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Ind. Eng. Chem. Prod. Res. Dsv. 1082, 21, 462-464
Electrophilic Additions to Mercurated Polystyrene Richard T. Taylor,' Roger A. Cassell, and Lawrence A. Flood Department of Chemistry, Miami University, Oxford, Ohio 45056
Reactions of various electrophiies with mercurated polystyrene, formed by treatment of cross-linked polystyrene with mercuric trifluoroacetate, were examined. This sheif-stable reagent was found to be quite reactive, affording selective electrophillc demercuration. Under nonacidic conditions iodination (I2), nitrosation (NO'BF,), formylation (DMF/POCI,), sulfonation (CISO,SiMe,), and azo-compound formation (p-nitrophenyMiazoniumtetrafluoroborate) proceeded in fair to excellent conversions. Complications arising from competitive protodemercuration were observed upon reaction with more acklic or less reactive electrophiles, such as those used for thallation (TTFA), sulfonylation (CH,SO,CI/BF,), and carboxylic acid formation (chlorosulfonyl isocyanate). The relative reactivities and practical limitations of silylated, mercurated, and lithiated polystyrene derivatives are discussed.
Introduction The use of functionalized polystyrene resins as supports, catalysts,or reagents has been investigated extensively over the past several years (Mathur et al., 1980). While most functionalization schemes proceed via electrophilic reactions onto the polymer (Warshawsky et al., 1978), certain advantages may result from prior activation of the polymer followed by a subsequent electrophilic addition. These potential advantages include obviation of the need for Lewis acid catalysis, the ability to add less electrophilic groups, and better control over the degree of functionalization. In addition, such a refunctionalizationscheme may also afford a higher degree of site isolation (Chang and Ford, 1981). Lithiation, using either lithium-halogen exchange (Farrall and Frechet, 1976) or acid-base reaction (Grubbs and Su, 1976) has been used for such electrophilic functionalizations. Recently, we reported (Taylor et al., 1981) the formation and halogenation of a silylated polystyrene resin, a stable species which exhibits enhanced reactivity. In an effort to obtain a more reactive metalated polymer, while retaining stability, we investigated the polymerbound phenyl mercuric chloride (Burlitch and Winterton, 1978), and report the results herein. Experimental Section General Methods. Hydrocarbon and ethereal solvents were distilled from CaH2 prior to use. Halogenated solvents were distilled from CaC12. Polystyrene-2% divinylbenzene copolymer beads (200-400 mesh) were purchased from Eastman Kodak Co. Elemental analyses were carried out by Galbraith Laboratories, Inc. IR spectra were recorded on a Perkin-Elmer Model 680 or Digilab ITS 14C instrument. The usual workup procedure for each polymer reaction consisted of filtration of the polymer on a Buchner funnel, washing with chloroform, acetone, and methanol, and drying overnight in an Abderhalden apparatus at 0.1 torr and 65 "C. Mercuration of Polystyrene-DivinylbenzeneCopolymer Beads. In an adaptation of the literature procedure (Burlitch and Winterton, 1978), 100 g (0.957 equiv) of the resin was suspended in 2.0 L CH2C12at 0 "C. To the suspension was added slowly a solution of HgO (105 g, 0.485 mol) in trifluoroacetic acid (500 mL) and CH2C12 (1.0 L). The slurry was stirred for 18 h at room temperature, filtered, and washed with 3.0 L methanol (caution, evolution of HF). The solid was then stirred with a solution of tetrabutylammonium chloride (150 g, 1.35 mol) in methanol (1.5 L). The usual workup afforded the mercurated polymer. Anal. Found: Hg, 44.97% (0.224 01 96-4321 18211221-0462$01.25/0
mol/100 g of polymer); C1, 8.10% (0.228 mol/100 g of polymer). Standard Conditions for Electrophilic Additions. To a slurry of the mercurated polymer in the indicated solvent was added the requisite amount of the electrophilic reagent, and the resultant mixture was stirred at room temperature until completion. The usual workup afforded the product which was analyzed by IR spectroscopy and, when appropriate, submitted for elemental analysis. Reaction with Iz. In the standard fashion, 8.0 g of the polymer was treated with 4.7 g (1equiv) of I2 in CH2C12 for 2 h. Anal. Found: I, 37.37% (0.294 mol/100 g of polymer); Hg, 1.24% (0.006 mo1/100 g of polymer). Reaction with Nitrosonium Tetrafluoroborate. In the standard fashion, 4.0 g of polymer was treated with 1.5 g (slight excess) of NOBF4 in CH2C12for 6 h. Anal. Found: N, 3.12% (0.223 mol/100 g of polymer). Reaction with ClS03Si(CH3)3.In the standard fashion, 3.0 g of the polymer was treated with one equivalent of C1S03SiMe3in cyclohexane for 120 h. Reaction with Vilsmeier Reagent (POCl,/DMF). In the standard fashion, 2.0 g of the polymer was treated with a large excess of POCl:, in N,N-dimethylformamide (in a 1:l molar ratio). After stirring for 10 h, 15 mL of 95% ethanol was added. The usual workup followed. Reaction with p -Nitrophenyldiazonium Tetrafluoroborate. In the usual fashion, 4.0 g of the polymer was treated with 2.5 g (large excess) of the diazonium salt in methanol for one week. After workup, the polymer was treated with HC1 in methanol, then worked up in the usual fashion. Anal. Found: N, 0.33% (0.024 mo1/100 g of polymer). Reaction with Thallium(II1) Trifluoroacetate (TTFA). In the standard fashion, 1.0 g of polymer was treated with 1.5 g of TTFA (excess) in CH2C1,. Reaction with CH3SO2C1/BF3. In the standard fashion, 4.0 g polymer was treated with 1.0 mL CH3SOpCl (excess) and a catalytic amount of boron trifluoride etherate in CHC13. Anal. Found: 0.15%S (0.005 mol/100 g). Reaction with Chlorosulfonyl Isocyanate (CSI). In the usual fashion, 4.0 g of polymer was treated with 1.5 g of CSI (excess) in CHC13. The filtrate was subsequently treated with methanol and worked up in the usual fashion. Results and Discussion Formation of the mercurated polymer proceeded in excellent conversion (eq 1). While previous work (Burlitch
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and Winterton, 1978) had demonstrated that such a species 0 1982 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 3, 1982 483 112 5
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could be generated, only a very lightly loaded polymer was formed. From the present work it is evident that a highly functionalized resin can be obtained via this methodology. Under these conditions, the load obtained corresponds to functionalization of a full 49.9% of the aromatic units available. Thus, approximately 98% of the available mercury is incorporated into the polymer. Also noteworthy is the close correspondence between the Hg and C1 analyses, indicating complete ligand exchange between trifluoroacetate and chloride. The infrared spectrum of the mercurated resin is shown in Figure 1. While analysis of the spectrum is not precise enough to allow definite assignment of the attachment of the HgCl moiety to the arene (0,m, or p ) , the para attachment is assumed, in analogy with the known reactivity pattern in electrophilic reactions (Letsinger et al., 1964). Given the high degree of reactivity of aryl mercury species for electrophilic reagents (Traylor et al., 1972), we felt that similar reactivity would be observable for a polymeric system. In order to assess both the selectivity and reactivity of this activated polymer, iodination was carried out. We had previously (Taylor et al., 1981) found molecular iodine to be inert to the silylated polymer, while IC1 afforded a nonselective reaction. Treatment of the mercurated resin with one equivalent of I, gives clean iododemercuration (eq 2). Under the present conditions,
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49.85% of the arene sites are now iodinated and 1.05% mercurated, correlating nicely with the original 49.9% mercury functionalization. The remaining HgCl sites can be deleted via protodemercuration with HC1. The IR spectrum of the polymer-bound iodobenzene is shown in Figure 2. From the above result, it was concluded that this reagent was, indeed, quite reactive. As a result, we investigated
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reaction with a series of electrophiles which had proven to be unreactive with the silylated polymer. Electrophilic nitrosation was most conveniently accomplished via the use of nitrosonium tetrafluoroborate, since the side reactions brought about by Bronsted acids could be avoided. Even so, incomplete nitrosation was observed, the nitroso content being only 24.9% of the arene rings. IR analysis showed the presence of the nitroso groups, with a strong absorption at 1500 cm-' arising (Silverstein et al., 1981). The Vilsmeier formylation reagent, formed by addition of POC13 with N,N-dimethylformamide, is known to be rather unreactive (Buehler and Pearson, 1970). In conjunction with the mercurated reagent, however, formylation occurs readily, giving the polymer-bound benzaldehyde. This functionalization is nicely confirmed in the IR spectrum, as evidenced by a strong absorption at 1695 cm-' (Frechet and Pelle, 1975). Azo compound formation proceeded, but not to a very large extent. A major complication in this reaction was competitive decomposition of the p-nitrodiazonium tetrafluoroborate in solution (as evidenced by the bright red color which developed in solution after 3 days). Reexposure of the polymer to additional diazonium ion resulted in little change in composition. Upon demercuration of the polymer with HC1, the dark brown product was found to possess the azo functionality. The IR spectrum clearly showed the nitro group absorbances 1515 and 1340 cm-' (Silverstein et al., 1981). Since aromatic sulfonations are normally carried out under acidic conditions, such a reaction would result in substantial protodemercuration. However, use of C1S03SiMe3allows reaction (Felix et al., 1979) in a similar fashion without the concomitant acid. While sulfonation using this method operated cleanly with the silylated polymer (unpublished results), the reagent also added to the mercurated species, subsequent hydrolysis affording the sulfonic acid (eq 3). The IR
spectrum (Figure 3) clearly demonstrates the presence of
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Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 464-470
electrophilic reaction at the site of metalation. The lithiated polymer is by far the most reactive, but is not shelf-stable. Additionally, the exact degree of functionalization is difficult to control. The mercurated species can be loaded to the greatest extent and retains quite favorable reaction characteristics. By virtue of its reactivity and loading capabilities, the mercurated resin is nearly always superior to the silylated species, except in those cases where acid sensitivity presents a problem, at which point the silyl compound becomes more appropriate. Literature Cited
Figure 3. IR spectrum of sulfonation of mercurated polymer.
the sulfonic acid moiety, in analogy to previously reported spectra (Zundel, 1969). Substitution for mercury could not be obtained cleanly when electrophiles were used which possess appreciable acidity or which form highly sensitive functions. Thus, reaction with TTFA, CH3SO2C1/BF3,and CSI afforded only unfunctionalized polystyrene resin, the product of protodemercuration.
Conclusion Silylated, mercurated, and lithiated polystyrene comprise a hierarchy of metalated reagents activated toward
Buehler, C. A,: Pearson, D. E. "Survey of Organic Synthesis"; Wiley: New York, 1970; Vol. 1, p 586. Burlitch, J. M.; Winterton, R. C. J. Organomet. Chem. 1978, 759, 299. Chang, Y. H.; Ford, W. T. J. Org. Chem. 1981, 4 6 , 3756. Farrall, M. J.; Frechet, J. M. J. J. Org. Chem. 1976, 4 1 , 3877. Felix, G.; Dunogues, J.; Calas, R. Angew. Chem. Int. Ed. Engl. 1979, 18, 402. Frechet, J. M. J.; Pelle, G. J. Chem. SOC. Chem. Commun. 1975, 225. Grubbs, R. H.; Su, S. H. J. Organomet. Chem. 1976, 122, 151. Letsinger, R. L.; Kornet, M. J.; Mahadevan, V.; Jerina, D. M. J. Am. Chem. SOC. 1964, 8 6 , 5163. Mathur, N. K.; Narang, C. K.; Williams, R. E. "Polymers as Aids in Organic Chemistry"; Academic Press: New York, 1980. Silverstein, R. M.; Bassler, G. C.; Morrell, T. C. "Spectrometric Identification of Organic Compounds", 4th ed.; Wiley: New York, 1981; p 169. Taylor, R. T.; Crawshaw, D. 9.; Paperman, J. B.; Flood, L. A.; Cassell, R. A. Macromolecules 1981, 74, 1134. Traylor, T. G.; Berwin, H. J.; Jerkunica, J.; Hall, M. L. Pure. Appl. Chem. 1972, 30, 599. Warshawsky, A,; Kaler, R.; Patchnornik, A. J. Org. Chem. 1978. 43. 3151. Zundel, G. Angew. Chem. I n t . Ed. Engl. 1989, 8 , 499.
Received for review October 28, 1981 Revised manuscript received December 2, 1981 Accepted January 22, 1982
Part of this work was reported at the 33rd Southeastern Regional Meeting of the American Chemical Society, Lexington, KY, Nov 5,1981; Abstract p 109. Acknowledgement is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for the support of this research. Funds for the purchase of the Perkin-Elmer Model 680 spectrometer were provided in part by the National Science Foundation through Grant TFI-8022902.
Solubilities in the Systems C3H6N6-S02-S03-H20 at 25 and 50 "C and C3H6N6-NH3=SO3-H20at 25 "C Joe Gautney," A. Wllllam Frazler, Yong K. Kim, and John D. Hatfleld Division of Chemical Development, National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals. Alabema 35660
Solubilities in the systems C3H,N,-SO2-SO3-H2O at 25 and 50 OC and C3H,N,-NH3-S03-H20 at 25 OC were studied. The two systems include the absorption and chemical regeneration steps, respectively, of the melamine scrubbing process. The system C3H,N,-SO2-SO3-H2O is characterized by saturation fields of C3H6N,, (C3H6N6),.H2S04.4H20, (C3H6Ne)2.H2SO,*2H2O, (C3H,Ne)2.H2SO3.4H2O, (C3H,Ne)5'3H2S03.4H20, and C&&N,*H2SO3. Four invariant POlntS were identlfied in this system at 25 OC: ~3H,N,-(C3H,N,)4~H2~04~4HzO-(C3~,N,),~Hz~~3~4H2~ at pH 5.73, (C3H ~ N ~ ) ~ ~ H ~ S O ~ ~ 4 H ~ O - ( C ~ H e N B )at2 pH ~ H 5.2~1,~(C3H6N,)2.H2S03.4H20-(C3H,N6)2. O ~ * 4 H ~ ~ - ( ~ ~ ~ ~ ~ ~ ) ~ ~ ~ H2SO,.2H20-(C3H~N~)~.3H2so3.4H2o at pH 3.35, and (C3H~N,)2.H2S04.2H2O-(c3H~N~)5.3H2~o3.4H2o-c3H~N~'H2~o3 at pH 2.81. All but the last invariant point were also obtained at 50 OC. The system C3H,N6-NH3-S03-H20 over the pH range 5 to 11 at 25 "C is characterized by saturation fields of C3H,N, (C3H6N,)2.H2S04.2H20, (C3H6N6),-H2S0,.4H20, (NH,),SO, and a melamine sulfuric acid adduct-ammonium sulfate double salt tentatively identified Four invariant points were identified, each forming a corner of the double as (C3H6N6)4.H2S04.(NH,)2S04.2Hz0, salt saturation field.
Solubilities in the systems C3H6N6-S02-S03-H20 and C3H6N6-NH3-S03-H20 are of interest because these two systems include the absorption and chemical regeneration This article not subject to
U S . Copyright.
steps, respectively, of the melamine scrubbing process (Kohler et al., 1979). In the absorption step of the melamine scrubbing process, a gas stream containing sulfur
Published 1982 by the American Chemical Society
