal surface. The silica gel used by Tundo had a surface area of 500 m2/g and average pore diameter of 60 A.116). Phosphonium ion catalyst 28 gave rates of iodide displacements that decreased as the 1-bromoalkane chain length increased from C4 to Cg to C16, The selectivity of 28 was slightly less than that observed with soluble catalyst hexadecyltri-n-butylphosphonium bromide U8). Consequently the selectivity cannot be attributed to intraparticle diffusional limitations. 

Polymer-supported multi-site phase-transfer catalysis seems to require the use of less material in order to provide activity comparable to others253 (Table 27). Quaternary phosphonium ions on polystyrene latices, the particles of which are two orders of magnitude smaller than usual, were shown to be capable of higher activity coagulation of the catalysts under reaction conditions was minimized by specific treatment904. The spacers may also contain ether linkages. 

Tomoi, M., and W. T. For Mechanisms of Polymer-Supported Catalysis 1. Reaction of 1-Bromooctane with Aqueous Sodium Cyanide Catalyzed by Polystyrene-Bound Benzyltri-n-butyl-phosphonium Ion, /. ner. Chem Soc., 103,3821 (1981). 

Reactions of benzylic phosphonium salts were carried out at 20 °C using 10 mL of methylene chloride, 1.5 mmol of the polymeric phosphonium salt, and 3 mL of 50% NaOH (aq). The linear polystyrene had a MW of 150,000 with 2.7 mmol of -PPh2/g of polymer. The cross-linked polystyrene contained 3.0-3.5 mmol of -PPh2/g of polymer. The halogenated phosphonium ion was prepared from phos-phinated polystyrene having 0.4 mequiv of -PPh2/g of polymer and was allowed to react with para-tolualdehyde at 50 C for 16 h. 

Polvstvrvlmethvlltriphenvlphosphonium Ions. The phosphonium ions used for formation of alkenes on cross-linked polystyrenes by the Wittig reaction have been prepared by reaction of triphenylphosphine with chloromethylated polystyrene in chlorobenzene at reflux (25). More highly nucleophilic phosphines such as tri- -butylphos-phine require only 80-100 °C to form phosphonium salts with chloromethylated... 

Phase transfer catalyzed reactions in which ylides are formed from allylic and ben-zylic phosphonium ions on cross-linked polystyrenes in heterogeneous mixtures, such as aqueous NaOH and dichloromethane or solid potassium carbonate and THF, are particularly easy to perform. Ketones fail to react under phase transfer catalysis conditions. A phase transfer catalyst is not needed with soluble phosphonium ion polymers. The cations of the successful catalysts, cetyltrimethylammonium bromide and tetra-n-butylammonium iodide, are excluded from the cross-linked phosphonium ion polymers by electrostatic repulsion. Their catalytic action must involve transfer of hydroxide ion to the polymer surface rather than transport of the anionic base into the polymer. Dicyclohexyl-18-crown-6 ether was used as the catalyst for ylide formation with solid potassium carbonate in refluxing THF. Potassium carbonate is insoluble in THF. Earlier work on other solid-solid-liquid phase transfer catalyzed reactions indicated that a trace of water in the THF is necessary (40). so the active base for ylide formation is likely hydrated, even though no water is included deliberately in the reaction mixture. 

Quaternary ammonium and phosphonium ions bound to insoluble polystyrene present an even more complicated mechanistic problem. Polystyrene beads lacking onium ions (or crown ethers, cryptands, or other polar functional groups) have no catalytic activity. The onium ions are distributed throughout the polymer matrix in most catalysts. The reactive anion must be transferred from the aqueous phase to the polymer, where it exists as the counter ion in an anion exchange resin, and the organic reactant must be transferred from the external organic phase into the polymer to meet the anion. In principle, catalysis could occur only at the surface of the polymer beads, but kinetic evidence supports catalysis within the beads for most nucleophilic displacement reactions and for alkylation of phenylacetonitrile. 

There is one report of triphase liquid/liquid/solid catalysis in a continuous flow reactor. Ragaini and Saed l passed a mixture of 1-bromooctane in o-dichlorobenzene and aqueous potassium iodide upward through a bed of polystyrene-bound phosphonium ion catalyst. 

Stable indefinitely in polymer-bound catalysts under phase transfer conditions that require the presence of hydroxide ion at the ion exchange site. Benzyltrialkylammonium and phosphonium ions are much less stable in base than non-benzylic tetraalkylammonium and phosphonium ions. Industrial applications of polystyrene-supported onium ion catalysts under strongly basic conditions will require catalysts such as 7, 1 rather than the usual commercially available... 

Quaternary ammonium (3) and phosphonium ions (61), crown ethers such as (62), cryptands such as (63) and poly(ethylene glycol) ethers (64) bound to PS are catalysts for reactions of water insoluble organic compounds with organic insoluble inorganic salts. " Silica gel, alumina, polystyrene-polypropylene composite fibers, nylon capsule membranes, and polyethylene (Mn 1000-3000) have also been used as supports. The reactions are called phase-transfer-catalyzed because one or both of the reactants are transported from the normal liquid or solid phase into a polymer phase, where the reaction proceeds. 

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