International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017
Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases Nashwan O. Tapabashi, Khalid. M. Al-Janaby, Samira. A. Mohammed
Abstract— A series of azo-Schiff bases and bis azo-Schiff bases were prepared by condensation reaction of azo-salicylaldehyde with different aromatic amines and azo-amines with various aromatic aldehydes in absolute ethanol. Thermal performances as well as photostabilities of the prepared compounds were tested by subjecting them as solutions in dimethyl sulfoxide to direct sunlight using a special exposure tool manufactured for this purpose. The results of exposure showed an improvement in the thermal performances of the prepared azo-Schiff bases comparing with the blank, the starting azo-amines and azo-aldehyde ranged between 3-7 degrees. The photostability studies against the sunlight proved stability of the prepared azo-Schiff bases compared to Congo red dye, one of the most famous azo dyes that have been selected as a reference for comparison, as well as to the azo-amines derived from. However azo-salicylicaldehyde was more photostable than its some azo-Schiff bases derivatives. Index Terms— Azo- Schiff bases, azo-amines, photostability, thermal performance.
aldehydes in absolute ethanol to try them as colorants to serve as photochemical convertors. II. EXPERIMENTAL All of the reagents and solvent involved in the synthesis were of analytically grade and used as received without any further purifications. Compound (1) was prepared as described previously [22].The structure of all synthesized compounds were confirmed by IR spectra, recorded on a FTIRspectrophotometer model Perkin-Elmer 2002 as pressed KBr disks in the region of 400-4000 cm-1 , as well as elemental analysis. The purity of prepared compounds was checked by TLC. Electronic spectra were recorded using a Schimadzu UV/VIS spectrophotometer; model 1650 PC as solutions in DMSO at room temperature. Melting point of all prepare compound were determined on Electro thermal BL-210 S apparatus. CHEMICAL SYNTHESIS
I. INTRODUCTION The continuous depletion of fossil fuel by the man led to adverse effect, such as environmental pollution that threatens human health as well as greenhouse gases linked to global warming and the consequent undesirable serious changes in climate such as melting of snows at the poles, raising of water levels in the seas and devastating floods sweeping the lowlands [1-6]. Therefore, the search for alternative energies that are renewable and environmentally friendly has become of paramount importance, and solar energy is one of these available options [6]. The chemical storage, being one of various applications of the photochemical conversion of solar energy, was the subject of series of researches which examined a wide spectrum of organic dyes such as, Rhodamine B, Congo red, Schiff bases, etc. as photochemical convertors [7-16]. Solar collectors, solar stills were designed and tested using those organic dyes as absorbers instead of black paints [17]. The extension of the strong electronic absorption maximum of azo compounds towards longer wavelength region by the presence of various aromatic moieties in combination with the fact that azo groups are relatively robust and chemically stable has prompted extensive study of azo-containing Schiff base compounds as dyes and colorants [18-21]. This motivated us in this work to prepare azo-Schiff and bis azo-Schiff bases from condensation reaction of azo-salicylaldehyde and some aromatic amines as well as azo-amines with various aromatic
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General procedure for the synthesis of azo-Schiff bases precursors (2a, 5a, 10a) 4- Phenylazo aniline (2a) was prepared by the general procedure given in [22]. Whereas 4-(4-nitrophenylazo) aniline (5a) and 4-(2, 4-dichlorophenylaszo) aniline (10a) were prepared according to the well-known literature procedure [23-31]. General procedure for the synthesis of azo-Schiff bases (3a-g, 6a-f, and 11a-f) 1 mmol of compounds (2a, 5a, 10a) in separate were dissolved in 25 mL of absolute ethanol with 1 mmol of appropriate aldehydes. The reaction mixture was refluxed with continuous stirring and then allowed to cool to room temperature. The product was collected and recrystallized from absolute ethanol. The period of reaction was controlled using thin layer chromatography (TLC) technique. The physical constants of all prepared compounds, time of reflux are shown in tables (1, 2, 3, and 4). IR (KBr) (cm-1) 1427-1483 (N=N), 1585-1625 (HC=N), 3000-3070 (C-H aromatic), 3217-3398 (OH), 1515 asy, 1343 sy (NO2). Synthesis of N,N-(1,4-Phenylene bis (methan)yl-1-ylidene)) bis (4-(phenyldiazynyl)amine (4a) Terphthalic aldehyde (1 mmol) and (2 mmol) of 4-(4-nitrophenylazo) aniline, 2a were condensed by refluxing in 10 mL of absolute Ethanol in presence of two drops of acetic acid for 8 hr. The solution was left at room temperature. The product was obtained as orange powder, filtered off, recrystallized from absolute ethanol, m.p.210-212°C, (65%).
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Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases IR (KBr) (cm-1) 1439 (N=N), 1620 (HC=N), 3022 (C-H aromatic). Synthesis of N, N-(1, 4-phenylene bis (4-nitro-yl-1-ylidene) bis (4-(phenyldiazynyl) amine diazo (7a) Terphthalic aldehyde (1 mmol) and (2 mmol) of 4-(4-nitrophenylazo) aniline, 5a were condensed by refluxing in 25 mL of absolute Ethanol in presence of two drops of acetic acid for 16 hr. The solution was left at room temperature. The product was obtained as orange powder, filtered off, recrystallized from absolute ethanol, m.p.212-214°C, (60%). IR (KBr) (cm-1) 1448 (N=N), 1583 (HC=N), 3000 (C-H aromatic). Synthesis of 4,4- bis (4-aminophenyliazo) biphenyl,12a (1.84 gm, 10 mmol) of finely powdered benzidine in in (8 mL) concentrated hydrochloric acid and (8 mL) of distilled water was heated at 80 °C to complete solution. The clear solution was drowned into an ice-water mixture, and was diazotized at 0- 5 °C with 5 mL, 2 gm sodium nitrite within 1 minute. The diazo solution was added in portions with continuous stirring during 15 minutes at 0 °C to 9 mL of 10% NaOH solution containing (0.02 mol) of aniline. The coupling mixture was stirred for further 0.5 hr in ice bath and then in room temperature. The dark green precipitate formed, filtered and washed with petroleum ether (60-80 °C), m.p 210 °C). IR (KBr) (cm-1) 1480 (N=N),), 3091 (C-H aromatic), 3298, 3421 (N-H) General procedure for the synthesis of azo-Schiff bases (13a-d) 20 mmol of appropriate aromatic aldehyde and (0.392 gm, 10 mmol) of the corresponding diamine 4,4- bis (4-aminophenyliazo) biphenyl, 12a was fused gently for 10-20 min. Upon cooling the solid mass washed with hot petroleum ether (60-80 °C), and with boiling ethanol for several times. The physical constants of all prepared compounds and time of fusion are shown in tables (5). IR (KBr) (cm-1) 1431-1449 (N=N), 1607-1621 (HC=N), 3005-3050 (C-H aromatic), 4000 (OH). General procedure for the synthesis of azo-Schiff bases (15a, 16a-b, and 17a-b) A mixture of (0.001 mol) 3-(p-Nitrophenylazo)-6-hydroxybenzaldehyde, 14a which was prepared according to the mentioned procedure in [27, 31] and the corresponding amines (0.001 mol) was refluxed in absolute ethanol. Excess solvent was distilled off and the solid formed was collected and recrystallized from ethanol. Table (6) shows the detailed physical properties of the prepared compounds and time of refluxes. IR (KBr) (cm-1) 1427-1524 (N=N), 1616-1622 (HC=N), 3000-3107 (C-H aromatic), 3392-3400 (OH), 1486 asy, 1342 sy (NO2). General procedure for the synthesis of azo-Schiff bases (18a-c) A mixture of (10 mmol) 3-(p-Nitrophenylazo)-6-hydroxybenzaldehyde, 14a and the corresponding diamine (5 mmol) was refluxed in dark with stirring in absolute ethanol. The solid formed upon cooling was collected and recrystallized from ethanol. Table (7) shows the detailed physical properties of the prepared
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compounds as well as time of reflux. IR (KBr) (cm-1) 1428-1542 (N=N), 1610-1614 (HC=N), 3000-3100 (C-H aromatic), 3392-3400 (OH), 1521 asy, 1339 sy (NO2). PHOTOCHEMICAL EXPERIMENTS Manufacture of the exposure system Exposure system, shown in fig. 1, was manufactured from two square shaped wooden pieces with (40X40 cm) in dimensions fastened to each other by pair of hinges, one served as a movable facial part and the other as a fixed base. A protractor was fixed to the joint point of the two part edges in order to adjust the angle of exposure to sun light. An angle of 45 degree was chosen as an optimum one during mid-year in Iraq. Twenty test tubes with 3 cm in diameter for each were arranged on the facial part in two rows, each row contained ten test tubes which were fastened to the wood by nylon arc wire. Hourly measurements of solution temperature were recorded throughout exposure time. The system was derived on an arc facing the geographical south to attain a permanent direct incidence of sunlight on the test solutions during irradiation hours by tracking the sun.
Fig. 1: Sketch of the exposure tool Thermal performance Experiments 20 mL of 1x10-4- 5x10-3 M solutions of each of the prepared compounds in Dimethyl sulfoxide replaced in 19 test tubes of 25 ml in size, whereas the twentieth test tube was filled with the solvent to serve as blank. All the test tubes were fitted with hollowed corks to insert thermometers till the middle part of the tubes to measure the hourly temperature of the solutions during three days of continuous direct exposure to sunlight by tracking the sun of the same group of solutions. Readings of the used thermometers were corrected through one week exposure in water as solvent and another week in dimethylsulfoxide. Photostability Experiments 20 mL of 1x10-4 M solutions of each of the prepared compounds in Dimethyl sulfoxide were replaced in 20 test tubes of 25 ml in size. All the test tubes were closed with corks and exposed continuously to direct sunlight radiation by tracking the sun. Photostability of the irradiated solution were followed by recording the values of absorbance of the solutions using Uv- visible spectrophotometer each six hours for three days exposure to the same set of solutions. Fig. 2 demonstrates the exposed solutions.
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International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017
Fig. 2: The exposed solutions demonstrated on the facial of the exposure tool
III. RESULTS AND DISCUSSION The compounds used in this research were prepared according to the following schemes:
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Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases
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International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017
UV-Visible spectroscopy of Azo-Schiff bases The uv-visible spectrum of the precursor azo-amines (2a, 5a, 8a, 10a, 12a) (1x10-4M) solution in Dimethyl Sulfoxide, DMSO showed two bands, the first at the range of (248-285)
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nm due to (π→π*) transition of the aromatic ring and the second in the visible area of the spectrum at the range (412426 )nm ascribed to (π→ π*) including the whole electronic system of the azo molecule. Whereas the lower intense band
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Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases due to (n→ π*) of the azo group was not identified. The absorption spectra of azo-Schiff bases (3a-g, 4a, 6a-f,7a, 9a-f, 11a-f, 13a-d, 15a, 16a-b, 17a-b, and 18a-c) which were derived from the precursors (azo compounds), recorded as solutions ranging between (10-3-10-4 M) in DMSO at room temperature, showed three main bands: The first band in the range of (225-268) nm is due to the moderate energy transfer (π → π*) of the aromatic ring [27,28]. This band appears at its absorption location close to absorption of 236 nm generally ascribed to the local induction of the benzene ring bonded to nitrogen atom (PhN=), in order to obtain a reciprocal effect between the lone pair of electrons on nitrogen atom and the (π) electron system of the aromatic ring itself [32,33]. The second band at the range (278-308) nm, in general, but in rare cases extended to 353 nm is due to the (π → π*) low energy transfer of the azomethine group, this band appears to be close to the characteristic absorption of (phCH=N-) group of the Schiff bases at (262.5) nm. This absorption was previously attributed by a number of researchers to (charge transfer), since the benzene ring bonded to the carbon atom is the electron donating group, whereas azomethine group acts as
electron accepting group [32-36].The third band at the visible area of the spectrum at the range of (410-647) nm ascribed to (π →π*) including the whole electronic system of the azo molecule masking the weaker and lower intense band due to (n →π*) of the azo group which appears at this region of the spectrum. Bands at the region of (218-225) nm which is usually observed in aromatic Schiff bases attributed to local induction of benzene ring bonded to carbon atom (phC=) was not distinctly identified here [34,37]. The absorption spectrum for (1x10-3 M) DMSO solution of compound 15a showed red shift compared with compound 14a and a new band due to (n → π*) of azo group at 497 nm was recorded besides the two main bands belonging to parent azo-salicyaldehyde, 14a at 223 nm and (305-328) nm ascribed to (π → π* ) transitions of aromatic ring [31]. Tables (1-7) summarize the physical properties of the azo-Schiff bases besides the absorption bands in uv- visible region.
Table (1): The physical properties and uv-visible spectral data of azo-Schiff Bases (3a-g)
N
Comp. No.
Ar
3a 3b
OCH3
N
N
CH Ar
UV-visible Spectral data (λmax,nm), DMSO 248 285,308, 353sh 410 308, 353sh 520
Molecular Formula
Color of the solid state
M.P. °C
yield %
Time of reflux, hr
C19H15N3
Light brown
136-138
95
3
C20H17N3O
Reddish orange
140-142
85
5
C21H19N3O2
Dark yellow
122-124
92
1
300,353sh 515
C21H20N4
Reddish orange
164-166
83
1
300,353sh, 520,542,550
H3CO
3c
OCH3
CH3
3d
N CH3
3e
OH
C19H15N3O
Black
156-158
75
1
3f
Br
C19H14N3Br
Brown
160-162
79
4
3g
NO2
C19H13N4O4
Orange
178-179
61
5
300, 520,545 306, 353sh, 472 245 287,308, 353sh 521
Table (2): The physical properties and uv-visible spectral data of azo-Schiff Bases (6a-f)
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International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017 O2N
Comp. N0.
Ar
6a H3CO
6b
OCH3
CH3
6c
N CH3
N
N
N
C H
Ar
Color
M.P. °C
Yield %
Time of reflux, hr
C19H14N4O 2
Light Brown
149-151
37
3
251 314,345,362sh 414
C21H18N4O 4
Dark Yellow
165-167
60
3
268 425
C21H19N5O 2
Reddish Yellow
180-182
70
4
Molecular Formula
6d
OH
C19H14N4O 2
Reddish Brown
159-161
67
4
6e
Br
C19H13N4O 2Br
Dark Brown
170-172
55
6
6f
NO2
C19H13N5O 2
Light Yellow
155-157
40
10
UV-visible Spectral data (λmax,nm), DMSO
252 348,352sh,361sh 427 245 310sh,343 448 240 303,310,353sh 432 248 353sh 412
Table (3): The physical properties and uv-visible spectral data of azo-Schiff Bases (9a-f)
H Ar C O2N
N
N N N
Comp. N0.
Ar
9a
OCH3
H C
Ar
Molecular Formula
Color of the solid state
M.P. °C
Yield %
Time of reflux , hr
C29H24N5O3
Reddish black
dec 188
65
3
C30H27N5O4
Dark brown
dec 190
70
2
C30H29N7O2
Brown
dec 172
50
3
H3CO
9b
OCH3
CH3
9c
N CH3
9d
OH
C26H19N4O4
Brownish black
dec 150
65
3
9e
Br
C26H18N5Br2
Dark brown
dec 182
75
4
9f
NO2
C28H21N6O5
Brown
dec 210
60
8
UV-visible Spectral data (λmax,nm), DMSO 222 300, 343sh 411 240 341, 350sh 430 263 343, 353sh 422 223 330, 353sh 423 220 327, 353sh 422 265 348, 353sh 440
dec.: Decomposition point
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Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases Table (4): The physical properties and uv-visible spectral data of azo-Schiff Bases (11a-f) Cl Cl
Comp . N0.
Ar
11a 11b
OCH3
N
N
N
H C
Ar
Color
M.P. °C
Yield %
Time of reflux, hr
C19H13N3Cl2
Yellowish Orange
130-132
62
5
C20H15N3Cl2
Brownish Yellow
120-125
38
7
C21H17N3O2Cl 2
Reddish orange
139-141
65
6
222 300 531,542sh, 647
C21H18N4Cl2
Light brown
140-142
60
5
250 305 520,560sh
Molecular Formula
H3CO
11c
OCH3
UV-visible Spectral data (λmax,nm), DMSO 300 520,542sh,610sh 222 300 531,542sh, 644
CH3 N
11d
CH3
11e
Br
C19H12N3Cl2Br
Orange
125-127
65
8
11f
NO2
C19H12N4O2Cl 2
Orange
160-162
40
14
267 353 520,564sh,601sh 267, 335 422sh,531, 542sh, 638
Table (5): The physical properties and uv-visible spectral data of azo-Schiff Bases (13a-d)
Ar
Comp . N0.
C H
Ar
N
N
N
N
N
N
C H
Color
M.P. °C
Yield %
Time of fusion, min.
C42H36N6O4
Reddish black
dec 260
67
10
C42H36N8
Dark Brown
dec 275
50
10
Molecular Formula
H3CO
13a
OCH3
CH3
13b
N
Ar
CH3
13c
OH
C38H27N6O2
Brownish black
dec 250
86
20
13d
Br
C38H26N6Br2
Brown
dec 200
70
15
26
UV-visible Spectral data (λmax,nm), DMSO 227 343 441 244 350 435 225 350 440 223 355 435
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International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017 Table (6): The physical properties and uv-visible spectral data of azo-Schiff Bases (16a-b, 17a-b]
HC O2N
Comp. N0.
Ar
N Ar
N
OH
Molecular Formula
Color
M.P. °C
Yield %
Time of reflux , hr
C19H17N7 O5
Reddish black
dec 220
61
4
C19H13N5 O5
Brown
dec 250
55
1
C25H18N6 O3
Orange
dec 295
87
2
C25H17N7 O5
Light Brown
203-205
71
5
N
HO
16a
16b
NO2
17a
17b
N N
N
N
NO2
UV-visible Spectral data (λmax,nm), DMSO 222 328, 352sh 542, 585 220 325, 352sh 542, 563 224 304,309,328,352sh 493 221 300,307,329,349sh 490
Table (7): The physical properties and uv-visible spectral data of azo-Schiff Bases (18a-c) HC O2N
Comp. N0.
X
18a
18b
18c
CH2(CH2)4CH2
N
N
Molecular Formula
N X
N
CH HO
OH
N
N
NO2
Color
M.P. °C
Yield %
Time of reflux, hr
C38H26N8O6
Light red
dec 295
45
4
C32H30N8O6
Dark red
178-180
29
4
C32H22N8O6
Brownish red
dec 268
55
4
Thermal performances of Azo-Schiff bases Thermal performance of aqueous solution of well-known individual and mixed dyes absorbing light in the different wave lengths of solar spectrum was recorded earlier [104,105]. Compounds which gave maximum possible thermal performance in the visible region of the solar spectrum were tested in solar collectors [17, 38, 39]. The selection of optimal concentrations of the dyes used was found to depend on their molar extinction coefficient, photostabilities, besides synthesis and operating cost thereof in liquid solar collector [38, 39]. Previous studies have shown that the thermal performance of dyes exposed to direct sunlight, whether alone or in combination, depends on how stable the dyes are toward the chemical reactions between the molecules and the photochemical reactions (dissociation and
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UV-visible Spectral data (λmax,nm), DMSO 224 285,352sh,427 449,490 220 323,328 541, 611 258 305,352sh 422
oxidation). The concentrations of the dye mixtures having highest thermal performance and most stable against direct sun light were determined for each single dye separately [38, 39]. Thermal performance for all of the prepared compounds in this work was studied as dimethyl sulfoxide (DMSO) solutions plus the solvent by exposing them to direct sunlight for two-three clear days, twelve hours a day starting from 7 o’clock morning till 6 o’clock evening using the system shown in fig. 1. The hourly measurements recorded at the beginning of each hour of the day showed an increase in the temperature of the solutions compared to the solvent ranged between 3-7 degrees. The results of thermal performances are exhibited in the tables (8-13), as it was exposed as six batches. The results of each batch are shown in single table in compare with the solvent used.
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Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases Table (8): Thermal performance of compounds (2a, 3ag) Temperature of solutions exposed to sunlight (°C)
Exposure timing
DMSO 34 43 47 51 51 53 54 55 54 52 51 45
7 am 8 am 9 am 10 am 11 am 12 pm 1 pm 2 pm 3 pm 4 pm 5 pm 6 pm
Exposure timing 7 am 8 am 9 am 10 am 11 am 12 pm 1 pm 2 pm 3 pm 4 pm 5 pm 6 pm
2a 34 44 48 52 52 55 55 55 55 54 50 44
3a 38 49 52 54 54 55 56 57 56 56 53 49
3b 35 45 50 54 54 56 57 58 56 55 51 47
3c 37 49 51 55 56 56 57 58 56 54 51 47
3d 37 48 52 55 55 57 57 58 58 57 53 48
3e 36 46 51 55 55 56 57 58 57 57 52 48
3f 39 48 51 53 55 57 58 57 57 57 54 47
3g 38 47 51 54 56 57 57 57 56 55 52 47
Table (9): Thermal performance of compounds (4a, 5a, 6a-f, 7a) Temperature of solutions exposed to sunlight (°C) DMSO 36 37 39 41 43 47 47 48 46 46 43 40
Exposure timing
7 am 8 am 9 am 10 am 11 am 12 pm 1 pm 2 pm 3 pm 4 pm 5 pm 6 pm
4a 37 38 41 44 46 49 51 51 49 50 46 42
5a 35 36 39 43 44 46 46 50 45 50 41 40
6a 37 37 40 42 43 48 48 52 47 52 43 40
6b 38 40 40 44 47 51 50 51 50 51 47 42
6c 39 41 42 43 46 52 51 51 50 51 48 43
6d 39 40 42 44 45 50 50 54 48 52 45 42
6e 39 40 42 44 45 50 50 53 48 52 45 42
6f 38 40 43 45 46 51 50 50 49 48 47 41
7a 38 39 42 44 45 50 50 53 50 51 45 42
Table (10): Thermal performance of compounds (8a, 9a-f) Temperature of solutions exposed to sunlight (°C)
DMSO 39 47 49 52 50 51 53 55 55 53 39 39
8a 39 48 51 54 52 51 53 57 55 53 37 39
9a 43 53 56 59 56 56 57 60 58 56 41 43
9b 42 54 56 57 57 56 57 58 56 55 51 47
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9c 41 51 54 57 54 54 55 58 57 55 39 41
9d 43 54 56 59 59 59 58 58 56 55 50 43
9e 41 50 54 58 56 55 56 59 58 56 40 41
9f 43 52 55 58 57 56 58 60 58 56 41 43
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International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017 Table (11): Thermal performance of compounds (10a, 11a-f) Exposure Temperature of solutions exposed to sunlight (°C) timing DMSO
10a
11a
11b
11c
11d
11e
11f
47 48 55 56 58 54 55 55 55 53 49 44
46 59 57 58 59 55 55 56 56 53 48 46
47 50 56 58 60 57 57 58 58 55 50 49
47 51 58 59 62 62 61 60 59 57 52 49
45 50 59 59 60 59 59 59 58 56 53 48
48 50 59 61 61 58 58 58 59 55 51 48
47 52 59 60 61 58 58 58 58 56 52 49
47 51 58 61 61 62 61 60 59 56 53 48
7 am 8 am 9 am 10 am 11 am 12 pm 1 pm 2 pm 3 pm 4 pm 5 pm 6 pm
Table (12): Thermal performance of compounds (12a, 13a-d) Exposure Temperature of solutions exposed to sunlight (°C) timing
7 am 8 am 9 am 10 am 11 am 12 pm 1 pm 2 pm 3 pm 4 pm 5 pm 6 pm
Exposure timing
7 am 8 am 9 am 10 am 11 am 12 pm 1 pm 2 pm 3 pm 4 pm 5 pm 6 pm
DMSO
12a
13a
13b
13c
13d
39 47 49 52 51 51 53 55 55 53 39 36
42 50 54 57 56 56 57 59 58 56 41 39
43 52 56 61 60 59 59 59 58 57 43 40
43 53 57 60 58 57 58 60 60 58 42 40
41 50 54 57 55 54 54 57 58 56 40 37
41 50 54 58 56 55 56 59 58 56 39 37
Table (13) thermal performance of compounds (14a, 15, 16a-b, 17a,b, 18a-c) Temperature of solutions exposed to sunlight (°C)
DMSO 35 45 49 52 54 52 56 55 53 52 47 41
14a 34 46 50 53 55 52 57 55 54 53 47 44
15a 38 50 53 57 57 58 58 58 58 56 51 44
16a 38 49 53 57 56 56 57 57 56 56 51 43
16b 37 48 53 56 57 56 56 56 55 55 52 45
Photostability of Azo-Schiff bases Photostabilities of the same compounds were also studied using the same exposure system for thirty six hours of exposure, in total, during three consecutive days at the first
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17a 37 48 52 56 57 57 56 56 55 54 53 44
17b 38 49 53 57 57 56 57 56 55 55 53 44
18a 38 49 54 58 60 57 60 60 57 56 51 43
18b 35 47 52 57 58 57 58 58 56 55 49 41
18c 36 47 54 56 59 58 58 57 56 55 51 44
week of July at the site of Kirkuk University, college of science. This study deliberately experimented exposing the prepared compounds to solar radiation in summer season to examine the possible severe conditions of testing. The choice
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Thermal Performance, Photostability and UV-Visible Spectroscopic Studies of Some Synthesized azo- Schiff and Bis-azo-Schiff bases of DMSO as a solvent in the preparation of solutions was an attempt to overcome the solubility problem of our certain compounds as well as to avoid utilization of aqueous solutions, due to tendency of them toward hydrolysis. Some facts were taken in consideration in choosing exposure solutions which were; working in the optimum ranges of concentrations recorded in previous studies [38-40], to avoid the mirror effect (i.e. very concentrated solutions of the dyes serves as mirror reflecting light beams preventing access of light into the solutions), as well as matching the spectrum of the exposed solution with solar spectrum in the visible region. Some earlier work indicated that high molecular weights organic dyes having larger number of extended double bonds, containing electro-donating and electro-withdrawing groups and multiple molecules covalently bonded to each other are the most photostable compounds [41]. In this investigation, single and multiple azo as well as multiple azomethine moieties of azo-Schiff bases were prepared to examine the effect of multiplicity of azo and azomethine groups on their photostabilities. Photostabilitiy studies showed distinct stabilities of the prepared azo-Schiff bases, in general, compared to the Congo red dye, one of the most important azo dyes selected for comparison, and to their precursor azo-amines under the same climate condition of exposure. This study showed the instability of Congo red as solution in DMSO, average rate of its phtodecomposition was the faster (9.01 x10-5 M hr-1), since previous studies recorded its photofading in aqueous solutions [42, 43].Table (8) exhibits the average rate of photodecomposition of (1x10-4 M) DMSO solutions of the azo-Schiff bases being calculated from their photodecomposition curves in comparison with their azo precursor. In all cases the azo-amine precursors were less photostable than their azo-Shiff derivatives (i.e. it had the faster average rate of photodecomposition). However the azo-salicyaldehyde precursor (compound 14a) was more stable (R=2.40x10-7 M hr-1) than some of its azo-Schiff
derivatives (compounds 15a, 16a-b,17a,-b, 18a-c-). Since the aim of this work was to introduce the energetically rich azomethine group into the azo compounds in order to take advantage of their long wavelengths in the visible region of solar spectrum and to study the potential contribution of the azomethine group, through extended conjugation, in increasing basicity of the (-N=N-) group to protect it from photodecomposition, our results reveals some success in achieving this goal. Our study, also, did conclusively demonstrate the effect of multiplicities of the both groups on enhancing photostability, besides it served to push the absorption spectrum bathochromatically toward the middle of solar spectrum (in this wavelengths 500-600 nm) by introducing the active azomethine into azo compounds (the cases of compounds, 16a-b, 17a-b,18a-c). These facts make our compounds candidates to be efficient if they were chosen as absorbers in solar liquid collectors in the future, or if it were preferred as photosensitizers in three component systems, provided that their oxidation potentials matched with the reduction potential of some relay systems like methyl viologen [9]. The decrease in the absorption values of the dyes over time is an evidence of decreasing of the concentration with continuation of irradiation period which is a normal result for decomposition of the dyes. Earlier studies have shown that high temperatures accompanied by direct exposure to sunlight accelerate the fragmentation of each dye as result of the increase in the speed of primary and secondary photochemical reactions [41, 43]. Since the highly energetic photons absorbed by the dye molecules, transferring them to their excited state, cause oxidative reactions of the excited molecules ending with the decomposition of the molecule and loss of color. In azo dyes, for example, the nucleus is broken in the presence of light to form azoxy group (R-N=N-O) which cause the dissociation of the molecule in the subsequent steps [42, 44].
Table (8) Average rate of photodecomposition (1x10-4 M) DMSo solutions of Azo-Schiff bases compared (3-10,12-17, 19-32,34-37, 39-46) with their azo precursors (2,11,18,33) Cp. R (M hr-1) Cp. R (M hr-1) Cp. R (M hr-1) Cp. R (M hr-1) Cp. R (M hr-1) No. No. No. No. No. 2a 2.20 x 10-6 5a 3.43 x10-6 9a 2.11 x 10-6 11c 1.08 x 10-6 14a 2.40 x 10-7 3a 1.12 x 10-6 6a 2.05 x10-6 9b 1.11 x 10-6 11d 9.89 x 10-7 15a 2.81 x 10-6 3b 6.11 x 10-7 6b 1.37 x 9c 1.00 x 10-6 11e 1.63 x 10-6 16a 2.28 x 10-6 10-6 3c 4.76 x 10-7 6c 8.30 x 9d 3.17 x 10-7 11f 2.40 x 10-6 16b 2.02 x10-6 10-7 3d 1.58 x10-6 6d 2.86 x 9e 2.11 x 10-7 12a 4.76 x 10-6 17a 1.87 x 10-6 10-6 3e 2.19 x 10-7 6e 1.97 x 9f 4.19 x 10-7 13a 2.53 x 10-7 17b 9.50 x 10-7 10-6 3f 4.71 x 10-7 6f 1.60 x 10a 1.48 x 10-6 13b 1.08 x 10-6 18a 8.76 x 10-7 10-6 3g 5.87 x 10-7 7a 1.07 x 11a 1.71 x 10-6 13c 2.23 x 10-7 18b 8.20 x 10-7 10-6 4a 5.68 x 10-7 8a 2.11 x10-6 11b 7.70 x 10-7 13d 4.08 x 10-7 18c 2.89 x 10-6 R: Average rate of photodecomposition
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International Journal of Engineering and Advanced Research Technology (IJEART) ISSN: 2454-9290, Volume-3, Issue-7, July 2017 [44] A. J. Abdul-Ghani, N. O. Tapabashi, and S. N. Maree, J. Solar Energy Research, 1988, 6(1), 31.
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Nashwan O. Tapabashi, Dep. Of Chemistry, College of Science, University of Kirkuk, Iraq Khalid. M. Al-Janaby, Dep. Of Chemistry, College of Education for pure science, University of Tikrit, Iraq Samira. A. Mohammed, Dep. Of Chemistry, College of Education for pure science, University of Tikrit, Iraq
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