Solid-Phase Synthesis of Iron(III) Acetylacetonate

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the yield of the products of this process were studied ... The IR spectra of the starting reagents, reaction mixtures, and products were recorded on an UR-20.
Russian Journal o f Inorganic Chemistry, Vol. 45, No. 3, 2000, pp. 328 -3 3 1 . Translated fro m Zhurnal N eorganicheskoi Khimii, Vol. 45, No. 3, 2000, pp. 390 -3 9 4 . O riginal Russian Text C opyright © 2000 by Petrova. Borisov, Aleshin, Makhaev. English Translation C opyright © 2000 by M A IK “ N a uka/lnterperiod ica " (Russia).

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Solid-Phase Synthesis of Iron(III) Acetylacetonate upon Mechanical Activation L. A. Petrova, A. P. Borisov, V. V. Aleshin, and V. D. Makhaev Institute o f N e w C h em ica l P roblem s, R ussian A c a d e m y o f Sciences, p /o C h em o g o lo vk a , N og in sk ii raion, M o sco w o b la st, 142432 R u ssia Received February 26, 1999 A b str a c t— The solid -p h ase interaction o f iron(III) chloride and sodium acetylacetonate with form ation o f iron(III) acetylacetonate and sodium chloride in the course o f m echanical treatment in a vibratory ball m ill w as studied. T his interaction proceeded w ith the interm ediate form ation o f an activated m ixture, w hich, being heated or m ech an ically activated for a longer tim e, gave the reaction products. The effects o f the m echanical treatm ent con d ition s on the process, on the yield o f iron(III) acetylacetonate, and som e properties o f the acti­ vated m ixtures w ere studied. T he y ield o f iron(III) acetylacetonate reaches -8 0 % under optim al con d ition s. A fter a prelim inary m echanical activation o f a reaction m ixture, the syn th esis o f iron(III) acetylacetonate can be carried out in the self-propagating m ode.

Chlorides of 3d metals, iron(III) chloride among them, react with sodium acetylacetonate upon mechan­ ical activation of feeds of crystalline reagents to form acetylacetonates of corresponding metals [1]. The effects of the parameters of mechanochemical activa­ tion on the course of the solid-phase interaction of chromium(III) and alkali metal (3-diketonates and on the yield of the products of this process were studied in [2, 3]. Chromium(III) (3-diketonates can be obtained in the self-propagating mode after a preliminary mechan­ ical activation of a mixture of solid reagents [2, 3]. In this work, we studied the solid-phase mechanochemical interaction of iron(III) chloride with sodium acetylace­ tonate. EXPERIMENTAL All manipulations with the starting reagents as well as with reaction mixtures were performed in a dry box under a nitrogen atmosphere. Sodium acetylacetonate was obtained by interaction of an aqueous solution of sodium hydroxide and acetylacetone with subsequent heating of the product under vacuum [2]. The anhy­ drous iron(III) chloride of high-purity grade (POCh Gliwice) was used as received. X-ray powder diffraction analysis of samples was performed on a DRON-2 diffractometer (CuK a radia­ tion). The IR spectra of the starting reagents, reaction mixtures, and products were recorded on an UR-20 spectrophotometer in a range of 400-4000 cm-1. The samples were mineral-oil mulls (a capillary layer between KBr plates). Thermal investigations were carried out on a Q -1000 MOM derivatograph in a temperature range of 20-500°C (the heating rate was 10 K/min, and the sam­ ple weight was approximately 100 mg). The integral

intensities of the DTA peaks were derived from the area of the appropriate peak normalized to the sample weight. The heating temperatures and melting points were determined with a Boetius heating stage. Mechanical treatment of the reaction mixtures was performed in stainless steel reactors of ~80 cm3 volume with the use of a vibratory ball mill manufactured at the Institute of New Chemical Problems [4], The operation frequency was 12 Hz, and the amplitude was 11 mm. The steel balls of 12.3 and 7 mm in diameter were used as an activating packing. The reactor was filled with weighed portions of iron(III) chloride, alkali metal (3-diketonate, and of the activating packing. The reactor was sealed, placed on the vibratory mill, and vibrated for a set period of time. Then the reactor was opened, and the reaction mixture was separated. To carry out the reaction in the mode of self-propa­ gating synthesis, a mechanically activated mixture of ~1 g weight was placed in a quartz tube 7.1 mm in diameter and -1 4 mm in height and manually com­ pacted. The reaction was initiated by heating the bot­ tom end of the tube on a heating stage at a rate of -3 0 K/min from room temperature until a reaction interface commenced movement. The propagation of the reaction interface was observed by the change in the mixture color. The linear rate of the reaction propaga­ tion was derived from the duration of the process and the rod height. The temperature in the reaction zone was measured with the use of a Chromel-Alumel ther­ mocouple (the wire diameter was -0.2 mm). The tem­ perature profile of a reaction wave was recorded with a KSPP-4 recording potentiometer. The error of the tem­ perature measurements was +2°C.

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SO L ID -P H A S E SY N T H E SIS OF IRON(III) A C E T Y L A C E T O N A T E

The iron acetylacetonate was isolated either by sub­ limation or by extraction. A weighed portion of the reaction mixture was placed in a sublimator and heated in vacuo (the temperature of an outer heater (oil bath) was 160-170°C; the pressure was 13.3 Pa). Benzene was used as a solvent for extraction. The yield was determined in relation to the weighed portion of the reaction mixture taken. The products were identified by chemical analyses and by physicochemical methods. Chemical analyses were performed at the chemicalanalytical laboratory of the Institute of New Chemical Problems.

Preparation

of

iron(IH)

/, rel. units

Y ield, %

25

20

acetylacetonate,

Fe(Acac)3. A mixture o f0 .1 9 1 8 g (1 .1 8 mmol) FeCl3 and 0.4340 g (3.55 mmol) sodium acetylacetonate in the presence of the activating packing (20 steel balls 12.3 mm in diameter weighing -150 g) was mechani­ cally treated for 4 min, after which a 0.2463-g portion of the reaction mixture was used to isolate the product by sublimation. Iron acetylacetonate was obtained in red-colored crystals. The yield was 0.128 g (77.7%). The melting point was 177-178°C (the literature of [4]: Tm = 179°C). For C i5H2|0 6Fe anal, calcd. (%): Fe, 15.8. Found (%): Fe, 15.6.

15

10 5

Fig. 1. The parameters of the reaction o f iron chloride with sodium acetylacetonate vs. the time of mechanical activa­ tion: (a ) the yield o f Fe(Acac ) 3 isolated by sublimation, (b) the yield o f Fe(Acac)3 isolated by extraction, and (c) the integral intensity / o f the exotherm in the range of 50-150°C in the DTA curves o f the activated mixtures.

RESULTS AND DISCUSSION The stoichiometric mixture of sodium acetylaceto­ nate and iron(III) chloride becomes homogeneous and gray in color after being mechanically activated for 2 ' 3 min. The gray color gradually changes to dark brown (in 3-20 min) and then to red (in 45-60 min). A red crystalline sublimate is formed by heating the activated reaction mixtures in vacuo. The sublimate is found to be iron(III) acetylacetonate. According to the data of X-ray diffraction and chemical analyses, the residue after sublimation consists largely of NaCl. At the same weight of the activated packing and the same activation time (1 min), the yield of the product is -70% and is little affected by the packing ball diameter (12.3 and 7 mm). A decrease in the packing weight compared to the one mentioned above leads to a decrease in the product yield in the beginning of the reaction. Studying the yield of iron(III) acetylacetonate as a function of the duration of the mechanical treat­ ment showed that the highest yield was -80% and was achieved after 5 min of activation (Fig. 1, curve a) (Fe( Acac), was isolated by sublimation). The mechan­ ical treatment for more than 20 min leads to a decrease in the product yield, which is probably due to the mechanical destruction of the product [3]. The X-ray diffraction data show that the mixture becomes amorphous in the course of mechanical treat­ ment already within the first 3 min: The reflections of the initial crystalline phases vanish, and a broad, intense peak appears in the region of 20 = 20°-30°, indicating the presence of an amorphous phase. The RUSSIAN JOURNAL OF INORGANIC CHEMISTRY

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90 29 , deg Fig. 2. X-ray diffraction patterns of Fe(Acac)j, NaAcac, and of the reaction mixtures after mechanical activation for (a) 5 min, (b) 10 min, and (c) 30 min. The reflections of NaCl are marked bv dots. No. 3

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3 30

P E T R O V A e t al. A bsorbance, %

v , cm 1 Fig. 3. IR spectra o f Fe(Acac)3, NaAcac, and o f the reaction mixtures after mechanical activation for (a) 1 min and (b) 30 min.

intensity of this peak first increases, reaches the maxi­ mum in 5 min, and then decreases until its almost com­ plete disappearance. Simultaneously, the X-ray diffrac­ tion patterns of the reaction mixtures show the reflec­ tions of the crystal phase of sodium chloride, which first broaden, then gradually become narrower and grow in intensity (Fig. 2). After 10 min of treatment, the reflections of the crystal phase of the second product of the reaction (iron(III) acetylacetonate) become evident in the X-ray diffraction patterns. The reflections of the exchange reaction products increase in intensities with increasing activation time to a some limiting value. Even after a mechanical treatment for 1 min, the absorption bands of the initial sodium acetylacetonate in the IR spectra of the reaction mixtures decrease in intensity, and new absorption bands appear, which are the same as for individual Fe(Acac)3 (Fig. 3). The IR spectrum of the activated mixture recorded after heat­ ing it to 100-150°C or after carrying out the self-prop­

agating reaction (see below) becomes almost identical to the spectrum of the individual Fe(Acac)3. Therefore, chemical analysis, IR spectroscopy, and X-ray diffraction provide evidence that the mechanical treatment of the mixture of solid sodium acetylaceto­ nate and solid iron trichloride leads to their interaction with formation of iron(HI) acetylacetonate. Our find­ ings let us to assume that the reaction studied is a pure mechanochemical process, in which the product is formed in the course of mechanical action. However, the results of our comprehensive thermal study of the reaction mixtures show that the process under study is more complicate. The mechanical treatment gives rise to a new exothermic peak in a range of ~50-100°C in the DTA curves for the activated mixtures in addition to an endothermic peak at 178°C (corresponding to melt­ ing of iron acetylacetonate [4]). As the duration of the mechanical treatment increases„.so the integral inten­ sity of this exothermic peak first increases, reaches the maximum in 5 min, and then decreases until its com­ plete disappearance (when the treatment time is longer than 30 min). This peak is initially broadened and dras­ tically narrows after 2 min of treatment. In this process, the onset temperature of this peak remains almost unchanged, and its peak temperature is reduced from 85 to 65°C (Fig. 4). The mixture after being heated becomes as bright red (the color of iron acetylaceto­ nate) as after being subjected to a prolong mechanical action. The results obtained indicate that the mixture of solid sodium acetylacetonate and solid iron trichloride, after being mechanically activated, generate the reac­ tion products (which were found by IR spectroscopy and X-ray diffraction) as well as the intermediate activated mixture. The activated intermediate can be converted upon heating into the reaction products. The presence of this activated intermediate is established by DTA. It seemed to be of interest to elucidate which amount of iron acetylacetonate was formed due to mechanical treatment and which one due to heating. By analogy with the solid-phase mechanochemical reac­ tion of chromium(III) chloride with alkali metal P-diketonates studied previously [2, 3], we presumed that extraction of the activated mixture with organic solvents would enable us to separate the product of the mechanochemical reaction from the activated mixture. Unfortunately, the isolation of the product from the reaction mixtures by extraction with benzene did not lead to this separation. The product yield upon extrac­ tion with benzene was nearly the same as the yield upon isolation by sublimation (Fig. 1, curve b). A check run showed that the solution of FeCl3 in benzene immedi­ ately turned reddish on adding sodium acetylacetonate (in the ratio 1 : 3). This solution being stirred for two days becomes red and gives Fe(Acac)3 in a yield of 60%. On adding benzene, the components of the acti­ vated mixtures react virtually instantaneously to form Fe(Acac)3.

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Grinding the starting reagents (separately) and their subsequent mixing give rise to the same DTA exotherm as the treatment on the vibratory mill. In the chromium(III) chloride-sodium acetylacetonate system, a mechanically activated mixture can be stored for a long time (several months) without a loss of reactivity and without conversion into the products. Unlike this sys­ tem, the activated mixture of iron(IH) with sodium acetylacetonate stored for 1-2 weeks turned red and converted into reaction products.

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AT, °C

By analogy with the solid-phase reaction of chromium(III) chloride and alkali metal p-diketonates [2, 3], we assumed that the exotherm in the DTA curves of the activated mixtures of iron chloride with sodium acetyl­ acetonate is indicative of the self-propagating interac­ tion between the components [6]. Indeed, heating the bottom end of the rod (compacted and activated for 5 min) to ~50°C leads to the appearance of bright red reaction front at the heated end of the rod. The reaction front moves along the dark brown rod until the material is run out. The temperature in the reaction zone reached ~150°C, and the linear propagation rate of the process was about 5 mm/s. At the same time, heating the mixtures of sepa­ rately ground reagents did not initiate a self-propagat­ ing reaction. Therefore, the mechanical activation of the mixtures of iron(III) chloride and sodium acetylacetonate (taken in the stoichiometric amounts) leads to the solid-phase interaction between the components with formation of ■iron(III) acetylacetonate. This interaction is sustained by the heat of the reaction. The properties of the activated mixtures of sodium acetylacetonate with iron(III) chloride and the parame­ ters of the self-propagating process depend on the qual­ ity of the starting reagents, the mechanical treatment conditions, and other factors. For example, the much longer duration of mechanical action is needed to reach the same conversion as the active charge increases. In some cases, an exchange reaction in mechanically acti­ vated mixtures commenced even either at their com­ pacting or on heating to 36°C. A temperature jump in the reaction zone varied from run to run from 70 to 158°C, and a linear propagation rate measured was in a range of 0.3-6 mm/s.

Fig. 4. DTA curves for Fe(Acac )3 and for the reaction mix­ tures after mechanical activation for (a) 2.5 min, (b) 3 min, (c) 15 min, and (d) 30 min.

were simultaneously observed in the course of mechan­ ical action. ACKNOWLEDGMENTS We are grateful to E.G. Klimchuk for his help in the work and in discussion of the results.

Therefore, studying the physicochemical properties of the mixtures of iron(III) chloride and sodium acetyl­ acetonate as dependent on the mechanical treatment conditions allowed us to find a new example of selfpropagating synthesis promoted by mechanical activa­ tion. As opposed to the chromium(III) chloride-sodium acetylacetonate system studied previously, where the formations of the activated mixture and the reaction products were separated in time, in the system under study, the activated mixture and the reaction products

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REFERENCES 1. Borisov, A.P., Petrova, L .A ., and M akhaev, V .D ., Zh. O bshch. K him ., 1992, vol. 62, no. 1, p. 15. 2. M akhaev, V .D ., B orisov, A.P., A lesh in , V.V., and P et­ rova, L .A ., Izv. A kad. Nauk, Ser. K h im ., 1995, no. 6. p. 1150. 3. Makhaev, V.D., Borisov, A.P., Karpova, T.P., and Petrova, L .A ., Zh. N eorg. K him ., 1996, vol. 4 1 , no. 3, p. 411. 4. M akhaev, V .D ., B orisov, A.P., A lesh in , V.V., and P et­ rova, L .A ., K oord. K h im ., 1996, vol. 2 2 , no. 5, p. 361. 5. B erg, E.W. and Truemper, J.T., J. Phys. Chem ., 1960. vol. 64, no. 4, p. 4 8 7 . 6. M erzhanov, A .G ., Int. J. Self-P rop. H igh Temp. Synth.. 1995, vol. 4, no. 4, p. 323.

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