Analytical characterization of some pyrazolones and their copolymers with some vinyl compounds

Talanra,

Vol. 37, No.

11, pp.

0039-9140/9083.00+ 0.00 Pergamon Press plc

1081-1085,1990

Printed in Great Britain

ANALYTICAL CHARACTERIZATION OF SOME PYRAZOLONES AND THEIR COPOLYMERS WITH SOME VINYL COMPOUNDS E. IVANOVA,0. TODOROVA,A. TEREBENINA and N. JORDANOV Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, BG-1040 Sofia, Bulgaria G. BORI~OV Central Laboratory of Polymers, Bulgarian Academy of Sciences, BG-1040 Sofia, Bulgaria (Received 25 May 1989. Revised 15 November 1989. Accepted 16 March 1990) Summary-Some new pyraxolones have been synthesized and their copolymers with styrene, methylmethacrylate and methacrylic acid prepared. The pyraxolones and their styrene and methylmethacrylate copolymers are insoluble in water but form chelate complexes with some alkaline-earth and transition metal ions. The water-soluble methacrylic acid copolymers do not form complexes with these elements, however, probably because of hydrogen-bonding of the chelating groups to the methacrylic acid carboxyl groups. Special attention was paid to the complexation of Au(III), which was assumed to proceed mainly through the nitrogen atoms of the pyrazolone ring.

Several pyrazolone reagents are known to act as extractants and sorbents with good complexation properties. ‘A They react with metal ions either through available chelating groups,z*3 or through the nitrogen atoms of the pyrazolone ring,5 providing selective or group complexation of metal ions, according to the conditions used. The polymerization of vinyl derivatives is widely used in the synthesis of ion-exchange resins, since it yields products of uniform structure and high capacity.6 Chelating sorbents, however, have rarely been prepared by this procedure, owing to difficulties in the preparation of the monomers and to the complex nature of the polymerization.4 The purpose of the present work was the analytical characterization of the reagents 3-methyl1-phenyl-4-crotonoylpyrazolone-5 (MPCP) and 3 - methyl - I- phenyl - 4- cinnamoylpyrazolone - 5 (MPCyP) and of their copolymers with styrene, methylmethacrylate and methacrylic acid. EXPERIMENTAL

The pyrazolones were synthesized according to Todorova et al.’ Their purity was checked by TLC on Merck GFZS4 silica gel plates, with iron(II1) chloride as developing agent. The purity and molecular weights of the polymeric products were determined by gel-permeation chromatography on a Waters apparatus

equipped with a WISP 712 automatic injector and either ultrastyragel columns with pore sizes of lo’, 104, lo3 and 500 A, or a linear ultrahydrogel column. The structural studies were performed on samples in KBr discs or in chloroform solution with a Bruker IFS 113V Fourier transform IR spectrometer. The polymer composition was determined by elemental analysis for nitrogen and titrimetric analysis for carboxylic groups. The analytical characterization of the products involved studies of the pH-dependence, capacity and kinetics of complexation with various metal ions. The metal ion solutions (1 mg/ml) were prepared from Merck “Titrisol” solutions. Dependence of the distribution coeficients on pH Extraction studies. A 5-ml portion of solution at fixed pH (adjusted with hydrochloric acid or a buffer solution) containing 10 pg of the analyte element and 1 ml of a 0.05% aqueous solution of the reagent were extracted with 5 ml of methyl isobutyl ketone (MIBK). The concentration of metal ion in the extract was determined by flame atomic-absorption spectrometry (AAS). The degree of extraction R was calculated from

1081

R=

1OOD D + K&g

E. IVANOVA er al.

1082

where D is the distribution coefficient of the metal ion and I/orpand Vagare the volumes of the organic and aqueous phases, respectively. Sorption studies. A lo-mg portion of the sorbent was stirred with 10 ml of an aqueous solution (at fixed pH) containing 50 pg of the analyte element, until equilibrium was reached. The concentration of metal ion (Me) left in solution was determined by flame AAS. The distribution coefficient D was calculated from amount of Me on the sorbent D= amount of Me in solution ml of solution ’ g of dry sorbent Sorption capacity

The capacity was determined under the optimum sorption conditions by stirring 10 mg of the sorbent with a solution containing 1 mg of the metal ion until equilibrium was reached, and determining the residual concentration of metal ion in solution by flame AAS. RESULTS

AND DISCUSSION

Characterization of the monomeric andpolymeric products

The reaction of 3-methyl-l-phenylpyrazolone5 with crotonic and cinnamic acid chlorides yielded the compounds MPCP (1) and MPCyP (2) containing a chelating group of fl-diketonate type. The copolymerization of MPCP and MPCyP with styrene (St), methylmethacrylate (MMA) or methacrylic acid (MAA) yielded products (3)-(8). The structures are shown in Scheme 1. In the infrared spectra of the copolymers, the vibrational bands characteristic for the pyrazolone ring (1552-1484 cm-‘) were preserved, which indicates that the polymerization proceeded through the double bond of the acyl residue of the monomers (1) and (2), without of the pyrazolone ring. The breakage vibrational bands of the carbonyl group (16001736 cm-‘) were also present in the spectra of the copolymers, which signified that the /?-diketonate chelating groups were preserved. As a result, the copolymers should exhibit complexation behaviour analogous to that of the monomeric pyrazolones. The pyrazolone content and weight average molecular weights of the copolymers are presented in Table 1. Clearly, the type of vinyl monomer strongly affects both characteristics.

Table 1. Charactersitics of the copolymers

Copolymer

Pyrazolone, %

MPCP-St (3) MPCP-MMA (4) MPCP-MAA (5) MPCyP-St (6) MPCyP-MMA (7) MPCyP-MAA (8)

34.4 10.5 19.7 42.2 11.2 50.3

Weight average molecular weight 3.6 x 3.8 x 6.5 x 2.8 x 1.5 x 5.7 x

104 104 104 lo4 104 104

The products (3), (5), (6) and (8) were obtained in powdered form, (5) and (8) being water-soluble owing to the free carboxylic groups. Products (4) and (7) were obtained in film form. The solids did not swell noticeably in water. Extraction properties

The extraction curves are shown in Fig. 1. Only the monomeric pyrazolones extracted all the metal ions examined. The polymers extracted only Au(II1) to a significant extent. The crotonoyl derivative (MPCP) was more efficient than the cinnamoyl one, and its extraction efficiency was comparable to that of 1-phenyl-3methyl-4-benzoylpyrazolone-5 (PMBP), which is the most widely used pyrazolone,‘s* forming chelate complexes of /?-diketonate type with the elements examined. Like PMBP, MPCP gives >95% extraction, but over a narrower pH range. This can be attributed to the MPCP complexes being less stable than those with PMBP, as a result of which hydrolysis prevails over complexation at higher pH values. The lack of extraction by products (5) and (8) can be attributed to blockage of the chelating groups by the free carboxylic groups of MAA, through intramolecular hydrogen bonding. The broad and intense band at 2500-3700 cm-’ (characteristic of hydrogen bonding) in the infra-

1

Fig. 1. Extraction curves for use of the pyrazolones MPCP (l), MPCyP (2) and the water-soluble copolymers MPCP-MAA (5) and MPCyP-MAA (8).

Analytical

W

W

CHs

I

I

i-I-fi-“‘CH

“\

1083

of some pyrazolones

char~tion

‘31

I

I

li’-fi-h-CH=CH

“\

/‘\,H” i

r\oHo ‘i CIHI

G.Hs MPCP (1)

MPCyP (2)

Cd&

-FH

WI

“i To 1-i “\T-OH

MPCP-st

I

-CH--f

Hai To 1-1 “\/c-OH

MPCyP-St

I

I I

I

H’ii=”

(6)

GHa

CHs

-f-,--C--);;

-f-CH--C+

I WI

I

(3)

CHs

+CH-C&J;;

+CH-

I

I

CHqm

-f-CH,-C--);;

“i i=”

COOCHl

c-c

CH3 I I COOCHs

II II “\ /c-OH

MPCP-MMA

(4)

MPCyP-MMA

CHs

f

I ---Ct+

CH

I

CH,

f

GA

CH,

I I tCH--CH+,,l f-W--C--);; I I COOH H’i To

I W--c--);; I

bOOH

MPCP-MAA

(7)

(5)

MPCyP-MAA Scheme

1

(8)

E.

1084

IVANOVA et al.

red spectra of these products supports this assumption. The extraction of Au(II1) (see Fig. l), is assumed to take place by another mechanism. It is known that pyrazolones readily react with Au(II1) not through the /I-diketonate groups, but through the nitrogen atoms of the pyrazolone ring.5g8On the other hand, Au(II1) is extracted from hydrochloric acid medium by organic oxygen-containing solvents (S), e.g., MIBK, I. . . I. * . . I. . . as the solvated ion-pair H +[(H, O),S, AuCl,] - .9 1357P 13 5 7 013 5 7 The greater extraction of Au(II1) by the two Fig. 2. Sorption curves for use of the solid copolymers. The pyrazolones can be attributed to the co-ordinacurves are representative for all these reagents. tion of these reagents through the nitrogen atoms of the pyrazolone ring to Au(II1) by calculated on the basis of a stoichiometric reacsubstitution for water molecules in the solvated tion between the sorbent and the metal ion, and complex anion. The polymeric reagents (5) and the content of pyrazolone in the sorbent. (8) were also co-ordinated to Au(II1) (a colour The capacity found was higher than expected, change in the aqueous phase was observed), but and this is attributed to non-stoichiometric their limited solubility in both the acid and the interaction, probably by sorption of metal ions organic phase caused the appearance of a third at non-chelating active sites. Partial reduction of phase, which contained some of the extracted Au(II1) to Au(I) on the sorbent is also possible. species (the presence of Au in the third phase The powdered sorbents had a higher capacity was proved qualitatively). The solubility of the than the film sorbents. This could be attributed two pyrazolones and the polymeric reagents and both to the lower content of pyrazolone comof the corresponding complexes was lower in ponent in the MMA-based copolymers (c$ o-xylene than in MIBK, and a third phase Table 1) and to the lower accessibility of the containing the Au(II1) complexes was formed in functional groups in the dense structure of these all four cases. This would be in accord with the copolymers. This will only affect the completefact that o-xylene would be unable to solvate the ness of sorption at high concentrations. AuCl; anion in the same way as MIBK. The kinetic studies also showed a difference between the powdered and film sorbents: contact for 3-5 min was sufficient for equilibrium to Sorption properties of the solid copolymers be reached with the powdered sorbents, whereas The dependences of the sorption efficiency on for the film sorbents equilibration required 2-3 pH are shown in Fig. 2. Most of the elements times longer contact. tested were quantitatively sorbed from neutral or slightly alkaline medium. Pd(I1) was insignifiComplexation behaviour of the pyrazolones and cantly sorbed over the whole range examined. the copolymers Au(II1) was quantitatively sorbed between pH 3 Comparison of Figs. 1 and 2 reveals that the and 7. properties of the pyrazolone The sorption efficiency of the copolymers was complexation the same irrespective of the type of vinyl com- monomers are preserved in the solid copolymers, but not in the water-soluble copolymers. pound and of the form of the sorbent (powder The difference between reagents (1) and (2) is or film). The sorption capacity of the sorbents was a methyl (1) or phenyl (2) group in the sidechain of the molecule. These substituents affect determined for Au(II1) and Mg. The expected and experimentally determined values are pre- the chelation properties of the pyrazolones but sented in Table 2. The expected values were have no effect on the properties of the solid s

I

I

Table 2. Sorption capacity, MPCP-St Species Au Mg

MPCP-MMA

meq/g

MPCyP-St

MPCyP-MMA

Expected

Found

Expected

Found

Expected

Found

Expected

Found

0.5 0.7

1.0 7.3

0.1 0.2

0.03 1.2

0.5 0.7

0.4 6.7

0.1 0.2

0.02 0.4

Analytical characterization

copolymers. This may be attributed to delocalization of the electron density over the network of the solid copolymers. The same applies to the complexation with Au(II1) taking place through the nitrogen atoms of the pyrazolone ring. The difference in the extraction and sorption behaviour of the reagents towards Au(II1) in the acidic range may also be related to the lower electron density of the pyrazolone rings in the structure of the solid copolymer. The increase in the degree of sorption of Au(II1) in the pH range 3-7 correlates with the deprotonation of the /I-diketonate groups in this pH range, which leads to an increase in the electron density of the pyrazolone ring and thus to an increase in the basicity of the nitrogen atoms. At pH > 7 partial hydrolysis of Au(II1) takes place. CONCLUSIONS

The reagents 3-methyl-l -phenyl4-crotonoylpyrazolone-5 and 3-methyl- 1-phenyl4-cinnamoylpyrazolone-5 react with some transition elements, lead and palladium through chelating groups of /I-diketonate type and extract these elements from neutral or slightly alkaline medium. Selective extraction of gold takes place in acidic medium, through co-ordination with the nitrogen atoms of the pyrazolone ring.

of some pyrazolones

1085

The complexation properties of the pyrazolones and their solid copolymers with styrene and methylmethacrylate are analogous. These copolymers may be used for the simultaneous preconcentration of alkaline-earth and transition metals, lead and gold from neutral medium. The chelating groups of the initial reagents are also preserved in the water-soluble methacrylic acid copolymers, but are blocked by hydrogen bonding to the carboxylic groups of the acid. REFERENCTS 1. E. Ivanova, N. Jordanov, A. Terebenina, S. Mareva and G. Borisov, Comm. Dept. Chem. Bulg. Acad. Sci., 1981, 14, 167. 2. Yu. A. Zolotov and N. M. Kuz’min, Ekstraktsiya metallov atsylpyrazolonami, Nauka, Moscow, 1971. 3. 0. Todorova, E. Ivanova, A. Terebenina, N. Jordanov, K. Dimitrova and G. Borisov, Talanta, 1989, 36, 817. 4. G. V. Myasoedova and S. B. Sawin, Kbelatoobrazuyuchie sorbenty, Nauka, Moscow, 1984. 5. V. S. Soldatov, S. B. Makarova, A. L. Braulavskaya, L. V. Novizkaya and V. N. Avilina, Khim. Promysl., 1978, 8, 584. 6. K. M. Saldadze and V. D. Kopylova-Valova, Komplexoobrazuyuchie ionity, Khimiya, Moscow, 1980.

7. 0. Todorova, A. Terebenina, I. Gizov, G. Mitov and G. Borisov, J. Polym. Sci., Polym. Chem. Ed., in the press. 9. S. Trofimenko, Chem. Rev. 1972, 72,497. 10. N. Jordanov and I. Havezov, Z. Anal. Chem., 1969,244, 176.