Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines

Heravi, Majid M.; Sadjadi, Samaheh; Oskooie, Hossein A.; Shoar, Rahim Hekmat; Bamoharram, Fatemeh F.

doi:10.3390/12020255

Open AccessArticle

Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines

by

Majid M. Heravi

^1,*,

Samaheh Sadjadi

¹,

Hossein A. Oskooie

¹,

Rahim Hekmat Shoar

¹ and

Fatemeh F. Bamoharram

²

¹

Department of Chemistry, School of Sciences, Azzahra University, Vanak, Tehran, Iran

²

Department of Chemistry, School of Sciences, Azad University, Khorasan Branch, Mashhad, Iran

^*

Author to whom correspondence should be addressed.

Molecules 2007, 12(2), 255-262; https://doi.org/10.3390/12020255

Submission received: 8 January 2007 / Revised: 10 February 2007 / Accepted: 12 February 2007 / Published: 26 February 2007

(This article belongs to the Special Issue Heterocycles)

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Abstract

:

Synthesis of 3,1,5-benzoxadiazepines from the condensation of o-phenylenediamine (o-PDA) and acyl chlorides in the presence of a catalytic amount of various heteropolyacids (HPAs) is reported.

Keywords:

3,1,5-Benzoxadiazepines; recyclable catalysts; heteropolyacids; heterocycle

Introduction

Heteropolyacids (HPAs) are well defined molecular clusters that are remarkable for their molecular and electronic structural diversity and their quite diverse significance in many areas, e.g., catalysis, medicine, and materials science [1,2].

The applications of heteropolyacids, HPAs, in the field of catalysis are growing continuously. These compounds possess unique properties such as Brönsted acidity, possibility to modify their acid-base and redox properties by changing their chemical composition (substituted HPAs), ability to accept and release electrons, high proton mobility, easy work-up procedures, easy filtration, and minimization of cost and waste generation due to reuse and recycling of these catalysts [3,4,5,6,7]. Because of their stronger acidity, they generally exhibit higher catalytic activity than conventional catalysts such as mineral acids, ion exchange resins, mixed oxides, zeolites, etc. [8]. In the context of Green Chemistry, the substitution of harmful liquid acids by solid reusable HPAs as catalysts in organic synthesis is the most promising application of these acids [9,10].

Benzoxadiazepines have been found to possess marked biological effects as CNS stimulants. They have also been reported as antibacterial and anti-inflammatory agents, pesticides and insecticides [11]. Few methods are reported in the literature for the synthesis of benzoxadiazepines [12,13,14]. During the course of our studies towards the development of HPAs as efficient heterogeneous catalysts [15,16,17,18] herein we wish to report the synthesis of 3,1,5-benzoxadiazepines derivatives by cyclization of o-PDA and acyl chlorides in the presence of a catalytic amount of various type of HPAs, including H₁₄[NaP₅W₃₀O₁₁₀], H₅[PMo₁₀V₂O₄₀] and H₆[P₂W₁₈O₆₂]. (Scheme1).

Scheme 1.

Results and Discussion

Due to the ever-mounting environmental concern in the field of chemistry, it is advisable to use easily recovered and recycled catalysts, especially expensive or toxic metallic ones [19]. In this respect, only few of the aforementioned catalysts meet this Green Chemistry criterion.

In connection with our program of using heteropolyacids in organic reactions [20] we wish to report the results of a study on the use of three type of HPAs, including Preyssler, H₁₄[NaP₅W₃₀O₁₁₀], Keggin, H₄[PMo₁₁VO₄₀] and Wells-Dawson types H₆[P₂W₁₈O₆₂] in the synthesis of 3,1,5-benzoxa-diazepines and the effects of reaction parameters such as the type of HPA, temperature and reaction times on the reaction yields.

The results indicate that the nature of the catalyst plays an important role on their catalytic activities. As shown in Table 1, H₁₄[NaP₅W₃₀O₁₁₀] showed the highest activity and gave better yields.

Table 1. Synthesis of 3,1,5-benzoxadiazepines derivatives using various heteropolyacids under refluxing conditions.

**Table 1.** Synthesis of 3,1,5-benzoxadiazepines derivatives using various heteropolyacids under refluxing conditions.
Entry	R₁	R₂	R₃	R₄	Catalyst	Yield %^a
1	H	H	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	80
2	H	H	H	CH₃	H₆[P₂W₁₈O₆₂]	74.8
3	H	H	H	CH₃	H₅[PMo₁₀V₂O₄₀]	60
4	H	CH₃	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	85.7
5	H	CH₃	H	CH₃	H₆[P₂W₁₈O₆₂]	78.25
6	H	CH₃	H	CH₃	H₅[PMo₁₀V₂O₄₀]	61

a) Yields were analyzed by GC.

Preyssler’s anion, [NaP₅W₃₀O₁₁₀]^14-, has an approximate D₅h symmetry and consists of a cyclic assembly of five PW₆O₂₂ units. A sodium ion is located within the polyanion on the fivefold axis and 1.25 above the pseudo mirror plane that contains the five phosphorus atoms [21]. Preyssler polyanion as a large anion can provide many ‘‘sites’’ on the oval-shaped molecule that are likely to render the catalyst effective.

The Keggin anions have an assembly of 12 corner-shared octahedral MoO₆ from trimetallic groups [Mo₃O₁₃] around a heteroatom tetrahedron PO₄. The introduction of vanadium (V) into the Keggin framework of [PMo₁₂O₄₀]³^- is beneficial for catalysis reactions. Usually positional isomers are possible and coexist when two or more vanadium atoms are incorporated into the Keggin structure. Studies on these isomers in catalytic reactions indicate that different isomers cause to show different reactivities.

With respect to the catalytic performance of these catalysts and the overall effects of all isomers, we cannot control the reaction conditions for the synthesis of positional vanadium-substituted isomers separately, indicating that the relationship between the H₃₊_xPMo₁₂_-_xVxO₄₀ (x = 1) structures and hence study of their catalytic activity is difficult. However, because the metal substitution may modify the energy and composition of the LUMO and redox properties, for mentioned heteropolyacids with different charges, the energy and composition of the LUMOs have significant effects on the catalytic activity. Substitution of vanadium ions into the molybdenum framework stabilize the LUMOs because these orbitals derive, in part, from vanadium d-orbitals which have been assumed to be more stable than those of molybdenum and tungsten [22]. The abundance of different isomers may also play an important role in catalytic performance. In addition, different positional Mo atom(s) substituted by the V atom(s) in [PMo₁₂O₄₀]³^- may create different vanadium chemical environments, thus causing these catalysts to exhibit varying catalytic performances. Considering the above explanations we suggest that the rigidity, steric hindrance and lower number of protons in H₄[PMo₁₁VO₄₀] are tentatively assumed to be responsible for its observed lower activity. The larger number of protons may lower the activation barrier to the reaction.

As noted from the data in Table 1, electron-donating groups on o-PDA increased the yield of the reactions. The effect of temperature was studied by carrying out the reactions at different temperatures [room temperature, 25°C, 50°C and under refluxing temperature (82°C)]. As shown in Table 2, the reaction yields increased as the reaction temperature was raised. From these results, it was decided that refluxing temperature would be the best temperature for all reactions.

For investigation of the best reaction time the reaction yields were studied at different times (0.5, 1, 2, 3, 4h). The results indicate that in each reaction, the yield is a function of the reaction time and the best time for all reactions was optimized to be 4h.

When 4-nitrophenylenediamine, 3,5-dinitrophenylenediamine and benzoyl chloride were used as substrates in this reaction the corresponding benzodimidazoles were obtained instead of 3,1,5-benzoxadiazepines (Scheme 2).

Scheme 2.

Table 2. Effect of different reaction time and temperature on synthesis of 3,1,5-benzoxadiazepines derivatives using various heteropolyacids.

**Table 2.** Effect of different reaction time and temperature on synthesis of 3,1,5-benzoxadiazepines derivatives using various heteropolyacids.
Entry	R₁	R₂	R₃	R₄	Catalyst	Time (h)	Yield%^a
Entry	R₁	R₂	R₃	R₄	Catalyst	Time (h)	25°C	50°C	82°C
1	H	H	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	0.5	41	44	50
2	H	H	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	1	50	55	59
3	H	H	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	2	56	60	65
4	H	H	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	3	67	69	74
5	H	H	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	4	73	77	80
6	H	H	H	CH₃	H₆[P₂W₁₈O₆₂]	0.5	38	43	48
7	H	H	H	CH₃	H₆[P₂W₁₈O₆₂]	1	47	51	55
8	H	H	H	CH₃	H₆[P₂W₁₈O₆₂]	2	54	59	63
9	H	H	H	CH₃	H₆[P₂W₁₈O₆₂]	3	59	67	68
10	H	H	H	CH₃	H₆[P₂W₁₈O₆₂]	4	65	70	74.8
11	H	H	H	CH₃	H₅[PMo₁₀V₂O₄₀]	0.5	23	27	29
12	H	H	H	CH₃	H₅[PMo₁₀V₂O₄₀]	1	29	33	37
13	H	H	H	CH₃	H₅[PMo₁₀V₂O₄₀]	2	33	38	42
14	H	H	H	CH₃	H₅[PMo₁₀V₂O₄₀]	3	46	49	53
15	H	H	H	CH₃	H₅[PMo₁₀V₂O₄₀]	4	53	57	60
16	H	CH₃	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	0.5	44	52	58
17	H	CH₃	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	1	52	59	63
18	H	CH₃	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	2	61	67	71
19	H	CH₃	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	3	60	69	76
20	H	CH₃	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	4	66	72	85.7
21	H	CH₃	H	CH₃	H₆[P₂W₁₈O₆₂]	0.5	39	42	48
22	H	CH₃	H	CH₃	H₆[P₂W₁₈O₆₂]	1	48	52	57
23	H	CH₃	H	CH₃	H₆[P₂W₁₈O₆₂]	2	55	59	64
24	H	CH₃	H	CH₃	H₆[P₂W₁₈O₆₂]	3	64	68	70
25	H	CH₃	H	CH₃	H₆[P₂W₁₈O₆₂]	4	70	72	78.25
26	H	CH₃	H	CH₃	H₅[PMo₁₀V₂O₄₀]	0.5	22	30	36
27	H	CH₃	H	CH₃	H₅[PMo₁₀V₂O₄₀]	1	29	35	40
28	H	CH₃	H	CH₃	H₅[PMo₁₀V₂O₄₀]	2	35	41	48
29	H	CH₃	H	CH₃	H₅[PMo₁₀V₂O₄₀]	3	49	51	53
30	H	CH₃	H	CH₃	H₅[PMo₁₀V₂O₄₀]	4	57	59	61

a) Yields were analyzed by GC.

The products were characterized using ¹H-NMR and IR spectroscopy and GC–MS analysis. Analytical data were in accord with those reported for authentic samples.

The results are summarized in Table 3. It is presumed that the amine group meta to the NO₂ group participated in the reaction, while the amine groups para or ortho to the nitro could not participate because the latter are considered to be powerful electron withdrawing groups and may reduce the nucleophilicity of the amine. In the case of benzoyl chloride the steric effect of phenyl groups prevent the formation of 3,1,5-benzoxadiazepines.

Table 3. Synthesis of benzimidazole derivatives using various heteropolyacids under refluxing conditions.

**Table 3.** Synthesis of benzimidazole derivatives using various heteropolyacids under refluxing conditions.
Entry	R₁	R₂	R₃	R₄	Catalyst	Yield %^a
1	H	NO₂	H	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	98.5
2	H	NO₂	H	CH₃	H₆[P₂W₁₈O₆₂]	97
3	H	NO₂	H	CH₃	H₅[PMo₁₀V₂O₄₀]	95.7
4	H	NO₂	H	C₆H₅	H₁₄[NaP₅W₃₀O₁₁₀]	98
5	H	NO₂	H	C₆H₅	H₆[P₂W₁₈O₆₂]	94
6	H	NO₂	H	C₆H₅	H₅[PMo₁₀V₂O₄₀]	85
7	NO₂	H	NO₂	CH₃	H₁₄[NaP₅W₃₀O₁₁₀]	97
8	NO₂	H	NO₂	CH₃	H₆[P₂W₁₈O₆₂]	95.7
9	NO₂	H	NO₂	CH₃	H₅[PMo₁₀V₂O₄₀]	90.4
10	NO₂	H	NO₂	C₆H₅	H₁₄[NaP₅W₃₀O₁₁₀]	85.7
11	NO₂	H	NO₂	C₆H₅	H₆[P₂W₁₈O₆₂]	78.2
12	NO₂	H	NO₂	C₆H₅	H₅[PMo₁₀V₂O₄₀]	77.3

^a yields are analyzed by GC

As shown in Table 3, the reaction yields for the synthesis of benzimidazole derivaties are high. Thus, heteropolyacids can be used as efficient catalysts for the synthesis of benzimidazoles, especially for derivatives with electron withdrawing groups (such as nitro groups). The more electron withdrawing groups present the lower the yields obtained were. On the other hand, the steric effect of phenyl groups also reduced the yield of reactions. The same trend of catalyst efficiency was observed for this reaction. Thus the same explanation could be applied here.

Experimental

General

All chemicals were obtained from Merck and used as received. H₁₄[NaP₅W₃₀O₁₁₀] was prepared according to earlier reports [8,16,4]. H₄[PMo₁₁VO₄₀] and H₅[PMo₁₀V₂O₄₀] were prepared according to the literature [22]. The Wells-Dawson species H6[P2W18O62] was prepared as described elsewhere [23], from an aqueous solution of α/β K6P2W18O62·10H₂O salt, which was treated with ether and concentrated (37%) HCl solution. GC–MS analyses were performed on a GC–MS system consisting of an Agilent 5973 network mass selective detector and a model 6890 GC. IR spectra were obtained with a Buck Scientific 500 spectrometer. ¹H-NMR spectra were recorded on a Bruker 90 MHz FT-NMR.

General Procedure

o-PDA (6 mmol) was dissolved in acetonitrile (10 mL) and acyl chloride (12 mmol) was added to the solution, followed by the catalyst (0.1 mmol). The reaction mixture was heated at reflux temperature for 4 h. The progress of the reaction was monitored by TLC using 1:2 EtOAc-hexane as eluent. After completion of the reaction, the catalyst was filtered off and the solvent was evaporated. The pure products were obtained by column chromatography. All products were identified by comparison of their physical and spectroscopic data with those reported for authentic samples.

Spectral data for selected samples

2,4-Dimethyl-3,1,5-benzoxadiazepine (Table 1, Entry 1): IR (KBr/υ): 1673 (C=N), 1042 (C-O-C) cm^-1; ¹H-NMR (CDCl₃): 7.2 (m, 4H, Ar-H), 2.2 (s, 6H, CH₃); MS: m/z 174 [M⁺].

6-Nitro-2-methyl-1H-benzimidazole (Table 3, Entry 1): IR (KBr/υ): 1604 (C=N), 1355 (NO₂), 3261 (NH) cm^-1; ¹H-NMR spectra (CDCl₃): 7.7 -8.0 (m, 3H, Ar-H), 2.4 (s, 3H, N=C-CH₃), 4 (br. s, 1H, N-H); MS: m/z 177 [M⁺].

6-Nitro-2-phenyl-1H-benzimidazole (Table 3 Entry 4): IR (KBr/υ): 1604 (C=N), 1355 (NO₂), 3261 (NH) cm^-1; ¹H-NMR (CDCl₃): 7.6 -8.4 (m, 3H, Ar-H), 7.3-8.1 (m, 5H, N=C-C₆H₅), 4.5 (br. s, 1H, N-H); MS: m/z 239 [M⁺].

5,7-Dinitro-2-methyl-1H-benzimidazole (Table 3, Entry 7): IR (KBr/υ): 1604 (C=N), 1355-1400 (NO₂), 3261 (NH) cm^-1; ¹H-NMR (CDCl₃): 8 (s, 1H, Ar-H), 8.7 (s, 1H, Ar-H), 2.58 (s, 3H, N=C-CH₃), 4 (br. s, 1H, N-H); MS: m/z 222 [M⁺].

5,7-Dinitro-2-phenyl-1H-benzimidazole (Table 3, Entry 10): IR (KBr/υ): 1604 (C=N), 1355-1400 (NO₂), 3261 (NH) cm^-1; ¹H-NMR (CDCl₃): 8 (s, 1H, Ar-H), 8.7 (s, 1H, Ar-H), 7.3-8 (m, 5H, N=C-C₆H₅), 4.5 (br. s, 1H, N-H); MS: m/z 284 [M⁺].

Catalyst reusability

At the end of the reaction, the catalyst could be recovered by a simple filtration. The recycled catalyst could be washed with dichloromethane and used in a second run of the reaction process. The results of the first and subsequent experiments were almost consistent in yields.

Acknowledgments

The authors are thankful for the partial financial assistance from Alzahra University Research Council.

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Sample Availability: Samples of the compounds presented in this paper are available from authors.

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Heravi, M.M.; Sadjadi, S.; Oskooie, H.A.; Shoar, R.H.; Bamoharram, F.F. Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines. Molecules 2007, 12, 255-262. https://doi.org/10.3390/12020255

AMA Style

Heravi MM, Sadjadi S, Oskooie HA, Shoar RH, Bamoharram FF. Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines. Molecules. 2007; 12(2):255-262. https://doi.org/10.3390/12020255

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Heravi, Majid M., Samaheh Sadjadi, Hossein A. Oskooie, Rahim Hekmat Shoar, and Fatemeh F. Bamoharram. 2007. "Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines" Molecules 12, no. 2: 255-262. https://doi.org/10.3390/12020255

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Heteropolyacids as Green and Reusable Catalysts for the Synthesis of 3,1,5-Benzoxadiazepines

Abstract

Introduction

Results and Discussion

Experimental

General

General Procedure

Spectral data for selected samples

Catalyst reusability

Acknowledgments

References

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