Ion Exchange Properties of a Terpolymer Resin Derived from 2 , 4-Dihydroxybenzaldehyde , Oxamide and Formaldehyde

Terpolymer resins (2,4-DHBOF) were synthesized by the condensation of 2,4-dihydroxybenzaldehyde and oxamide with formaldehyde in the presence of hydrochloric acid as catalyst, proved to be selective chelation ion exchange terpolymer resins for certain metals. Chelation ion exchange properties of these polymers were studied for Fe, Cu, Hg, Cd, Co, Zn, Ni and Pb ions. A batch equilibrium method was employed in the study of the selectivity of the distribution of a given metal ions between the polymer sample and a solution containing the metal ion. The study was carried out over a wide pH range and in a media of various ionic strengths. The polymer showed a higher selectivity for Fe, Cd and Co ions than for Cu, Hg, Zn, Ni and Pb ions.


Introduction
Ion exchange may be defined as the reversible exchange of ions between the substrate and surrounding medium.Ion exchange technique can remove traces of ion impurities from water/process liquors and given out a product of ultra pure quality in a single efficient and techno-economically viable manner.Ion exchangers are widely used in analytical chemistry, hydrometallurgy, antibiotics, purification and separation of radioisotopes and find large application in water treatment and pollution control 1,2 .Lutfor et al 3 prepared a chelating ion exchange resin containing amidoxime functional group.The chelating poly (amidoxime) resin was characterized by FTIR spectra, TG and DSC analyses.The chelating behavior of the prepared resin was studied with Cu(II), Zn(II), Ni(II), Cd(II) and Pb(II) metal ions.Samir et al 4 synthesized ion exchange resin from 8-quinolinyl methacrylate and characterized by conventional methods.The thermal analysis was carried out using TGA and DSC.The metal ion uptake capacities of synthesized copolymers were estimated by batch equilibration method using different metal ion solutions under different experimental conditions.
Three phenol-formaldehyde chelating resins, poly (8-hydroxyquinoline-5,7 diylmethylene), poly (8-hydroxyquinoldine-5,7 diylmethylene) and poly (2-aminophenol-5,7 diylmethylene) were synthesized and characterized by Ebraheem 5 .The chelating characteristics of these polymers were studied by a batch equilibrium technique.The ion exchange capacity, effect of electrolyte on metal ion up take, rate of metal uptake and distribution of metal ion at different pH with resin copolymer derived from thiosemicarbazone derivatives of phenolic compound shows higher order than the resin copolymer derived from semicarbazone derivatives 6 .Recently much work has been carried out to study the ion exchange properties of anchoring functional chelating groups on the polymeric network.But as compared to anchored resins, the synthesized resins are more advantageous because the synthesized insoluble functionalized polymer can provide good stability and good flexibility in working conditions.
Rivas B. L 7 synthesized crosslinked poly [3-(methacryloyl-amino)-propyl]-dimethyl(3sulfopropyl)ammoniumhydroxide-co-2-acryl-amidoglycolic acid [PCMAAPDSA-co-AGCO] by radical polymeri-zation and tested the synthesized polymer as an absorbent under competitive and non-competitive conditions for Cu(II), Cd(II), Hg(II), Zn(II), Pb(II) and Cr(III) by batch and column equilibrium procedures.They reported that resin metal ion equilibrium was achieved before 1 h. the resin showed a maximum retention capacity value of 1.084 m.equ.g -1 for Hg(II) at pH 2. The recovery of the resin was investigated at 20 0 C under different concentration of HNO 3 and HClO 4 .
Jadhao M.M. and coworker 8 synthesized a terpolymer resin by condensation of 2,2'dihydroxybiphenyl and formaldehyde in the presence of acid catalyst.They studied chelating ion exchange properties of this polymer for Fe(III), Cu(II), Ni(II), Zn(II), Cd(II) and Pb(II) ions.A batch equilibrium method was employed in the study of the selectivity of metal ion uptake involving the measurement of the distribution of a given metal ion between the polymer sample and a solution containing metal ions.The study was carried out over a pH range and in media of various ionic strengths.They reported that the polymer showed a higher selectivity for Fe(III), Cu(II) and Ni(II) than for Co(II), Zn(II) Cd(II) and Pb(II) ions.
So for no resin based on 2,4-dihydroxybenzaldehyde-oxamide-formaldehyde in acidic media has been synthesized for the quantitative separation of transition metal ions.As industrial influence often rich in transition metal ions, removal of these metals use an important task for industries.Therefore we have studied the use of ion exchanger for removal and separation of heavy metal ions.In this paper synthesis and characterization of the above resin are reported together with the condition for the effective separation of transition metal ions.

Experimental
The chemicals 2,4-dihydroxybenzaldehyde, oxamide and formaldehyde (37%) used are of A. R. grade and chemically pure which is purchased from Merck.Solvents like N, N-dimethyl formamide and dimethylsulphoxide were used after distillation.

Preparation of 2, 4-DHBOF terpolymers
The 2,4-DHBOF-I terpolymer resin was prepared by condensing 2, 4dihydroxybenzaldehyde (1.66 g, 0.1 mol) and oxamide (0.88 g, 0.1 mol) with formaldehyde (7.5 M l, 0.2 mol) in the presence of 2 M HCl as a catalyst at 126±2 0 C in an oil bath for 5 h (Scheme 1).The brown colored solid product obtained was immediately removed and extracted with diethyl ether to remove excess of 2, 4-dihydroxybenzaldehyde-formaldehyde copolymer, which might be present along with the 2, 4-DHBOF-I terpolymer.It was further purified by dissolving in 8% NaOH and then filtered.The terpolymer was then reprecipited by drop wise addition of 1:1 (v/v) conc.HCl / water with constant stirring and filtered.The process was repeated twice.The resulting polymer sample was washed with boiling water and dried in a vacuum at room temperature.The purified terpolymer resin was finely ground to pass through 300-mesh size sieve and kept in a vacuum over silica gel.The yield of the terpolymer was found to be about 80-83 % (Table 1).Similarly, the other terpolymers viz.2, 4-DHBOF-II, 2, 4-DHBOF-III, 2, 4-DHBOF-IV were synthesized by varying the molar ratios of the reacting monomers i. e. 2, 4-dihydroxybenzaldehyde, oxamide and formaldehyde in the ratios of 2:1:3, 3:1:4, 4:1:5 respectively.

Analytical and physicochemical studies
The intrinsic viscosities were determined using a Tuan-Fuoss viscometer 9 at six different concentrations ranging from 0.3 wt % to 0.05 wt % of resin in DMF at 300 o C. Intrinsic viscosity (η) was calculated by the Huggin's 9 eq.( 1) and Kraemer 9 eq (2).
The elemental analysis was carried out on a Perkin Elmer 2400 Elemental Analyser instruments.The UV-Visible studies were out carried using Hitachi 330 UV-VIS-NIR Spectrometer in the range 200-850 nm.The Infrared spectrum was recorded in the region of 500-4000 cm -1 on Perkin Elmer Spectrum RX1 FT-IR Spectrometer. 1 H-NMR studied using Bruker Avance-II FT-NMR Spectrometer in DMSO-d 6 solvent.All the analytical and spectral studies for the newly synthesized terpolymer were carried out at Sophisticated Analytical Instrumentation Facility (SAIF) Punjab University, Chandigarh.

Ion exchange properties
To decide the selectivity of 2, 4-DHBOF terpolymers, we studied the influence of various electrolytes, the rate of metal uptake and distribution of metal ions between the terpolymer and solution.The results of the batch equilibrium study carried out with the terpolymer samples are presented in Tables 5-7.

Determination of metal uptake in the presence of electrolytes of different concentrations
The terpolymer sample (25 mg) was suspended in an electrolyte solution of NaNO 3 (25 mL) of known concentration.The pH of the suspension was adjusted to the required value by using either 0.1 N HCl or 0.1 N NaOH.The suspension was stirred for a period of 24 h at 25 0 C. To this suspension 2 mL of 0.1 M solution of the metal ion was added and the pH was adjusted to the required value.The mixture was again stirred at 25 0 C for 24 h and filtered.
The solid was washed and the filtrate and washings were combined and the metal ion content was determined by titration against standard EDTA.The amount of metal ion uptake of the polymer was calculated from the difference between a blank experiment without polymer and the reading in the actual experiments.The experiment was repeated in the presence of other two electrolytes such as NaCl and NaClO 4 .

Evaluation of the rate of metal uptake
In order to estimate the time required to reach the state of equilibrium under the given experimental conditions, a series of experiments of the type describe above were carried out, in which the metal ion taken up by the chelating resins was determined from time to time at 25 0 C (in the presence of 25 mL of 1 M NaNO 3 solution).It was assumed that under the given conditions, the state of equilibrium was established within 24 h.The rate of metal ions uptake is expressed as percentage of the amount of metal ions taken up after a certain time related to the time, which required for the state of equilibrium.

Evaluation of the distribution of the metal Ions at different pH
The distribution of each one of the five metal ions i.e.Fe +3 , Cu +2 , Hg +2 , Cd +2 , Co +2 , Zn +2 , Ni +2 and Pb +2 between the polymer phase and the aqueous phase was determined at 25 0 C and in the presence of a 1 M NaNO 3 solution.The experiments were carried out as described above at different pH values.The distribution ratio 'D' is defined by eq. ( 3).

Results and Discussion
The terpolymers which have been use in the present investigation were prepared by the reaction scheme 1.The resin sample was brown in color, insoluble in commonly used solvent, but was soluble in DMF, DMSO, THF, pyridine, concentrated H 2 SO 4 .No precipitation and degradation occurs of resin in all the solvents.These resins were analyzed for carbon, hydrogen and nitrogen content (Table 2).

Viscometric study
Viscometric measurements were carried out in DMF solution at 30 0 C using a Tuan Fouss 9 viscometer.Reduced viscosity versus concentration (3% -0.5%) was plotted for each set of data.The intrinsic viscosity [η] was determined by the corresponding linear plots (Figure 1).
The following equations were used to determine Huggin's 9 and Krammer's 9 constant, respectively:

Electronic spectra
The UV-visible spectra (Figure 2) of all 2, 4-DHBOF terpolymer samples in pure DMSO were recorded in the region 190 nm -800 nm.All the four 2,4-DHBOF terpolymers samples displayed two characteristic broad bands at 280 nm and 320 nm.These observed position for absorption bands indicate the presence of a carbonyl (>C=O) group having a carbon oxygen double bond which is in conjugation with the aromatic nucleus.The later band can be accounted for a π→π* transition while the former band (less intense) may be due to a n→π* transitions 11 .The bathochromic shift (shift towards longer wavelength) from the basic value of the C=O group viz.310 nm and 240 nm respectively, may be due to the combine effect of conjugation and phenolic hydroxyl group (auxochrome) 12,13 .It may be observed from the electronic spectra of the 2, 4-DHBOF terpolymers that the absorption intensity gradually increases in the order 2,4-DHBOF -I < 2,4 -DHBOF -II < 2,4 -DHBOF -III < 2,4 -DHBOF -IV.The observed increasing order may be due to introduction of more chromophores (C=O group) and auxochromes (phenolic OH) in the repeat unit structure of the terpolymers.

Infrared spectra
The IR-spectra of all four 2, 4-DHBOF terpolymers are presented in Figure 3.The IRspectra revealed that all these terpolymers give rise to nearly similar pattern of spectra (Table 3).A band appeared in the region 3337 cm -1 -3316 cm -1 may be assigned to the stretching vibration of the phenolic hydroxy groups exhibiting intermolecular hydrogen bonding 12 .The presence of weak peak at 2878 cm -1 -2878 cm -1 describes the -NH-in biuret moity may be ascribed in the terpolymeric chain 12,13 .The presence of methyl and methylene vibrations at 2950 cm -1 -2846 cm -1 gives sharp and weak peaks.The sharp band displayed at 1631 cm -1 -1628 cm -1 may be due to the stretching vibration of carbonyl group of both, ketonic as well as biuret moity 14 .The sharp and weak bond obtained at 1381 cm -1 -1380 cm -1 suggests the presence of -CH 2 -methylene bridges 15 in the terpolymer chain.The presence of 1, 2, 3, 4, 5 -pentasubstitution of aromatic ring is recognized from the weak bond appearing at 898 cm -1 -897 cm -1 respectively 15 .
Wavelength nm.On the basis of the nature and reactive position of the monomer elemental analysis, electronic, IR, NMR spectra and molecular weight, the most probable structures have been proposed for these terpolymers as shown in Figure 5.

Ion-exchange properties
The results of the batch equilibrium study carried out with the terpolymer samples 2, 4-DHBOF-I, 2, 4-DHBOF-II, 2, 4-DHBOF-III and 2, 4-DHBOF-IV are presented in Tables 5 -7.From the study with eight metal ions under limited variation of experimental conditions, certain generalization may be made about the behavior of the terpolymer sample.

Effect of Electrolytes on Metal Uptake
We examine the effect of NO - 3 , Cl -, ClO - 4 and SO 4 -2 at various concentrations on the equilibrium of metal-resin interaction.Table 5 shows that the amount of metal ions taken up by a given amount of terpolymer depends on the nature and concentration of the electrolyte present in the solution.In the presence of nitrate, chloride and perclorate ions the uptake of Fe +3 , Cu +2 , Hg +2 , Cd +2 , Co +2 , Zn +2 , Ni +2 and Pb +2 ions increasing with increasing concentration of electrolytes.However in the presence of sulphate ions the uptake capacity decreases with increasing concentration.Moreover the uptake of Fe +3 , Cd +2 , Co +2 ions increases with increasing concentration of nitrate, chloride and perclorate ions [16][17][18] as compare to Cu +2 , Hg +2 , Zn +2 , Ni +2 and Pb +2 ions whereas decreases in presence of sulphate ions.Above nitrate, chloride and perclorate ions form weak complex with the above metal ions while sulphate ions form stronger complex thus the equilibrium is affected This may be explained on the basis of the stability constants of the complexes with those metal ions [16][17][18] .This type of trends has been observed by the other investigator in this field.

Rate of metal Ion uptake
The rate of metal adsorption was determined to find out the shortest period of time for which equilibrium could be carried out while operating as close to equilibrium condition as possible.Table 6 show the dependence of the rate of metal ion uptake on the nature of the metal.The rate refers to the change in the concentration of metal ions in the aqueous solution, which is in contact with the given polymer.The results showed that the time taken for the uptake of the different metal ions at a given stage depends on the nature of the metal ion under given conditions.

Conclusion 1)
The 2,4-DHBOF terpolymer based on the condensation polymerization of 2,4dihydroxybenzaldehyde and oxamide with formaldehyde in the presence of acid catalyst has been prepared.

Table 5 .
Evaluation of the effect of different electrolytes on the uptake of several metal ions a by 2,4-DHBOF-I terpolymers resins.