ORIGINAL PAPER Selectivity enhancement of aromatic halogenation reactions at the micellar interface: effect of highly ionic media Bhupesh S. Samant • Sunil S. Bhagwat Received: 25 March 2011 / Accepted: 27 October 2011 / Published online: 29 November 2011 Ó Springer-Verlag 2011 Abstract Halogenation (iodination and bromination) of various aromatic compounds has been studied in micellar media in order to observe the effect on regioselectivity and conversion of the reaction. The addition of surfactant causes a change in the chemical shifts of the aromatic proton resonance of phenol which proves the orientation of the aromatic compound on the micellar surface. However, increase in ionic strength of the reaction media affects the selectivity of reaction by disturbing this spatial orientation of the aromatic compound in the micelle. Selectivity towards particular isomers is dependent on the concentra- tion of the surfactant. In bromination of chlorobenzene (deactivated aromatic compound) enhancement in selec- tivity and conversion towards the para isomer has been observed. Keywords Micelles Á Aromatic halogenation Á Electrophilic substitution Introduction Micelles are self-assembled nanostructures of amphiphilic monomers forming a hydrophilic outer shell area and a hydrophobic core. The use of micelles as reaction media is widespread and has been investigated in detail for different reactions in aqueous and organic media [1]. Most aromatic compounds have a very low solubility in water and the presence of water adversely affects the product yield; hence organic solvents (nonpolar media) are often used for aromatic substitution reactions [2]. The cost-effective and eco-friendly use of micellar aggregates as microreactors enhances the scope of organic reactions. The interface of micellar aggregates is located between the outer hydro- philic bulk and the inner organic (hydrophobic) core. This anisotropic area is known as the palisade layer. It provides a useful reaction site to enhance the conversion and selectivity of various reactions [3]. As part of our ongoing research into selectivity improvement in organic synthesis [4–12], we have already described improvement in the regioselectivity of chlorination of phenol and o-chloro- phenol in the presence of micelles [4]. We now present a study of selectivity enhancement in aromatic halogenation reactions. Halogenated aromatic compounds are of great use in pharmaceuticals [13]. In the literature various methods have been reported to improve the regioselectivity in the iodination and bromination of activated aromatic com- pounds and these include employing specific techniques [14, 15], catalysts [16–18], and reagents [19–25]. However, most of these methods have some limitations such as the use of strong and/or specialized halogenating agents, toxic and expensive reagents, low yields, and long reaction times. The pioneering kinetic studies were done on chlo- rination and bromination reactions [26, 27]. Electronic supplementary material The online version of this article (doi:10.1007/s00706-011-0677-1) contains supplementary material, which is available to authorized users. B. S. Samant (&) Natural Product and Medicinal Chemistry (NPMC) Research Group, Division of Pharmaceutical Chemistry, Faculty of Pharmacy, Rhodes University, Grahamstown 6140, South Africa e-mail: B.Samant@ru.ac.za S. S. Bhagwat Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400019, India 123 Monatsh Chem (2012) 143:1039–1044 DOI 10.1007/s00706-011-0677-1