Bromine
Properties
| State | Liquid (dark reddish-brown, fuming, with pungent odor) |
| Color | Dark reddish-brown |
| Solubility | Moderately soluble in water (35 g/L at 20°C); miscible with organic solvents |
| Melting Point | -7.2°C |
| Boiling Point | 58.8°C |
About Bromine
Bromine is the only nonmetal that is a liquid at standard temperature and pressure (mercury is the only other liquid element), and the dark reddish-brown color and the pungent reek that gave it its name — Greek bromos, 'stench' — come from the same place: a relatively narrow HOMO-LUMO gap in the Br2 molecule that puts strong absorption in the green/blue, plus a vapor pressure of about 23 kPa at 25 °C that means a sealed bottle is always saturated with brown vapor. Antoine Balard isolated it from Mediterranean salt-marsh brine in 1826, racing Carl Löwig (who had bromine from a Bad Kreuznach mineral spring but was slower to publish) by a few months. In organic chemistry Br2 is the workhorse electrophilic addition reagent — drip it into an alkene or alkyne in CCl4 or CH2Cl2 and the reddish-brown color disappears as fast as you can stir, because the pi electrons of the C=C bond polarize the Br-Br bond and form a bromonium ion that opens stereospecifically anti to give a vicinal dibromide. That decolorization is the basis of the bromine test that every organic chemistry student runs in the first month of lab. Industrially the largest single use is brominated flame retardants — TBBPA, decabromodiphenyl ether (decaBDE, now restricted under Stockholm Convention), and HBCD — added to circuit boards, polystyrene insulation, and upholstery to slow ignition. Bromine also goes into clear brine completion fluids for oil and gas wells (CaBr2 and ZnBr2 solutions tunable to densities up to 2.3 g/mL), pharmaceutical intermediates (about 30 percent of small-molecule drugs in development carry at least one bromine atom, often as a Suzuki coupling partner), and silver-bromide grain photographic emulsions where they remain in specialty films. World production runs about 600,000 tonnes per year, mostly from the Dead Sea (Israel and Jordan) and Arkansas Smackover Formation brine.
Where you'll encounter it
If you've ever seen the inside of an organic teaching lab, you've smelled the faint background tang of bromine — there's almost always a bottle being decanted somewhere. Mistakes with bromine show up fast: a single drop on a lab coat raises a yellow-brown stain that won't wash out, and a knocked-over bottle in a hood produces a brown plume dense enough that you can watch it pour across the bench like a liquid. In a Suzuki cross-coupling reaction, a chemist might dispense an aryl bromide onto a balance pan in milligram quantities — the strong C-Br bond is just labile enough that Pd(0) catalysts insert into it readily, but stable enough to survive normal storage at room temperature.
Common Uses
- Brominated flame retardants (TBBPA, HBCD) for circuit boards and polystyrene insulation
- Electrophilic addition reagent for alkene and alkyne functionalization in synthesis
- Aryl-bromide synthon for Suzuki-Miyaura cross-coupling in pharmaceutical chemistry
- Clear brine completion fluids (CaBr2, ZnBr2) for high-density oil and gas well control
- Hot-tub and spa disinfectant via bromine tablets that hydrolyze to HOBr in water
Safety Information
GHS: Acute Tox. 1 (inhalation), Acute Tox. 3 (oral), Skin Corr. 1A, Eye Dam. 1, Aquatic Acute 1. Occupational limits sit at a fraction of a part per million, and the concentration considered immediately dangerous to life is only a few times higher — the margin between a working exposure and an incapacitating one is narrow. Vapor density 5.5 times air, so leaks pool on the floor and ventilation has to draw from low in the hood. A spill needs immediate evacuation; cover with sodium thiosulfate or sodium bicarbonate to neutralize, never water (which spreads the liquid and intensifies the vapor cloud). Skin contact causes deep painful burns that can take weeks to heal — wash immediately with copious water, then sodium thiosulfate solution, then seek medical attention.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.