Phosphonium ions polymer-bound, reactions

Table 10. Activities of Polymer-bound Crown Ether and Phosphonium Salts for Reactions of 1-Bromooctane in Toluene with Iodide or Cyanide Ions at 90 °C149)...

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). 

By GPC it was shown that all phosphorus detected in the raw polymer was either bound to the polymer as a phosphonium ion or existed as cation 2. Polymer-bound phosphorus was detected only at high temperatures or high concentrations of phosphine (as initiator). This was taken as evidence against the zwitterion mechanism. However, a more detailed look at the data given in Ref. [759] reveals that reactions of the following type could not be excluded (Figure 10). 

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. 

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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