научная статья по теме SYNTHESIS, CHARACTERIZATION AND APPLICATION OF COBALT HYDROGENSULFATE AS A NEW HETEROGENEOUS, REUSABLE AND EFFICIENT CATALYST IN ONE-POT SYNTHESIS OF 14-ARYL-14H-DIBENZO[A,J]XANTHENES AND 1,8-DIOXOOCTAHYDROXANTHES Химия

КИНЕТИКА И КАТАЛИЗ, 2014, том 55, № 4, с. 450-455

УДК 542.973:547.655.1:543.422.8.2

SYNTHESIS, CHARACTERIZATION AND APPLICATION OF COBALT HYDROGENSULFATE AS A NEW HETEROGENEOUS, REUSABLE AND EFFICIENT CATALYST IN ONE-POT SYNTHESIS OF 14-ARYL-14H-DIBENZO[a,j]XANTHENES AND 1,8-DIOXOOCTAHYDROXANTHES

© 2014 H. Eshghi*, M. Rahimizadeh, M. Eftekhar, M. Bakavoli

Department of Chemistry, Faculty of Sciences, Ferdowsi University ofMashhad, 91775-1436 Mashhad, Iran

*E-mail: heshghi@um.ac.ir Received 14.08.2013

Cobalt hydrogensulfate is synthesized and characterized by XRD, FTIR and TEM measurements. The efficiency of this readily available, cheap, non-toxic, heterogeneous and reusable catalyst is shown in the one-pot preparation of aryl- and alkyl-14H-dibenzoxanthenes and 1,8-dioxooctahydroxanthene derivatives by cyclocondensation of substituted benzaldehydes and P-naphthol or 5,5-dimethyl-1,3-cyclohexanedione respectively. Among advantages of these methods are high yields, a clean reaction strategy, simple methodology, green conditions and easy workup.

DOI: 10.7868/S0453881114040042

Metal hydrogen sulfates are widely used as efficient reagents in synthetic organic chemistry. A broad range of reactions including protection, deprotection, oxidation, C—C, C—N, and C—O bond formation and cleavage took place in the presence of these reagents. In addition, stability, cheapness, and efficiency and in many cases heterogeneity and reusability are other important advantages of these reagents [1—5].

The synthesis of xanthene derivatives, especially benzoxanthenes, has attracted attention of organic chemists due to their wide range of biological and therapeutic properties such as antibacterial [6] and antiviral efficiency [7] and also because they can be used for photodynamic treatments (PDT) [8]. Benzoxanthenes are used in production of dyes [9], in laser technologies [10], and in manufacturing of fluorescent materials for visualization of biomolecules [11]. Many procedures are disclosed to synthesize xanthenes and benzoxanthenes like trapping of benzynes by phenols [12], cyclocondensation between 2-hydroxy aromatic aldehydes and 2-tetralone [13], interamolecular phe-nyl-carbonyl coupling reaction of benzaldehydes and acetophenones [14]. In addition, 14H-dibenzoxan-thenes and related products are prepared by dehydration reaction of P-naphthol with aldehyde. In this context some methods and catalysts suitable for the synthesis of benzoxanthenes have been reported. Among these are acetic acid and sulfuric acid [15], silica and sulfuric acid [16], p-toluene sulfonic acid [17], amberlyst-15 [18], ferric hydrogensulfate [19], and heteropolyacids (HPAs) [20]. On the other hand, the

an increased application both in the field of medicinal chemistry and material science produced a renewed interest in the synthesis of 1,8-dioxooctahydroxan-thene compounds. In recent years, synthesis of1,8-di-oxooctahydroxanthenes was focused on the condensation of dimedone (5,5-dimethyl-1,3-cyclohexanedi-one) with various aromatic aldehydes, by using different catalysts such as silica sulfuric acid [21], Dowex-50W [22], HClO4-SiO2 and PPA-SiO2 [23], NaHSO4-SiO2 and silica chloride [24], ^-dodecylbenzenesulfonic acid [25], Fe3+—montmorillonite [26], amberlyst-15 [27], di-ammonium hydrogen phosphate [28], TMSCl [29], tetrabutylammonium hydrogensulphate [30], and hydrochloric acid [31].

In spite of potential utility of aforementioned routes for the synthesis of xanthenes derivatives, many of these methods have serious shortcomings. They use expensive reagents, strong acidic conditions, and long reaction times but afford low yields. Moreover, excess of reagents/catalysts and toxic organic solvents are involved in the synthesis. A possible approach to correct these problems is a search for new active, efficient and recyclable catalysts and simple work-up for the preparation of xanthenes under neutral, mild and practical conditions. In the present paper, we report a one-pot synthesis of aryl-14H-dibenzoxanthene and 1,8-di-oxooctahydroxanthene derivatives by the reaction of various aromatic aldehydes with P-naphthol or dime-done, respectively in the presence of Co(HSO4)2 as an heterogeneous catalyst (Scheme 1).

3a R = C6H

3b R 3c R 3d R 3e R

6H5

4-O2NC6H.

6n4

4-MeC6H4 4-HOC6H4 4-MeOC6H

3k R = C2H5

4-BrC6H4

6n4

3f R 3g R 3h R 3i R

3j R = 2-OMe

31 R = C5H11

4-ClC6H4 3-O2NC6H4 2-ClC6H4

Scheme 1. Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes.

EXPERIMENTAL

All materials and solvents were procured from "Merck" and "Fluka" chemical companies. Melting points were determined in open capillary tubes using an IA 9000 melting point apparatus ("Electrothermal"). IR spectra were recorded using Avatar 370 FT-IR spectrometer ("Therma Nicolet"). XH NMR spectra were recorded with a Bruker-100 MHz instrument ("Bruk-er") using tetramethylsilane (TMS) as an internal standard. The mass spectra were scanned on a Varian Mat CH-7 instrument ("Varian") at 70 eV Elemental analyses were obtained on a Flash EA microanalyzer ("Thermo Finnigan").

Preparation of Co(HSO4)2

A 50 mL suction flask was equipped with a dropping funnel. The gas outlet was connected to a vacuum system through an alkaline solution trap. Cobalt chloride (10 mmol) was charged into the flask and concentrated sulfuric acid 98% (30 mmol) was added drop wise over a period of 30 min at room temperature. Gaseous HCl was evolved immediately. After adding sulfuric acid, the mixture was shaken for 30 min at 100°C, while the residual HCl was removed by suction. Finally, Co(HSO4)2 was obtained in 95% yield.

General procedure for the preparation of 14-aryl- or alkyl-14H-dibenzo[aj]xanthenes 3a—l

A mixture of 2-naphthol (0.145 g, 1 mmol), aldehyde (0.5 mmol), and Co(HSO4)2 (0.025 g, 0.1 mmol) in 1,2-dichloroethane (DCE, 10 mL) was allowed to stir at reflux condition for appropriate time according to Table 1. TLC monitored the progress of the reaction. After reaction, the reaction mixture was filtered and the organic solvent was cooled and concentrated. The crystalline solid that was precipitated was recrys-tallized from ethanol to give a pure product. All products are known compounds, which were characterized

by IR and 1H NMR spectroscopic data and their melting points were compared with reported values.

14-(4-Hydroxyphenyl)-14H-dibenzo[a,j]xanthene 3d (Table 1, entry 4): pink solid. Yield: 90%. M.p.: 140-141°C, 1H NMR (CDCl3 100 MHz): 4.97 (br s, 1H, OH), 6.42 (s, 1H, CH), 6.56-8.36 (m, 16H, Ar-H). FTIR (KBr, cm-1): 1592, 1511, 1401, 1250, 1242, 816.

General procedure for the preparation of 9-aryl-1,8-dioxooctahydroxanthene 5a—l

A mixture of dimedone (2 mmol), aldehyde (1 mmol) and Co(HSO4)2 (0.1 mmol) was refluxed in dichloroethane. After the end of the reaction monitored by TLC, the reaction mixture was cooled to room temprature, extracted with EtOAc (3 x 15 mL), filtered to isolate the catalyst and the filtrate was concentrated to obtain crude product. The residue was crystallized in ethanol to obtain pure 9-aryl-1,8-di-oxooctahydroxanthene 5a—l as a crystalline solid. All the products obtained were fully characterized by spectroscopic methods such as IR, 1H NMR, 13C NMR and mass spectroscopy and also by comparison of the spectral data with those reported in literature.

3,3,6,6- Tetramethyl- 9 -phenyl- 3,4,6,7 - tetrahy-dro-2H-xanthene-1,8(5H, 9H)dione 5a (Table 2, entry 1): white solid. Yield: 90%. M.p.: 203-205°C,1H NMR (CDCl3, 100 MHz): 7.24-7.19 (m, 2H, ArH), 7.14-7.09 (m, 1H, ArH), 7.04-7.01 (d, J = 7.93 Hz, 2H, ArH), 5.47 (s, 1H, CH), 2.47-2.25 (m, 8H, 4CH2), 1.25 (s, 6H, 2CH3), 1.11 (s, 6H, 2CH3). FT-IR (KBr, cm-1): 2962, 2928, 1592, 1372, 1159, 1041, 842, 774, 692.

9 - (4-Chlorophenyl) - 3,3,6,6-tetramethyl- 3,4,6,7-tetrahydro-2H-xanthene-1,8(5H,9H)-dione 5g (Table 2, entry 7): white solid. Yield: 95%. M.p.: 228-230°C, 1H NMR (100 MHz, CDCl3): 7.25-7.18 (m, 2H, ArH), 6.97-6.95 (d, J = 8.12 Hz, 2H, ArH), 5.40 (s, 1H, CH), 2.46-2.25 (m, 8H, 4CH2), 1.22 (s, 6H,

Table 1. Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in the presence of Co(HSO4)2a

Entry Aldehyde Product Time, h Yieldb, % Melting p oint , ° C Observed Reported Reference

1 C6H4 3a 4 80 182-183 183-184 [19]

2 4-O2NC6H4 3b 1 95 308-310 311-12 [19]

3 4-MeC6H4 3c 4 90 239-240 238-240 [19]

4 4-HOC6H4 3d 3 95 140-141 140-141 [16]

5 4-MeOC6H4 3e 4 80 204-205 203-205 [19]

6 4-BrC6H4 3f 3 85 298-300 297-298 [19]

7 4-ClC6H4 3g 2 95 288-290 287-288 [16]

8 3-O2NC6H4 3h 2.5 80 210-212 211-212 [17]

9 2-ClC6H4 3i 3 75 214-216 215 [17]

10 2-MeOC6H4 3j 5 70 260-261 258-260 [17]

11 C2H5 3k 7 80 151-152 150-151 [19]

12 C5H11 31 6 70 99-101 98-100 [19]

a Reaction conditions: ß-naphthol (2.0 mmol), aromatic aldehyde (1 mmol), Co(HSO4)2 (0.1 mmol), DCE (10 mL) reflux. b Yields of the isolated product.

Table 2. Synthesis of 9-aryl-1,8-dioxooctahydroxanthenes in the presence of Co(HSO4)2a

Entry Aldehyde Product Time, h Yieldb, % Melting p oint, ° C Observed Reported Reference

1 C6H4 5a 4 85 203-205 204-205 [26]

2 4-O2NC6H4 5b 3 90 226-228 225-227 [23]

3 4-MeC6H4 5c 4 95 218-220 217-218 [25]

4 4-HOC6H4 5d 3.5 87 246-248 247-248 [26]

5 4-MeOC6H4 5e 3 85 242-244 244-246 [26]

6 4-BrC6H4 5f 4 85 233-235 234-236 [26]

7 4-ClC6H4 5g 3 95 228-230 229-230 [26]

8 3-O2NC6H4 5h 4 80 168-170 170-172 [26]

9 2-ClC6H4 5i 5 75 229-231 228-230 [26]

10 2-NO2C6H4 5j 6 75 258-260 258-260 [25]

11 3-OMeC6H4 5k 4 80 178-180 177-180 [25]

12 2-OMeC6H4 51 6 70 187-189 190-191 [25]

a Reaction conditions: dimedone (2.0 mmol), aromatic aldehyde (1 mmol), Co(HSO4)2 (0.1 mmol), DCE (10 mL) reflux. b Yields of the isolated product.

2CH3), 1.11 (s, 6H, 2CH3). FT-IR (KBr, cm--1): 2960, 2929, 1589, 1305, 1093, 887, 833, 720, 658.

Catalyst characterization

Powder X-ray diffraction (XRD). Figure 1 shows the X-ray diffraction patterns of the Co(HSO4)2 sample obtained by using Cu^a radiation. The XRD patterns show characteristic peaks corre

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