Chelate Ion Exchange Resins HARRY P. GREGOR, MARK TAIFERi, LOUIS CITAREL, AND ERNEST I. BECKER Polytechnic Institute of Brooklyn, Brooklyn 2, h'. Y .
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HE conventional ion exchange resins separate ionic constituents by means of several mechanisms or "bases of selec-
tivity." First, they absorb ionic constituents in the presence of nonionic substances. Second, anionic substances are taken up by the anion exchange resins, cationic substances by the cation exchange resins. Third, ions of higher valences are preferentially absorbed in dilute solutions. Fourth, with resins of high degrees of cross linking, the ion having a smaller (hydrated) ionic volume is preferentially absorbed (5, 6). Fifth, organic ions may be adsorbed by the hydrocarbon matrix of resins (6, 8). Sixth, an ion may interact chemically with a fixed exchange group and in that manner be taken up preferentially (4, 7 , 9, 14).
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MILLIEQWVALENTS OF BASE ADOED Figure 1. Titration with Sodium Hydroxide Solution of 0.3 g r a m of rn-phenylene diglycine in 100 m l . of water
While a resin may thus take up one ion species preferentially over another, this selectivity usually occurs to but a limited extent and ion separations can be effected only by careful elution procedures in a column, where many hundreds of fractionations can occur. The conventional ion exchange resins should then be classified as "selective" in t h a t they are characteristic for a comparatively small number of ions (10). A specific ion exchange resin may correspondingly be defined as one that under proper experimental conditions is characteristic of one ionic species only. This paper describes the first of a new class of ion exchange resins, in which chelate groups are substituents in a highly cross-linked and therefore insoluble hydrocarbon matrix. The use of organic chelate compounds is well known in analytical chemistry (3, 18). A chelate group suitable for uee in a resin must obviously have the following properties: (1) be capable of resin formation or substitution in a resin matrix; (2) be sufficiently stable to withstand the polymerization or resinification reaction; and (3) be compact so as not t o be hindered sterically by the dense resin matrix. An additional requirement which follows from the result of this study, is that both arms of the chelate structure be present on the same monomer in proper spatial configuration; thus, a specific juxtaposition of both arm6 in the resin is required. The chelate monomers used in this investigation include oaminophenol, anthranilic acid, and N , N '-biscarboxymethylene1
Present address, Abrasive Products, Inc., South Braintree, Masa.
m-phenylenediamine (m-phenylene diglycine). The abbreviated m-phenylene diglycine is referred to as MPDG. The former substances have been extensively reported in the literature as regards their chelating properties, while the latter is similar to the ethylenediamine tetraacetic acid compounds described by Schwarzenbach and Ackerman ( l a ) and Britzinger and Hesse (@. PREPARATION AND CONDITIOXING OF RESINS
PHENYLENE DIGLYCIKE RESIN. Zimmerman and Knyrim (19) reported the reaction of m- and p-phenylenediamines with ethyl chloroacetate to form the respective phenylene diglycines (C6"4)(NHCH&OOH)i after hydrolysis with strong hydrochloric acid. A modified procedure was followed. A mixture of 21.6 grams (0.2 mole) of redistilled m-phenylenediamine and 50.1 grams (0.4 mole) ethyl chloroacetate in 100 ml. of 2-propanol x a s refluxed for a total of 6 hours. During this time, the solution darkened and a voluminous precipitate of m-phenylenediamine dihydrochloride slowly separated. The cooled mixture was filtered and the gray-white precipitate was washed with fresh 2-propanol, then with ether, and was dried in air t o give 16.3 grams (91 yo)of the by-product. After concentrating the filtrate and chilling, the product precipitated and was filtered and washed, first with water and then sparingly with 2-propanol. Air-drying afforded 13.0 grams (46%) of the crude diglycine ester. One recrystallization from 2-propanol gave 11.0 grams of light-tan needles, melting point 73" to 75" C. (Zimmerman reports a melting point of 73" C.)
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Figure 2.
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TIME IN HOURS Rate of Absorption of N i + +from 0.001 M Solution a t Different pH Levels Using rn-phenylene diglycine resin
The amine ester was hydrolyzed by refluxing a mixture of 4.2 grams (0.015 mole) of amino ester and 50 ml. of concentrated hydrochloric acid for 4 hours. From the initially clear solution there slowly separated a white microcrystalline precipitate. The mixture mas refrigerated and filtered to give a white residue which was suspended in ice-cold 2-propanol, refiltered, washed with ether, and air-dried to give 3.8 grams (85%) of amino acid dihydrochloride, melting point 215" C. (dec.). The neutral equivalent ( I S )for C10H14C12N204 was calculated to be 74.2 and was found t o be 72.3. The nitrogen content vias calculated as 9.43% and was found t o be 9.2%. The resin itself was prepared by dissolving 60 grams of mphenylene diglycine dihydrochloride in 40 ml. of hot water and, after cooling, adding 32 grams of 37y0 formaldehyde solution.
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
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PH Figure 3. Absorption of Cobalt, Iron (Ferrous), and Copper from 0.001 M Solutions Using o-aminophenol resin
After a few moments of stirring, a black gel was formed. This was heated at 110' C. for 4 hours to form a hard, insoluble resin. ANTHRANILIC ACIDRESIN. Anthranilic acid will react with an excess of formaldehyde in acid solution to form a thermoplastic resinous substance, which, while insoluble in neutral and acid solutions, is soluble in alkaline solution. For that reason, attempts were made to cocondense this system with a suitable cross-linking agent. Phenol, urea, and aniline were all used, but did not appear t o affect the properties of the final product, possibly because the rate of reaction of anthranilic acid with formaldehyde and subsequent resinification was so rapid as to preclude combination with those agents. Since resorcinol is
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PH Figure 4. Absorption of Magnesium by m-Phenylene Diglycine Resin at p = 0.025 to 0.05
When no further odor of formaldehyde could be detected, 27 grams of resorcinol were added and the mixture was heated to a wine-red, viscous solution. This was cooled and 30 grams of 37% formaldehyde solution were added. The mass gelled and was cured a t 110' C. for 4 hours. O-AMINOPHENOL RESIN. o-Aminophenol (0.2 mole) and sodium hydroxide (0.2 mole) were dissolved in 20 ml. of water;
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PH Figure 5. Absorption of Iron by m-Phenylene Diglycine Resin a t I.( = 0.025 to 0.05
PH Figure 6. Absorption of Cobalt by mPhenylene Diglycine Resin a t u = 0.025 to 0.05
particularly reactive, it was then used, and a hard, brittle and insoluble resin resulted. The actual procedure is as follows: 34 grams of anthranilic acid were added to a solution containing 7.5 grams of sodium hydroxide in 10 ml. of water and 20 grams of 37% formaldehyde.
0.4 mole of 37% formaldehyde was added and gelation occurred. The gel was cured a t 100' C. for 4 hours. CONDITIONING OF RESINS. The resins were ground and screened to -20- to +3O-mesh size, placed in a column, and treated continuously with 1 M sodium hydroxide solution for a
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 44, No. 12
TABLE I. ABSORPTIOKOF METALSBY CHELATING RESIX WZ-PHEKYLEKE DIGLYCIZE (C
equilibrium concentration of metal in moles per liter; A = absorption i n millimoles per gram of resin; and except as noted)
=
fi =
ionic strength, which is 0.025 t o 0.05
pH Mg++
C A
Mgtr
C A B C
hfg +
+
re++ C0+-
co--
7 0.00100 0.000
0,0090 0.29
0.0071 0.81
O.OOS8
OIO058
0,0060 1.07
0.0063 1.02
0,098 0.513
0.094 1.64
0,092 2.06
0,0925
0.093 1.98
0.0935 1.92
0.00100 0.000
0.00100 0.000
0.00100 0.000
0.00046 0.11
0.00028 0.29
0.001 0.000
0.00098
0,00033 0,092
0 0005
0.14
0.00017
0.23
0.0073 0.73
0,006.i 0.98
0,0058
0.045
0,099 0.023
0.097 0.158
0.081
0.001 0.000
0.00098 0.0041
0.001 0.000
0.001
COT-
co+-
