Clay-Polymer Nanocomposite-Supported Brominating Agent

Abstract

The conventional methods of direct bromination of organic compounds with elemental bromine have several major drawbacks such as handling difficulty, corrosive effect, and toxicity, in addition to over-bromination and problems with isolation of products from the reaction mixture. Supported catalysts and reagents have become popular in the synthesis of organic chemicals over recent decades because they have overcome almost all of the drawbacks noted above. In the present study, a new clay polymer nanocomposite (CPN)-supported brominating agent was prepared from montmorillonite (Mnt) and styrene-co-vinyl pyridinium polymer. The reagent was obtained by the direct interaction of a two-fold excess of poly(styrene-co-N-methyl-4-vinylpyridinium) bromide with Na-montmorillonite (NaMnt) through ion exchange between Na⁺ of the NaMnt and pyridinium ions in the copolymer to provide CPN3 with free methylpyridinium bromide side chains. The structure of the CPN3 prepared was characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Treatment of the CPN3 with bromine using the bromide ions which remained led to the perbromide-supported reagent, CPN4. The activity of the resulting CPN4 brominating reagent was examined through direct bromination of some alkenes, arenes, and carbonyl compounds and compared with the effectiveness of a crosslinked polymeric perbromide reagent. The yields obtained from application of the reagent were moderate to excellent. The advantages of this reagent, such as stability at room temperature, ease of regeneration from the polymeric by-product, and the yields of the brominated products, confirm the viability of using a CPN-supported brominating agent as a reactive reagent in organic chemistry synthesis.