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Solid state reactivity of organic compounds with inorganic compounds II.

Reactions of cobalt acetate with aniline hydrobromides

Journal of Thermal Analysis and Calorimetry
Authors: P. Bassi, G. Chopra, and R. Prasher

Cobalt acetate reacts with aniline, 2-, 3- and 4-chloroanilinehydrobromides in the solid state to give the products CoBr2. 2 amine in which the acetate is replaced by bromide and the amine gets attached to the metal in a concerted step. The products have been identified by elemental, spectral and thermoanalytical methods. The kinetics of these reactions have been studied by the mass loss method. The values of energy of activation are 142.0, 41.0, 77.0 and 71.4 kJ mol−1. The greater reactivity of 2-chloro is due to ortho effect. An intermediate adduct (RNH3)2(Co(CH3COO)2Br2) has also been characterized.

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The Reaction Controlled Thermal Analysis techniques, RCTA, are very useful both in thermogravimetric and dilatometric studies. In the present paper this big family of techniques is divided into three main classes: Quasi-Isothermal techniques (QIA); Controlled Reaction Rate Thermal Analysis (CRTA) and Reaction (Event) Controlled Heating Rate Adaption. After a short presentation of these techniques and the general advantages of RCTA, two examples of kinetic studies on thermal decomposition of Ba- and Ce oxalates by using Stepwise Isothermal Analysis, SIA, introduced by the author is presented and discussed.

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The empirical regularities of the SEF for relative inorganic substances in binary and quasibinary systems (energetic and dimensional rules of linear approximation - ELAR and DLAR) are described.

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8-hydroxyquinoline (oxine) and uranyl acetate react in the solid state in 1∶3 stoichiometry to give UO2(C9H6NO)2·C9H6NOH. This reaction is diffusion controlled with an activation energy of 44.4 kJ mol−1. The reaction occurs by the surface migration of 8-hydroxyquinoline, which penetrates the product lattice to react with uranyl acetate. The isothermal decomposition of the solution phase product UO2Q2·HQ (Q=C9H6NO) obeys the Prout-Tompkins equation with an energy of activation of 53.3 kJ mol−1.

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New dihydrazinium divalent transition metal trimellitate hydrates of empirical formula (N2H5)2M(Html)2·nH2O, where n = 1 for M = Co or Ni, and n = 2 for M = Mn, Zn, or Cd (H3tml = trimellitic acid), and monohydrazinium cadmium trimellitate, [(N2H5)Cd(Html)1.5·2H2O] have been prepared and characterized by physico-chemical methods. Electronic spectroscopic, and magnetic moment data suggest that Co and Ni complexes adopt an octahedral geometry. The IR spectra confirm the presence of monodentate carboxylate anion (Δν = νasy(COO) − νsym(COO) > 190 cm−1) and coordinated N2H5 + ion (νN–N 1015 − 990 cm−1) in all the complexes. All the complexes undergo endothermic decomposition eliminating CO2 in the temperature region 200–250 °C, followed by exothermic decomposition (in the range of 500–570 °C) of organic moiety to give the respective metal carbonate as the end products except nickel and cobalt complexes, which leave respective metal oxides. X-ray powder diffraction patterns reveal that Ni and Co complexes are isomorphous as are those of, Zn(II) and Cd(II) of the type, (N2H5)2M(Html)2·2H2O.

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MgFe2(C2O4)3·6H2O was synthesized by solid-state reaction at low heat using MgSO4·7H2O, FeSO4·7H2O, and Na2C2O4 as raw materials. The spinel MgFe2O4 was obtained via calcining MgFe2(C2O4)3·6H2O above 500 °C in air. The MgFe2(C2O4)3·6H2O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform FT-IR, X-ray powder diffraction (XRD), and vibrating sample magnetometer (VSM). The result showed that MgFe2O4 obtained at 800 °C had a specific saturation magnetization of 40.4 emu g−1. The thermal process of MgFe2(C2O4)3·6H2O experienced three steps, which involves the dehydration of the six waters of crystallization at first, and then decomposition of MgFe2(C2O4)3 into amorphous MgFe2O4 in air, and at last crystallization of MgFe2O4. Based on Flynn–Wall–Ozawa equation, the average values of the activation energies associated with the thermal decomposition of MgFe2(C2O4)3·6H2O were determined to be 148.45 ± 25.50 and 184.08 ± 7.64 kJ mol−1 for the first and second decomposition steps, respectively. Dehydration of the six waters of MgFe2(C2O4)3·6H2O is multi-step reaction mechanisms. Decomposition of MgFe2(C2O4)3 into MgFe2O4 could be simple reaction mechanisms, kinetic model that can better describe the thermal decomposition of MgFe2(C2O4)3 is the F 3/4 model, and the corresponding function is g(α) = 1 − (1 − α)1/4.

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Copper hydrogenphosphate monohydrate, CuHPO4·H2O, was synthesized for the first time through simple and rapid method using the mixing of copper carbonate and phosphoric acid in acetone medium at ambient temperature. The obtained CuHPO4·H2O decomposed in three stages via dehydration and deprotonated hydrogenphosphate reactions, revealed by TG/DTG and DSC techniques. The kinetic triplet parameters (E a, A, and n) and thermodynamic functions (ΔH∗, ΔG∗, and ΔS∗) for the first two decomposed steps were calculated from DSC data. All the obtained functions indicate that the deprotonated HPO4 2− reaction for the second step occurs at a higher energy pathway than the dehydration reaction for the first step. The calculated wavenumbers based on DSC peaks were comparable with FTIR results, which support the breaking bonds of OH (H2O) and P-OH (HPO4 2−) according to decomposed mechanisms. All the calculated results are consistent and in good agreement with CuHPO4·H2O's thermal transformation mechanisms.

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The MnV2O6·4H2O with rod-like morphologies was synthesized by solid-state reaction at low heat using MnSO4·H2O and NH4VO3 as raw materials. XRD analysis showed that MnV2O6·4H2O was a compound with monoclinic structure. Magnetic characterization indicated that MnV2O6·4H2O and its calcined products behaved weak magnetic properties. The thermal process of MnV2O6·4H2O experienced three steps, which involves the dehydration of the two waters of crystallization at first, and then dehydration of other two waters of crystallization, and at last melting of MnV2O6. In the DSC curve, the three endothermic peaks were corresponding to the two steps thermal decomposition of MnV2O6·4H2O and melting of MnV2O6, respectively. Based on the Kissinger equation, the average values of the activation energies associated with the thermal decomposition of MnV2O6·4H2O were determined to be 55.27 and 98.30 kJ mol−1 for the first and second dehydration steps, respectively. Besides, the thermodynamic function of transition state complexes (ΔH , ΔG , and ΔS ) of the decomposition reaction of MnV2O6·4H2O were determined.

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The thermal decomposition kinetics of nickel ferrite (NiFe2O4) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different heating rates. The activation energy (E α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS), which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe2O4 precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.

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