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An Efficient Microwave Assisted Synthesis of Triphenodioxazines Using Chloranil as Oxidizing Agent.

Byline: Muhammad Najeeb Ullah, Munawar Ali Munawar, David William Knight, Misbahul Ain Khan, Amran Waheed and Khalid Mohammed Khan

Summary: An efficient new method for the preparation of triphenodioxazines (TPDOs) using p- chloranil as oxidizing agent in conc. H2SO4 under microwave irradiation at 120C is reported. This method is more efficient than the previously described microwave method using potassium persulfate as oxidising agent in conc. H2SO4 as it provides the cyclized product within 8-10 minutes with comparatively higher yields.

Keywords: Synthesis, Dyes, TPDOs, Heterocycles, Microwave, p-chloranil

Introduction

Triphenodioxazines (TPDOs) are nitrogen and oxygen containing heterocycles involved in a number of biological processes. A brief description of the conventional and other non-microwave methods for the preparation of TPDOs and their applications has been reported in our previous article [1]. In addition several of their useful biological applications have been reported. Both TPDOs and triphenodithiazines (TPDTs) show encouraging applications as pharmaceuticals as they inhibit the growth of bacteria and are capable of removing muscular tensions [2, 3]. These compounds act as valuable hypnotic agents as they are involved in inducing sleepiness to provide calmness [4]. Furthermore, these materials have been proved as powerful antifungals [5, 6] and show remedial effect for inflammation and have been proved anti- inflammatory by Belen'kii and Kruchkovskaya [7].

The TPDOs and TPDTs work as promising anticancer agents by stopping the progressive, uncontrolled cell division [8, 9] and are capable of treating paranoia, schizophrenia and other psychotic disorders [10]. Allergic reactions caused by histamines in human beings may be controlled by the use of the aforementioned compounds [11], which are useful depressant drugs to treat anxiety and tension disorders and act as tranquilizers as well [12]. In addition TPDOs have been proved to be useful as air-stable semiconducting materials in organic field effect transistors (OFETs) [13]. TPDOs also find applications in the field of organic electronics. Nicolas et al have recently shown that nitrile and triisopropylsilylethynyl (TIPS) substituted TPDOs are air stable, soluble and exhibit n-type properties in OFETs [14]. Suitably substituted push and pull unsymmetrical TPDOs find promising use in dye- sensitized solar cells (DSSCs) with maximum power conversion efficiency of 6.3% [15].

In our previously reported method [1] a combination of potassium persulfate and conc. sulfuric acid was used along with microwave heating to get up to 75 % yield of the cyclized product. The method however, has a disadvantage that at high temperature potassium persulfate starts decomposing and the decomposition increased significantly with increasing temperature [16]. So potassium persulfate in acidic medium as oxidizing agent at higher temperature is not practical. Since in our previously reported method persulfate was heated in the presence of 95-97% sulphuric acid, the decomposition of persulfate decreased its effectiveness as oxidizing agent. The decomposition reaction as described by Palm [16] has been shown in scheme-1.

(Equation)

So there is a need to improve this microwave method. In the present communication we would like to report thereof p-chloranil as alternative oxidizing agent which might be used to avoid decomposition under microwave heating conditions.

Recently chloranil was employed as cyclising agent for the synthesis of dissymmetric TPDOs, however, the product was obtained indirectly through bisphenoxy or phenoxazine tricyclic intermediate [14, 15] instead of dianilide intermediate. In addition the reaction time was longer and the reacting mixture was stirred overnight in comparison to our MW reaction time which is far more less and ranges from 8-10 minutes. Experimental General Information All reagents were purchased from Aldrich and Alfa aesar and were used as such without any further purification. CEM DISCOVERY instrument was used for microwave experiments. Bruker DPX spectrometer (400 MHz) was used to obtain 1H NMR spectra. All the 1H NMR spectra were run at room temperature and chemical shifts in ppm were obtained by comparing with Trimethylsilane (TMS: d = 0.00). Coupling constants (J) values are given in Hz.

JASCO-v-570 spectrophotometer was used to measure UV-Vis spectra. Nicolet Impact-410 Fourier Transform Infrared (FTIR) spectrophotometer was used to record IR spectra. VG Plateform II Quadrupole spectrometer was used to obtain low resolution mass spectra. Electron impact (EI, 70 eV) and atmospheric pressure chemical ionization (ApcI) modes of ionizations were used for mass analysis. Similarly, the modes of ionization for high resolution mass spectra are specified. Kofler hot stage instrument was used to obtain melting points of the purified compounds. Perkin Elmer 2400 Elemental Micro analyser was used to obtain the elemental ratio of the synthesized compounds.

General procedure for the syntheses of Benzoquinone intermediates (A)

All the intermediate dianilides were prepared according to the literature method [1]. This method was modified a little in order to get the maximum yields. The modifications are mentioned in the appropriate sections.

2,5-Bis(4-aminophenylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione (1A)

The purified brown coloured product 1A showed m.p. > 300C,; max(KBr)/cm-1 3380, 3252, 1651, 1575, 1514, 1490, 1434, 1329, 1291, 1256, 1197, 1170, 1084, 1016, 890, 833, 757, 701, 650, 616; dH (DMSO-d6) 6.01 (4 H, br. s, 2 x NH2), 6.69 (4 H, d, J = 8.5 Hz, 4 x Ar-H), 6.95 (4 H, d, J = 8.5 Hz, 4 x Ar-H), 9.57 (2 H, s, 2 x NH); m/z (MS ES+, 4.60e12), 392 (14 %, M+4), 391 (38, M+3), 390 (2, M+2), 389 (2, M+1), 388 (6%, M+), 313 (38), 312 (14), 311 (57), 310 (12), 309 (100); Calc. for C18H14Cl2N4O2: C, 55.54; H, 3.63; N, 14.39. Found: C, 54.96; H, 3.65; N, 15.03.

2,5-Bis(4-methoxyphenylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione (2A)

Brown solid, m.p. 282C (decomp.); max(KBr)/cm-1 3223, 3011, 1651, 1609, 1566, 1510, 1485, 1416, 1322, 1306, 1244, 1195, 1171, 1112, 1032, 1012, 945, 892, 827, 800, 755, 737, 710, 696, 649, 622; dH (DMSO-d6) 3.74 (6 H, s, 2 x OMe), 6.90 (4 H, d, J = 8.3 Hz, 4 x Ar-H), 7.11 (4 H, d, J = 8.3 Hz, 4 x Ar-H), 9.62 (2H, s, 2 x NH); m/z (EI+, 3.09e+003) 424 (7 %, M+6) , 423 (10, M+5) , 422 (42, M+4), 421 (17, M+3), 420 (70, M+2) , 419 (5, M+1), 418 (18, M+), 400 (15) , 389 (5), 388 (17), 387 (14), 386 (57), 385 (6), 384(16), 383 (4), 371 (14), 350 (35), 174 (22), 123 (32), 108 (45), 84 (14), 58 (100); Calc. for C20H16Cl2N2O4: C, 57.30; H, 3.85; N, 6.68. Found: C, 56.94; H, 3.86; N, 6.71.

2,5-Bis(p-tolylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione (3A)

Green powder, m.p. = 310C (decomp.); max(KBr)/cm 3230, 1640, 1611, 1561, 1510, 1470, 1404, 1322, 1304, 1248, 1198, 1171, 1108, 1033, 1021, 944, 890, 820, 800, 760, 739, 710, 695, 650, 628; dH (DMSO-d6) 2.30 (6 H, s, 2 x Me), 7.05 (4 H, d, J = 8.2 Hz, 4 x Ar-H), 7.15 (4 H, d, J = 8.2 Hz, 4 x Ar-H), 9.63 (2 H, s, 2 x NH); m/z (EI+, 1.20e+003), 392 (10 %, M+6), 391 (16, M+5), 390 (35, M+4), 389 (24, M+3), 388 (100, M+2), 387 (23, M+1), 386 (78, M+), 371 (14), 358 (8), 357 (14), 356 (22), 355 (44), 354 (13), 353 (14), 352 (11), 351 (35), 315 (38), 267 (28), 192 (17), 158 (18), 129 (19), 128 (12), 127 (79), 106 (23), 91 (24), 84 (52), 63 (77); Calc. for C20H16Cl2N2O2: C, 62.03; H, 4.16; N, 7.23. Found: C, 62.08; H, 4.09; N, 7.18.

2,5-Bis(9-ethyl-9H-carbazol-3-ylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione (4A)

A suspension of p-chloranil (4.68 g, 19.05 mmol) in ethanol (20 mL) was added to a mixture of 3-amino-9-ethylcarbazole (8.0 g, 38.10 mmol) and sodium acetate (3.2 g, 39.0 mmol) in ethanol (30 mL) in small portions. The reaction was left at 45C for a period of 1 hour and then the temperature was increased slowly to 60C and maintained for two hours. The progress of the reaction was assessed by using silica gel TLC plates and n-hexane: acetone: DMR, 1:4:0.5 as solvent system.

After completion, the reaction mixture was concentrated under reduced pressure and the residue was mixed with water (100 ml).

The precipitates were filtered, washed first with water (100 mL) and then with ethanol (50 mL) and dried under vacuum to give brown 4A, 9.62 g, 85.3 %. Mp > 310C; FTIR max(KBr/cm-1): 3410, 3240, 3058, 2924, 1645, 1575, 1495, 1473, 1436, 1310, 1220, 1170, 1140, 1090, 1023, 915, 875, 804, 740, 680, 657. 1H-NMR; dH (400 MHz, DMSO-d6, ppm): d 1.3 5 (t, 6H, J = 7.1 Hz, 2 CH3), d 4.4 8 (q, 4H, J = 7.1 Hz, 2 CH2), d 7.21 (t, 2H, J = 7.6 Hz, 2 Ar-H), d 7.35 (dd, 2H, J = 8.7, 1.7 Hz, 2 Ar-H), d 7.48 (ddt, 2H, J = 8.0, 0.9 Hz, 2 Ar-H), d 7.60 (d, 4H, J = 8.7 Hz, 4 Ar-H), d 7.62 (d, 2H, J = 8.3 Hz, 2 Ar-H), d 8.01 (d, 2H, J = 1.5 Hz, 2 Ar -H), 8.15 (d, 2H, J = 7.6 Hz, 2 Ar-H), d 9.91 (s , 2H, 2NH). m/z (ES+, 1.40e4), 595 (5 %, M+3), 594 (9, M+2), 593 (6, M+1), 592 (13, M+), 523 (4), 522 (9), 521 (8), 180 (37), 167 (100), 91 (28); Calc. for C34H26Cl2N4O2: C, 68.81; H, 4.42; N, 9.44. Found: C, 68.73; H, 4.41; N, 9.52.

2,5-Bis(4-phenylazophenylamino)-3,6-di chlorocyclohexa-2,5-diene-1,4-dione (5A)

4-phenylazophenylamine (7.0 g, 35.53 mmol) was reacted with p-chloranil (4.37 g, 17.76 mmol) in the presence of sodium acetate (2.95 g, 36.0 mmol) in ethanol. The temperature of the reaction ion was maintained at 45C for 4.5 hours. The reaction course was tested by using silica gel TLC with hexane: acetone: DMF solvent system in a ratio of 1:3: 0.5. After completion of the reaction, the mixture was cooled and a precipitate was formed, filtered, washed with water (200 mL) and dried under vacuum to give 5A as brown powder 7.84 g, 77.8 %.

Mp > 310C; brown solid; FTIR max (KBr/cm-1): (cm-1), 3322, 3278, 3062, 2942, 1650 1595, 1565, 1496, 1470, 1400, 1321, 1290, 1241, 1190, 1150, 1107, 1070, 1000, 925, 890, 840, 768, 740, 700, 685, 642. 1H-NMR, (400 MHz, DMSO-d6, ppm): d 7.24 (d, 4H, J = 8.8 Hz, 4 Ar-H), d 7.34 (d, 4H, J = 8.8 Hz, 4 Ar-H), d 7.59 (m, 6H, 6 Ar-H), d 7.89 (m, 4H, 4 Ar-H), d 9.92 (br. s, 2H, 2 -NH); Calc. for C30H20Cl2N6O2: C, 63.50; H, 3.55; N, 14.18. Found: C, 63.42; H, 3.56; N, 14.27.

General procedure for the Syntheses of triphenodioxazines (B)

All the five triphenodioxazines were prepared by the oxidative cyclisation of the benzoquinone intermediates. The condensed p-benzoquinone intermediate (0.30 mmol) was mixed with p-chloranil (0.66 mmol) and transferred to the microwave tube. 2.5 ml of 95-97% conc. H2SO4 was added and the microwave tube was sealed. The tube was then heated at 120C, at 50 W power for 8-10 minutes with stirring. After the completion of reaction, the tube was cooled and removed from the microwave. The contents of the tube were poured onto 10 g of ice and then filtered with suction. The residue was washed with water to remove the acid contents. The filtrate also contained some amount of the product dissolved in acidic solution. The pH of the filtrate was adjusted to 7.00 with a sodium bicarbonate solution. The precipitated product was filtered and washed with water and dried under vacuum.

A little amount of the product was dissolved in 2 ml of DMF and purified through column chromatography using ethyl acetate: petroleum ether (60:40) as eluent. All triphenodioxazine compounds were recrystallized from DMF. The percentage yield of the isolated and purified triphenodioxazine compounds is given in Table-1, along with the comparison of persulfate method.

Table-1: Comparison of persulfate and p-chloranil methods under microwave conditions.

Product###Time (min)###Isolated yield (%)

###Persulfate###p-chloranil###Persulfate###p-chloranil

###Method###method###method###method

1B###15###8###62###58

2B###15###8###73###84

3B###20###10###71###86

4B###--###8###--###85

5B###--###8###--###73

All the five triphenodioxazines were prepared according to the method B.

3,10-Diamino-6,13-dichlorotripheno dioxazine (1B)

By the general procedure, oxidative cyclisation of the benzoquinone 1A gave the TPDO 1B. The completion of the reaction was monitored by TLC on silica gel plates {hexane: acetone: DMF (2:3:0.5)}. Mp > 300C; yield = 67.3 mg, 58.0 % (67.3 mg); wine red powder, lmax = 560.5 nm (DMF); FTIR max(KBr/cm): 3345, 3219, 2364, 2342, 1529, 1445, 1318, 1271, 1242, 1208, 1130, 1024, 898, 873; dH (DMSO-d6) 5.99 (4H, br. s, 2 NH2), 6.62 (2H, d, J = 2.3 Hz, 4- and 11-H), 6.68 (2H, dd, J = 8.6, 2.3 Hz, 2- and 9-H), 7.41 (2H, d, J = 8.6 Hz, 1- and 8-H); Calc. for C18H10Cl2N4O2: C, 56.12; H, 2.62; N, 14.54. Found: C, 55.89; H, 2.59; N, 14.20.

6,13-Dichloro-3,10-dimethoxytripheno dioxazine (2B)

By the general procedure, oxidative cyclisation of the benzoquinone 2A gave the TPDO 2B. The reaction was monitored by TLC on silica gel plates {hexane: acetone: ethanol: DMF (2:1:2: 5 drops)}. Mp > 300C; purple solid; % yield = 83.9 % (104 mg); lmax = 540.5 nm (DMF); FTIR max(KBr/cm-1): 3042, 2980, 2936, 1632, 1609, 1600, 1560, 1545, 1480, 1440, 1250, 1222, 1150, 1115, 1101, 1049, 1020, 850; dH (DMSO-d6) 3.79 (6H, s, 2 OMe), 7.08 (2H, d, J = 2.4 Hz, 4- and 11-H), 7.20 (2H, dd, J = 8.7, 2.4 Hz, 2- and 9-H), 7.58 (2H, d, J = 8.7 Hz, 1- and 8-H); m/z (MS EI+, 4.52e12), 418 (11, M+4), , 417 (14, M+3), 416 (65, M+2), 415 (23, M+1), 414 (100, M+); Calc. for C20H12Cl2N2O4: C, 57.85; H, 2.91; N, 6.75. Found: C, 59.17; H, 2.88; N, 6.58.

6,13-Dichloro-3,10-dimethyltriphenodiox azine (3B)

By employing the general procedure, oxidative cyclisation of the benzoquinone 3A gave the TPDO 3B. The reaction was monitored by TLC on silica gel plates {hexane: acetone: ethanol: DMF (2:1:2: 5 drops)}. Mp > 300C; Red solid; yield = 85.7 %, 98.6 mg; lmax = 532 nm (DMF); FTIR max(KBr/cm-1): 3033, 2978, 1621, 1572, 1550, 1480, 1440, 1402, 1290, 1245, 1154, 1120, 1111, 1085, 1070, 1020, 855, 830, 792, 730, 700; dH (DMSO-d6) 2.39 (6H, s, 2 Me), 7.02 (2H, d, J = 2.2 Hz, 4- and 11-H), 7.08 (2H, dd, J = 8.4, 2.2 Hz, 2- ad 9-H), 7.44 (2H, d, J = 8.4 Hz, 1- and 8-H); Calc. for C20H12Cl2N2O2: C, 62.68; H, 3.16; N, 7.31. Found: C, 62.20; H, 3.09; N, 7.21.

9, 19-Dichloro-5,15-diethyl-5,15-dihydroindolo(2, 3- c: 2', 3'- n)triphenodioxazine (4B) and 8,18-Dichloro-5,15-diethyl-5,15-dihydrodiindolo (3,2-b: 3',2'- m)triphenodioxazine (4B1)

By adopting the general procedure described in section 2.3, 4A (178 mg, 0.30 mmol) was converted to 4B and 4B1 (150 mg, 84.8 %) in the presence of p-chloranil (162 mg, 0.66 mmol) and conc. H2SO4 (95-97 %, 2.5 mL). The reaction was monitored by TLC on silica gel plates {PE: EA: ethanol: DMF (1.5:1:2: 5 drops)}. Mixed m.p. > 310C; Violet solid powder; yield = 84.8 % (150 mg); lmax = 572, 607 nm (DMF); FTIR max(KBr/cm-1): 3376, 3060, 2924, 1634, 1542, 1472, 1383, 1305, 1238, 1153, 1114, 1027, 940, 885, 797, 567. 1H- NMR, (400 MHz, DMSO-d6, ppm): d 1.35 (t, 6H, J = 7.2 Hz, 2 CH3), d 4.51 (m, 4H, 2 CH2), d 7.58 (m, Ar- H), d 7.68 (m, Ar-H), d 7.76 (d, 2H, J = 8.5 Hz, 2 Ar- H), d 7.84 (d, 2H, J = 8.5 Hz, 2 Ar-H), d 7.95 (m, Ar- H), d 8.01 (m, Ar-H), d 8.36 (s, Ar-H), d 8.79 (s, Ar- H); Calc. for C34H22Cl2N4O2: C, 69.28; H, 3.76; N, 9.50. Found: C, 68.81; H, 3.75; N, 9.40.

Attempted synthesis of 6,13-dichloro-3,10-bis(phenylazo)triphenodioxazine (5B)

5A (170 mg, 0.30 mmol) was oxidatively cyclised in the presence of p-chloranil (162 mg, 0.66 mmol) and conc. H2SO4 (95-97 %, 2.5 mL) to 1B as a wine red solid. The reaction was monitored by TLC on silica gel plates {hexane: acetone: DMF (2:3: 10 drops)}. Mp > 310C; % yield = 70.4 % (86.3 mg); lmax = 560.5 nm (DMF); FTIR max(KBr/cm-1): 3342, 3223, 2354, 2341, 1529, 1444, 1316, 1278, 1242, 1208, 1132, 1024, 894, 873, 778, 620. 1H-NMR, (400 MHz, DMSO-d6, ppm): d 5.99 (4 H, br. s, 2 NH2), d 6.61 (d, 2H, J = 2.0 Hz, 4- and 11-H), d 6.68 (dd, 2H, J = 8.6, 2.0 Hz, 2- and 9-H), d 7.40 (d, 2H, J = 8.6 Hz, 1- and 8-H); Calc. for C30H16Cl2N6O2: C, 63.96; H, 2.86; N, 14.92 and for C18H10Cl2N4O2: C, 56.12; H, 2.62; N, 14.54. Found: C, 57.02; H, 2.58; N, 14.48.

Results and Discussion

In the present work, p-chloranil was used as an oxidising agent in 95-97% H2SO4. The p-chloranil is stable to heat even at high temperatures; it melts with sublimation at around 180C, so higher temperatures can be employed. Conventionally higher temperatures were preferred for the preparation of TPDOs and the reactions could be completed within 3-6 hours. The high boiling point solvents used for this purpose were nitrobenzene (200-210C), chloronaphthalenes (160-180C) and polyhalobenzenes (150-180C) [17]. In the present method cyclization step has been carried out at 120C. The selected temperature is higher than the temperature used in persulfate method [1], but it is still lower than the temperature used in the conventional methods [18, 19]. Temperatures much higher than 120C were avoided because at higher temperatures considerable pressure is generated in the microwave tube.

The pressure of the microwave tube can however be controlled at 120C within the instrumental control limits for 3-5% of water in 95-97% H2SO4. The cyclisation process ran smoothly and could be completed within just 8-10 minutes. Initially 2,5-bis(4-aminophenylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione intermediate was cyclised and then this cyclisation process was extended to other aromatic amines and was found equally efficient (Scheme-2 and 3).

The yield of the reaction is generally higher than the persulfate method [1] but a little lower in the case of 2,5-bis(4-aminophenylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione (1A). This intermediate carries two amino and two a, b -unsaturated carbonyl functionalities. These moieties increase the chances of side products formation when p-chloranil is used as oxidizing agent. Furthermore, the chloro groups of p-chloranil are susceptible to nucleophilic displacement by the amino groups of 1A. With regard to the electronic effects our results matched with the reported results [20]. 2,5-bis(4-nitrophenylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione did not give any cyclised product under the modified microwave reaction conditions. A comparison of the persulfate method with the p-chloranil method is given in Table-1 and summary of the amines used to form corresponding intermediates and their cyclised products is given in Table-2.

Azo containing benzoquinone intermediate failed to give the expected triphenodioxazine compound containing both the TPDO and azo groups; rather it gave free diaminotriphenodioxazine compound as confirmed from its spectroscopic data. One reasonable explanation is the reduction of azo products as a result of oxidative cyclisation of benzoquinone intermediate 1A (scheme-4).

The cyclization of 2,5-bis(9-ethyl-9H-carbazol-3-ylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-dione (4A) produced an inseparable mixture of two isomers, one having a linear structure 4B while the other angular 4B1 (CV 23). The NMR spectrum of this mixture was resolved using MestReC 4.9.9 computerized software. Two deshielded singlets at 8.36 ppm and 8.79 ppm gave a clue of linear structure while the two multiplets at 7.95 ppm and 8.01 ppm represent angular structure. The presence of two isomers (4B and 4B1) was also indicated by its UV-Vis spectrum. There were two maxima at lmax = 607 nm and lmax = 572 nm.

Conclusion

The existing microwave method for the preparation of triphenodioxazine compounds has been modified. In the modified method p-chloranil was used as oxidizing agent along with 95-97% sulphuric acid. By using this new method, the time of the reaction has been reduced from 20 minutes to just 8-10 minutes as compared to our previously reported persulfate MW method and from long hours to just a few minutes in comparison to conventional methods. The temperature of the reaction has also been decreased from 200C to 120C when the newly reported method is compared with the conventional methods. This method has also improved the yield of the reaction in comparison with the persulfate microwave method.

Acknowledgements

We gratefully acknowledge the financial assistance granted by the HEC (Higher Education Commission) of Pakistan under the Indigenous 5000 PhD Programme and IRSIP (International Research Support Initiative Programme) to PhD Students.

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Author:Ullah, Muhammad Najeeb; Munawar, Munawar Ali; Knight, David William; Khan, Misbahul Ain; Waheed, Amr
Publication:Journal of the Chemical Society of Pakistan
Article Type:Report
Date:Apr 30, 2016
Words:4338
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