Thermal studies of hypervalent iodine reagents
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Thermal studies of hypervalent iodine reagents Vikas Verma • Kuldeep Singh • Ashok Kumar Devinder Kumar
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Received: 19 July 2012 / Accepted: 12 December 2012 / Published online: 13 January 2013 Ó Akade´miai Kiado´, Budapest, Hungary 2013
Abstract The thermal properties of hypervalent iodine reagents (iodobenzene diacetate, bis(trifluoroacetoxy)iodobenzene, [hydroxyl(mesyloxy)]iodobenzene, [hydroxy(tosyloxy)] iodobenzene) and polymer-supported hypervalent iodine reagents (polystyrene-supported iodobenzene diacetate, polystyrene-supported bis(trifluoroacetoxy)iodobenzene, polystyrene-supported[hydroxyl(mesyloxy)]iodobenzene, polystyrenesupported [hydroxy(tosyloxy)] iodobenzene) were investigated using thermogravimetry (TG) and differential scanning calorimetry (DSC). The polystyrene-supported iodobenzene diacetate, synthesized from polystyrene, was a precursor to other three polymer-supported hypervalent iodine reagents (PS-HTIB, PSHMIB and PS-BTI). The TG curves of hypervalent iodine reagents and their polymer analogues show mainly one-step mass loss behaviour, whereas enthalpy change (DH) and onset temperature were calculated from a DSC curve which that shows hypervalent iodine reagents and their polymer analogues decompose endothermically. The results suggest that the polymer-supported hypervalent iodine reagents are more stable than hypervalent iodine reagents and therefore may be used in reactions without decomposition up to 350–410 °C in comparison to the polymer-supported hypervalent iodine reagents that are stable up to 132–160 °C. Keywords Hypervalent iodine reagents Polymersupported hypervalent iodine reagents DSC TG
V. Verma K. Singh A. Kumar D. Kumar (&) Department of Chemistry, Guru Jambheshwar University of Science & Technology, Hisar 125001, Haryana, India e-mail: [email protected]
Introduction Hypervalent iodine reagents have gained significance in chemistry including interesting applications in the synthesis of natural products and are also considered as environmentally benign reagents [1–14]. The growing interest in iodine compounds is mainly due to the very useful oxidizing properties enabling powerful coupling reactions and mild oxidations for the simpler synthetic procedures for development of compounds of biological importance. The general reactivity pattern consists of carbon–carbon, carbon–heteroatom, heteroatom–heteroatom reactions and oxidation and rearrangements. In particular, trivalent iodine reagents are often an interesting alternative to transition metal (lead and thallium) derivatives, the toxicity of which makes that incompatible in pharmaceutical environment. Hypervalent iodine reagents (Fig. 1) are easy to handle and show high chemoselectivity. However, the iodobenzene formed during the reaction causes problems in the isolation of the products and their purification. Keeping in view the problem associated with the contamination of the product with iodobenzene, polymer-supported hypervalent iodine reagents have been developed to overcome the above problems. The polymer-
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