Abstract
A new synthesis of hydroxytriarylmethane derived from the reaction of 2-sulfobenzoic anhydride and phenols in the presence of heteropolyacids as green, reusable, and efficient catalyst (using catalytic amount) under ultrasonic irradiation is reported in this paper.
1. Introduction
Triarylmethanes (TAMs) are highly colored materials and have been used as dyes and pigments for a very long time [1]. They have received much attention and have been widely used for many purposes such as for photochromic agents [2], protective groups [3], building blocks for dendrimers and NLOs [4, 5]. Some triarylmethanes have shown a wide range of pharmaceutical properties such as antioxidant, antivirus, and antitumor activities [6, 7].
Two basic methods to synthesize triarylmethanes (TAMs) are the Grignard reaction of various carbonyl compounds like benzophenone and methyl benzoate, and the aromatic electrophilic substitution reaction in acidic media [8, 9]. Symmetric triarylmethanes (TAMs) were prepared by the treatment of electrophilic reagents such as triethyl orthoformate or chloroform with arene nucleophiles [10, 11].
Recently, an efficient synthesis of unsymmetrical triarylmethanes has been reported by Friedel-Crafts reaction of aromatic nucleophiles with heteroarylcarbinols [12]. Werbel et al. have reported a facile method for the synthesizing of triarylmethane by the catalytic hydrogenation of the diaryl ketone and the subsequent treatment of the carbinol with aryl amines and HCl [13].
The selective condensation of oxophilic metal phenolates with an aromatic aldehyde at the ortho position of the starting phenol has been utilized in the synthesizing of a 2,2′-di-hydroxy triphenylmethane, another TAM derivative [7].
Development of methods using heteropolyacids (HPAs) as catalysts for fine organic synthetic processes related to fine chemicals, such as flavors, pharmaceuticals, and food industries have been under attention in the last decade. The catalysts based on HPAs have many advantages over liquid acid catalysts. They are not corrosive and environmentally benign, presenting fewer disposal problems. Solid HPAs have attracted much attention in organic synthesizing owing to easy workup procedures, easy filtration, and minimization of cost and waste generation because of reusing and recycling of the catalysts [14, 15].
Newly some books and papers have been published which show that the synthesizing of compounds has been accelerated by ultrasound irradiation. In comparison with the traditional methods, this method is more convenient and easier to work up [16, 17].
Herein, we report a simple method for synthesizing of hydroxytriarylmethane derivatives from reaction of 2-sulfobenzoeic anhydride with phenols in the presence of catalytic amounts of H14[NaP5W30O110], H4SiW12O40 and H3PW12O40, under ultrasonic irradiation (Scheme 1).
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2. Experimental
2.1. Chemicals and Apparatus
All the chemicals were obtained from Merck, Fluka, and Aldrich Companies and were used without further purification. Melting points were measured using Thermo-Fisher Scientific. IR spectra were recorded by Bruker tensor 27, FT-IR Spectrophotometer. All 1H NMR and 13C NMR spectra were recorded on a Bruker 400 MHZ Spectrophotometer. Chemical shifts are reported in parts per million (ppm), using tetra methyl silane (TMS) as an internal standard. The microanalyses for C and H were performed on Perkin-Elmer elemental analyzer. The ultrasonic apparatus was the cleaning bath Wiseclear 770 W (Seoul, Korea). The operating frequency was 40 kHz and the output power was 200 W, estimated calorimetrically. The reaction flasks were located in the maximum energy area in the water bath, where the surface of reactants (reaction vessel) was slightly lower than the surface level of the water, and the addition or removal of water which controlled the temperature of the water bath. The temperature of the water bath was controlled at 55–65°C. Silica-supported Preyssler nanoparticles were prepared according to [18].
2.2. General Procedure
A mixture of 2-sulfobenzoeic anhydride (20 mmol), phenol derivatives (60 mmol), and catalytic amount of heteropolyacid (0.03 mmol) in 10 mL CH3CN was irradiated under ultrasound at 55–65°C for required reaction time. The progress of the reaction was monitored by TLC. When the reaction was completed, the catalyst was filtered off, the solvent was evaporated under vacuum, and the product was poured into 100 mL NaOH 10%. Then, the solution was acidified by HCl. The precipitate was collected under filtration. All products were identified by their physical and spectroscopic data (Tables 1 and 2).
2.3. Recycling of the Catalyst
After filtration of the catalyst, it could be recycled, washing it with diethylether in each case. The recovered catalyst could be dried and reused for the next reaction with only a modest loss in activity. The catalyst has been recovered and reused for six times in reactions. The obtained results are summarized in Table 3.
3. Results and Discussions
The progress of reaction 2-sulfobenzoeic anhydride with phenols was monitored by TLC and reported yields were based on isolated products. The results showed that the highest yield of the products was achieved when H14[NaP5W30O110] was used as the catalyst.
Comparison of the catalysts in Tables 4 and 5 showed that H14[NaP5W30O110] is the catalyst of choice. Comparison of supported and nonsupported Preyssler catalyst showed that, in all cases, the supported Preyssler catalyst was less active than the nonsupported one. One plausible interpretation of this observation is that, in supported type, there are polyanion-support interactions of an acid-base nature. Some protons of the polyacid and some basic sites of the support (e.g., hydroxyl groups) can interact. This would lead to diminished availability of hydrogens because of this extra ionic interaction [19]. Interestingly, this behavior is similar to that of Keggin heteropolyacids. However, when H3[PW12O40] or H4[SiW12O40] were used instead of H14[NaP5W30O110] the yield of product was slightly decreased.
The results point out that the catalytic effectiveness may be enhanced as the number of tungsten atoms (or the number of protons) is increased. Both possibilities stand to reason. In addition, the large anion also provides many “sites” on the oval-shaped molecule that are likely to render the catalyst effectiveness. Interestingly, the comparison of Preyssler heteropolyacid, with its exclusive properties, with Keggin heteropolyacids, ZnCl2, and H2SO4 showed that the activity for H14[NaP5W30O110] is the most. The compression of efficiency of heteropolyacids has been carried out. The results are shown in Table 6. It is clear that H14 [NaP5W30O110] gave the better yields than others. The catalytic activity is increased in the following order: H14[NaP5W30O110] > H3[PW12O40] > H4[SiW12O40].
Phenols with electron withdrawing groups gave hydroxytriarylmethane derivative in low yields. To show the merit of this method, reaction has been performed using the same catalyst repeatedly under classical heating condition. As it is shown under heating condition the higher reaction time is required. The results are shown in Tables 7 and 8.
As ultrasound generated intense turbulence and microscale liquid circulation currents, uniform mixing at microlevel has occurred and the mass transfer resistances have been eliminated [20]. This explanation can justify the shorter reaction time observed for reactions under ultrasonic condition.
This catalyst retained its activity over six consecutive runs (Table 3).
4. Conclusion
We developed a new method using heteropolyacids under ultrasonic irradiation for synthesis of hydroxytriarylmethanes. The short reaction times, high yields, reusability of catalyst, and easy work up procedure are some advantages of this method.
Acknowledgment
The author thanks Payame Noor University (PNU) of Kerman for the financial support.