772
Znd. Eng. Chem. Res. 1991,30, 772-778
Reshetov, S. A.; Zhvanetakii, I. B.; Platonov, V. M. Determination of the types of singular pointa for multicomponent solutions of non-electrolytes. Russ. J. Phys. Chem. 1983,57, 1463. Shealy, G.S.; Hagewiesche, D.; Sandler, S. I. Vapor-Liquid Equilibrium of ethanol-water-N,N-dimethylformamide. J. Chem. Eng. Data 1987,32, 366. Tamir, A,; Wisniak, J. Correlation and prediction of boiling temperatures and azeotropic conditions in multicomponent systems. Chem. Eng. Sci. 1978,33,657. Van Dongen, D. B.; Doherty, M. F. Design and synthesis of homogeneoue azeotropic distillations. I. Problem formulation for a
single column. Ind. Eng. Chem. Fundam. 1986,24, 464. Wade, J. C.; Taylor, Z. L. Vapor-liquid equilibrium in perfluorobenzene-benzene-methylcyclohexanesystem. J. Chem. Eng. Data 1973, 18, 424.
Yamakita, Y.; Shiozaki, J.; Matauyama, H. Consistency test of ternary azeotorpic data by use of simple distillation. J. Chem. Eng. Jpn. 1983, 16, 145.
Received for review April 24, 1990 Revised manuscript received October 16, 1990 Accepted October 29, 1990
Development of Bifunctional Polymers for Metal Ion Separations: Ionic Recognition with Polymer-Supported Reagents Spiro D. Alexandratos,* Darrell W. Crick, and Donna R. Quillen Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
A set of polymers has been synthesized, each operating through a mechanism that displays a high degree of specificity toward a target metal ion. Bifunctionality has been found to be a critical variable in defining the metal ion specifity of different polymers. The phosphinic acid polymer has the highest level of recognition for the mercuric ion across a wide range of conditions through its redox reaction which produces mercury metal. The phosphonate diester/monoester polymer displays a supported ligand synergistic interaction with silver ions. Ionic recognition is found to be an inherent property of polymers that couple a n access mechanism with a recognition mechanism, subject to reaction control or steric control. Reaction control implies a strong ion/ligand interaction (e.g., reduction, coordination, or precipitation) while steric control implies a specificity imposed by hindrance to an expected complexation for all but the target species. A parallel to the mechanisms of action displayed by oxidoreductase and hydrolase enzymes is drawn.
Introduction The development of polymer-supported reagents with the ability to selectively separate one component from a multicomponent solution is an area of continuing importance. In the case of metal ions, the preparation of polymers which can recognize a target ion through any of a number of mechanisms, is important for a fundamental understanding of polymel-metal interactions and for their application to critical problems involving the environmental recovery of metal ions (King, 1987). The use of polymers in metal ion separations has been the subject of a number of reviews (Kantipuly et al., 1990; Sherrington and Hodge, 1988; Sahni and Reedijk, 1984). A wide variety of polymers have been examined for metal ion complexations of varying selectivity, including a polymeric pyrazole (Roozemond et al., 1988), a polyethylenimine (Rivas et al., 19891, a polybenzimidazole (Chanda and Rempel, 1989),and a macrocyclic Schiff base (Matsushita et al., 1988). The concept of using reactive polymers in metal ion reactions has been discussed (Helfferich, 1965; Janauer et al., 1974). The current phase of our research has focused on the design and development of a series of polymers with significant ionic selectivity (Alexandratos, 1988). The fully functionalized styrene-based polymers operate through an access mechanism and a subsequent recognition mechanism. These dual-mechanism bifunctional polymers (DMBPs) have a hydrophilic cation exchange ligand allowing for access into the polymer network coupled to another ligand whose reactivity is responsible for the observed specificity. The ideal ligand controlling the access mechanism would allow for ion exchange to occur over a wide range of solution pH values but would also be able to shift to a coordinative interaction when the solution pH 0888-5885/91/2630-0772$02.50/0
fell significantly below the ligand’s pK,. Phosphorus acid ligands are thus the access ligands of choice because of their ability to ion exchange over a wide pH range and to coordinate metal ions through the phosphoryl oxygen in highly acidic solutions (Sekine and Hasegawa, 1977). The recognition mechanisms developed to date are reduction, coordination, and precipitation of the target metal ion. The present study examines the ion-exchange/redox resin A (class I DMBP) and the ion-exchange/coordination resins B and C (class I1 DMBPs). Monofunctional polymers D-G were synthesized as controls in order to isolate the importance of bifunctionality to ionic recognition. A metal ion selectivity series is thus detailed for polymers A-G, and a general principle is derived from the resulk3 which is used in the continuing design of selective polymers.
Experimental Section All of the metal ion selectivity series studies were performed with styrene-based polymer beads (0.150-0.250 mm) prepared via suspension polymerization. Functionalization of the beads produced the following polymersupported reagents (phosphorus capacities (unless otherwise noted), in mequiv/g dry resin, are given in parentheses): phosphinic acid A (5.261, phosphonic acid D (4.111, dimethylamine E (total anion exchange capacity (TAEC) 4.13), dimethylamine/phosphonic acid C (TAEC 3.25/0.74 mequiv of P), phosphonate monoethyl ester F (4.14), phosphonate diethyl ester GEt (3.411, diester/ monoester B (3.93; 4258 ratio), dimethyl ester G% (3.691, and dibutyl ester GBu (3.31). The polymers were crosslinked with 2% divinylbenzene (DVB). The conventional sulfonic acid resin (5.22 mequiv acid capacity/g dry resin) was also synthesized for comparative purposes; it was prepared with 10% DVB thus yielding a microporosity (as 0 1991 American Chemical Society
Ind. Eng. Chem. Res., Vol. 30,No. 4, 1991 773 \ n
P
O
H
CH2#-OH
H
bR
A -
B X=P(O) C X=
(OEt)p,
We2,
3.5
R=Et
R=H
Fe P H 2 $ + O H )
E -
D -
0.0 -0.5 -
-F
G
43
(R=Me,
t
Zn
,
E t , Bu)
measured by retention of water) comparable to the phosphorus resins. AU but two resins were prepared from vinylbenzyl chloride; the sulfonic and phosphinic acid resins were prepared from styrene. Syntheses of the sulfonic acid (Alexandratos, et al., 19851, phosphinic acid (Alexandratos and Wilson, 1986), phosphonic acid, amine, and amine/acid (Alexandratos et al., 1987a) resins have been detailed. Preparation of the ester resins is presented below. The diester resin synthesis is a significant improvement over that reported earlier (Alexandratos et al., 1987a): FeC13catalysis is now utilized in place of AlC13 resulting in a fully functionalized resin. Phosphonate Ester Resins. Poly(vinylbenzy1chloride) beads (20 g) were contacted with 160 mL of PC13 for 1h in a 500-mL round-bottom flask equipped with an overhead stirrer, thermometer, and condenser. FeC1, (42.51 g) was added and the mixture was refluxed for 4 h. After cooling, the PC13/FeC13was siphoned off the resin, which was then washed with 150 mL of toluene for 30 min; this was repeated twice followed by an overnight wash in 200 mL of toluene and an additional three washes with 150 mL of toluene. The last wash solution was siphoned off and the resin prepared for the quench solution by adding 50 mL of toluene for fluidity and cooling the flask in an ice bath. The diethyl ester resin was prepared by adding a quench solution of 64.5 g of ethano1/64.5 g of toluene at a rate that maintained a temperature below 5 OC. The mix was stirred 1h, after which point the solution was siphoned off and a second quench solution added. After stirring 16 h at room temperature, the resin was then washed and conditioned as has been described (Alexandratm et al., 1987a). The dimethyl and dibutyl ester resins followed the same procedure except for the use of 44.8 g of methanol and 103.6 g of butanol, respectively. The wash sequence also used the appropriate alcohols. The phosphonate monoester resin followed the same procedure except for the first and second quench solutions which consist of 64.5 g of ethanol/ll0.7 g of pyridine followed by a 16-h reflux. For reasons not yet determined, the second quench solution should be added to the resin without siphoning off the initial solution in order to produce a resin with a monoester content exceeding 90%. The bifunctional diester/monoester resin followed a procedure identical with that of the monoester resin up to the end of the first quench solution. Then, after the 1-h stir period, the solution was siphoned off and ethanol
PH Figure 1. Log D/pH correlations with sulfonic acid resin. 5.0
4.0
3.5 3.0
-0.5 -1.0
-0.5
0.0
0.5
1.0
PH Figure 2. Log D/pH correlations with phosphinic acid resin.
added until all of the solid (pyridinium hydrochloride) had been removed from the resin. Toluene was added for fluidity (50 mL) and the second quench solution added (64.5g of ethanol/ 110.7 g of pyridine) followed by the 16-h reflux and washing and conditioning procedure. Metal Ion Selectivity Series. The metal ion solutions consisted of lo4 N Fe(NOJ3, Hg(N03)2,AgN03, Mn(N0 3 ) 2 , and ZII(NO~)~, each in 4,2,1, and 0.2 N HN03 with enough NaN03 added to yield a constant 4 N nitrate background. Acidic solutions were utilized in order to prevent hydrolysis of the metal ions. Five milliliters of each solution was vigorously shaken for 17 h with enough resin to yield 1mequiv of ligand sites. A 17-h equilibration period is known to be more than sufficient (Alexandratos et al., 1987b; Kaiser, 1990). Each solution contained a trace level of a y-emitting isotope of the appropriate metal salt P9Fe, 203Hg,llDmAg,MMn, and =Zn). A t the end of the contact time, a 1-mL aliquot was counted by use of a NaI-TlI well-type counter. The amount of metal abeorbed was calculated by comparing the counts per minute (an average of two 1-min counts) with those of a blank sample (Le., solution that was shaken without contacting resin).
774 Ind. Eng. Chem. Res., Vol. 30, No. 4,1991
4.5
q
5.0 4.5
0 2.5
0.5
--
0.0-0.5 -1.0
-0.5
0.0
0.5
Mn
; I I
E l , A
Zn
I
1
1.0
PH Figure 3. Log D/pH correlations with phosphonic acid resin.
3.5
3.0 3*0$ 2.5
F 2.0+
4
Mn
l.0-c
-0.5
-1.0
-0.5
0.0
0.5
1.0
PH
-1.0
-0.5
0.0
0.5
10
PH
Figure 4. Log D/pH correlations with dimethylamine resin.
Figure 6. Log D/pH correlations with monoester resin.
The equilibrium distribution coefficient (0) is defined as the amount of metal on 1g of resin divided by the amount remaining in 1mL of solution (Strelow, 1960). The values are reproducible to * 5 % . The log D is correlated with the equilibrium solution pH, and each resin’s selectivity series is derived from comparing the log D values across the range of metal ions.
affinity under the acidic conditions used here; interestingly, a moderate Hg affinity is found, less affinity for Ag, and negligible levels for Fe, Mn, and Zn. Amines are known to coordinate with Hg(1I) in acidic solutions (Caban and Chapman, 1972), and perhaps the same mechanism is operative here. The bifunctional amine/acid resin (Figure 5; Fe > Hg > Ag > Mn > Zn) operates through its acid ligands with Fe, which leads to the same high sorption levels as with the phosphonic resin. Hg never reaches the levels of the phosphonic resin but, rather, is complexed to the same moderate levels of the pure amine resin. Ag displays a log D of 1 for the acid, amine, and amine/acid resins, while Mn and Zn remain a t uniformly low levels. The phosphonate monoethyl ester resin (Figure 6) complexes both Fe and Hg (as well as Mn and Zn)at the same levels as the phosphonic resin, but Ag sorption is significantly higher with the former (log D of 2.7 vs 1.0 with the latter). As a result, the affinity for Ag is greater than Hg in all but the last solution. Results with the purely coordinating phosphonate diester resin (Figure 7; Ag > Hg > Fe > Zn > Mn) indicate that selective Ag sorption requires a strong coordinative interaction: the diester resin
Results Comparing the log D/pH plots of the sulfonic acid and phosphinic acid resins (Figures 1and 2) shows the latter to be a far more selective resin with a selectivity series of Fe > Hg > Ag > Mn > Zn in high acid/high ionic strength solutions. (Note that access under these conditions is through the phosphoryl oxygen rather than through the acidic -OH site.) The phosphonic acid resin (Figure 3; Fe > Hg > Ag > Mn = Zn) differs from the phosphinic resin primarily in the precipitous drop in Hg affinity with all but the least acidic background solution; there is also a lower affinity for, and leas selectivity between, Mn and Zn. The dimethylamine resin (Figure 4; Hg > Ag > Fe 1 Mn = Zn) was not expected to display significant metal ion
Ind. Eng. Chem. Res., Vol. 30,No. 4,1991 775
"I
Table I. Distribution Coefficients for Fe, Hg, and Ag Nitrates with Monoester, Diester, Mixed Diester Monoester, and Bifunctional Diester/Monoester Resins HNOn/NaNOnsolutions 4N 2 N/2 N 1 N/3 N 0.2 N/3.8 N D(Fe/monoester) 3802 7244 16218 40738 1 1 2 6 D(Fe/diester) 1350 D(Fe/mix) 2927 5399 17918 D(Fe/ bifunctl) 692 1820 309 5248 42 58 D(Hg/monoester) 23 13804 3 21 D(Hg/diester) 6 9 23 D(Hg/ mix) 43 88 3689 26 44 15 D(Hg/ bifunctl) 3020 D(Ag/monoester) 439 680 638 793 463 D(Ag/diester) 373 291 69 630 D(Ag/ mix) 481 205 489 2924 D(Aglbifunct1) 2594 2155 1843
Diethyl Ester
+
3.5
3.0
I 0.0
Uptake of Ag
-0.5
-1.0
-0.5
0.0
0.5
1.0
PH
Figure 7. Log D/pH correlations with diethyl ester resin.
i:;!60% Monoester
1500
1000
Fe
4.0
-3.0 --
Monoester
3.5
-1.0
-00 2.0--
0.5
0:o PH
-0.5
0 2.5-
1 .o
Figure 9. D(AgNOS)/pH correlations with diester/monoester, monoester, diester, and mixed-bed resins.
-1.0 -0.5 -0.0 -1.5
-0.5
! -1.0
4.0 3.5 I
1
-0.5
I I
1 I
0.0
0.5
I
1.0
PH Figure 8. Log D/pH correlations with diester/monoester resin.
sorbs Ag to a higher level than Hg or Fe, especially from the most acidic solutions. Since the absence of strongly hydrophilic ion-exchange ligands could limit accessibility into the diester resin, the bifunctional diester/monoester resin was synthesized with a 2:3 ratio of the ligands. The log D/pH correlation (Figure 8) points to am important result: while Hg may be sorbed solely through the monoester ligand (the correlation is identical with that with the pure monoester resin), and the sorption of Fe is less than that with the monoester resin, Ag sorption by the bifunctional resin k significantly greater than that found with either the monoester or diester resins. This is clearly indicated by the distribution coefficient data given in Table I for the sorption of Ag, Hg, and Fe by the diester, monoester, and diester/monoester resins. In order to isolate the effect of having the two ester ligands on the same polymer support in the bifunctional resin, sorption studies were also carried out with a mixed bed of monofunctional diester and monoester resins in a ratio identical with that found with the bifunctional resin (Table I). With Hg, the mixed-bed results parallel the results with the bifunctional resin and both perform at a significantly lower
1.o 0.5 0.0
-0.5 -1.0
-0.5
0.0
0.5
1.0
PH Figure 10. Log D/pH correlations with dimethyl ester resin.
level than the monoester resin. The Fe/mixed-bed results are also consistently lower than those with the monoester resin. The results with Ag are unique in that the bifunctional resin markedly outperforms the two monofunctional resins as well as the mixed bed (Figure 9). The data thus point to a unique synergistic interaction with polymeric ligands in the complexation of Ag, as will be discussed in the following section. The mechanisms through which diester resins are more selective for Ag than for other metals being considered here
776 Ind. Eng. Chem. Res., Vol. 30,No. 4, 1991
-
I
I
2*ot r””i
? 1.5i ’
-1.0 -0.5
0.0
0.5
1.0
PH Figure 11. Log D/pH correlations with dibutyl ester resin.
become more evident by considering the log D/pH correlations with the dimethyl ester (Figure 10) and dibutyl ester (Figure 11)resins. The bulkier dibutyl ester shows a well-defined series of Ag > Hg > Fe > Mn = Zn while the dimethyl ester resin yields a series that is pH-dependent. The diester resin data may thus indicate that optimum metal ion complexation from the solution phase occurs when the polarizability/acidity properties of the ligand and metal are complementary (as expected from hard-wft acid-base theory (Ho, 1977))while superimposed steric factors form an additional constraint on the complexation (vide infra).
Discussion The phosphinic acid resin illustrates the importance of a metal-specific reaction in producing a polymer with a high level of ionic recognition. The ability of the phosphinic ligand to control the recognition mechanism through the reduction reaction with the Hg(I1) ion allows for that ion’s separation from a wide range of aqueous solutions to a consistently higher level than found with other polymers. Additionally, the phosphinic resin does not show a loading effect with Hg(I1) due to its reduction to the free metal (Alexandratm and Quillen, 1989b). Mercury metal is thus recovered from ionic solutions as the polymer is oxidized (Alexandratos and Wilson, 1986). The inherent selectivity of the phosphorus acid ligands is seen by comparing their performance with that of the sulfonic acid ligand. It has been established that the sulfonic resin displays a low selectivity toward metal ions due to a narrow range of reaction free energy values (Boyd et al., 1967). Results under the current conditions confirm this nonselectivity: the correlations in Figure 1are clustered together and the near-zero slopes indicate that the resin is complexing sodium ions, which are present in excess over the transition-metal ions. Comparison of ioncomplexation studies, in the presence and absence of competing sodium ions, show that ion exchange is the dominant sorption mechanism for the sulfonic resin and that it is, in both cases, nonselective (Alexandratos and Quillen, 1989a). The phosphonic resin’s behavior with Fe, Hg, and Ag ie representative of that ligand’s mechanism of action: the amount of Hg and Ag complexed is relatively low in the first three solutions due to the successful competition for
phosphoryl oxygen coordination sites by H+(Alexandratm and Quillen, 1990); in the least acidic solution, there are fewer protons to coordinate with the phosphoryl oxygen and this allows it to display a much higher affinity for Hg than for Ag. (An alternative explanation involves the intervention of ion exchange to explain the high Hg affinity; it, though, is probably not operative here since the solution pH is 0.70 and phosphonic acid’s pK, is approximately 4.0 (Peppard et al., 1965)J The compiexation of Fe is high in all solutions due to the phosphoryl oxygen’s greater affinity for it than for H+ (postulated as an entropy-driven coordination (Alexandratos and Quillen, 1989a)). The uniformly high level of Hg sorption found only with the phosphinic resin is most likely due to the reduction reaction. A comparable phosphoryl oxygen coordinative affinity for Hg is displayed by the phosphonic acid, phosphonate monoester, and bifunctional diester/monoester resins. That the mechanism of action is dependent upon coordination to the phosphoryl oxygen is supported by the performance of the bifunctional amine/acid resin. The dimethylamine sites are protonated in all four solutions; if the protons are coordinatively shared with the phosphoryl oxygens, the sorption of Hg could remain low in the least acidic solution (it is at the low levels found with the phosphonic resin in the first three solutions) due to the continued protonation of the phosphoryl oxygens by the R3NH+ ligands. The Fe affinity displayed by the amine/acid resin is similar to that of the phosphonic resin: Fe is able to displace the protons on the phosphoryl oxygens in the amine/acid resin, as expected from the high Fe affinity displayed by the phosphonic acid resin. Ag, Mn, and Zn affinities are relatively low in both monofunctional amine and acid resins and remain low in the bifunctional resin. The highest distribution coefficients for resins with phosphorus acid ligands are found with Fe. That complexation, though, is adversely affected by the presence of diester ligands. Complexation onto the diester/monoester resin is lower than on the pure monoester resin, and it is much lower still on the pure diethyl ester resin. It is thus proposed that diester ligands hinder complexation of ferric salts and that this steric hindrance can be an additional variable in controlling the recognition mechanism. Results with the dimethyl and dibutyl ester resins support this concept: the dibutyl results confirm the low level of complexation found with the diethyl ester resin, while the dimethyl resin, with its less bulky ligands, sorbs more Fe, especially in the least acidic solution where there is less H+competition for phosphoryl oxygen coordinating sites. Significant complexation between Fe and the phosphoryl oxygen is thus possible only in the absence of steric factors, and this allows for an additional adjustable variable, viz., steric control of the recognition mechanism, in the design of highly selective complexing polymers. Esterification of the phosphorus acid ligands is critical to the complexation of high levels of Ag. The monoester resin coordinates Ag to a far higher level than the phosphonic acid resin, and this may reflect a better electronic match in ligand/metal polarizability with the former resin due to its electron-donating ethyl group. Ag is the highest loaded species on the diethyl ester resin, which reflecta the inherent affmity for Ag by the relatively soft ligand as well as the absence of steric hindrance to complexation onto the bulky ligand; this last point is supported by the precipitous drop in complexation of the mercury dinitrate and iron trinitrate salts.
Ind. Eng. Chem. Res., Vol. 30, No. 4, 1991 777 The bifunctional diester/monoester resin displays a unique mechanism of complexation. While the affinity of the resin for Hg is identical with (and for Fe is lower than) that of the phosphonic resin, its affinity for Ag is greater than that of any phosphorus resin synthesized in this study. The bifunctional resin coordinates far more Ag than expected from the performance of the two monofunctional resins, while the monoester resin outperforms both the bifunctional and diester resins for Hg and Fe. The phenomenon wherein two ligands on a bifunctional polymer cooperate to complex more of the target species than either one could alone is thus termed supported ligand synergistic interaction. Synergism between soluble, low molecular weight metal ion complexing agents has been observed (Sekine and Hasegawa, 1977); it is now extended to polymeric reagents. Table I provides further evidence for supported ligand synergistic interaction by comparing the distribution coefficients of bifunctional resins with those of mixed beds, wherein metal nitrate solutions are contacted with a mixture of the monofunctional diester and monoester resins in a ratio equivalent to that of the ligands on the bifunctional support. While the mixed bed performs in a manner comparable to the bifunctional resin for Hg (as expected if the two types of ligands were operating independently) and is somewhat better than the bifunctional resin for Fe (which would be true if the diester ligands were hindering complexation of the trinitrate salt within the resin), sorption of Ag occurs to a greater extent with the bifunctional resin relative to the mixed bed, implying synergistic AgN03 coordination by the ligands on the same polymer. The purely coordinating dimethyl, diethyl, and dibutyl phosphonate ester resins display trends in selectivity that are quite different from resins containing phosphorus acids. The diester resins have significant selectivity for Ag, at least from highly acidic solutions, while Fe has the highest sorption levels with phosphorus acid resins under the same conditions. Mn and Zn do best with the phosphinic acid resin and then only from the least acidic solution; ion exchange is thus most important with the hard divalent ions. In developing polymer-supported reagents whose specificity derives from their reactivity, it may be that bifunctionality is a critical variable in defining a polymer’s substrate specificity. In the present case, polymers with different recognition mechanisms are used to react with targeted metal ions. Of particular importance are the phosphinic acid and diester/monoester resins: both are bifunctional and can interact with metal ions through a recognition mechanism (reduction and coordination, respectively). When the results of the current study are combined with the third class of dual-mechanism bifunctional polymers (Alexandratosand Bates, 19881, a principle is suggested that summarizes the results and sets a direction for future syntheses: Ionic recognition is an inherent property of polymers that couple an access mechanism to a recognition mechanism subject to reaction control or steric control. Reaction control of the recognition mechanism implies a strong ion/ligand interaction (e.g., reduction, coordination, and precipitation) whereas steric control implies a specificity imposed by a hindrance to complexation for all but the target species. Conclusions Polymer-supported reagents with significant metal ion recognition have been developed. Substrate recognition by the dual-mechanism bifunctional polymers has a direct parallel with the selectivities displayed by enzymes. En-
zymes are placed into one of six classes depending upon the nature of their involvement in the reaction being catalyzed (Palmer, 1985). The classifications include the oxidoreductases which allow for the transfer of hydrogen, oxygen, and electrons on the way to product formation and the hydrolases which catalyze hydrolytic reactions. The multifunctionality of enzymes is critical to their specificity, which entails substrate recognition followed by product formation (Tabushi, 1984). An enzyme’s active site consists of complexing moieties (which bind the substrate) and reactive moieties (which form the product). The DMBPs operate in a conceptually similar manner through an access mechanism and a subsequent recognition mechanism. The ion-exchange/redox resins can thus be viewed as simple oxidoreductase models. The ion-exchange/coordination resins can be effective models for the hydrolase enzymes, and their effect on the kinetics of ester hydrolysis is being determined. New class I ion-exchange/redox resins that are more closely modeled after the oxidoreductases will be reported in a subsequent publication. Research is continuing into the synthesis of new ion-exchange/coordinationresins with varying bifunctionality ratios and a range of coordinating ligands in order to generalize the conditions under which synergism can be expected. The ligands will also have different degrees of steric control superimposed on the coordinative interaction in order to further influence the selectivity. Acknowledgment We gratefully acknowledge the continuing support of the Department of Energy, Office of the Basic Energy Sciences, through Grant DE-FG05-86ER13591. The metal ion radiotracer studies were carried out with the cooperation of W. Jack McDowell and Dr. Bruce Moyer at the Oak Ridge National Laboratory (Chemistry Division). We especially thank Ms. Faith Case (ORNL) for technical assistance in carrying out the radiotracer experiments. We are also grateful to the Dow Chemical Company for a generous gift of vinylbenzyl chloride monomer. Registry No. Hg,7439-97-6; Ag, 7440-22-4; phosphinic acid, 6303-21-5; phosphonic acid, 13598-36-2.
Literature Cited Alexandratos, S. D. Design and Developmcnt of Polymer-Based Separations: Dual Mechanism Bifunctional Polymers as a New Category of Metal Ion Complexing Agents with Enhanced Ionic Recognition. Sep. Purif. Methods 1988, 17, 67-102. Alexandratos, S.D.;Wilson, D. L. Dual Mechanism Bifunctional Polymers: Polystyrene-Based Ion Exchange/Redox Resins. Macromolecules 1986,19,280-287. Alexandratos, S. D.; Bates, M. E. Enhanced Ionic Recognition by Polymer-SupportedReagents: Synthesis and Characterizationof Ion Exchange/Precipitation Resins. Macromolecules 1988, 21, 2905-2910. Alexandratos, S. D.; Quillen, D. R. Mechanism of Polymer-Based Separations. I. Comparison of Phosphinic Acid with Sulfonic Acid Ion Exchange Resins. Solu. Extr. Zon Exch. 19898, 7, 511-525. Alexandratos, S.D.; Quillen, D. R. Mechanism of Polymer-Based Separations. 111. Metal Ion Loading Capacities of Reactive Polymers with Specific Recognition Mechanisms. Solv. Extr. Zon EX&. 198913, 7,1103-1109. Alexandratos, S. D.; Quillen, D. R. Mechanism of Polymer-Based Separations. 11. Targeted Metal Ion Complexation by Reactive Polymers. React. Polym. 1990,13, 255-265. Alexandratos, S.D.; Wilson, D. L.; Strand, M. A.; Quillen, D. R.; Walder, A. J.; McDowell, W. J. Metal Ion Extraction Capability of Phosphinic Acid Resin. Macromolecules 1985, 18, 835-840. Alexandratos, S. D.; Quillen, D. R.; Bates, M. E. Synthesis and Characterization of Bifunctional Ion Exchange/Coordination Resins. Macromolecules 1987a, 20, 1191-1196.
Znd. Eng. Chem. Res. 1991,30, 778-783
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Alexandratos, S. D.; Wilson, D. L.; Kaiser, P. T.; McDowell, W. J. Phosphinic Acid Ion Exchange/Redox Resins and the Kinetics of Metal Ion Complexation. React. Polym. 1987b,5,23-35. Boyd, G.E.; Vaslow, F.; Lindenbaum, S. Thermodynamic Quantities in the Exchange of Zinc with Sodium Ions in Variously CrossLinked Polystyrene Sulfonate Cation Exchangers at 25'. J. Phys. Chem. 1967,71,2214-2219. Caban, R.; Chapman, T. W. The Extraction of Mercuric Chloride from Acid Chloride Solutions with Trioctylamine. AIChE J . 1972, 18,904-913. Chanda, M.; Rempel, G. L. Attaching Chelating Ligands to Polybenzimidazolevia Epoxidation to Obtain Metal Selectve Sorbents. J . Polym. Sci., Polym. Chem. Ed. 1989,27,3237-3250. Helfferich, F. Ion Exchange Kinetics. V. Ion Exchange Accompanied by Reactions. J . Phys. Chem. 1965,69,1178-1187. Ho, T.L. Hard and Soft Acids and Bases Principle in Organic Chemistry; Academic Press: New York, 1977. Janauer, G. E.; Ramseyer, G. 0.;Lin, J. W. Selective Separations by Reactive Ion Exchange with Common Polystyrene Type Resins. Anal. Chim. Acta 1974, 73,311-319. Kaiser, P. T.Synthesis, Characterization and Mechanistic Studies of Novel Dual Mechanism Bifunctional Polymers for Ionic and Molecular Recognition. Ph.D. Dissertation, University of Tennessee, 1990. Kantipuly, C.; Katragadda, S.; Chow, A.; Gesser, H. D. Chelating Polymers and Related Supports for Separation and Preconcentration of Trace Metals. Talanta 1990,37,491-517. King, C. J., Chairman. Separation and Purification: Critical Needs and Opportunities; Committee on Separation Science and Technology; National Academy Press: Washington, DC, 1987.
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Receiued for review June 28, 1990 Accepted October 19,1990
GENERALRESEARCH Oxygen Evolution from KC103 Catalyzed by Metal Oxides as Air Bag Inflators Hideaki Iwakura,t Noriyoshi KakutaYtAkifumi Ueno,*ptKazuo Kishi,*and Jun Katot Department of Materials Science, Toyohashi University of Technology, Tempaku, Toyohashi Aichi 440, Japan, and Daicel Chemical Industry Company, Toranomon, Mitui Building, Kasumigaseki, Chiyoda, Tokyo 110, Japan
Oxygen evolution during thermal decomposition of potassium chlorate was studied using 23 kinds of metal oxides as catalysts. Pure potassium chlorate metals at 350 "C and then decomposes at 635 OC. Addition of metal oxides to the chlorate lowered the decomposition temperature to some extent, though the melting temperature did not change. Thus, the metal oxides added work as catalysts for the decomposition of the molten potassium chlorate, resulting in oxygen evolution a t lower temperatures. The metal oxides used here were clearly classified into three groups, depending on the extents of decrease in the decomposition temperature. Introduction Decomposition of alkali-metal chlorates and perchlorates has been of interest for understanding the elementary steps of the solid-state reactions. Markowitz and Boryta (1961) have studied the decomposition kinetics of LiC104 and reported two different types of kinetics; for up to 40% of the decomposition, the kinetics follow the autocatalytic Prout-Tompkins rate law with an activation energy of 218 kJ/mol and N then conform to first-order kinetics with an activation energy of 259 kJ/mol. Markowitz et al. Toyohashi University of Technology. Chemical Industry Company.
t Daicel
(1964) have extended the study to other alkali-metal chlorates and observed two peaks in the DTA (differential thermal analysis) spectrum of the respective chlorate. The first peak was detected at temperatures ranging from 200 to 400 "C,ascribed to the fusion of the chlorates. The second peak was observed between 300 and 700 OC due to the decomposition of the molten chlorates to the corresponding alkaline chlorides and oxygen. Addition of MnOz to alkali-metal chlorates has been reported by Markowitz and Boryta (1966) to reduce the decomposition temperatures, suggesting catalytic performance of the metal oxide for the decomposition of the chlorates. Furuichi et al. (1974) have studied the catalytic performances of cr-Fe203and AZO3for the decomposition
0888-5885/91/2630-0778$02.50/00 1991 American Chemical Society
