N-Bromosuccinimide

Abstract

[128-08-5] C4H4BrNO2 (MW 177.99) (radical bromination of allylic and benzylic positions; electrophilic bromination of ketones, aromatic and heterocyclic compounds; bromohydration, bromoetherification, and bromolactonization of alkenes) Alternate Names: NBS; 1-bromo-2,5-pyrrolidinedione. Physical Data: mp 173–175 °C (dec); d 2.098 g cm−3. Solubility: sol acetone, THF, DMF, DMSO, MeCN; slightly sol H2O, AcOH; insol ether, hexane, CCl4 (at 25 °C). Form Supplied in: white powder or crystals having a faint odor of bromine when pure; widely available. Purification: in many applications the use of unrecrystallized material has led to erratic results. Material stored for extended periods often contains significant amounts of molecular bromine and is easily purified by recrystallization from H2O (AcOH has also been used). In an efficient fume hood (caution: bromine evolution), an impure sample of NBS (200 g) is dissolved as quickly as possible in 2.5 L of preheated water at 90–95 °C. As filtration is usually unnecessary, the solution is then chilled well in an ice bath to effect crystallization. After most of the aqueous portion has been decanted, the white crystals are collected by filtration through a bed of ice and washed well with water. The crystals are dried on the filter and then in vacuo. The purity of NBS may be determined by the standard iodide–thiosulfate titration method. Handling, Storage, and Precautions: should be stored in a refrigerator and protected from moisture to avoid decomposition. One of the advantages of using NBS is that it is easier and safer to handle than bromine; however, the solid is an irritant and bromine may be released during some operations. Therefore, precautions should be taken to avoid inhalation of the powder and contact with skin. All operations with this reagent are best conducted in an efficient fume hood. In addition, since reactions involving NBS are generally quite exothermic, large-scale operations (>0.1 mol) should be approached with particular caution.