Phosphorus halides polymer-bound

Problems of isolation which may arise for higher boiling or temperature sensitive acid halides can be circumvented by the use of polymer-bound phosphorus halides. Thus, a suspension of trisubstituted phosphine dichlorides, chemically connected to cross-linked polystyrene, reacted with carboxylic acids in methylene chloride almost quantitatively according to equation (3). ... 

Product isolation is very simple as only the solvent has to be removed after separation from the polymer. The polymer can be returned to the active chlorinating agent by reaction with carbonyl chloride. A variation of this procedure does not require polymer-bound phosphorus halide but uses Lewis acid-Lewis base complexes between anion-exchange resins, such as Amberlite IRA 93, and phosphorus pentachloride (equation 4). Again, isolation of the resultant acid chloride is simple and the exhausted polymer can be regenerated for further use by simply washing it with aqueous acidic and basic solutions. Yields range from 51 % for crotonic acid chloride to 86% for decanoic acid chloride. 

The reactions of thionyl chloride and phosphorus halides, also in their polymer-modifled form, involve the formation of hydrogen halide and cannot, therefore, be applied without complications to acid sensitive compounds. The combination of triphenylphosphine and tetrachloromethane as reagent provides conditions under which, for instance, pelargonic acid can be converted to the acid chloride in good yield according to equation (5). ° This method has been recently applied to polymer-bound triphenylphos-phine. Table 2 lists some examples of acids treated in this manner. 

Analysis of Phosphonium Ion Polymers. The equivalent weight of a reagent must be known for synthetic use. That is not necessarily easy with polymer-bound reagents. Polymer-bound phosphonium ions, however, can be analyzed well. The halide counterions at the phosphonium sites can be determined titrimetrically after they have been displaced from a small sample of the reagent by another anion such as nitrate (13). The solvent swollen reagent can be analyzed qualitatively by C-13 and P-31 NMR, and P-31 NMR can even be used quantitatively (although with less accuracy than the titrimetric analysis for halide) by peak area comparison with an internal standard (391. Elemental analyses for phosphorus and halide should be used periodically to confirm the results of analyses performed in the chemist s own laboratory. 

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