Rapid and Efficient Synthesis of Hydroxytriarylmethanes under Ultra Sonic Irradiation Using Keggin Heteropolyacids and Preyssler Catalysts in Green Conditions

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].