New copper(II) benzothiazolylformazane complexes were synthesized and immobilized on AN-18 anion exchanger. The influence of the composition of the coordination core of copper(II) benzthiazolylformazanates and temperature on their catalytic properties in decomposition of H2O2 and oxidation of Na2S in aqueous solution was studied

Gorbatenko, Y. A.

Lipunov, I. N.

Lipunova, G. N.

Maslakova, T. I.

Pervova, I. G.

Sigeikin, G. I.

Russian Journal of Applied Chemistry

English

Electronic archive of the Ural State Forest Engineering University

1070-4272/05/7806-0936   2005 Pleiades Publishing, Inc.Russian Journal of Applied Chemistry, Vol. 78, No. 6, 2005, pp. 936 939. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005,pp. 957 961.Original Russian Text Copyright   2005 by Gorbatenko, Pervova, Lipunova, Maslakova, Lipunov, Sigeikin.CATALYSIS                                                                       Synthesis and Catalytic Properties of Copper(II)1-Aryl-5-BenzothiazolylformazanatesYu. A. Gorbatenko, I. G. Pervova, G. N. Lipunova, T. I. Maslakova,I. N. Lipunov, and G. I. SigeikinUral State Forestry Engineering University, Yekaterinburg, RussiaUral State Technical University, Yekaterinburg, RussiaInterdepartmental Center for Analytical Investigations in Physics, Chemistry, and Biology,Presidium of the Russian Academy of Sciences, Moscow, RussiaReceived April 2, 2004; in final form, December 2004Abstract New copper(II) benzothiazolylformazane complexes were synthesized and immobilized on AN-18anion exchanger. The influence of the composition of the coordination core of copper(II) benzthiazolyl-formazanates and temperature on their catalytic properties in decomposition of H2O2 and oxidation ofNa2S in aqueous solution was studied.Development of heterogenized catalysts with a highconcentration of active centers of known composi-tion is an efficient way to obtain stable catalysts witha good reproducibility and high activity. The composi-tion of active centers of such catalysts is similar tothat of active centers of homogeneous catalysts; how-ever, the active centers themselves are chemicallybound with one or more ligands fixed on an insolublesupport. Such complex catalysts combine properties ofboth homogeneous complexes (possibility of varyingthe type of the central atom and its ligand environ-ment) and heterogeneous systems (formation of co-ordination-saturated structures on the support surface[1]). Ion exchangers of various types are widely usedas solid supports. Their modification with functionalcomplexing groups allows synthesis of new catalysts[2].Anion exchangers with hetarylformazane groupshave been prepared previously [3, 4], and it wasshown that the formazan structure and the synthesisprocedure substantially affect the catalytic activity ofmetal formazan complexes in decomposition of H2O2in aqueous solutions and liquid-phase oxidation ofNa2S.In this study, we prepared certain copper(II) ben-zothiazolylformazanates and examined their composi-tion and catalytic properties at various temperatures inthe same reactions.EXPERIMENTALTo synthesize copper(II) complexes to be im-mobilized on the polymeric support, we used 1-aryl-3-alkyl-5-benzothiazolylformazans I III:R3 N=NC=NNH  R1R2 SN1 2 3 4 5where R1, R2, R3 are CH3, H, 4-SO3H (I); CH2Br,H, H (II); and CH2Br, OH, 4-NO2 (III), respectively.It is known [5] that hetarylformazans are ratherlabile polydentate ligands and can form metal com-plexes of various compositions and structures depend-ing on the substituent in 1-, 3-, and 5-positions.First, the complexation of compounds I III withcopper(II) acetate in solution was studied by spec-trophotometric titration. This method allows directmonitoring of the complexation process and calcula-tion of the stoichiometry of the complexes formed[6, 7].The clearest spectral pattern is observed with form-azan I. In the course of titration of the ethanolic solu-tion of this compound (cI = 3  105 M) with a cop-per(II) acetate aqueous solution (cCuAc2 = 103 M),the intensity of the absorption band of the initialformazan (max = 430 nm) gradually decreases, andRUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 6 2005SYNTHESIS AND PROPERTIES COPPER(II) 1-ARYL-5-BENZOTHIAZOLYLFORMAZANATES 937that of the band at max = 640 nm grows (Fig. 1).The spectral curves intersect at two isobestic points oftitration, which indicates formation of two complexes.The complex with L : M = 2 : 1, showing a broadenedband at 47 0 500 nm, and 1 : 1 complex with max =640 nm are formed when the copper(II) salt is indeficiency and excess, respectively.Titration of formazan II with copper(II) acetatesolution is also accompanied by a decrease in the in-tensity of the band of the initial compound (max =370 nm) and by appearance of a weak band at 610 nm.Only one isobestic point is observed in the titrationcurves, which corresponds to formation of the CuLcomplex. In the case of formazan III, the spectralpattern for titration with the copper(II) salt is morecomplex and cannot be interpreted unambiguously.Based on the spectrophotometric titration data, wesynthesized crystalline complexes of copper(II) withformazan I at L : M ratio of 1 : 1 and 2 : 1 complexesIV and V, with formazan II, at L : M = 1 : 1 com-plex VI, and with formazan III, at L : M = 1 : 1 and2 : 1 complexes VII and VIII (Table 1).Copper(II) formazanates IV VIII were preparedby the following general procedure. To a solutionof 0.15 mmol (or 0.30 mmol) of formazan in a min-imal amount of ethanol (or aqueous ethanol for form-azane I), a solution of 0.15 mmol of copper(II) sulfatein the minimal amount of water was added at 40Cwith stirring, and the mixture was left for 1 h. The pre-cipitate thus formed was filtered off, washed withwater, and dried.It follows from the elemental analysis that comp-lexes IV, VI, and VII have the composition CuL,and V and VIII, CuL2 (Table 1). All the compoundsare crystal solvates with ethanol. The electronic ab-sorption spectra of complexes IV VIII in ethanol areFig. 1. Electronic absorption spectra of formazan I inethanol in titration with aqueous solution of copper(II)acetate. cI = 3  105 M, cCuAc2 = 103 M, () Wave-length; (A) transmittance.similar to the spectra of Cu(II) formazanates obtainedin titration of formazans I III.The ESR spectra of copper(II) formazanates in tol-uene [8] suggest formation of a Cu4N distortedtetrahedron for V, Cu4N square-planar structure forVIII, and mixed nitrogen oxygen Cu3N, O struc-ture for VII.Our and published (for similar ligands [5]) datasuggest structure A for copper(II) formazanates V andVIII:	NS CNNCuN  R2R3NA R1Table 1. Characteristics of copper(II) formazanates IVVIII  mp,max, Found, %   Calculated, %        C  nm  C  H  N  Cu Empirical formula  C  H  N  Cu       (S)      (S) IV I  1 : 1 >250 640  40.0  4.0  13.8  11.5 C15H12N5S2O3Cu 2C2H5OH  40.0  4.5  13.2  12.0    430   (12.5)    (12.1)V I  2 : 1  235 640  44.8  3.8  15.9  7.6 C30H24N10S4O6Cu 2C2H5OH  45.2  4.0  15.6  7.0      (14.4)    (14.2)VI II  1 : 1 >250 610  41.3  2.9  (6.9) 13.8 C15H11N5SBrCu  41.2  2.5  (7.3) 14.6VII III  1 : 1 >250 470  37.3  3.1  15.3  11.7 C15H9N6SBrO3Cu C2H5OH  37.6  2.8  15.5  11.7    640    (6.0)     (5.8)VIII III  2 : 1  240 470  40.0  3.0  16.0  5.4 C30H20N12S2Br2O6Cu 3C2H5OH  40.4  3.5  15.7  5.9    640    (5.9)     (6.0)RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 6 2005938 GORBATENKO et al.Fig. 2. Kinetic curves of decomposition of 1% H2O2 aque-ous solution in the presence of copper(II) formazanates.T = 20C, V= 27 ml, and cCu = 0.01 M. (VO2) oxy-gen volume and () reaction time. Compound: (1) VIII,(2) VII, (3) VIIIp, and (4) VIIp; the same for Fig. 3.Fig. 3. Temperature (T ) dependence of the rate constant ofH2O2 decomposition (1% aqueous solution) in the presenceof copper(II) formazanates.The structure of complexes IV and VI, correspond-ing to the composition L : M = 1 : 1, is probablyformed by additional coordination of CuSO4 to nitro-gen atoms of the benzothiazole fragment.For complex VII, the structure B is the most prob-able:S NCH2BrNCuONNO2N NBTo obtain metal complexes suitable for heteroge-neous catalysis, we immobilized formazanates IV VIII on AN-18 styrene-divinybenzene anion exchang-er. The presence in its structure of primary and sec-ondary amino groups allowed immobilization of form-azanates IV and V containing sulfonate group in theligand by ion exchange and of complexes VI VIIIcontaining labile bromine by covalent bonding.Immobilization of Cu(II) formazanates was per-formed as follows. To a solution of IV in ethanol,a sample of AN-18 anion exchanger was added sothat the copper ion concentration in the polymer was0.01 mmol g1, and the mixture was stirred to com-plete decolorization of the solution. The modifiedanion exchanger was filtered off, washed with ethanol,and dried in air. In such a way, formazanate IVpwas prepared. Similarly, formazanates V VIII wereimmobilized to obtain catalysts Vp VIIIp, whichexhibit a high activity and can be easily separatedfrom the reaction products.The ESR data show the square-planar structure ofthe coordination core Cu4N for formazanate VIIIpand Cu3N, O for VIIp, similarly to the initial com-plexes VIII and VII [8, 9]. Presumably, immobiliza-tion of formazanates IV VI on the polymeric supportdoes not change the structure of the coordination core.The catalytic properties of copper(II) formazanatesIV VIII and IVp VIIIp were studied in the modelreaction of H2O2 decomposition (1% aqueous solu-tion). It is known [4] that complexes containing nomore than 0.01 mmol of Cu(II) per gram of the poly-meric matrix have the highest catalytic activity. There-fore, we studied the catalytic activity of IV VIII andIVp VIIIp under the similar conditions as follows.A sample of copper(II) formazanate [([0.1 g for IVp VIIIp and 0.0028 0.0061 g for IV VIII) was addedto 27 ml of 1% H2O2 aqueous solution. The reactioncurse was monitored by the volume of liberated oxy-gen at 20, 40, and 60C.The kinetic curves of H2O2 decomposition at 20Cfor VII, VIIp, VIII, and VIIIp are shown in Fig. 2.Formazanates VII and VIII exhibit a high catalyticactivity in H2O2 decomposition, which is probablycaused by the square-planar structure of the metalchelate core. Copper(II) formazanates immobilized onthe anion exchanger (VIIp and VIIIp) behave similar-ly. It should be noted that the related metal complexsystems studied in [3, 4] show lower rate constantsof H2O2 decomposition under the same conditions(0.12 11.78  104 mmol1 s1).Proceeding with the previous studies [3, 4], we ex-amined the H2O2 decomposition in the presence ofcopper(II) formazanates at 40 and 60C. The kineticdata obtained were used to calculate the rate constantsof H2O2 decomposition [10] (Table 2).The temperature dependences of the rate constantsof H2O2 decomposition for complexes VII, VIIp,VIII, and VIIIp, as examples, are shown in Fig. 3.RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 78 No. 6 2005SYNTHESIS AND PROPERTIES COPPER(II) 1-ARYL-5-BENZOTHIAZOLYLFORMAZANATES 939Table 2. Catalytic activity of copper(II) formazanatesin decomposition of 1% H2O2 aqueous solution and liquid-phase oxidation of 0.03% Na2S solution at various tem-peraturesCom- k  104, mmol1 s1  Degree ofpound  conversion S2, %no. at indicated temperature, C 20  40  60  20  40  60IV  46.8  89.9  203.6      IVp  0.7  2.6  11.2  31.2  64.0  71.3V  57.5  95.1  219.0      Vp  1.2  5.6  17.3  34.1  64.9  74.1VI  42.4  71.3  162.4      VIp  2.9  8.3  20.4  59.9  62.8  67.1VII  82.3  114.8  212.0      VIIp  16.1  23.7  51.3  32.7  54.3  74.7VIII  86.5  133.6  254.6      VIIIp  17.8  27.1  58.5  38.3  58.3  73.5As can be seen from Fig. 3 and Table 2, the de-composition rate increases with temperature. For cop-per(II) formazanates IVp VIIIp, the rate constants arelower than those for IV VIII. Probably, this is causedby partial solubility of the free complexes, whichincreases with the temperature of the reaction mixture,thereby making the reaction conditions similar thosein homogeneous catalysis.In spite of the relatively low catalytic activity ofIVp VIIIp as compared to their crystalline analoguesIV VIII, they can be successfully used in heteroge-neous catalysis, since their composition and the struc-ture of the coordination core, and hence the catalyticproperties, do not change in repeated use [11].The liquid-phase Na2S oxidation with molecularoxygen and calculation of the degree of catalytic con-version S2  SO42 were performed by the methoddescribed in [11]. The use of IV VIII as oxidationcatalysts was unsuccessful because of their solubilityin the reaction mixture. The catalytic activity of form-azanates IVp VIIIp in liquid-phase Na2S oxidationis virtually independent of the composition and struc-ture of the complexes (this is characteristic of the pre-viously studied benzothiazolylformazanates [3, 4])and slightly changes with the reaction temperature(Table 2).CONCLUSIONS(1) Complexation of 1-aryl-5-benzothiazolylform-azans with copper(II) was studied by spectrophotom-etric titration, and the stoichiometry of complexesformed was calculated.(2) It was found that the coordination core hasthe Cu4N or Cu3N, O structure. The crystallinecopper(II) complexes synthesized were immobilizedon a AN-18 solid support.(3) The catalytic activity of immobilized copper(II)formazanates was studied in comparison with the ini-tial analogues. The complexes with the square-planarcopper environment show the highest activity.ACKNOWLEDGMENTSThe study was financially supported by the RussianFoundation for Basic Research (projects nos. 02-03-96 424-r2002 Ural and 03-03-32 044).REFERENCES1. Boreskov, G.K., Geterogennyi kataliz (HeterogeneousCatalysis), Moscow: Nauka, 1988.2. Pomogailo, A.D., Polimernye immobilizovannye me-tallokompleksnye katalizatory (Polymeric ImmobilizedMetal Complex Catalysts), Moscow: Nauka, 1988.3. Lipunov, I.N., Pervova, I.G., Lipunova, G.N., et al.,Koord. Khim., 1997, vol. 23, no. 12, pp. 934937.4. Pervova, I.G., Lipunova, G.N., Yushkova, O.G., et al.,Sorb. Khromatogr. Prots., 2002, vol. 2, nos. 56,pp. 609615.5. Buzykin, B.I., Lipunova, G.N., Sysoeva, L.P., andRusinova, L.I., Khimiya formazanov (Chemistry ofFormazans), Moscow: Nauka, 1992.6. Shlefer, G.L., Kompleksoobrazovanie v rastvorakh(Complexation in Solutions) Leningrad: Khimiya,1964.7. Babko, A.K. and Pilipenko, A.T., Fotometricheskiianaliz (Photometric Analysis), Leningrad: Khimiya,1968.8. Vishnevskaya, G.P., Frolova, E.N., Pervova, I.G.,et al., Strukt. Dinam. Mol. Sist., 2003, no. 10, part 3,pp. 190195.9. Molochnikov, L.S., Gorbatenko, Yu.A., Vishnev-skaya, G.P., et al., Abstracts of Papers, XVII Mendele-evskii s’ezd po obshchei i prikladnoi khimii (XVIIMendeleev Conf. on General and Applied Chemistry),Kazan, 2003, vol. 4, p. 439.10. Kopylova, V.D., Frumkina, E.L., Mochalova, L.D.,et al., Kinet. Katal., 1978, vol. 19, no. 15,pp. 13561370.11. Astanina, A.N., Fung, T.Sh., Kopylova, V.D., et al.,Available from VINITI, July 5, 1983, no. 3676.Vestn. Mosk. Univ., Ser. Khim., 1984, vol. 25,pp. 8588.

Synthesis and catalytic properties of copper(II) 1-aryl-5-benzothiazolylformazanates

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Synthesis and catalytic properties of copper(II) 1-aryl-5-benzothiazolylformazanates

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