A Facile and Convenient Method for Synthesis of Thiiranes Under Mild Condition Using Phase Transfer Catalyst
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ORIENTAL JOURNAL OF CHEMISTRY ISSN: 0970-020 X CODEN: OJCHEG An International Open Free Access, Peer Reviewed Research Journal 2013, Vol. 29, No. (4): Pg. 1657-1660 www.orientjchem.org A Facile and Convenient Method for Synthesis of Thiiranes under Mild Condition Using Phase Transfer Catalyst Maryam GORJIZADEH* and MOZHGAN AFSHARI Department of Chemistry, Shoushtar Branch, Islamic Azad University, Shoushtar Iran, 64517-41117, Iran. *Corresponding author E-mail: [email protected] http://dx.doi.org/10.13005/ojc/290454 (Received: October 31, 2013; Accepted: November 15, 2013) ABSTRACT A mild and efficient process for preparation of thiiranes with KSCN in water at room temperature using a catalytic amount of 1,4-bis(triphenylphosphonium)-2-butene dichloride is described. Key words: Epoxide; thiirane; 1,4-bis(triphenylphosphonium)-2-butene dichloride; Phase transfer catalysts. INTRODUCTION complexes12 and cyanuric chloride13 have been used for the conversion of oxiranes to thiiranes. However Epoxides are among the most useful many of these methods suffer from using strongly synthetic intermediates towards the synthesis of acidic or oxidizing conditions, undesirable side many biologically active compounds1 and a large reactions, long reaction time, high temperature, use variety of reagents are known for the ring opening of organic solvents and desulfuration of the resulting of these compounds.2 Their electrophilic reactions thiirane to the olefin. with different nucleophilic anions have been an interesting subject in organic synthesis.3 Of these The toxic and volatile nature of many organic anions, the reaction of thiocyanate ion with epoxides solvents, particularly chlorinated hydrocarbons, that has been widely studied and is a suitable method are widely used in organic synthesis have posed a for the preparation of thiiranes.4 Other reagents such serious threat to the environment. Consequently as phosphine sulfide,5 methylbenzothiazol-2-thione,6 methods that successfully minimize their use are and dimethylthio formamide7 have been reported to the focus of much attention. Water as a solvent is produce thiiranes from oxiranes. Usually with these safe, economical and environmentally benign.14 In sulfurating agents, several different Lewis acids such view of the advantages of using water as a solvent, 8 9 10 as RuCl3, BiCl3 and TiO(CF3COO)2 or a protic we explored the synthesis of various types of acid like TFA5 or oxalic acid 11 have been employed thiiranes from oxiranes and potassium thiocyanate as catalysts. More recently the b-cyclodextrin in presence of 1,4-bis(triphenylphosphonium)-2- 1658 GORJIZADEH & AFSHARI, Orient. J. Chem., Vol. 29(4), 1657-1660 (2013) butene dichloride as an efficient PTC in water at 6.3 (m, 2H), 7.7-8.0 (m, 30H). 13C NMR, (CDCl3): ´ room temperature. = 20.7, 120.8, 132.15, 134.2, 137.01, 140.17. Anal. Calcd: C, 73.055; H, 5.5396; P, 9.5421. found: C, Phase transfer catalysts (PTCs) are 73.9599; H, 5.5469; P, 9.5531%. powerful reagents in chemical transformations,15 the characteristics of which include mild reaction Conversion of oxiranes to thiiranes: General conditions, safety, operational simplicity and Procedure selectivity. PTCs are often used in nucleophilic The epoxide (1 mmol), potassium displacement reactions to facilitate reactions thiocyanate (1 mmol), BTPBDC (0.2 mmol) and between organic reactants and ionic inorganic salts. water (10 mL) were stirred at room temperature for Although many phase transfer catalysts are known, an appropriate time. The progress of each reaction Phosphonium salts are practically important and was monitored by TLC. The reaction mixture was used in many of organic reactions. extracted with diethylether (3×10 mL). The organic solution was concentrated in vacuo, the resulting EXPERIMENTAL product was directly charged on a small silica gel 60 (0.2-0.5 mm) column 25 Cm and eluted with a All products were characterized by 1H mixture of ethylacetate and n-hexane (1:4) to afford NMR, 13C NMR, IR and by comparison with authentic the pure thiirane. samples6,9,16-18. The IR spectra were recorded on Bomem FT-IR spectrometer. 1H NMR and 13C RESULTS AND DISCUSSION NMR spectra were taken on a 400 MHz Broucker spectrometer. The C, H, P analyses were performed 1,4-bis(triphenylphosphonium)-2-butene by the microanalytical service of research institute dichloride [BTPBDC] was easily prepared by reacting of petroleum industry (N. I. O. C). Melting points 1,4-dichlorobutene with triphenylphosphine in were measured on a mettler FP5 apparatus. 1,4- chloroform under reflux condition (Scheme 1). The bis(triphenylphosphonium)-2-butene dichloride was reaction is very clean and phase transfer catalyst prepared and other chemicals were purchased from can be easily precipitated in acetone. the Merck chemical company Darmstadt, Germany. The purity determination of the products and reaction We examined the catalytic ability of monitoring were accomplished by TLC on polygram BTPBDC for conversion of epoxides to thiiranes. SILG/UV 254 plates. Therefore, phenyl glycidyl ether (1 mmol) was reacted with potassium thiocyanate (1 mmol) in Preparation of 1,4-Bis(triphenylphosphonium)- the presence of BTPBDC in different solvents. The 2-butene Dichloride (BTPBDC) results were clearly shown water was the best solvent To a solution of 1,4-dichlorobutene (0.625g, among those tested. TLC analysis was showed at 5 mmol) in CHCl3 (10 mL) in a 50 mL round-bottomed room temperature, conversion was completed after flask equipped with a magnetic stirrer and a reflux 2.5 h and corresponding thiirane was produced in condenser was added triphenylphosphine (2.62g, 87% isolated yield. According to obtained results, 10 mmol). The reaction mixture was refluxed on this catalyst acted very effciently and it was observed a water bath for 2.5 h. The solution was cooled to that only 0.2 M equivalent of the catalyst is enough to room temperature and then, while vigorously stirred, convert different epoxides carrying electron donating diethylether was added dropwise until an oily product or with-drawing groups to their corresponding separated. The ether was removed by decantation thiiranes in high isolated yields (Scheme 2, Table and acetone (40 mL) was added. Stirring the acetone 1). solution for 40 min afforded a white precipitate which was filtered, washed with acetone (20 mL) and dried. It is noteworthy that no evidence for the Yield 2.596g (80%), m.p. 278-279 °C. IR (KBr):Å formation of olefins as by-product of the reaction = 3053(m), 2755(w), 1613(m), 1575(s), 1478(s), was observed. In organic solvents; the reaction did 1437(s), 1258(s), 754(s), 693(s), 556(s) Cm-1. 1H not complete after 3 h and was contaminated by diol NMR(CDCl3): ´ = 5.7 (dd, JPH=15.7, JHH=8, 4H), and thiocyanohydrine formation. In the absence of GORJIZADEH & AFSHARI, Orient. J. Chem., Vol. 29(4), 1657-1660 (2013) 1659 Table 1: Reaction of different epoxides with KSCN using BTPBDC as catalyst Entry Substrate Product(s)a Time(h) Yieldb(%) O S 1 Ph Ph 2.5 87 O S 2 PhOCH2 PhOCH2 2.5 87 O S ClCH ClCH 3 2 2 3 92 O S 4 CH2=CHCH2OCH2 CH2=CHCH2OCH2 2 85 S O (CH ) CHOCH 5 (CH3)2CHOCH2 3 2 2 3 91 O S CH3(CH2)2CH2OCH2 CH3(CH2)2CH2OCH2 6 2.5 89 CH3 S CH 3 O O O H2C H2C 7 O O 2 95 O S 8 CH3CH2 CH3CH2 3 93 S O 9 3.5 85 aProducts were identifed by compared of their physical and spectral data with those of authentic samples. catalyst, the conversion of oxiranes was very slow the epoxides for the reactions to occur. Secondly, and the yields were also very low (20% in 6 h). It is the phosphonium functionalities on these catalyst believed that BTPBDC can catalyze the formation can interact as a Lewis acid with the oxygens of the of thiiranes from epoxides in the aqueous phase epoxides to facilitate the attack of the thiocyanate in two ways. Firstly by swelling in the aqueous anion as the nucleophile. It is worthy to note that media it can act as phase transfer catalyst for the reaction medium was almost neutral, sensitive the the epoxides, and can therefore provide the functionalities such as carbon-carbon double bonds necessary microenvironment for the water-soluble remain intact. nucleophile, that is, SCN-, to be in the vicinity of + CHCl3 + Cl Cl + 2 PPh3 PPh3 - PPh Reflux 2Cl 3 Scheme 1 O S KSCN, H2O, r.t. BTPBDC R R Scheme 2 1660 GORJIZADEH & AFSHARI, Orient. J. Chem., Vol. 29(4), 1657-1660 (2013) In conclusion, we have developed a economical and environmental points of view, use of novel, eco-friendly, and efficient protocol for water as solvent is favorable than organic solvents. the synthesis of thiiranes with KSCN using 1,4- bis(triphenylphosphonium)-2-butene dichloride as ACKNOWLEDGEMENTS a catalyst. This method offers several advantages including mild reaction conditions, high conversions, We are grateful to the Islamic Azad short reaction times and high isolated yields. It can University Shoushtar Branch for support of this be emphasized that the reaction is clean and from work. REFRENCES 1. Corey, E.J.; Shibata, S.; Bakshi, R.K. J. Org. 9. Mohammadpoor-Baltork, I.; Alian, H. Synth. Chem. 53: 2861(1988). Commun. 28: 3943 (1998). 2. (a) Iranpoor, N.; Baltork, I.M. Synth. Commun. 10. Iranpoor, N.; Zeyni-Zaadeh, B. Synth. 20: 2789 (1990). Commun. 28: 3913 (1998). (b) Cha, J.S.; Park, S.J. Bull. Korean Chem. 11. Kazemi, F.; Kiasat, A. R. Phosphorus, Sulfur, Soc., 30: 2823 (2009). and Silicon, 178: 1333 (2003). (c) Kim, Y.S.; Lee, Y.; Kim, G.J. Bull. Korean 12. Surendra, K.; Krishnaveni, N.S.; Rao, R.S. Chem. Soc. 30: 1771 (2009).