The use of pyridinium bromide perbromide for brominations.

Abstract

The chemistry instructor usually assigns bromination reactions to the students after much deliberation and anxiety. This is quite understandable because of the hazards associated with bromine. The latter not only causes severe burns but the fumes produce a suffocating effect and are a source of much irritation. However, in the last few years various solid brominating agents have become commercially available, notably pyridinium bromide perbromide,1 2and N-bromosuccinimide.5 An excellent discussion of the reactions conducted with N-bromosuccinimide has been published.3Brominations with pyridinium bromide perbromide are safe and convenient. Since pyridinium bromide perbromide, C6Hf,NBr-Br2 is a relatively stable red crystalline compound/.5 having a melting point of 135-6°C. (dec.), there are no annoying fumes to contend with during handling; no elaborate apparatus is necessary for weighing out the required amounts of pyridinium bromide perbromide and when spilled it can be easily brushed off clothing, hands, or face with no accompanying danger of burns. Moreover, the student feels safer when handling "solid" bromine. In contrast to disagreeable and dangerous bromine, pyridinium bromide perbromide can be safely stored in the laboratory with no danger of spillage and annoyance to students and instructors.The brominations herein reported have been undertaken because they are usually the most common reactions performed in university and college laboratories. An attempt has been made to follow the normal procedures from the references indicated, but substituting pyridinium bromide perbromide for the bromine, assuming that the perbromide contained 45 per cent of available bromine. The manufacturer has reported 45 to 50 per cent bromine available. However, the lower limit has been utilized so as to insure complete bromination. From some of the reactions conducted it was evident that more than 45 per cent bromine was 1

Recent Advances in Bromination of Aromatic and Heteroaromatic Compounds

“…73 Other possible alternatives to Br 2 are ionic tribromides, such as pyridinium tribromide. 74,75 Both these classes of reagents were recently developed.…”

A Multistep Synthesis Incorporating a Green Bromination of an Aromatic Ring

“…The organic synthesis chemical education community has developed green methods that allow students to gain experience in aromatic halogenation reactions without being exposed to the hazards presented by traditional procedures. One reagent that has shown promise in achieving this task is pyridinium tribromide, which generates elemental bromine in situ as the reaction progresses, avoiding the handling of liquid bromine. , However, a large quantity of waste is produced and product yields are appreciably affected by the temperature and concentration dependences of the bromine-generating reagent.…”

“…One reagent that has shown promise in achieving this task is pyridinium tribromide, which generates elemental bromine in situ as the reaction progresses, avoiding the handling of liquid bromine. 7,8 However, a large quantity of waste is produced and product yields are appreciably affected by the temperature and concentration dependences of the bromine-generating reagent.…”