untitled European Journal of Chemistry 6 (4) (2015) 404‐409 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2015 Atlanta Publishing House LLC ‐ All rights reserved ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.6.4.404‐409.1299 European Journal of Chemistry Journal webpage: www.eurjchem.com Synthesis, characterization, fluorescence, and thermal studies of a new series of Schiff bases derived from sulfaproxylene Jabbar Saleh Hadi Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah, 61004, Iraq * Corresponding author at: Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah 61004, Iraq. Tel.: +964.771.0822193. Fax: +964.771.0822193. E‐mail address: jshalkabi2@gmail.com (J.S. Hadi). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.6.4.404‐409.1299 Received: 10 July 2015 Received in revised form: 06 August 2015 Accepted: 08 August 2015 Published online: 31 December 2015 Printed: 31 December 2015 A new series of Schiff bases were synthesized by the condensation of sulfaproxylene with various aldehydes in ethanol. The structures of Schiff bases were characterized by using elemental analysis, IR, 1H NMR, 13C NMR and Mass spectrometry techniques. Thermal stability of the prepared compounds was investigated using TG and DTG. The kinetic and thermodynamic parameters such as activation energy (E), enthalpy of activation (ΔH), entropy of activation (ΔS), and Gibbs free energy change of the decomposition (ΔG) were evaluated following Coats‐Redfern method. In addition, the compounds were studied for their fluorescence properties, where compound 1 yielded the strongest intensity in 1×10‐4 M DMSO solution. KEYWORDS Sulfa drug Schiff base Fluorescence Coats‐Redfern Sulfaproxylene Thermal analysis Cite this: Eur. J. Chem. 2015, 6(4), 404‐409 1. Introduction Schiff bases or imines are compounds that are represented with the general formula R1R2C=NR3, where R1, R2 and R3 are substituted by alkyl, aryl, hetero‐aryl or hydrogen [1‐8]. The Schiff bases derived from sulfa drugs with different R3 repre‐ sent a wide variety of sulfa moieties and, in several decades, these vital compounds demonstrate a broad spectrum of activities in industrial, biological, analytical, medicinal, and pharmaceutical applications [9‐29]. One of the more interes‐ ting applications of Schiff bases derived from sulfa drugs is the possibility to use them as effective antibacterial, antifungal, and anti HIV [30,31]. Schiff bases like Salen‐type are fluorescent at low temperature and in solution [25]. In addition, the Schiff bases derived from sulfa drugs has a potential for trace analysis of some transition metals with fluorometric method [32]. Based on thermal stability of Schiff bases, they can be used as stationary phase in gas chromatography [33]. Prompted by these observations, in the present study, a new series of Schiff base have been synthesized and charac‐ terized on the basis of spectroscopic methods including IR, 1H and 13C NMR, and mass spectroscopy as well as elemental analysis. Also, the newly synthesized compounds have been utilized by thermogravimetric (TG/DTG) analyses as themostly used techniques and the widely applied Coats‐ Redfern calculation procedure for the kinetic analysis [34]. The kinetic and thermodynamic parameters (A, E, ∆H, ∆S and ∆G) have been calculated using Coats‐Redfern method based on thermal data analysis. In addition, fluorescence charac‐ terization used to verify the proposed assignments. 2. Experimental 2.1. Materials All solvents employed in synthesis were extra pure grad and used as received without further purification. Sulfaproxy‐ lene was purchased from Himedia, aldehydes were obtained from BDH, Merck, and Fluka and used as received. 2.2. Physical measurement Melting points were determined in open capillary tube using thermal scientific melting point apparatus. IR spectra were recorded by using Shimadzu FT‐IR type affinity spectrophotometer in the region 4000‐400 cm‐1 in KBr pellet. The 1H and 13C NMR spectra were recorded on a Bruker 400 (400 MHz for 1H and 100 MHz for 13C). Hadi / European Journal of Chemistry 6 (4) (2015) 404‐409 405 O -V an ill in Indol-3-carboxaldehyde p -H yd ro xy b en za ld eh yd e O-H yd ro xy ben za ld eh yd e Pyrole-2-carboxaldehyde Scheme 1 TMS as the internal standard was used as referenced to 0.0 ppm and DMSO‐d6 was used as solvent. The mass spectra were scanned by EI technique at 70 eV with Agilent Technologies 5973C spectrometer. Fluorescence spectra were recorded on Cary Eclipse Florescence spectrophotometer (Agilent technologies). The thermal analyses (TG and DTG) were carried out in dynamic nitrogen atmosphere (20 mL/min) with a heating rate 10 °C/min using Rheumatic Scientific Thermal Analyzer. Elemental analysis was performed in a CHNS‐932 LECO apparatus. 2.3. Synthesis methods 2.3.1. Preparation of Schiff bases (1‐7) The Schiff bases (1‐7) were synthesized by the condensation of sulfaproxylene with different aromatic and hetero aldehydes in molar ratio 1:1 either by refluxing in absolute ethanol, direct fusion or microwave irradiation. The reaction proceeded smoothly producing the corresponding Schiff bases in good yield. Also compounds 1, 4 and 5 were prepared by microwave irradiation assisted method using acidic alumina as a catalyst. The synthesis of Schiff bases were performed in accordance with reaction Scheme 1. 2.3.1.1. Synthesis of N‐((4‐((2‐hydroxy‐3‐methoxybenzylide ne)amino)phenyl)sulfonyl)‐4‐isopropoxybenzamide (1) Compound 1 was prepared by the condensation of 1 mmol of sulfaproxylene and 1 mmol of indol‐3‐carboxaldehyde in 25 mL of ethanol. The resulting mixture was then refluxed for 2hrs to give a yellow solid. It was cooled down to room temperature then it was filtered, washed with cold ethanol and dried over anhydrous CaCl2. The purity was checked by TLC (ethyl acetate: benzene) (3:7). Rf: 0.67. M.p.: 142‐145 °C. Yield: 77%. This compound was also prepared by microwave irradiation (under 100% power for 20 min) in presence of acidic alumina. The solid product dissolved in hot ethanol, filtered to give the yellow solid (Scheme 1). Color: Yellow. Yield: 77%. M.p.: 142‐145 °C. FT‐IR (KBr, , cm‐1): 3452(s)(N‐ H, Indole), 3337 (s) (NH, sulfa), 1654 (s) (C=O), 1631 (s) (C=N), 1343 (s), 1165 (m) (O=S=O), 950 (s) (N‐S), 829 (s)(C‐S). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.26 (d, 6H, J = 6 Hz, 2CH3), 4.72 (m, 1H, CH), 6.59‐7.80 (m, 13H, Ar‐H), 8.32 (s, 1H, CH=N), 9.93(1H, NH, indole), 11.89 (1H, NH, sulfa). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.5 CH (proxylene), 111.0‐137.1 (Ar‐C), 153.0 (C‐O), 160.0 (C=N), 164.2 (C=O). Anal. calcd. for C25H23N3O4S: C, 65.06; H, 5.02; N, 9.10. Found: C, 65.13; H, 4.94; N, 9.22%. λFlu (DMSO, max, nm): 422. λExc (DMSO, max, nm): 342. 2.3.1.2. Synthesis of N‐(4‐(2‐hydroxy‐3‐methoxybenzylidene amino)phenylsulfonyl)‐4‐isopropoxybenzamide (2) Compound 2 was prepared by direct condensation of an equimolarratio of o‐vanillin and sulfaproxylene on water bath at 60‐70 °C for 30 min. The obtained orange solid dissolved in acetone and precipitate after addition water, and then the solid filtered and dried (Scheme 1). Color: Orange. Yield: 65%. M.p.: 165‐167 °C (Dec.). FT‐IR (KBr, , cm‐1): 3411 (s) (OH), 3257 (s) (NH.‐sulpha), 1657 (s) (C=O), 1601 (s) (C=N), 1339 406 Hadi / European Journal of Chemistry 6 (4) (2015) 404‐409 (s), 1165 (m) (O=S=O), 950 (s) (N‐S), 833 (s) (C‐S). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.26 (d, 6H, J = 6 Hz, 2CH3), 3.84 (s, 3H, OCH3), 4.72 (m, 1H, CH), 6.61‐8.01 (m, 11H, Ar‐H), 8.98 (1H, CH=N), 11.85 (s, 1H, NH), 12.32 (br., 1H, OH). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.5 CH (proxylene), 56.3 (OCH3), 115‐139.1 (Ar‐C), 149.2 (C‐OCH3), 151 (C‐OH, phenolic), 153 (C‐O, proxylene), 162.3 (C=N), 167 (C=O). Anal. calcd. for C24H24N2O6S : C, 61.52; H, 5.16; N, 5.98. Found: C, 62.03; H, 5.08; N, 6.07%. λFlu (DMSO, max, nm): 436. λExc (DMSO, max, nm): 374. 2.3.1.3. Synthesis of 4‐isopropoxy‐N‐(4‐(pyridin‐2‐yl methyleneamino)phenylsulfonyl)benzamide (3) Compound 3 was prepared by addition of 1 mmol of pyridine‐2‐carboxaldehyde in 10 mL of ethanol to a hot solution of 1 mmol of sulfaproxylene in 20 mL of ethanol. The reaction mixture was poured in crash ice, then pink solid filtered and dried (Scheme 1). M.p.: 185‐187 °C (Dec.). Yield: 63%. Color: Pink. Yield: 43%. M.p.: 185‐187 °C (Dec.). FT‐IR (KBr, , cm‐1): 3263 (s) (NH.‐sulpha), 1658 (s) (C=O), 1612 (s) (C=N), 917 (s) (N‐S), 839 (s) (C‐S). 1H NMR (400 MHz, DMSO‐ d6, δ, ppm): 1.26 (d, 6H, J = 6 Hz, 2CH3), 4.72 (m, 1H, CH), 6.50‐ 7.41 (m, 12H, Ar‐H), 8.31 (s, 1H, CH=N), 11.85 (1H, NH). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.3 CH (proxylene), 111‐132 (Ar‐C), 151 (OH, phenolic), 153 (C‐O, proxylene), 162 (C=N), 164 (C=O). Anal. calcd. for C22H21N3O4S : C, 62.40; H, 5.00; N, 9.92. Found: C, 61.93; H, 4.97; N, 9.95%. λFlu (DMSO, max, nm): 436. λExc (DMSO, max, nm): 374. 2.3.1.4. Synthesis of N‐(4‐((1H‐pyrrol‐2‐yl)methyleneamino) phenylsulfonyl)‐4‐isopropoxybenzamide (4) Compound 4 was prepared by direct fusion in oil bath of an equimolar ratio of pyrol‐2‐carboxaldehyde and sulfaproxy‐ ene for 30 min. The dark solid dissolved in acetone and re‐ precipitated from cold water, filtered and washed with water and ether, to give a pink solid (Scheme 1). M.p.: 182‐183 °C. Yield: 41%. This compound was also prepared by microwave irradiation (under 80% power for 6 min) in presence of acidic alumina, the solid product dissolved in ethanol and filtered to remove the title compound. It was filtered again and washed with ether to give a pink solid. Color: Dark pink. M.p.: 182‐183 °C. Yield: 74%. FT‐IR (KBr, , cm‐1): 3462 (s) (NH, pyrole), 3377 (s) (NH, sulpha), 1654 (s) (C=O), 1627 (s) (C=N), 1317 (s), 1165 (m) (O=S=O), 951 (s) (N‐S), 829 (s) (C‐S). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.26 (d, 6H, J = 2.2 Hz, 2CH3), 4.72 (m, 1H, CH), 6.50‐8.35 (m, 11H, Ar‐H), 8.81 (s, 1H, CH=N), 11.51 (s, 1H, NH pyrrol), 11.81 (s, 1H, NH). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.5 CH (proxylene), 112‐130 (Ar‐C), 153.0 (C‐O, proxylene), 162.0 (C=N), 164.2 (C=O). Anal. calcd. for C21H21N3O4S : C, 61.30; H, 5.14; N, 10.21. Found: C, 61.64; H, 5.01; N, 10.33%. λFlu (DMSO, max, nm): 438. λExc (DMSO, max, nm): 381. 2.3.1.5. Synthesis of N‐(4‐(4‐hydroxybenzylideneamino) phenylsulfonyl)‐4‐isopropoxybenzamide (5) Compound 5 was prepared by direct fusion of 4‐ hydroxybenzaldehyde and sulfaproxylene in oil bath for 30 min. The yellow solid dissolved in acetone and water then kept it in refrigerator overnight. It was filtered, washed with water to give a pale yellow crystal (Scheme 1). M.p.: 183‐184 °C. Yield: 52%. This compound was also prepared by microwave irradiation (under 100% power for 16 min) in presence of acidic alumina. The product was purified by the same method of compound 4. Color: Pale yellow. Yield: 52%. M.p.: 184‐186 °C. FT‐IR (KBr, , cm‐1): 3478 (br)(OH), 3282 (s)(NH. sulpha), 1653 (s) (C=O), 1617 (s) (C=N), 1342 (s), 1152 (m) (O=S=O), 949 (s) (N‐S), 836 (s) (C‐S). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.26 (d, 6H, J = 2.2 Hz, 2CH3), 4.72 (m, 1H, CH), 6.50‐7.82 (m, 12H, Ar‐H), 8.31 (1H, CH=N), 11.88 (s, 1H, NH), 12.03 (br., 1H, OH). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.5 CH (proxylene), 114.0‐128.1 (Ar‐C), 160.0 (C‐O, phenolic), 153.0 (C‐O, proxylene), 160.0 (C=N), 167.3 (C=O). Anal. calcd. for C23H22N2O5S: C, 63.00; H, 5.06; N, 6.39. Found: C, 63.21; H, 5.00; N, 6.52%. λFlu (DMSO, max, nm): 440. λExc (DMSO, max, nm): 371. 2.3.1.6. Synthesis of N‐(4‐(4‐chlorobenzylideneamino) phenylsulfonyl)‐4‐isopropoxybenzamide (6) Compound 6 was prepared by direct fusion of an equimolar ratio of salicaldehyde and sulfaproxylene in water bath at 50‐70 °C for 30 min. The orange solid recrystallized from acetone: water (9:1, v:v) (Scheme 1). Color: Orange. Yield: 68%. M.p.: 224‐226 °C. FT‐IR (KBr, , cm‐1): 3444 (m) (OH), 3250 (s) (NH. sulpha), 1683 (s) (C=O), 1620 (s) (C=N), 1350 (s), 1168 (m) (O=S=O), 962 (s) (N‐S), 848 (s) (C‐S). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.26 (d, 6H, J = 6 Hz, 2CH3), 4.72 (hep., 1H, J = 6 Hz, CH), 6.60‐7.80 (m, 12H, Ar‐H), 8.98 (s, 1H, CH=N), 11.88 (s, 1H, NH), 12.44 (s, 1H, OH). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.5 CH (proxylene), 111.0‐132.0 (Ar‐C), 151.0 (C‐OH, phenolic), 153.0 (C‐O, proxylene), 162.0 (C=N), 164.4 (C=O). Anal. calcd. for C23H22N2O5S : C, 63.00; H, 5.06; N, 6.39; S, 7.31. Found: C, 63.16; H, 4.99; N, 6.61; S. 7.11%. λFlu (DMSO, max, nm): Not observed. λExc(DMSO, max, nm): 373. 2.3.1.7. Synthesis of N‐(4‐(2‐hydroxybenzylideneamino) phenylsulfonyl)‐4‐isopropoxybenzamide (7) Compound 7 was prepared by refluxing of 1mmol of p‐ chloro benzaldehyde and 1 mmol of sulfaproxylene in 25 mL of ethanol for 4 hrs. The solvent was evaporated and the resulting solid recrystallized from acetone:water (9:1, v:v) (Scheme 1). Color: Pale yellow. Yield: 71%. M.p.: 166‐168 °C. FT‐IR (KBr, , cm‐1): 3252 (br.) (NH. (sulpha), 1658 (s) (C=O), 1627 (s) (C=N), 1354 (s), 1136 (m) (O=S=O), 959 (s) (N‐S), 841 (s) (C‐S), 615 (s) (C‐Cl). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.26 (d, 6H, J = 2.2 Hz, 2CH3), 4.72 (hep., 1H, J = 6 Hz, CH), 6.60‐8.20 (m, 12H, Ar‐H), 8.79 (s, 1H, CH=N), 11.88 (s, 1H, NH). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 21.6 (CH3), 69.5 CH (proxylene), 114.0‐132.1 (Ar‐C), 136.7 (C‐Cl), 151.0 (C‐O, phenolic), 153.0 (C‐O, proxylene), 160.0 (C=N), 167.2 (C=O). Anal. calcd. for C23H21ClN2O5S : C, 60.46; H, 4.63; N, 6.13. Found: C, 59.57; H, 4.69; N, 6.53%. 3. Result and discussion The Schiff bases (1‐7) were synthesized by the conden‐ sation of sulfaproxylene with different aromatic and hetero aldehydes in molar ratio 1:1 either by refluxing in absolute ethanol, direct fusion or microwave irradiation. The reaction proceeded smoothly producing the corresponding Schiff bases in a good yield. Also compounds 1, 4 and 5 prepared by microwave irradiation assisted method using acidic alumina as a catalyst. The synthesized compounds are soluble in ethanol, chloroform, ethyl acetate, DMSO and DMF but insoluble in hexane, benzene and ether. All synthesized Schiff bases are stable and non‐hydroscopic. 3.1. IR spectra The IR spectra data of the synthesized Schiff bases (1‐7) exhibited a characteristic band in the range 1601‐1631 cm‐1 assigned to stretching vibration of azomethine group [23,31] thus it clearly shows an evidence for the formation of Schiff bases. All compounds shows a band resulting to ν(NH) of the sulfa moiety in the range 3250‐3377 cm‐1 [35]. In case of compound 1, the IR spectrum shows two sharp and strong bands including one band at 3452 cm‐1is attributed to the Hadi / European Journal of Chemistry 6 (4) (2015) 404‐409 407 indolemoiety [36] and the other band appears at 3337 cm‐1 is attributed to the ν(NH) of sulfaproxylene. Also compound 4 shows two sharp bands which are attributed to ν(NH) of sulfaproxylene and pyrrole moiety at 3337 and 3462 cm‐1, respectively [36]. Compounds 2 and 6 display a broad band resulting from hydrogen bonds ν(OH) at 3411 (2) and 3444 cm‐1 (6). The compound 7exhibits a strong band at 615 cm‐1 assigned to ν(C‐Cl). All compounds present a strong band attributed to ν(C=O) in the range 1653‐1683 cm‐1. The two strong bands appear at the range of 1317‐1354 and 1136‐ 1181 cm‐1 are due to asymmetric and symmetric stretching of O=S=O. Similarly all compounds exhibit bands at 937‐962 cm‐1 attributed to stretching of S‐N and at 829‐848 cm‐1 attributed to stretching of C‐S [36,37]. 3.2. NMR spectra 1H NMR spectra observed that all compounds spectra shows a doublet signal due to 6 protons of the two methyl groups of sulfaproxylene moiety at δ 1.26 ppm and a multiplet signal due to CH protons at δ 4.72 ppm. Also all compounds display the azomethine proton signal (CH=N) in the range of δ 8.30‐8.98 ppm. Compound 1 demonstrates the NH proton of indole moiety at δ 9.93 ppm as a singlet signal [23]. Spectra of compounds 2 and 6 display a broad signal for hydroxyl group proton at δ 12.32 and 12.44 ppm, respectively. It confirms the hydrogen bonding of a nitrogen atom of azomethine group. While a hydroxyl proton of compound 5 appears as a sharp singlet signal at 12.03 ppm. Similarly, compound 4 displays pyrole NH proton as a singlet signal at δ 11.51 ppm, as expected [38]. 13C NMR spectra of compounds (1‐7) display the azomethine carbon at δ 160‐162 ppm which clearly confirms the formation of Schiff bases. In addition, a signal at 21.6ppm in all compounds spectra is attributed to the two methyl groups’ carbon of salfaproxylene, while the CH carbon of proxylene moiety appears at δ 69.3‐69.5 ppm. Furthermore, all compounds show a signal of carbonyl at δ 164‐167.2 ppm. By details, compounds 2 and 6 spectra show a signal attributed to carbon attached to OH group at δ 151 and 153.1 ppm, respectively. Finally, compound 7 displays a signal at δ 136.7 ppm attributed to carbon attached to Cl. 3.3. Mass spectra analysis Under the following conditions, direct prop injection program, started at initial temp 50 °C with heating rate 70 °C/min with the final temperature 230 °C, the mass spectra of all synthesized compounds were recorded. The results demonstrate that all compounds display a molecular ion [M+] with low relative abundance 10%. The molecular ion peaks are in a good agreement with proposed formulas. The cleavage of S‐N and N‐C of sulfaproxylene moiety generates an intense peak represent the base peak in case of compounds 5 and 6. The mass spectra of a compounds 4 and 7 show the base peak at m/z = 121 attributed to ion (i). The common fragments of compounds are shown in Scheme 2. Scheme 2 All spectra display these peaks at m/z = 172, 156 and 92 attributed to the ions (ii, iii, iv), respectively. 3.4. Fluorescence spectra An additional fluorescence spectra characterization is used as a supplementary study to confirm the validity of the results. The synthesized Schiff bases are subject of fluorescence study based on their structures. Therefore, the absorption and fluorescence spectra of prepared compound in DMSO were analyzed. The fluorescence band position including absorption maximum λabs, fluorescence λFlu, and stocks shift data are supplied in the experimental section. The results show that the fluorescence bands of all compounds are broad. Compound 1 shows a high intensity (Figure 1), conversely, compounds 3 and 4 (Figure 2) shows less intensity in comparison with compound 1. Bands of compounds 2 and 6, are not observed, this may be attributed to intramolecular hydrogen bonding [39], between the OH group in ortho‐position and azomethine group in both compounds (Figure 3). Figure 1. 3D fluorescence spectrum of compound 1 in DMSO. (a) (b) (c) Figure 2. 1D (a), 2D (b) and 3D (c) fluorescence spectra of compound 4 in DMSO. 300 400 500 600 0 50 100 150 Wavelength (nm) In te n si ty ( a .u .) 43 8. 93 300 400 500 600 0 50 100 150 Wavelength (nm) In te n si ty ( a .u .) 44 0. 90 0 Z A x is Wavelength (nm) 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 200.00 250.00 300.00 350.00 400.00 450.00 500.00 550.00 600.00 650.00 700.00 750.00 800.00 850.00 172.53 159.07 145.62 132.16 118.71 105.25 91.80 78.34 64.89 51.43 37.98 24.52 11.07 -2.39 408 Hadi / European Journal of Chemistry 6 (4) (2015) 404‐409 Table 1. TG data and kinetic parameters of the complexes using the Coats‐Redfern equation. r ΔG (kJ/mol) ΔS (J/mol.K)ΔH (kJ/mol)E (kJ/mol) A (s‐1) Steps Temp (oC) a Compound 0.938168.581 ‐0.109107.527112.1672.23×107 1st 163 1 0.917158.803 ‐0.18556.77761.3492.33×103 1st 224 2 0.963185.005 ‐0.19863.56368.6595.72×102 2nd 0.995 143.208 0.723 51.3852 51.8118 5.89×105 1st 231 3 0.989191.422 ‐0.25231.58636.84985.15×102 2nd 0.997113.571 ‐0.11161.94163.1363.31×106 1st 225 4 0.99182.711 ‐0.13259.71461.2882.89×104 2nd 0.96459.731 ‐0.10646.63548.2541.05×108 1st 252 5 0.96757.013 ‐0.12435.75937.8222.35×107 2nd 0.97283.162 ‐0.10159.32161.1681.291×1091st 227 6 0.978 92.229 ‐0.154 70.664 73.360 3.281×1010 2nd 0.98378.144 ‐0.10160.98163.0811.297×1071st 241 7 0.986101.965 ‐0.11375.44578.3318.391×1062nd a Initial decomposition temperature. (a) (b) (c) Figure 3. 1D (a), 2D (b) and 3D (c) fluorescence spectra of compound 6 in DMSO. 3.5. Thermal analysis The thermal analysis (TG and DTG) of the compounds were utilized to get information about the thermal stability of the compounds [34,40‐42]. The compounds were subjected to a TG analysis under nitrogen atmosphere up to 800 °C with heating rate 10 °C/min. The initial decomposition temperature is reported in Table 1. As shown in Table 1, most compounds have two steps decomposition process. An investigation of Table 1 illustrates that compound 5 is the most stable compound but compound 1 the least stable compound. A comparison between compounds 2, 5 and 6 shows that compound 5 is more stable than compound 2 and 6 which all these compounds contain OH group where in compound 5, it positioned inpara position but in compound 6, it placed at ortho‐position. It clearly indicates that it has no effect on hydrogen bonding in the thermal stability. The compound 2 which contains an additional OCH3 group is less thermal stability in this comparison with compound 5 and 6 (Figure 4). In general, all compounds indicate a very fast decomposition rate after 300 °C and it continues up to 800 °C. Then, we cannot distinguish the nature of the decomposition product. Figure 4. TG/DTG of compound 2. 3.6. Kinetic and thermodynamic analysis data The thermal decomposition of the compounds was studied kinetically using the integral method applying the Coats‐ Redfern method [43‐45]. The activation energy (E), frequency factor (A), enthalpy of activation (ΔH), entropy of activation (ΔS) and Gibbs Free energy change (ΔG) have also been evaluated for each step and the results are reported in Table 1. The parameters are evaluated graphically from TG data by employing the Coats‐Redfern relation in the following form [43]: log 1 . (1) Where Wf and Wt are weight loss at end of stage and weight at temperature (t), respectively. Also, E, R, A and θ are the activation energy, the universal gas constant, pre‐ exponential factor and heating rate (here, 10 °C/min), respectively. The correlation coefficient (r) was calculated using the least square (LSR) method by plotting the left‐hand side versus 1000/T. The values of the correlation coefficient are changed in the range of 0.97‐0.99 which confirms the validity of results. Activation energy for each step was calculated from slope. It summarized for the first step of decomposition, maximum E obtained from compound 5 and for the second step, maximum E resulted for compound 7. The frequency factor showsa significant variation in both the first and second steps. Changes in entropy (ΔS) are calculated by using the following equation, . ∆ (2) where Kb and hare Boltzmann and Plank constant, respectively. The negative values of ΔS indicate that the 300 400 500 600 0 50 100 150 200 Wavelength (nm) In te n si ty ( a .u .) 43 8. 93 0, 74 300 400 500 600 0 50 100 150 200 Wavelength (nm) In te n si ty ( a .u .) 4 38 .9 30 ,7 4 Z A xi s Wavelength (nm) 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 200.00 250.00 300.00 350.00 400.00 450.00 500.00 550.00 600.00 650.00 700.00 750.00 800.00 850.00 132.40 122.02 111.65 101.28 90.91 80.54 70.17 59.79 49.42 39.05 28.68 18.31 7.93 -2.44 Hadi / European Journal of Chemistry 6 (4) (2015) 404‐409 409 activated compound has a more ordered than the reactants and shows that the decomposition reactions processes occur at very low rate [46]. The positive values of ΔH indicate that the decomposition processes are endothermic reactions, as expected. All value of ΔG was calculated from known Gibbs relation: ΔG = ΔH ‐ TΔS (3) The obtained positive value confirms that all steps are non‐spontaneous. 4. Conclusion The reported compounds were synthesized from a general procedure by the condensation of an equimolar ratio of sulfaproxylene with aldehydes either by refluxing in ethanol or direct fusion. In addition, compounds 1, 4 and 5 were synthe‐ sized by microwave irradiation. Spectroscopic techniques including IR, 1H and 13C NMR, fluorescence and mass analysis as well as elemental analysis were used to identify the products. To study the structural properties of studied molecules, complete analyses of thermal decomposition of complexes as well as some kinetic and thermodynamic properties of all complexes was reported. The kinetic and thermodynamic parameters as important values for stability index revealed high chemical reactivity of synthesized compounds in chemical reactions. References [1]. Patai, S. The Chemistry of the Carbon‐Nitrogen Double Bond; Science, John Wiley & Sons Ltd, London,1970. [2]. Maurya, M. R.; Uprety, B.; Avecilla, F.; Tariq, S.; Azam, A. Eur. J. Med. 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