J. Chem. Eng. Chem. Res. Vol. 1, o. 4, 2014, pp. 246-252 Received: June 24, 2014; Published: ctober 25, 2014 Journal of Chemical Engineering and Chemistry Research Synthesis and Spectroscopic Study of Some Phenolic Azo Derivatives Ramadan Ali Bawa and Ebtisam Mohammed Alzaraide Chemistry Department, Faculty of Science, Misurata University, P.. Box 875, Misurata, Libya Corresponding author: Ramadan Ali Bawa (ramadanali70@yahoo.com) Abstract: A previous study on the 4-(9-anthrylazo) phenol 1, revealed that two tautomers, 4-(9-anthrylazo)phenol (the azo phenol tautomer) and 4-[2-(anthracen-9-yl)hydrazono]cyclohex-2,5-dienone (the hydrazone tautomer) were formed. The two tautomers were observed in the proton MR of the product from which the ratio of these two tautomers have been found to be almost (1:1) yielding 53% of the phenol azo tautomer and 47% of the other tautomer. In this contribution, three new phenolic azo derivatives consisting of anthracene moiety were synthesized by coupling 9-anthryldiazonium slat with candidate phenols. The structures of these azo compounds were confirmed using spectroscopic techniques such as IR, MR and mass spectroscopy. According to the spectroscopic data, an azo/hydrazone tautomerism has been observed in some synthesized azo dyes in which they existed as two tautomers. The spectroscopic study revealed that two of the three synthesized compounds (4-(9-anthrylazo)-2-nitrophenol 2 and 4-(9-anthrylazo)-3-nitrophenol 3) showed no sign of tautomerism, whereas the third derivative 5-[2-(anthracene-9-yl)hydrazono]cyclohex-3-ene-1,2-dione 4 resulted from two consecutive tautomeric processes. Key words: Phenolic azo derivatives, synthesized, spectroscopic techniques, tautomerism. 1. Introduction Dyes are aromatic organic compounds absorb light at wavelengths ranging between 700-350 nm [1, 2]. The variety of colors of azo dyes is based on absorbing light in the visible region of the spectrum with the help of delocalized n- and -electrons throughout the structures of these aromatic dyes [3, 4]. The use of azo dyes in industries like textile, food, paper printing, cosmetic and electronic industries has notably been increased which attracted the attention of many research groups to further work on the synthesis, characterization, purification and the applications of such important molecules [5-11]. Azo dyes that have at least one conjugated proton donating group with the azo group could show azo hydrazone tautomerism [12]. This type of intramolecular proton transfer process in azo molecules was first noticed by Liebermann in 1883. The labile hydroxyl proton in 1-phenylazo-2-naphtol was reported to be capable bind to one of the two nearby nitrogens of the azo group [13]. A previous study regarding the azo hydrazone tautomerism on the 4-(9-anthrylazo) phenol 1, revealed that the formation of both tautomers, 4-(9-anthrylazo) phenol (the azo phenol tautomer) and 4-[2-(anthracen-9-yl) hydrazono] cyclohex-2,5-dienone (the hydrazone tautomer) was further proved by the proton MR of the product from which the ratio of these two tautomers have been measured and was found to be almost (1:1) yielding 53% of the phenol azo tautomer and 47% of the other tautomer [14]. Herein, a number of azo derivatives have been synthesized. These azo derivatives were compared with the previously synthesized 4-(9-anthrylazo) phenol 1 [14] (Fig. 1).
Synthesis and Spectroscopic Study of Some Phenolic Azo Derivatives 247 2 2 1 2 3 4 Fig. 1 Targeted azo derivatives. 2. Experimental 2.1 Materials itric acid, hydrochloric acid, anthracene, sodium hydroxide and methanol were purchased from Carloerba. Glacial acetic acid, sodium nitrite and sulfuric acid were purchased from Avonchem. Tin (II) chloride was purchased from PSPARK. o-itrophenol was purchased from Riedel De Haen, whereas m-nitrophenol and DMS were purchased from BDH Chemicals. All chemicals were used without further purification. 2.2 Instrumentation Melting point was measured on a Barnstead electrothermal IA 9100. Uv-vis absorptions were recorded on Uv-vis spectrophotometer-uv mini 1240-Shimadzu. ph was measured using Jenway ph meter 3505. 1 HMR spectrum was recorded on a Bruker Avance 300 spectrometer. Residual proton signal from the deuteriated solvents were used as references [DMS ( 1 H, 2.50ppm, 13 C, 39.51 ppm) and CDCl 3 ( 1 H, 7.24 ppm, 13 C, 77.23 ppm)]. Coupling constants were measured in Hz. Infrared spectrum was recorded on Jasco FT/IR-4100 Fourier transform infrared spectrometer. Mass spectrum was recorded on a Micromass Autospec M spectrometer. 2.3 Preparation of 4-(9-anthrylazo)-2-nitrophenol 2 An adapted literature procedure was followed [13-16] for synthesizing compound 2. 9-aminoanthracene 4 (0.77 g, 4.00 mmol) was dissolved in concentrated sulfuric acid (10 cm 3 ). The resulting solution was cooled to 0-5 C, to which a pre-cooled (0-5 C) aqueous solution of sodium nitrite (0.55 g, 8.00 mmol; in 30 cm 3 water) was added while stirring for 30 min maintaining the temperature between 0-5 C. An alkaline solution of the o-nitrophenol [0.56 g, 4.00 mmol; in 40 cm 3 of (2 a and 2.5 g sodium carbonate)] was cooled to 0-5 C and then added to the reaction vessel. The reaction mixture was stirred for an extra 1½ h at 0-5 C. A green precipitate was formed, filtered, washed with cold water (3 10 cm 3 ) and air dried. The crude material was recrystallized from glacial acetic acid, filtered, washed with water (3 10 cm 3 ) and air dried to give the azo dye 2 (0.93 g, 2.72 mmol, 68% yield) as a green fine powder. m.p 277 C; λ max 325 nm (CHCl 3 ); FT-IR(KBr disc): 3,447 cm -1 (Ar-), 1,583 cm -1 (=), 1,277 cm -1 (C-); δ H (400 MHz; DMS) 7.78-7.75 (3H, m, Ar-CH), 7.55-7.44 (4H, m, Ar-CH), 7.30-7-22 (2H, m, Ar-CH), 7.15-7.13 (1H, m, Ar-CH), 7.09-7.07 (1H, m, Ar-CH), 7.01-6.97 (1H, m, Ar-CH), 5.03 (H, s, Ar-); δ C (100 MHz; DMS) 183.70 (Ar-C-), 153.13 (Ar-C- 2 ), 136.52 (2 Ar-C-=) 135.86 (4 Ar-C), 134.32 (2 Ar-C), 129.10 (Ar-C), 128.51 (4 Ar-C), 127.15 (2 Ar-C), 126.50 (2 Ar-C), 120.16 (Ar-C), m/z (C 20 H 13 3 3, Mwt. 343.10) 342.89 (65%), 312.33 (17%), 298 (67%), 284.80 (27%). 2.4 Preparation of 4-(9-anthrylazo)-3-nitrophenol 3 A modified literature procedure was followed [13-16] for synthesizing compound 3. 9-aminoanthracene 4 (0.77 g, 4.00 mmol) was dissolved in concentrated hydrochloric acid (20 cm 3 ). The resulting solution was cooled to 0-5 C, to which a pre-cooled (0-5 C) aqueous solution of sodium nitrite (0.55 g, 8.00 mmol, in 30 cm 3 water) was added while stirring for 30 min maintaining the temperature between 0-5 C. An alkaline solution of the m-nitrophenol [0.56 g, 12.00 mmol, in 30 cm 3 of (2 a and 2.5 g sodium carbonate)] was cooled to 0-5 C and subsequently added to the reaction mixture. The reaction mixture was stirred for further 1½ h at
248 Synthesis and Spectroscopic Study of Some Phenolic Azo Derivatives 0-5 C. A bright brown precipitate was formed, filtered, washed with cold water (3 10 cm 3 ) and air dried. The crude material was recrystallized from ethanol 96%, filtered, washed with water (3 10 cm 3 ) and air dried affording the desired azo dye 3. (0.48 g, 1.40 mmol, 35% yield) as a fine bright brown powder, m.p 262 C; λ max 421 nm (CHCl 3 ); FT-IR (KBr disc): 3,473 cm -1 (Ar-), 1,530 cm -1 (=), 1,277 cm -1 (C-); δ H (400 MHz; DMS) 8.25-8.20 (2H, m, Ar-CH), 7.95-7.92 (2H, m, Ar-CH), 7.75-7-73 (2H, m, Ar-CH), 7.50-7.41 (4H, m, Ar-CH), 6.98-7.01 (2H, m, Ar-CH), 5.02 (H, s, Ar-); δ C (100 MHz; DMS); 183.94 (Ar-C-), 141.08 (Ar-C- 2 ), 135.85 (4 Ar-C), 134.32 (2 Ar-C-=), 133.44 (2 Ar-C), 130.41 (2 Ar-C), 129.09 (2 Ar-C), 128.04 (4 Ar-C), 126.85 (2 Ar-C); m/z (C 20 H 13 3 3, Mwt. 343.10) 342.99 (30%), 344.98 (10%), 312.03 (20%), 298.09 (55%). 2.5 Preparation of 5-[2-(anthracene-9-yl) hydrazono] cyclohex-3-ene-1,2-dione 4 A modified literature procedure was followed [13-16] for the synthesis of compound 4c. 9-aminoanthracene 5 (0.77 g, 4.00 mmol) was dissolved in concentrated sulfuric acid (10 cm 3 ). This solution was cooled to 0-5 C, to which a pre-cooled (0-5 C) aqueous solution of sodium nitrite (0.55 g, 8.00 mmol, in 30 cm 3 water) was added while stirring for 30 min maintaining the temperature between 0-5 C. An alkaline solution of the catechol [0.44 g, 4.00 mmol, in 30 cm 3 of (2 a and 2.5 g sodium carbonate)] was cooled to 0-5 C after which it was added to the reaction mixture. The reaction mixture was stirred for further 1½ h at 0-5 C. A black solid material was formed, filtered, washed with cold water (3 10 cm 3 ) and air dried. The crude black substance was recrystallized from glacial acetic acid, filtered, washed with water (3 10 cm 3 ) and air dried to give a mixture of the two hydrazone derivatives 68b and 68c (0.72 g, 2.29 mmol, 57% yield) as a fluffy black solid. m.p 371 C; λ max 254 nm (CHCl 3 ); FT-IR (KBr disc): 3,457 cm -1 (Ar-), 1,671 cm -1 (C=), 1,510 cm -1 (=), 1,277 cm -1 (C-); δ H (400 MHz; DMS) 7.74 (1H, d, Ј = 7.60, Ar-CH), 7.44-7.35 (4H, m, Ar-CH), 7.24-7.22 (2H, m, Ar-CH), 7.06-7.02 (2H, m, Ar-CH), 6.78 (1H, d, Ј = 9.10, CH) 6.72 (1H, d, Ј = 8.00, CH), 1.96 (2H, s, CH 2 ); δ C ( 100 MHz; DMS); 183.94 (1 Ar-C=), 173.82 (1 Ar-C=), 154.07 (1 Ar-C-), 145.32 (1 Ar-C=), 142.11 (2 Ar-C), 135.92 (4 Ar-C), 134.39 (2 Ar-C), 128.11 (4 Ar-C), 126.84 (1 Ar-C), 110.26 (2 CH=CH), 32.04 (1 CH 2 ); m/z (C 20 H 14 2 2, Mwt. 314.11) 316.18 (100%), 311.19 (48%), 296.99 (28%), 282.94 (48%). Selected peaks for tautomer 7, δ H (400 MHz; DMS) 6.94 (1H, d, Ј = 8.00, CH) 6.84 (1H, d, Ј = 8.70, CH), 5.00 (1H, s, Ar-), 1.89 (2H, s, CH 2 ). 3. Results and Discussion A previously reported literature procedure [14] was followed towards the synthesis of the phenolic azo dyes 4-(9-anthrylazo)-2-nitrophenol 2 and 4-(9- anthrylazo)-3-nitrophenol 3. Azo derivatives 2 and 3 were obtained in 68%, 35% yields respectivel-y throughout cross coupling reactions between the 9-anthryl diazonium salt 6 and an alkaline solution of o-nitrophenol or m-nitrophenol respectively (Scheme 1). The azo compound 2 absorb light at 431.0 nm to 337.0 nm with λmax 386.0 nm. The FTIR spectrum of this azo dye showed an absorption band at 1,583 cm -1 for the azo functional group (-=-) along with a weak broad stretching band at 3,447 cm -1 for a phenolic hydroxyl group, which could indicate that an intramolecular hydrogen bonding might be taking place H 2 2 Z i ii 5 6 Z may be HS 4 or Cl Reaction conditions and Reagents: (i) Conc. H 2 S 4 or HCl, a 2, 0-5 C; (ii) a, 0-5 C Scheme 1 Synthesis of azo dyes 2 and 3. X Y X= 2 and Y=H; 68% yield of azo derivative 2 X=H and Y= 2 ; 35% yield of azo derivative 3 X Y
Synthesis and Spectroscopic Study of Some Phenolic Azo Derivatives 249 between the hydrogen of the phenolic hydroxyl group and the oxygen of the adjacent nitro group. This puts the hydrogen atom in fixed six-membered ring like shape (Fig. 2). Such cyclic shape limits the stretching movement of the oxygen hydrogen bond (-H) to the minimum, which is thought to be the reason behind the shrinking in the band. The 1 HMR of the azo compound 2 shows no sign for a tautomerism as the distinctive doublets for the expected α-β-unsaturated keto system do not appear in the spectrum. The intramolecular hydrogen bonding in azo 2 might be the key factor for disallowing the tautomerism from taking place (Fig. 3). Fig. 2 IR spectrum of compound 2. Fig. 3 1HMR spectrum of azo derivative 2.
250 Synthesis and Spectroscopic Study of Some Phenolic Azo Derivatives The other azo derivative 3 was found to absorb light at wavelengths ranging between 580.0 nm and 210.0 nm with λ max of 430 nm, in chloroform. The IR spectroscopic data showed a rather broad stretching band for the hydroxyl group at 3,453 cm -1 along with an absorption band for the azo group (-=-) at 1,660 cm -1 (Fig. 4). The 1 HMR of the azo dye 3 confirms the formation of this azo compound as a single geometrical isomer which might be the thermodynamic stable trans-isomer. It s also worth mentioning that the 1 HMR spectrum of the azo compound 3 shows no sign for the hydrazone tautomer (Fig. 5). Fig. 4 IR spectrum of compound 3. Fig. 5 1HMR spectrum of azo derivative 3.
Synthesis and Spectroscopic Study of Some Phenolic Azo Derivatives 251 However, when the same synthetic procedure was carried out using the catechol, the 5-[2-(anthracene-9-yl)hydrazono]cyclohex-3-ene-1,2- dione 4 was obtained as a major product and no sign for the expected azo dye (Scheme 2). The structural formula of the product was confirmed by various spectroscopic techniques. The uv-vis spectrum showed that the product absorbs light at wavelengths ranging from 603.0 nm to 202.0 nm with λ max 371.0 nm, in chloroform. The IR data showed a rather weak band for a hydroxyl group at 3,468 cm -1 and weak absorption bands for the carbonyl group and the azo group at 1,671 cm -1 and 1,584 cm -1 respectively (Fig. 6). The 1 HMR showed two doublet peaks for the two aliphatic protons of the α,β-unsaturated keto system along with a singlet peak equivalent to the two protons of the methylene group in the 5-[2-(anthracene-9-yl) hydrazono]cyclohex-3-ene-1,2-dione tautomer 4. Another tautomer was also observed in 1 HMR spectrum as two doublets appeared at 6.94 ppm and 6.84 ppm belonging to the two asymmetric aliphatic proton of the α,β-unsaturated enol 7. Furthermore, the singlet peak of the hydroxyl group at 5.00 ppm as well as the singlet peak of the two protons of the methylene group were also observed at 1.89 ppm. This matches perfectly the two tautomers 5-[2-(anthracene-9-yl) hydrazono] cyclohex-3-ene- 1,2-dione 4 and the 5-(anthracene-9-yldiazenyl) -2-hydroxycyclohexa-2,4-dienone 7 (Fig. 7). It is important to state that the 1 HMR does not show any presence of the 4-(9-anthrylazo)- 2-hydroxyphenol. 3. Conclusion Three azo derivatives have been synthesized in moderate to good yields. The spectroscopic data of these compounds was extensively analyzed. The spectroscopic study revealed that two of the three synthesized compounds (2 and 3) showed no sign of tautomerism, whereas the third derivative 4 resulted from two consecutive tautomeric processes. H 2 i 5 6 2 HS 4 ii 57% H Reaction conditions and Reagents: (i) Conc. H 2 S 4, a 2, 0-5 C; (ii) a, 0-5 C Scheme 2 Synthesis of compound 4. 4 Fig. 6 IR spectrum of compound 4.
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