OH OH
BrAbstract An effective approach to monobromination reactions utilizing room temperature ball-milling is introduced for the synthesis of aryl bromides and bromoketones with N-bromosuccinimide (NBS) and MCM-41-SO 3 H. Advantages of this technique are short reaction times and high regioselectivity. In contrast to other techniques using microwaves, ultrasound, or ionic liquids, handling of sensitive materials is possible and furthermore, this method has advantages over other solvent-free techniques that require a higher reaction temperature for high yield of products.Key words ball-mill, monobromination, regioselectivity, MCM-41-Halogenated compounds have diverse applications in various fields such as pharmaceuticals and agrochemicals. 1 Aromatic halides are the key fragments of coupling reactions such as Heck, Suzuki, Sonogashira, and hetero coupling reactions. [2][3][4][5] For the synthesis of brominated aromatic compounds, Br 2 is the traditional reagent, but results in the production of HBr and procedures often require careful control of temperature and amount of Br 2 . As a result, improved mild brominating agents have been developed, 6-13 but a fundamental disadvantage for many of these methods is unwanted oxidation of sensitive functional groups.To eliminate such problems, NBS has been used for brominating aromatic compounds 14 and several reaction conditions in organic solvents have been reported to activate the halogenating ability of NBS. [15][16][17] There are some reports that describe halogenations in the presence acidic catalyst, such as trihaloisocyanuric acid for halogenation of β-dicarbonyl compounds, 18a sodium hypochlorite for the halogenation of β-dicarbonyl compounds, 18b and NBS in the presence of acidic catalyst. 16 It became clear to us that combining an acidic catalyst and NBS leads to more efficient bromination reactions. In addition, using heterogeneous acidic nanocatalysts can be advantageous over homogeneous catalysts as a result of their high surface area, recyclability and simplified workup.A specific example of a silica material with ordered structure, narrow pore-size distribution (1.5-10 nm) and very high surface area (more than 1500 m 2 g -1 ) that can be used as a heterogeneous nanocatalyst is MCM-41. Modification of its surface can result in a solid acid with high uniformity, modified by covalent anchoring of different organic moieties in a well-ordered mesoporous material. Thus, nanoparticulate MCM-41-SO 3 H with covalently bound sulfonic acid was selected for investigation as a heterogeneous acidic nanocatalyst.It has been said that 'the best solvent is no solvent', but to obtain high yields under solvent-free conditions frequently involves high temperatures that are not suitable for materials that are temperature sensitive such as terminal alkynes. 19 One solution can be found in 'mechanochemistry', 20 which involves induction of a chemical reaction by the direct absorption of mechanical energy. 1 In mechanochemistry, mechanical energy in the solid state is used for bon...