Bizony, N. M.

Császár, József

English

Császár József

Bizony N. M.

University of Szeged

SPECTROSCOPIC STUDY OF SECONDARY AMINES AND THEIR COPPER(II) COMPLEXES By J. CSÁSZÁR and N. M. BIZONY (Institute of General and Physical Chemistry, Attila József University, Szeged, Hungary) The u.v. spectra and the complex-forming behaviour of secondary amines produced in the reduction of Schiff bases were studied. The changes observed in the spectra of the copper(II) comple-xes in pyridine solution can be interpreted in terms of the transformation [Cu(amine)(acetate)]2 -<-Cu(amine) (acetate) (py). Similarly to the corresponding Schiff base, the secondary amines of N-aryl-hydroxybenzylamine type are potentially bidentate chelating agents. Many authors discuss the reduction of aromatic Schiff bases by different methods [e.g. 1—4] and two earlier papers [5, 6] describe the preparation and spectral investigation of several secondary amines of N-aryl-o-hydroxybenzylamine and N,N'-polymethylene-o-hydroxybenzylamine type. These amines gave rise to mixed chelates of the type Cu(amine)(acetate), where amine represents the phenolate anion of the amine. We report here the synthesis and spectral properties of a series of 4-X-aniline (I) and pyridine (II) derivatives and of their copper(II) complexes. Reduction of Schiff bases to amines (I and II) was achieved using sodium borohydride in anhydrous methanol [3]. After the initial reaction the mixture was refluxed for ten minutes. The amines were liberated on addition of water; the crude products were recrystallized from water-ethanol 1:1. The analytical data and the melting points are listed in Table I. The copper(II) chelates were prepared by mixing the amine solutions in methanol with a warm aqueous solution of copper(II) acetate in 1:1 molar ratio. The dark-green crystals were recrystallized from chloroform; the composition was checked by Cu' and C analysis. (Received 20tb November, 1984) I il Experimental 7 3 0 J. CSÂSZÂR and N. M. BIZONY Table 1 Analytical data on several secondary amines studied X M.p.» C % H % Calcd. Found Calcd. Found NfCjHili 68.7 75.52 75.48 8.20 8.16 N(CH3)2 95.5 74.35 74.29 7.49 7.41 3,4-(OCH3)a 116.7 69.48 69.41 6.61 6.57 3,4,5-(OCHs)a 119.7 66.42 66.34 6.62 6.60 OC2H5 98.5 74.05 74.00 7.04 7.06 COCH3 145.2 -79.22 79.19 6.33 6.27 NHCOCH3 163:7 70.29 70.22 6.29 6.21 2-NHj-py** 107.2 71.98 71.90 6.04 6.00 2-NH2-3-CH3-py • . - - 101.6 - 72.87 72.81 6.59 6.50 2-NH2-4-CH3-py 144.9 72.78 6.54 2-NH2-5-CH3-py 134.0 72.85 6.49 2-NH2-6-CH3-py 95.6 72.85 6.56 * Uncorrected values; ** py=pyridine. The u.v. and visible spectra were measured at 298 K on a SPECORD UV VIS spectrophotometer in spectroscopically pure solvent, using quartz cells. The transformation in pyridine was followed spectrophotometrically at 298 K, using 1 cm quartz cells. The first-order rate constants were calculated from the E —En measured Et and extrapolated E0 and Em values, via the formula kt=\og —¡^—. Results U.v. spectra of amines. The u.v. spectral data on the aniline and pyridine deriva-tives are given in Tables II and III, respectively. The data in Table II, together with the earlier observations [3], show that these compounds may be characterized by two main bands, in the ranges 200—220 and 240—260 nm, respectively. These bands can probably be assigned to n* — 7i transitions. In 0.1 mol/dm3 acidic solution the positions and intensities of the first bands remain almost unchanged, but the second band shifts toward longer wavelength (270—280 nm) and the intensity decreases. This longer-wavelength band is characteristic of the protonated form of the amines. In alkaline solution (0.1 mol/dm3 NaOH) the spectra also contain two bands, at 240—260 and 290—300 nm; this spectral structure is characteristic of the ionized form resulting from the action of NaOH. The spectra of methylpyridine derivatives are more complicated (Table III, Fig. 1). In methanol, four bands can be measured in the ranges 200—205, 245—250, 275—285 and 300—320 nm, respectively. Variation in the position of the methyl substituent does not alter the spectral character significantly. In contrast with the former group, the spectra of pyridine derivatives show no significant change in acidic or in basic media. SPECTROSCOPIC STUDY OF SECONDARY AMINES .731 Table II U.v. spectral data on aniline derivatives measured in different media X Solvent nm and log e N(C2H5)2 MeOH 203(4.56) ~225 260(4.18) N(CH3)2 203(4.56) ~220 259(4.25) 317(2.73) 3,4-(OCH3)2 208(4.58) 247(4.03) ~275 ~305 3,4,5-(OCH3)3 215(4.67) 252(4.15) ~277 OC2H6 203(4.58) 243(4.18) ~275 310(3.43) COCH3 202(4.45) ~220 ~240 331(4.41) NHCOCH3 203(4.53) ~220 270(4.26) N(C2H6)2 Acid 202(4.46) 279(3.49) N(CH3)2 203(4.47) ~225 278(3.39) 3,4-(OCH3)2 206(4.65) ~238 280(3.93) 3,4,5-(OCH3)3 210(4.70) ~230 277(3.51) OC2Hs 202(4.54) 227(4.30) 277(3.61) COCH3 203(4.52) ~220 278(3.62) NHCOÇH3 203(4.57) 247(4.33) ~278 N(C2H6)2 Base 246(4.24) ~262 ~292 N(CH3)2 247(4.31) ~260 ~292 3,4-(OCH3)2 243(4.31) 295(3.82) 3,4,5-(OCH3)3 244(4.32) 293(3.87) OC2H6 243(4.37) 294(3.79) COCH3 239(4.14) ~290 338(4.45) NHCOCHs 244(4.13) 271(4.26) Table III U.v. spectral data on pyridine derivatives measured in different media X Solvent nm and log e 2-NH, -py MeOH 201(4.32) ~226 246(4.12) 280(3.33) 308(3.34) 2-NHj -3-CH3-py 202(4.44) ~227 245(4.15) 281(3.49) 305(3.44) 2-NHs -4-CH3-py 204(4.48) 226(3.99) 249(4.21) 282(3.51) 306(3.42) 2-NH, -5-CH3-py 202(4.48) ~226 248(4.32) 279(3.47) 314(3.59) 2-NHs -6-CH3-py 202(4.37) 227(3.89) 248(4.07) 281(3.35) 310(3.41) 2-NHÜ -py Acid 202(4.38) ~22 5 241(4.16) 281(3.67) 313(3.81) 2-NHs -3-CH3-py 203(4.48) ~225 240(4.17) 281(3.78) 308(3.94) 2-NHs -4-CH3-py 207(4.54) 243(4.17) 284(3.81) 308(3.90) 2-NH2 -5-CH3-py 202(4.50) 244(4.35) 281(3.73) 320(3.98) 2-NHs -6-CH3-py 202(4.36) ~227 242(4.08) 282(3.48) 320(3.88) 2-NHs - p y Base 244(4.30) 296(3.76) 2-NH2 -3-CH3-py 244(4.37) 298(3.95) 2-NH2-4-CH3-py 247(4.39) 298(3.90) 2-NHj -5-CH3-py 246(4.49) 300(3.90) ~318 2-NH2 -6-CH3-py 244(4.29) 303(3.85) 7 3 2 I. CSÁSZÁR and N. M. BIZONY Fig. 1. Spectra of the 2-NHa-5-CH3 derivati-ve in 1: methanol; 2: in 0.1 mol/dm3 H2S04/CH30H; 3: in 0.1 mol/dm3 NaOH/CH3OH. c=4.06-10"4 mol/dm3; d= 0.1cm; T= 298 K Visible spectra of copper (II) complexes The complexes have the general formula Cu(amine)(acetate). The dark-green crystalline compounds are soluble in common organic solvents. Their visible spectra contain only one medium-intensity band (log 1.7—2.7) in the range 640—700 nm (Table IV). On analogy with literature suppositions, these compounds have a binu-clear structure [5, 7]. The abovementioned band is assigned to the dz!—dxs_ys Table IV Visible spectral and kinetic data on copper(II) complexes X nm and log e k• 104 (sec) in MeOH in g.a.a. in pyridine N(C2H6)2 585(2.64) 683(1.97) • N(CH3)a ~600 679(2.15) * OCHa 670(1.98) 694(2.29) 668(2.33) 8.25 OC2H6 666(2.05) 691(2.30) 679(2.27) 6.55 OC4H9 666(2.03) 694(2.30) 683(2.29) 6.70 CH3 680(2.00) 694(2.29) 687(2.20) 5.75 c2H6 682(1.98) 698(2.30) 687(2.21) 6.67 H 686(1.83) 691(2.29) 687(2.15) 4.98 Cl 692(1.74) 694(2.29) 687(2.09) 5.67 Br 700(1.60) 691(2.30) 676(2.13) 3.95 I ~705 691(2.29) 687(2.08) * * Very low soluble. SPECTROSCOPIC STUDY OF SECONDARY AMINES 733 transition; the intensity corresponds to that of the d—d band characteristic of ad9 system in a strong ligand field with low symmetry. The complex structure in the range 350—400 nm is assumed to be closely related to the weak copper-copper interaction [8, 9]. The data in Table IV reveal that the band positions change similarly as the HAMMETT a p constants. In glacial acetic acid the bands shift only slightly to the red, but the intensity increases considerably. The structures of the spectra of the complexes in pyridine and in methanolic solutions are similar. The single band appears in the vicinity of 650—670 nm (Table IV). Fig. 2. Spectral changes of complexes with X=A: OCH3; B: H'm pyridine. /=2 , 10, 20, 30, 40, 50, 60min. 7"=298K; ¿=1.0cm; c=2.5* 10~3 mol/dm3 In pyridine solution the band appears at 650—690 nm, and its absorbancy increases with time. The spectral changes of two complexes (X=OCH3, H) are presented in Fig. 2. From the change in the absorbancy it is possible to calculate the first-order rate constants (Table IV). The changes in k and the HAMMETT constants <jp show the same tendency. The rate constants k decrease with decrease in the electronreleasing effects and with increase in the electron-withdrawing effects of the p-X substituents. - We presume that the charge density on the copper atom increases in the dimer molecules as a result of the electronreleasing effect of X, one of the copper-O(acetate) bonds splits, and one pyridine molecule is bound in the coordination sphere. 734 J. CSÁSZÁR and N. M. BIZONY: SPECTROSCOPIC STUDY OF SECONDARY AMINES Л с Г Ж Л ( V * In this way a species of low microsymmetry is formed; the increase in absorbancy may be interpreted in terms of this change. This assumption was supported by the fact that no change can be observed in the presence of 2-picoline or 2,6-lutidine; the steric effect of the CH3 groups prevents bond formation between the copper atom and the basic nitrogen. Investigations of these problems are in progress. References [1] Beretka, J., В. O. West, M. J. O' Connor: Austr. J. Chem., 17,192 (1964). [2] Roe, A., J. A. Montgomery: J. Amer. Chem. Soc., 75,911 (1953). [3] Billman, J. H., A. C. Diesing: J. Org. Chem., 22,1068 (1957), and references therein. [4] Harries, H. J., B. F. Orford: Inorg. Chim. Acta, 68,41 (1983). [5] Császár, J.: Acta Phys. et Chem. Szeged, 29,139 (1983). [6] Császár, J.: Acta Phys. et Chem. Szeged, 30, 62 (1984). [7] Figgis, B. N.. R. L. Martin: J. Chem. Soc., 3837 (1956). [8] Yamada, S., H. Nakamura, R. Tsuchida: Bull. Chem. Soc. Japan, 31, 303 (1958). [9] van Niekerk, J. N.. F. R. L. Schoening: Acta Cryst., 6,227 (1953). СПЕКТРОСКОПИЧЕСКОЕ ИЗУЧЕНИЕ ВТОРИЧНЫХ АМИНОВ И ИХ КОМПЛЕКСОВ С МЕДЬЮ(П) Й. Часар u Н. М. Бивонъ Изучены УФ-спектры и комплексообразующие свойства вторичных аминов, получен-ных при восстановлении оснований Шиффа. Изменеия, наблюдаемые в спектрах комплексов меди(П) в пиридиновых растворах, могут быть объяснены переходом [Си(амин)(ацетат)2] [Си(амин)(ацетат)(пиридин)]. 

Spectroscopic study of secondary amines and their copper(II) complexes

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Spectroscopic study of secondary amines and their copper(II) complexes

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