Catalysis by Anion Exchange Resins

Anion-exchange resins are excellent catalysts for base-catalyzed reactions such as Knoevenagel condensations and aldol condensations. 

Astle and Zaslowsky utilized a variety of anion-exchange resins to effect Knoevenagel condensations, aldol condensations, and cyanoethylation of alcohols. Knoevenagel condensation 

For Knoevenagel condensations and aldol condensations, weakly basic resins whose basicity is attributed to amino groups, were more effective than stronj y basic resins bearing quantemary ammonium ions strongly basic resins were more effective 

Schmidle and Mansfield reported on cyanohydrin formation, benzoin condensation, nitroalcohol formation by the condensation of aldehydes with nitroparaffins, and cyanoethylation. Application to Michael reaction has also been investigated. Anion-exchange resins are very useful catalysts for the production of silane by the disproportionation of dihydrodichlorosilane.  

Recently, Hodge et prepared polymer-bound chiral quaternary ammonium chlorides by the reaction of chlomethylated crosslinked polystyrene with cinchonidine, cinchonine or (— )-A -methylepledrine and carried out several Michael reactions. Catalysts prepared from cinchonidine(I) achieved optical yields of 27% of the S-adduct in the addition of methyl-l-oxoindan-2-carboxylate(II) to methyl vinyl ketone. 

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The majority of research on catalysis by anion-exchange resins is devoted to the use of resins in interfacial catalysis reactions [38-43]. In this connection, quaternary ammonium or phosphonium, onium salts have been commonly obtained [44]. Crown-ethers, cryptands and linear polyesters supported on polymers also catalyze similar reactions dealing with the interfacial transfer of reagents. In the simplest case, the mechanism of interfacial catalysis represents a substitution reaction of Sf 2 type typical for the interaction of the nucleophile, T , present in the aqueous solution with the alkyl halogenide, RX, in the organic phase ... 

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