Electrochemical study of quinizarin in the presence of arylsulfinic acids: Synthesis of new sulfone derivatives of quinizarin Davood Nematollahi ⇑ , Azam Sayadi, Fahimeh Varmaghani Faculty of Chemistry, Bu-Ali Sina University, Zip Code 65178-38683, Hamedan, Iran article info Article history: Received 14 November 2011 Received in revised form 16 January 2012 Accepted 1 February 2012 Available online 22 February 2012 Keywords: 1,4-Dihydroxyanthraquinone Arylsulfinic acids Cyclic voltammetry EC mechanism Digital simulation abstract Electrochemical oxidation of 1,4-dihydroxyanthraquinone (quinizarin) has been studied in the presence of arylsulfinic acids as nucleophiles in acetonitrile/water mixture by means of cyclic voltammetry as a diagnostic technique. The results indicate that the arylsulfinic acids participate in Michael type addition reaction with the oxidized form of quinizarin, converts it to the corresponding new sulfone derivatives of quinizarin. On the basis of our results, depending on the applied potential, two different series of prod- ucts are isolated. Furthermore, based on an EC mechanism, the observed homogeneous rate constants (k obs ) of the reaction of oxidized form of quinizarin with arylsulfinic acids were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated k obs was found to vary in the order p-toluenesulfinic acid (2a) > benzensulfinic acid (2b)> p-chlorobenzenesulfinic acid (2c). Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Hydroxy-derivatives of anthraquinones are interest as dyes and pigments [1]. They are also, as model chromophores for biologi- cally active compounds, such as the anthracycline antitumor drugs. These compounds are the main part in the chemical structure of antitumor drugs such as daunorubicin, doxorubicin, and mitoxan- trone. These drugs exhibit biological activity by intercalation of the anthracycline aromatic moiety between the DNA base pairs, result- ing in the inhibition of transcription by blockage of RNA polymer- ase [2–6]. On the other hand, organosulfones are important intermediates in organic synthesis because of their chemical prop- erties [7,8] and biological activities [9,10]. Diarylsulfones are important synthetic targets, and widely used synthons for syn- thetic organic chemists due to many applications of them [11,12]. Some of diphenylsulfones have been shown to inhibit HIV-1 reverse transcriptase and represent an emerging class of substances able to address toxicity and resistance problems of nucleoside inhibitors. They are useful in the practice of medicinal chemistry because the sulfone functional group is found in numer- ous drugs. The importance of these compounds has motivated us to synthesize a number of new diarylsulfones via electrochemical method [13–17]. In this work, we obtained two different series of sulfone deriv- atives in the same media, precursor and electrosynthesis cell con- ditions, only by controlling potential during electrolysis. In this direction, we investigated the electrochemical oxidation of 1, 4-dihydroxyanthraquinone (quinizarin) in the presence of aryl- sulfinic acids as nucleophiles and introduce oxidized form of quinizarin as a Michael acceptor for the first time. Also, we have reported an easy and one-pot electrochemical method for the syn- thesis of new sulfone derivatives of quinizarin with high atom economy under ambient conditions and in a divided cell using a carbon electrode in high yield and purity. 2. Experimental 2.1. Apparatus and reagents Cyclic voltammetry, and preparative electrolysis were per- formed using an Autolab model PGSTAT 20 potentiostat/galvano- stat. The working electrode used in the voltammetry experiments was a glassy carbon disk (1.8 mm diameter) and a platinum wire was used as the counter electrode. The working electrode used in controlled-potential coulometry and macroscale electrolysis was an assembly of four carbon rods (31 cm 2 ), while a large stainless steel gauze constituted the counter electrode. The working elec- trode potentials were measured versus SCE (all electrodes from AZAR Electrodes). More details are described in our previous paper [18]. 1,4-Dihydroxyanthraquinone, toluene, benzene and chloro- benzene derivatives of sulfinic acid were reagent-grade from Aldrich. Acetic acid and sodium acetate were of pro-analysis grade from E. Merck. These chemicals were used without further purifica- tion. Homogeneous rate constants were estimated by analyzing the cyclic voltammetric responses, using DigiElch simulation software 1572-6657/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2012.02.004 ⇑ Corresponding author. Tel.: +98 811 8282807; fax: +98 811 8257407. E-mail addresses: dnematollahi@yahoo.com, nemat@basu.ac.ir (D. Nematollahi). Journal of Electroanalytical Chemistry 671 (2012) 44–50 Contents lists available at SciVerse ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem