13 Polymeric Quaternary Ammonium
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Borohydride Reducing Agents M. M. COOK, P. R. DEMKO, S. E . WAGNER, R. A. MIKULSKI, and J. G. CLEMENTS Ventron Corp., Chemicals Division, Congress St., Beverly, MA 01915
Strong base anion-exchange resins containing borohydride counterions are a convenient source of insoluble, polymer-supported reducing agents. These materials have enhanced solvolytic stability and, in selected cases, increased reactivity (particularly in nonpolar solvents) over sodium or tetraethylammonium borohydride. Commercial anion-exchange resins in the borohydride form provide unique features in applications such as solvent purification, metal reduction, or arsine generation, where the introduction of soluble cations or anions is undesirable or where ultrapure borohydride is required. The preparation and regeneration of these polymeric borohydride reducing agents are based on standard ion-exchange methods.
'"phe high level of interest i n polymer-bound reagents is evidenced b y the numerous publications on this topic i n the past ten years. Despite the attractive potential for polymer-bound reagents, the expense involved in preparing a custom-synthesized resin and the frequent lack of regenerability has severely limited their practical use. T o overcome these limitations we have examined the use of commercially available ionexchange resins as polymeric supports for synthetic reagents. Specifically, we have examined strong base anion-exchange resins containing borohydride counterions as insoluble, polymer-supported reducing agents. The results of several studies on the use of these polymer-bound borohydrides are presented i n this chapter. Polymer-bound borohydride reagents were first reported i n 1961 by two independent groups (1,2). More recently other authors have reported on polymer-bound borohydride attached to ion-exchange resins 0-8412-0482-9/80/33-187-195$05.00/0 © 1980 American Chemical Society
In Ions in Polymers; Eisenberg, Adi; Advances in Chemistry; American Chemical Society: Washington, DC, 1980.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 12, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1980-0187.ch013
196
IONS IN
POLYMERS
(3) and to derivatized cellulose (4,5). Several other workers have investigated polymeric reducing agents containing borane groups covalently attached to the polymer backbone: polymeric amine boranes (6,7) and polymeric sulfide boranes ( 8 ) . W e have investigated the solvolytic stability and reactivity of polymer-bound borohydrides and have evaluated these materials i n 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. W i t h 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 p p m is the only impurity introduced into the treated medium. Both the preparation and regeneration of the polymeric borohydrides are quite straightforward. Since borohydride is a stronger anion than either chloride or borate, simply passing a borohydride solution through the resin bed serves to convert the anion-exchange resin to the borohydride form (see Figure 1). The detailed procedure given i n the experimental section includes a pre- and postpurification of the chloride and borohydride forms of the resin to assure maximum purity of the polymerbound borohydride. W e evaluated both gel and macroreticular types of styrene-divinylbenzene ( D V B ) and a c r y l a t e - D V B strong base anion-exchange resins, all having quaternary ammonium groups attached to the polymer backbone. W e used commercially available resins, specifically those of Rohm and Haas: Amberlyst A-26, Amberlite IRA-400, Amberlyst XE-279, and Amberlite IRA-458 ( a l l i n the chloride form). The A-26 and IRA-400 resins contain styrene-DVB skeletal structures, with IRA-400 being a gel-type resin and A-26 the macroreticular resin. Resins IRA-458 and XE-279 contain a c r y l a t e - D V B skeletal structures, where IRA-458 is a gel-type resin and XE-279 a macroreticular resin. These studies compare the properties of the borohydride form of these resins with sodium and tetraethylammonium borohydride. Experimental Procedure for Preparing the Polymer-Bound Borohydride Reducing Agent. The following procedure is recommended for preparing polymerbound borohydride from commercially available, strong base anionexchange resins. The procedure has been used and found effective with the IRA-400, A-26, XE-279, and IRA-458 anion-exchange resins, a l l commercially available from Rohm & Haas Corporation (chloride f o r m ) .
In Ions in Polymers; Eisenberg, Adi; Advances in Chemistry; American Chemical Society: Washington, DC, 1980.
In Ions in Polymers; Eisenberg, Adi; Advances in Chemistry; American Chemical Society: Washington, DC, 1980.
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