Polymer-bound solvent purification

Oxetanes have also been synthesized by the immobilization of 2,2 -disubstituted 1,3-diols with polymer-bound sulfonyl chloride, followed by intramolecular cyclization/cleavage from the solid support (Scheme 17) <2005TL643>. One percent divinylbenzene (DVB) cross-linked polystyrene and polyethylene glycol (PEG) (average Mn 3400) were used as polymer support in this reaction, and in both cases the properties of the polymer support allowed rapid purification of the intermediate. Intermediates on the insoluble cross-linked polystyrene support could be washed with a range of organic solvents to remove insoluble impurities, whereas the soluble PEG supported products could be purified by recrystallization from isopropanol. This is thought to represent the first reported polymer-supported synthesis of oxetanes. 

We have investigated the solvolytic stability and reactivity of polymer-bound borohydrides and have evaluated these materials in several applications such as solvent purification, arsine generation, and metal reduction. These polymer-bound borohydrides offer several advantages over sodium or tetraethylammonium borohydride. The primary advantages are the convenience of use and the minimal introduction of ionic species or organic by-products into the treated bulk media. With the polymer-bound borohydrides, the cation is bonded covalently to the insoluble resin while the borohydride anion or its oxidation product (borate) is retained by ionic bonding. Typically, boron at levels of less than 5 ppm is the only impurity introduced into the treated medium. 

We are continuing more detailed studies on the use of polymer-bound borohydrides for solvent and ethanol purification. 

Precipitation from poor solvents is routinely used in purification of polymers and in many or most cases is part of the synthetic workup used in making the polymer-immobilized catalysts described throughout this review. Solvent precipitation is also sometimes used incidentally as a way to recover catalysts that are more commonly recovered in some other way. Examples of this are seen in the use of hexane to precipitate the poly(AT-alkylacrylamide)-bound Pd-phosphine complexes 76 and 77 or the poly(JV-terf-butylacry-lamide)-bound sulfonic acid catalyst 78 [115-117], catalysts that are routinely recovered as solids by thermal precipitation (vide infra),... 

For synthetic purposes, Pd catalyst on a polymeric support was developed and the addition reaction was carried out with excellent product yields of 94-99% and excellent stereoselectivity >99 1 (Scheme 3.64) [113]. After completion of the reaction the catalyst was easily isolated by filtration and a pure product was obtained after solvent evaporation (>98% purity without any additional purification procedures). Unfortunately, this synthetic approach was not applicable to Ph2Se2 addition to alkynes, since, at 140 °C, triphenylphosphine bound to the polymer reacted with Ph2Se2, resulting in selenium atom transfer to the phosphorus (Se=PR3) and formation of Ph2Se as a by-product. The mechanism of this side reaction was addressed in a joint experimental and theoretical study, which revealed the relationship between the C-Z and Z—Z bonds activation by Pd complexes [114]. 

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