Bromine

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Bromine
Chemical formula Br
Atomic Number 35 
OTP appearance dark brown liquid 
Molar Mass(g/mol) 79.04 
Melting Point(°C) -7.2 
Boiling Point(°C) 58.8 
Density(g/cc) 3.1 
Immediate Danger to Life and Health 3ppm(inh)
NFPA 704
NFPA704.png
0
3
0
OX

Uses

Justification Questioned

Other

Natural Sources

  • Elemental bromine does not occur in nature.
  • Bromine occurs as salts in salt water at about 67.3 mg/L. (1 mol (79g) per 1216L)
  • Bromine occurs as salts in kelp and seaweed at 500 to 1000 ppm (by mass)

Hazards

Bromine is extremely toxic in elemental form

Production

Extraction

from sea water

Water from the ocean is pumped to the top of blowing-out towers, with sulfuric acid and chlorine being added just above the pumps so that mixing takes place during the ascent. About 1.3 kg of 10% sulfuric acid per ton of water is required to neutralize the natural hydrogen carbonates and bring the pH to 3.5; 15% excess chlorine over the theoretical requirement is used. Air is drawn up through the towers, sweeping out a mixture of bromine and chlorine (or bromine chloride) from the descending ocean water. The air is drawn next through absorber towers in which it is scrubbed counter-currently by sodium carbonate solution. ... To remove spray from the air, small packed chambers are interposed between the absorber towers and the fans. When the alkalinity of the scrubber solution is nearly depleted, the solution is brought first to a storage tank and then to a reactor in which it is treated with sulfuric acid and steamed to release bromine.[1]
  1. Bubble chlorine gas through brine, producing dilute bromine vapors in air
    2 MBr + NBr2 + 2 Cl2
    {H2SO4
    pH 3.5}
    2 MCl + NCl2 + 2 Br // M ∈ Na,K,Li ... N ∈ Ca, Mg ...
  2. Bubble bromine vapors through sodium carbonate producing bromide and bromate
    3 Br2 + 3 Na2CO3 5 NaBr + NaBrO3 + 3 CO2 // Carbonate reaction
    3 Br2 + 3 NaHCO3 2 NaBr + NaBrO3 + 3 CO2 + 3 HBr // Bicarbonate reaction
  3. Add sulfuric acid to a cool, concentrated bromide/bromate solution, giving liquid bromine
An alternative treatment of the chlorine/bromine/air mixture is to mix it with sulfur dioxide rather than sodium carbonate.

Bromine can be extracted from salt water by halide displacement, then condensation of the elemental bromine

  1. In a 26L closeable container, combine 25L of salt water and 1L of chlorine gas
  2. Bubble an excess of chlorine gas through salt water at below 65°C.
    2 NaBr(aq) + 10 Cl2(g)
    {t≤65 °C
    }
    2 NaCl(aq) + Br2(aq) + 8 Cl2(g)
  3. Fractionally distil the bromine from the solution
    H2O + Br2(aq)
    {t≥65 °C
    }
    H2O + Br2(g)

from kelp

To overcome several disadvantages incurred in iodine and bromine from kelp according to the old Wollaston method by means of sulphuric acid and peroxide of manganese, Prof Galloway of Dublin proposes to [substitute?] chlorine for those agents.
In working according to the Wollaston method the residue remaining after distilling of the two elements was thrown away. The loss caused thereby sometimes constituted much as fifty per cent of the entire cost of production. In using chlorine Galloway proceeds as follows:
The solution of kelp is first perfectly neutralized by sulphuric acid. This is done as kelp invariably contains quantity of alumina which renders the solution mucilaginous and unfit for crystallization and Galloway recommends, therefore, perfect neutralization The solution kelp is then evaporated down till the chloride of potassium formed is nearly completely crystallized out. The liquor is then again neutralized and an exactly quantity is well mixed in a graduated pipette with a quantity of bisulphide of carbon. Then chlorine water added in small quantities till the violet color has completely disappeared. This test, so often used to determine iodine quantitatively, only takes up one or two minutes time. After correctly noting the quantity of chlorine necessary convert the iodine into chloride of iodine the quantity chlorine water necessary for the entire quantity of liquid is measured out and added to the latter The quantity of iodine remaining in solution can be extracted benzole of bisulphide of carbon. After extraction of iodine the bromine is separated in a similar manner times as much chlorine water being required as for separation of iodine.
Sometimes it is desirable not to dilute the liquid as much as this would be the case by the addition of the entire quantity of chlorine water. In that case there would be a portion of the iodine and bromine lost. To prevent this the liquor may first be treated by chlorine gas and the finished by chlorine water.
This process does not take up much time and is very exact as far as that ma be said of the application of a analytical operation to a technical process After of the iodine the alkaline salts remaining in solution easily be obtained The precipitated iodine must be resublimed.[2]

Synthesis

from alkali halides

Alkali halides combined with sulfuric acid and an oxygen donor (manganese dioxide hydrogen peroxide, etc) produce the elemental halide (bromine, in this case).

  1. Fill alembic with manganese dioxide
  2. Add alkali bromide to alembic
  3. Add condenser, backflow trap, gas trap (NaOH)
  4. Repeat
    1. Add one drop of sulfuric acid, condensing any gas that evolves
      2 KBr + 2 H2SO4 + MnO2 K2SO4 + MnSO4 + 2 H2O + Br2
  5. Until no more gas evolves
  6. Replace receiver
  7. Place tight cap on receiver containing bromine liquid
  8. Raise temperature of alembic solution to 65°C, condensing any gas that evolves
  9. Wait for a few minutes
  10. Remove and cap receiver containing concentrated bromine water
  11. Redistill contents of both receivers as needed

Purification

Testing

Storage

  • Do NOT use plastic containers or seals.
  • Store liquid bromine under a layer of concentrated sulfuric acid to reduce fuming and keep the bromine dry
  • Keep cool (well below boiling point)

Disposal

See Also

References

  1. Mills, JF (2014) "Bromine".
    Ullmann's Encyclopedia of Industrial Chemistry 7th ed. John Wiley & Sons.
  2. Galloway, Robert (1883) "On the Extraction of Iodine and Bromine from Kelp"
    Proceedings of the Royal Irish Academy. 3; pp152-154. Royal Irish Academy
    link courtesy Google Books.