A simple molecule with two bromine atoms in it caused a whole generation of kings and priests to treat purple-dyed textiles as status symbols. Making that molecule in the 4th century wasn’t an easy task, though. The only thing that could do it then was a sea snail, and each snail could produce only a small amount. As many as 12,000 needed to be crushed to extract enough dye to colour the trim of a single garment.
Since then we’ve understood a lot about this element, and synthesising 6,6-dibromoindigo, the dye molecule, isn’t a difficult task these days. Bromine, abbreviated as Br, is one of the only two elements in the periodic table of 118 elements that is liquid at room temperature (the other is mercury, of course). Discovered in the 1820s by a German and a French chemist independently, Bromine is named after its characteristic stench. In practice, bromine does not just stink, but is also a highly toxic and corrosive gas.
In its native form it may be difficult to handle, but, as part of molecules, bromine has found many uses. Bromine is contained in many drugs some of which are used as analgesics, antihistamines and sedatives. Many energy companies use bromine to reduce mercury emissions. It was recently reported that bromine was much more effective than chlorine at oxidising toxic mercury, which is trapped in solid coal and is released during combustion in power plants.
But not all bromine compounds are useful or harmless. Some bromine compounds are 50 times more damaging to the ozone layer than their chlorine-containing counterparts. The destruction of ozone is caused through the formation of bromine monoxide (BrO). On exposure to light, bromine, which exists as diatom molecule, breaks into bromine free radicals that can readily react with ozone forming BrO. BrO can then react with itself regenerating bromine atoms and thus completes a cycle that destroys ozone, but preserves the bromine radicals.
Bromomethane, once an extensively used pesticide, and dibromomethane, which was used with leaded petrol to ensure removal of lead via exhaust gases, have both now been phased out to curb the depletion of the ozone layer. Bromide ions, which are found plenty in the salts in water, may be benign on their own, but in the process of ozonising drinking water it can be converted to bromate which is a suspected carcinogen (BrO3̅).
Keeping in-line with its halogen buddies - chlorine, fluorine and iodine, bromine also comes with a ‘handle with care’ sticker. It brings with it an array of very useful properties and compounds, but also toxicities and other harmful effects.