Fast, efficient and convenient method for the preparation of arylazo sulfides using aryl diazonium silica sulfates under mild and solvent-free conditions Amin Zarei a, * , Leila Khazdooz b , Abdol R. Hajipour c, d , Hamidreza Aghaei e a Department of Science, Islamic Azad University, Fasa Branch, Post Box No. 364, Fasa 7461713591, Fars, Iran b Department of Science, Islamic Azad University, Khorasgan Branch, Isfahan 81595-158, Iran c Department of Pharmacology, University of Wisconsin, Medical School, USA d Pharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan, Iran e Department of Chemistry, Islamic Azad University, Shahreza Branch, Shahreza 311-86145, Isfahan, Iran article info Article history: Received 3 November 2010 Received in revised form 28 December 2010 Accepted 16 February 2011 Available online 9 March 2011 Keywords: Aryl diazonium silica sulfates Sodium thiolates Arylazo sulfides Arylazo thiosulfonates Solvent-free Mild conditions abstract An efficient, fast, and straightforward procedure for the synthesis of arylazo sulfides and arylazo thio- sulfonates is described in the present paper by using aryl diazonium silica sulfates and sodium thiolates. Using the present method, different kinds of aryl diazonium silica sulfates, containing electron-with- drawing groups as well as electron-donating groups, were rapidly converted to the corresponding ary- lazo sulfides in good yield and short reaction time. These reactions were carried out at room temperature under mild and solvent-free conditions. The use of non-toxic and inexpensive materials, simple and clean work-up, short reaction times and good yields are the advantages of this method. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Aryl diazonium salts have been prepared and studied as powerful intermediates in classical and modern organic synthesis due to their easy availability and high reactivity [1e4]. Therefore, there is always an interest in the field of aromatic diazonium salts. Arylazo sulfides have been studied from their thermal [5,6] and photochemical [7,8] behavior as well as their applications in organic synthesis [9e20]. For example, it is known that the ther- molysis of these compounds is an important method for the preparation of arydiazenyl radicals [5,6]. Moreover, arylazo sulfides are one of the important precursors for S RN 1 reactions to produce a number of variously functionalized aromatic compounds [9e20]. Furthermore, some of the chlorinated phenylazo phenyl sulfides are used as agricultural pesticides and miticides. One of the useful procedures for the preparation of arylazo sulfides is the reaction of aryl diazonium salts with aryl mercaptans [21e24]. Although some of these methods are convenient protocols with good yields, some of them suffer from disadvantages such as the stench associated with using aryl mercaptans, tedious work-up, and low yields because of disulfide formation. In continuation of our studies on the stabilization of diazonium salts on silica sulfuric acid and their applications in organic synthesis [25e28], we report herein an efficient, fast, and convenient procedure for the synthesis of arylazo sulfides employing aryl diazonium silica sulfates in the presence of sodium thiolates under solvent-free conditions. In spite of the traditional methods, these reactions were carried out at room temperature and there was no need to employ low temperature (Scheme 1). 2. Experimental 2.1. General All reagents were purchased from Merck and Aldrich and used without further purification. Aryl diazonium silica sulfates were synthesized according to the previous works [25e28]. All yields refer to the isolated products after purification. The products were characterized by comparison with authentic samples and by spec- troscopic data (IR, 1 H NMR, 13 C NMR spectra and melting point). All melting points were taken on a Gallenkamp melting apparatus and were uncorrected. UV spectra were recorded on a JASCO V-570 * Corresponding author. Tel.: þ98 917 1302528; fax: þ98 311 2289113. E-mail address: aj_zarei@yahoo.com (A. Zarei). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2011.02.010 Dyes and Pigments 91 (2011) 44e48