Scalability of a Time- and Cost-Effective Procedure for the Synthesis of Picryl Bromide

An optimized synthetic procedure for the manufacture of picryl bromide on a 300 g scale is described. Previous procedures had different drawbacks such as two or more separate nitration steps with varying mixed acids, a complicated workup and purification procedure, expensive starting materials, or very long reaction times. An optimized and time-efficient method on a laboratory scale was described in an earlier conference contribution. The one-pot nitration of bromobenzene using a 5:1 mixed acid consisting of oleum (30%) and white-fuming nitric acid (10 equiv) was developed to prove the technical scalability of the reaction. By application of the optimized reaction parameters to a large-scale environment, crude picryl bromide yields of up to 72% can be achieved. The product contains only a minor picric acid impurity (2-3%), which is formed during the aqueous workup step. It can be removed by a single recrystallization from boiling chloroform to afford the target compound in pure form. This method combines the use of cheap materials with a time-efficient route of synthesis and a simple purification step, which is an improvement compared with the state-of-the-art methods.