untitled European Journal of Chemistry 7 (3) (2016) 380‐386 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2016 Atlanta Publishing House LLC ‐ All rights reserved ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.7.3.380-386.1442 European Journal of Chemistry Journal webpage: www.eurjchem.com Synthesis, characterization and thermal decomposition of 2’‐amino‐6’‐(1H‐ indol‐3‐yl)‐1‐methyl‐2‐oxospiro‐[indoline‐3,4’‐pyran]‐3’,5’‐dicarbonitrile under non‐isothermal condition in nitrogen atmosphere Ganesan Nalini 1, Natesan Jayachandramani 1, Radhakrishnan Suresh 2, Venugopal Thanikachalam 3,* and Govindasamy Manikandan 3 1 Department of Chemistry, Pachaiyappa’s College, Chennai, 600030, India 2 Department of Chemistry, Presidency College, Chennai, 600005, India 3 Department of Chemistry, Annamalai University, Annamalainagar, 608002, India * Corresponding author at: Department of Chemistry, Annamalai University, Annamalainagar, 608002, India. Tel.: +91.4144.239523. Fax: +91.4144.238080. E‐mail address: profvt.chemau@gmail.com (V. Thanikachalam). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.7.3.380-386.1442 Received: 24 April 2016 Accepted: 21 May 2016 Published online: 30 September 2016 Printed: 30 September 2016   The kinetics and decomposition of a new spirooxindole compound, 2’‐amino‐6’‐(1H‐indol‐3‐ yl)‐1‐methyl‐2‐oxospiro[indoline‐3,4’‐pyran]‐3’,5’‐dicarbonitrile was studied by thermo gravimetric technique under non‐isothermal conditions. The kinetic parameters were calculated using model‐free (Friedman, Kissinger‐Akahira‐Sunose and Flynn‐Wall‐Ozawa methods) and model‐fitting (Coats‐Redfern) methods. The results of the Friedman isoconversional analysis of the thermogravimetric data suggested that the investigated decomposition process follows a single‐step. KEYWORDS Spirooxindole Coats‐Redfern method Thermal decomposition Flynn‐Wall‐Ozawa method Thermodynamic parameters Kissinger‐Akahira‐Sunose method Cite this: Eur. J. Chem. 2016, 7(3), 380‐386 1. Introduction Synthetic or natural heterocyclic compounds containing spirooxindole framework are endowed with a wide range of pharmacological activities [1]. The 3‐substituted indole nucleus substructure is one of the most important heterocyclic found in natural products, pharmaceutical and medicinal chemistry [2]. The heterocyclic spirooxindoles are attractive targets of medicinal chemistry due to the wide range of pharmacological activities such as anticancer, anti‐microbial, anti‐malarial,anti‐mycobacterium, anti‐oxidant and anti‐fungal activities [3]. Catalytic stereo‐selective synthesis of diverse oxindoles and spirooxindoles were obtained from isatins [4]. Their preparative methods suffer from tedious synthetic routes, longer reaction time, drastic reaction conditions, as well as narrow substrate scope [5]. Spirocyclic oxindoles have been generated containing a six‐membered spiro cyclic moiety, especially a six membered piperidine structure. These compounds have a broad spectrum of biological activities, non‐peptidyl growth hormone secretagogues and potent non‐ peptide inhibitors that may have utility as anti‐cancer agents [6]. An effective reflexive‐Michael reaction has been disclosed to access drug‐like six‐membered spirooxindoles in good yields and excellent antio‐selectivities by using amino enzyme‐ catalysis [7]. Novel dispirooxindole‐pyrrolidine deri‐vatives have been synthesized through 1,3‐dipolar cycloaddi‐tion of an azomethineylide generated from isatin and sarco‐sine with the dipolarphile 3‐(1H‐indole‐3‐yl)‐3‐oxo‐2‐(2‐oxo indolin‐3‐ ylidene)propanenitrileand also spiro compound of acenapht‐ henequinone obtained by the same optimized reaction condition. The synthesized compounds were evaluated for their antimicrobial activity and all the compounds showed significant activity [8]. Recent advances in the synthesis of biologically active spirooxindoles with potential use as therapeutic agents were reported [9]. The search for novel anti‐cancer agents with more selectivity and lower toxicity continues to be an area of intense investigation. The unique structural features of spirooxindoles together with diverse biological activities have made them privileged structures in new drug discovery [10]. Non‐isothermal decomposition Nalini et al. / European Journal of Chemistry 7 (3) (2016) 380‐386 381 kinetics of chitosan [11], chitin [12], cephalosporins [13], procaine and benzocaine [14], theobromine [15] and spirooxindole [16] were studied in detail and appropriate kinetic models were proposed. 3‐Chloro oxindoles are versatile starting materials for asymmetric organo catalytic synthesis of spirooxindoles. Literature data show that no work has been reported on thermal decomposition of spirooxindoles by one‐pot multicomponent system at different heating rates (10, 15, 20 and 30 K/min) under non‐isothermal condition in nitrogen atmosphere. In this paper, we report the synthesis and thermal decomposition of 2’‐amino‐6’‐(1H‐indol‐3‐yl)‐1‐ methyl‐2‐oxospiro[indoline‐3, 4’‐pyran]‐3’, 5’‐dicarbonitrile (Figure 1) [17] and its thermal decomposition under non‐ isothermal dynamic nitrogen atmospheric condition. The kinetic and thermodynamic parameters were calculated by using model‐fitting and model free‐methods. Figure 1. Structure of AIMOIPD. 2. Experimental 2.1. Preparation of 2’‐amino‐6’‐(1H‐indol‐3‐yl)‐1‐methyl‐2‐ oxospiro[indoline‐3,4’‐pyran]‐3’,5’‐dicarbonitrile (AIMOIPD) To a stirred solution of N‐methyl isatin (0.147 g, 1 mmol), ethylcyano acetate (0.066 g, 1 mmol), 3‐cyanoacetyl indole (0.184 g, 1 mmol) in methanol (10 mL) and triethylamine (20 mol %) were added and stirring was continued for 30 min. On completion, the reaction mixture was poured into crushed ice and the precipitate formed was filtered, dried and purified by column chromatography to afford the pure product. The isolated product was further purified by recrystallization in ethanol and the appropriate yield of the product was 89%. Color: Pale brown solid. M.p.: 205‐208 °C. Rf: 0.27 (40%, AcOEt:Petroleum ether). FT‐IR (KBr, ν, cm‐1): 1152, 1250, 1356, 1416, 1471, 1526, 1617, 1666, 2202, 2368, 2929, 3171, 3360. 1H NMR (500 MHz, DMSO‐d6, δ, ppm): 3.19 (s, 3H, N‐ CH3), 7.12‐7.18 (m, 3H, Ar‐H), 7.23 (t, J = 6.85 Hz, 1H, Ar‐H), 7.38‐7.42 (m, 2H, Ar‐H), 7.49 (d, J = 8.4 Hz, 1H, Ar‐H), 7.65 ( s, 2H,‐NH2), 7.96 (d, J = 8.45 Hz, 1H, Ar‐H), 8.15 (d, J = 3.05 Hz, 1H, Ar‐H), 12.06 ( brs, 1H, NH). 13C NMR(125 MHz, DMSO‐d6, δ, ppm): 27.1, 50.1, 54.4, 81.4, 105.5, 109.7, 113.0, 117.5, 117.8, 121.8, 122.1, 123.4, 124.2, 124.9, 125.4, 130.6, 131.5, 136.5, 143.5, 158.5, 160.3, 176.0. MS (EI, m/z): 394.00 [M++H+]. Anal. calcd. for C23H15N5O2: C, 70.22; H, 3.84; N, 17.80. Found: C, 70.31; H, 3.85; N, 17.92%. 2.2. Instrumentation Elemental analysis was performed at Central Leather Research Institute (CLRI), Chennai, India. IR measurements were done as KBr pellets for solids using Perkin Elmer Spectrometer RXI FT‐IR. The 1H and 13C NMR spectra were recorded in DMSO‐d6, using TMS as internal standard with JEOL ECA‐500MHz high resolution NMR spectrometer. The mass spectrum was recorded using an Electrospray Ionization Method with ThermoFinnigan mass spectrometer. Melting point was determined in capillary tubes and is uncorrected. Analytical TLC was performed on pre‐coated plastic sheets of silica gel G/UV‐254 of 0.2mmthickness. The simultaneous TGA curves were obtained with the thermal analysis system model Perkin Elmer TAC7/DX (Thermal Analysis Controller TAC‐7). The TG/DTG analyzes of AIMOIPD were carried out under dynamic nitrogen atmosphere (100 mL/min) in an iron pan with the sample at the heating rates 10, 15, 20 and 30 K/min from 30 to 1150°C.TG/DTG was recorded at Indian Institute of Technology, Chennai, India. The kinetic parameters Ea and A were calculated using Microsoft Excel Software. The sample temperature which was controlled by a thermocouple, did not exhibit any systematic deviation from the preset linear temperature program. 2.3. Theoretical background 2.3.1. Model fitting method For non‐isothermal experiment, model fitting involves different models to α ‐ temperature (α‐T) curves and successfully determine Ea and A. There are numerous non‐ isothermal model fitting methods and the most popular one is the Coats and Redfern method [18]. This method has been most successfully used for studying the kinetics of dehydration and vaporization of different solid substances [19]. The kinetic parameters can be derived from modified Coats and Redfern Equation (1),                   * a 2 a a (α) AR 2RT ln =ln 1‐ ‐ T β RT Eg E E (1) where g(α) is an integral form of the conversion function (α), the expression of which depends on the kinetic model of the occurring reaction. If the correct g(α) function is used, a plot of ln[g(α)/T2] against 1/T should give a straight line from which the values of the activation energy, Ea and the pre‐exponential factor, A can be calculated. 2.3.2. Model free methods Friedman method [20] is a differential method and is one of the first used iso‐conversional methods. This model according to logarithmic form of Equation (3). a- =A.exp . (α) RT Ed f dt        (2) gives   a,α α α ln β =ln A . (α) - RT Ed f dT      (3) The plots of ln(β.dα/dT) vs 1/T (Equation (3)), at each α value were drawn and from the slope of the plots, we can calculate Ea values. The isoconversional integral method suggested independently by Flynn and Wall [21] and Ozawa [22], and is based on the Equation (4), a a0.0048.A. ln β = ln -1.0516 g(α).R RT E E      (4) and for Kissinger‐Akahira‐Sunose (KAS) method [23,24], Equation (5) is used. 382 Nalini et al. / European Journal of Chemistry 7 (3) (2016) 380‐386  2 a aA. ln β/T =ln - (α).R RT E E g       (5) The plots of ln(β dα/dT) vs 1/T (Equation (3)), lnβ vs 1/T (Equation (4)) and ln(β/T2) vs 1/T (Equation (5)) have been shown to give the values of apparent activation energies for the decomposition of AIMOIPD at different values of α. According to these equations, the reaction mechanism and shape of g(α) function do not affect the values of the activation energies of the decomposition stages. 2.3.3. Thermodynamic parameters The kinetic parameters, energy of activation (Ea) and pre‐ exponential factor (A) obtained from Kissinger single point [23] kinetic method uses the Equation (6):           a 2 m m a β AR ln = ‐ + ln T RT E E (6) where Tm is the temperature that corresponds to the maximum of d/dT. This model‐free kinetic method can be applied with a reasonable approximation without being limited to n‐order kinetics [25], by providing a single Ea value for each reaction step. Based on the values of activation energy and pre‐ exponential factor for the decomposition stage, the values of ∆S≠, ∆H≠ and ∆G≠ for the formation of activated complex from the reactant were calculated [25‐27]. 3. Results and discussion 3.1. Non‐isothermal TGA The TGA method of thermograms of pure AIMOIPD recorded in a dynamic nitrogen atmosphere at different heating rates of 10, 15, 20 and 30 K/min are represented in Figure 2. The thermal decomposition process of AIMOIPD was observed in three stages. The thermogravimetric curves showed that the first stage decomposition starts at 150 °C and ends at about 275 °C with the corresponding mass loss of 28.46%. The second‐stage decomposition starts at 275 °C and ends at about 550 °C with the corresponding mass loss of 41.26%. The third stage starts at 550 °C and ends at about 840 °C with the corresponding mass loss of 9.41%. 3.2. Model ‐free analysis The non‐isothermal decomposition kinetics of AIMOIPD was first analyzed by model‐free methods viz., Friedmann, Kissinger‐Akahira‐Sunose and Flynn‐Wall‐Ozawa. The data showed the decomposition of apparent activation energy Ea, as a function of extent of conversion α for the decomposition of AIMOIPD. At all the stages, Ea value increases slightly in the conversion range of 0.12 ≤ α ≤ 0.98. It was pointed out [28] that when Ea changes with α, the Friedmann and KAS isoconversional methods led to close values of Ea for all the stages. The applied isoconversional method does not suggest a direct way for evaluating either the pre‐exponential factor or the analytical form of the reaction model f(α) for the inves‐ tigated decomposition process of AIMOIPD. In the first stage decomposition of AIMOIPD, the values of Ea corresponding to the values of α for the decomposition process obtained by Friedmann, KAS and FWO methods are given in Figure 3. It is seen that Ea value depends upon the extent of conversion (α). The average values of Ea in the range 0.12 ≤ α ≤ 0.98 is 230.57±0.52 kJ/mol in Friedman method. From Figure 3, it is evident that the values of activation energy obtained by KAS and FWO methods are Ea = 229.76±0.43 kJ/mol, KAS; 226.45±0.42 kJ/mol, FWO. The apparent activation energy initially decreases slightly with increase in the degree of conversion 0.12 ≤ α ≤ 0.30 and then remains constant which indicates slower rate of decomposition and the gaseous products are not in equilibrium with the solid compound. Figure 2. TG and DTA curves of AIMOIPD at heating rates of (a) 10 K/min, (b) 15 K/min, (c) 20 K/min and (d) 30 K/min in nitrogen atmosphere. Nalini et al. / European Journal of Chemistry 7 (3) (2016) 380‐386 383 Figure 3. Ea versus α plot for the decomposition of AIMOIPD under non‐ isothermal condition (Stage I). For stage II, the variation of Ea with α for the decomposition is shown in Figure 4. The average value of Ea is 231.70±0.51 kJ/mol (KAS method). It is evident that the KAS method of activation energy is higher than the values of activation energy obtained by Friedmann (Ea = 228.68±0.41 kJ/mol) and FWO (Ea = 229.63±0.42 kJ/mol) methods. Figure 4. Ea versus α plot for the decomposition of AIMOIPD under non‐ isothermal condition (Stage II). For stage III, the values of apparent activation energies obtained by Friedman and KAS methods are higher than that of FWO method. The average values of Ea in the range 0.12 ≤ α ≤ 0.98 are 537.95±0.62 kJ/mol (Friedman), 535.21±1.72 kJ/mol (KAS) and 524.74±1.74 kJ/mol (FWO) (Figure 5) from the average values of Ea for each stage, the rate of decomposition is found to depend upon the nature of the intermediate formed during the decomposition and the third stage is slower than the other stages. The higher values activation energy for stage III than the other stages indicates that the intermediate compounds are thermally more stable and the decomposition process is slow. 3.3. Model‐fitting analysis After carrying out model free analysis, model fitting can be done in the conversion region where apparent activation energy is approximately constant where a single model may fit. The non‐isothermal kinetic data of AIMOIPD at 0.12 ≤ α ≤ 0.98 where model free analysis indicated approximately constant activation energy, were then fitted to each of the 15 models listed in the Tables 1‐3 for stages I, II and III, respectively. The values of Arrhenius parameters were computed by applying Coats‐Redfern method. It is found that these parameters are highly variable, exhibiting strong dependence on the reaction model chosen. The decomposition stages are also confirmed by invariant kinetic parameters method. Figure 5. Ea versus α plot for the decomposition of AIMOIPD under non‐ isothermal condition (Stage III). 3.4. Invariant kinetic parameters (IKP) analysis The invariant kinetic parameters were calculated for the heating rates of 10, 15, 20 and 30 K/min using Coats‐Redfern method, in the range 0.12 ≤ α ≤ 0.98 for AIMOIPD, the straight lines corresponding to Coats‐Redfern method is characterized by correlation coefficient values close to unity. For several groups of apparent activation parameters, obtained by different kinetic models, we tried to establish the best combination (r → 1), a better resolution in determining the Invariant kinetic parameters and closet value to the mean isoconversional activation energies [29‐31]. In stage I for AKM‐{A2}, the plot of ln A vs Ea has the highest correlation coefficient and is a straight line (Figure 6). The invariant kinetic parameters, Einv =231.89 kJ/mol and ln Ainv = 53.70 are obtained with r = 0.997 (Figure 6). For these group, the invariant activation energy is almost equal Ea = 231.89 kJ/mol compared to Friedman, KAS and FWO methods (230.57±0.52 kJ/mol, Friedmann; 229.76±0.43 kJ/mol, KAS; 226.45±0.42 kJ/mol, FWO). Figure 6. Supercorrelation (Compensation effect parameters) plot for the best combination of kinetic models (Stage I). For stage II, a better resolution in determining the invariant kinetic parameters and the correlation coefficients (Figure 7) show a good agreement of all kinetic models. 384 Nalini et al. / European Journal of Chemistry 7 (3) (2016) 380‐386 Table 1. Arrhenius parameters for non‐isothermal decomposition of AIMOIPD (Stage I) at various heating rates. Kinetic model β = 10 K/min β = 15 K/min β = 20 K/min β = 30 K/min Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r P2 48.07 9.73 ‐0.969 46.60 9.68 ‐0.971 46.15 9.79 ‐0.969 47.95 10.54 ‐0.969 P3 29.23 4.82 ‐0.963 28.23 4.91 ‐0.966 27.92 5.07 ‐0.963 29.09 5.72 ‐0.962 P4 19.86 2.25 ‐0.955 19.11 2.40 ‐0.958 18.86 2.58 ‐0.955 19.72 3.18 ‐0.954 F1 166.06 39.38 ‐0.996 161.42 38.41 ‐0.997 160.28 38.22 ‐0.997 166.04 39.68 ‐0.996 F2 253.91 61.41 ‐0.999 246.67 59.71 ‐0.999 245.18 59.34 ‐0.999 253.97 61.33 ‐0.999 F3 364.11 88.83 ‐0.993 353.56 86.19 ‐0.992 351.67 85.60 ‐0.993 364.27 88.27 ‐0.993 D1 230.22 61.36 ‐0.977 224.37 60.04 ‐0.979 222.70 59.66 ‐0.978 230.35 61.44 ‐0.977 D2 250.50 58.52 ‐0.984 243.85 56.96 ‐0.986 242.01 56.51 ‐0.985 250.54 58.45 ‐0.984 D3 293.68 67.82 ‐0.992 285.79 65.92 ‐0.993 283.76 65.37 ‐0.992 293.76 67.57 ‐0.992 D4 264.70 60.57 ‐0.987 257.64 58.90 ‐0.989 255.74 58.42 ‐0.988 264.75 60.44 ‐0.987 A2 78.86 17.83 ‐0.996 76.52 17.53 ‐0.997 75.93 17.57 ‐0.996 78.77 18.51 ‐0.996 A3 49.74 10.42 ‐0.995 48.16 10.34 ‐0.996 47.75 10.46 ‐0.996 49.62 11.22 ‐0.995 A4 35.26 6.62 ‐0.994 34.07 6.65 ‐0.996 33.75 6.80 ‐0.995 35.14 7.49 ‐0.995 R2 132.06 30.07 ‐0.988 128.39 29.38 ‐0.990 127.40 29.27 ‐0.988 132.01 30.52 ‐0.988 R3 122.56 27.93 ‐0.984 119.16 27.32 ‐0.986 118.22 27.23 ‐0.984 122.50 28.42 ‐0.984 Table 2. Arrhenius parameters for non‐isothermal decomposition of AIMOIPD (Stage II) at various heating rates. Kinetic model β = 10 K/min β = 15 K/min β = 20 K/min β = 30 K/min Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r P2 9.21 ‐1.82 ‐0.659 8.797 ‐1.575 ‐0.654 8.53 ‐1.40 ‐0.648 8.96 ‐0.89 ‐0.652 P3 2.85 ‐4.21 ‐0.373 2.553 ‐3.993 ‐0.349 2.35 ‐3.84 ‐0.328 2.61 ‐3.31 ‐0.348 P4 ‐0.31 ‐ 0.058 ‐0.550 ‐ 0.105 ‐0.72 ‐ 0.138 ‐0.55 ‐ 0.102 F1 51.49 8.79 ‐0.909 50.232 8.832 ‐0.912 49.50 8.88 ‐0.912 51.11 9.53 ‐0.910 F2 85.47 16.90 ‐0.960 83.480 16.747 ‐0.962 82.37 16.69 ‐0.963 84.97 17.47 ‐0.961 F3 128.48 26.88 ‐0.981 125.548 26.476 ‐0.982 123.97 26.27 ‐0.983 127.82 27.22 ‐0.981 D1 76.65 20.93 ‐0.876 75.164 20.909 ‐0.879 74.30 20.92 ‐0.880 76.45 21.64 ‐0.878 D2 78.66 13.34 ‐0.875 76.924 13.246 ‐0.877 75.89 13.21 ‐0.878 78.25 13.95 ‐0.876 D3 94.99 15.71 ‐0.902 92.915 15.530 ‐0.905 91.70 15.44 ‐0.905 94.52 16.24 ‐0.903 D4 84.02 13.11 ‐0.885 82.173 12.992 ‐0.888 81.08 12.94 ‐0.888 83.59 13.70 ‐0.886 A2 20.82 1.62 ‐0.868 20.168 1.820 ‐0.870 19.77 1.97 ‐0.868 20.53 2.51 ‐0.867 A3 10.58 ‐1.15 ‐0.797 10.126 ‐0.906 ‐0.796 9.84 ‐0.73 ‐0.791 10.31 ‐0.22 ‐0.792 A4 5.49 ‐2.84 ‐0.670 5.136 ‐2.597 ‐0.660 4.91 ‐2.42 ‐0.648 5.24 ‐1.91 ‐0.656 R2 38.56 4.89 ‐0.865 37.580 5.005 ‐0.867 36.99 5.10 ‐0.867 38.23 5.70 ‐0.865 R3 35.00 4.26 ‐0.848 34.085 4.395 ‐0.850 33.53 4.50 ‐0.850 34.68 5.09 ‐0.848 Table 3. Arrhenius parameters for non‐isothermal decomposition of AIMOIPD (Stage III) at various heating rates. Kinetic model β = 10 K/min β = 15 K/min β = 20 K/min β = 30 K/min Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r Ea (kJ/mol) ln A r P2 13.29 ‐2.87 ‐0.985 13.40 ‐2.45 ‐0.985 13.50 ‐2.16 ‐0.985 13.12 ‐1.86 ‐0.985 P3 3.36 ‐5.33 ‐0.894 3.42 ‐4.91 ‐0.894 3.46 ‐4.61 ‐0.893 3.17 ‐4.35 ‐0.881 P4 ‐1.57 ‐ 0.750 ‐1.54 ‐ 0.740 ‐1.53 ‐ 0.731 ‐1.78 ‐ 0.787 F1 73.60 6.21 ‐0.996 74.09 6.63 ‐0.997 74.54 6.94 ‐0.997 73.64 7.14 ‐0.996 F2 116.61 12.38 ‐0.978 117.39 12.82 ‐0.978 118.10 13.14 ‐0.978 116.79 13.24 ‐0.978 F3 170.28 19.84 ‐0.959 171.42 20.30 ‐0.960 172.47 20.63 ‐0.960 170.64 20.63 ‐0.959 D1 119.31 19.64 ‐0.998 120.04 20.08 ‐0.998 120.71 20.40 ‐0.998 119.68 20.55 ‐0.998 D2 119.09 10.64 ‐1.000 119.85 11.08 ‐1.000 120.56 11.39 ‐1.000 119.29 11.50 ‐1.000 D3 140.51 12.17 ‐1.000 141.41 12.62 ‐1.000 142.24 12.94 ‐1.000 140.78 13.00 ‐1.000 D4 126.15 10.14 ‐1.000 126.95 10.58 ‐1.000 127.70 10.90 ‐1.000 126.36 10.99 ‐1.000 A2 28.59 ‐0.04 ‐0.995 28.80 0.37 ‐0.995 28.99 0.67 ‐0.995 28.47 0.95 ‐0.995 A3 13.55 ‐2.56 ‐0.991 13.67 ‐2.15 ‐0.992 13.78 ‐1.85 ‐0.992 13.39 ‐1.55 ‐0.991 A4 6.08 ‐4.24 ‐0.980 6.16 ‐3.83 ‐0.981 6.22 ‐3.53 ‐0.982 5.89 ‐3.24 ‐0.979 R2 56.78 3.00 ‐1.000 57.16 3.42 ‐1.000 57.51 3.73 ‐1.000 56.76 3.96 ‐1.000 R3 52.05 2.55 ‐1.000 52.40 2.98 ‐1.000 52.72 3.28 ‐0.999 52.02 3.52 ‐1.000 The efficiency of IKP method is strongly revealed by AKM‐ {A2} (Figure 7) and even by AKM all kinetics models which comprise all the best‐fitting function that makes it a more powerful method. The invariant activation energy Ea =232.46 kJ/mol is close to KAS method. The invariant kinetic para‐ meters are Einv = 232.46 kJ/mol and ln Ainv = 46.11 obtained with r = 0.983. In third stage for AKM‐ {F3} the plots of ln A vs Ea has the highest correlation (r = 0.999) (Figure 8). Depending on the choice of kinetic models, the compensation effect parameters are obtained with different accuracies, their values and the derived invariant activation parameters varying substantially. For AKM‐{F3}, the invariant kinetic parameters are 540.56 kJ/mol and ln Ainv = 74.40 obtained with r = 0.999. For these groups, the invariant activation energy is slightly above 6 units (Ea = 537.95±0.62kJ/mol) and 14 units below (Ea = 524.74 kJ/mol) that obtained by Friedman and FWO methods. 3.5. Determination of kinetic models The most probable kinetic model for the first stage decomposition process of AIMOIPD is F2. By introducing the derived reaction g(α)=[(1‐α)‐1‐1] the following equation is obtained. -1 aA. [( ) ]= p(x) R 1 1 .β –α - E (7) The plots of [(1‐α)‐1‐1] against Ea p(x)/βR at the different heating rates are shown in Figure 9. By using Equation (7), the values of A was determined from the slope of the line shown in Figure 9. By applying second‐order F2 model Ea = 230.57±0.52 kJ/mol, the pre‐exponential (frequency) factor A = 2.097×1023/min (ln A = 53.70). The obtained value of ln A is in good agreement with values obtained by Friedman iso‐ conversional intercept. Nalini et al. / European Journal of Chemistry 7 (3) (2016) 380‐386 385 Figure 7. Supercorrelation (Compensation effect parameters) plot for the best combination of kinetic models (Stage II). Figure 8. Supercorrelation (Compensation effect parameters) plot for the best combination of kinetic models (Stage III). Figure 9. Determination of A value by plotting (1‐α)‐1‐1 against Ea p(x)/βR for the decomposition process of AIMOIPD at the different heating rates (β) (Stage I). The most suitable kinetic model for stages II and III is F3 (third‐order). By introducing the derived reaction model g(α)=0.5 [(1‐α)‐2 ‐1], the following equation is obtained. - a2 A. [( ) ]0.5 1–α p(x) R.β -1 = E (8) The plots of 0.5[(1‐α)‐2‐1] against Ea p(x)/R.β at the different (Figures 10 and 11) heating rates are considered. By using Equation (8), the values were calculated from the slopes of the line shown in Figures 10 and 11. By applying the third‐ order model F3, Ea = 228.68±0.41 kJ/mol; Ea = 537.95±0.62 kJ/mol, stages II and III, respectively, the pre‐exponential (frequency) factor A= 1.060×1020/min (ln A=46.11) and A = 2.048×1032/min (ln A=74.40) for stages II and III, respectively. The corresponding kinetic equations for describing the non‐ isothermal decomposition process of AIMOIPD in stages I, II and III are given by For stage I βdα/dT = 2.097×1023× exp(‐230.57/RT) [(1‐α)2] (9) For stage II βdα/dT = 1.060×1020× exp(‐228.68/RT) [(1‐α)3] (10) For stage III βdα/dT = 2.048×1032× exp (‐537.95 /RT) [(1‐α)3] (11) where (1‐α)2, (1‐α)3 represent the differential form of F2 (second‐order), F3 (third‐order) reaction model for stages I and II, III, respectively. Figure 10. Determination of A value by plotting 0.5[(1‐α)‐2‐1] against Ea p(x)/βR for the decomposition process of AIMOIPD at the different heating rates (β) (Stage II). 3.6. Thermodynamic parameters From the DTG curves, the peak temperatures for AIMOIPD are 491.09, 494.32, 496.35 and 498.52 K for stage I and 593.18, 596.95, 597.51 and 598.01 K for stage II and 891.73, 895.00, 897.49 and 898.82 K for stage III. These peak tempera‐ tures are used to determine the single point kinetic para‐ meters [23]. The calculated Ea values are 194.14, 414.20, 673.22 kJ/mol for stages I, II and III, respectively. The thermodynamic parameters ∆S≠, ∆H≠ and ∆G≠ were calculated at the peak temperatures in reference [32] TG and DTG curve for the corresponding stages [33]. Since the temperature characterizes the higher rate of decomposition, it is an important parameter. As can be seen from the Table 4, the value of ∆S≠ for all the stages are positive .It means that the corresponding activated complexes were with lower degree of arrangement than the initial state. The positive values of ∆H≠ and ∆G≠ for all the stages show that they are connected with absorption of heat and they represent non‐spontaneous processes at normal temperature. 386 Nalini et al. / European Journal of Chemistry 7 (3) (2016) 380‐386 Table 4.Values of kinetic and thermodynamic parameters for the thermal decomposition of AIMOIPD in nitrogen atmosphere. Parameter Stage I Stage II Stage III Ea (kJ/mol) 194.14 414.20 673.22 ln A 47.46 84.12 90.64 ∆G≠ (kJ/mol) 122.20 146.35 226.12 ∆H≠ (kJ/mol) 190.03 409.24 665.78 ∆S≠ (J/K.mol) 137.22 440.39 491.23 r 0.954 0.962 0.981 Figure 11. Determination of A value by plotting 0.5[(1‐α)‐2‐1] against Ea p(x)/βR for the decomposition process of AIMOIPD at the different heating rates (β) (Stage III). 4. Conclusion The thermal decomposition of AIMOIPD was investigated in detail by TG and DTG analyses. The kinetic parameters of decomposition were obtained by the iso‐conversional and invariant methods. AIMOIPD decomposed in three stages. The rate of decomposition of third stage is slow due to high energy of activation when compared to stages I and II. The decomposition reaction is endothermic as shown by the positive values of ∆G≠ and ∆H≠ for all the stages, which indicates that the decomposition processes are non‐ spontaneous processes. 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