hypo
(Hive Addict)
06-21-03 15:31
No 441543
      OTC synthesis of cuprous bromide (CuBr)
(Rated as: excellent)
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OTC synthesis of cuprous bromide (CuBr)

this is a simple synthesis from OTC ingredients, which gives a
reasonably pure product.

To a stirred solution of 14.63g CuSO4.5H2O (cupric sulfate pentahydrate,
blue vitriol) in 25ml H2O is added a solution of 7g KBr in 20ml H2O. To
the resulting dark green solution with a white precipitate is added 6.3g
sodium bisulfite (NaHSO3) in 50 ml H2O. A white precipitate forms
immediately (Note: as opposed to [1] no brown coloration was observed).
The solution and the precipitate are poured into 900ml well stirred H2O
containing 2ml 48% HBr and 1g sodium bisulfite. After a few minutes of
stirring, the mixture is allowed to stand until the precipitate has settled and
the bluish/green solution is decanted. The precipitate is washed into a suction
filter using generous amounts of dil. H2SO4. It is then washed 4 times
with 20ml AcOH to remove a brown impurity of unknown composition, 3
times with 30ml alcohol (Note: [1] calls for absolute alcohol) to remove the
blue coloration and  6 times with ether (Note: [1] calls for anhydrous ether).
During all washings, there should always be a layer of liquid that covers
the salt. The white precipitate is sucked dry and dried at about 100°C for
1 hour to obtain 5.5g of a white shiny powder, which is stored in an airtight
container.

Slightly adapted from [1]: Inorganic Syntheses 2, 1-4 (1946)

Miscellaneous Notes:

CuBr is sensible to air oxidation when not perfectly dry, that's why
the first procedure in ../rhodium/chemistry /cucl.txt is not
suited for the production of the powder.

This procedure can surely be optimised, but why bother when the
precursors are so damn cheap.

A green tint is indicative of Cu(2+) traces.

The chemistry behind all this is quite interesting. One would expect
Cu(+) ions to disproportionate, but the low solubility makes them
actually synthetisable from aqueous solutions...


Another synthesis of cuprous bromide (CuBr)
 
Not tried. The inert atmosphere is probably overkill.

In a 250ml three neck flask equipped with a condenser and under
inert atmosphere is refluxed a mixture of 50g cupric sulfate
pentahydrate, 25g sodium bromide and 20g copper powder in 76.8ml
48% HBr until the blue color has disappeared. The still hot solution
is decanted from the precipitate and poured into 1l degassed water
containing SO2 (i guess adding some bisulfite works too). CuBr
precipitates. The solution is decanted, the residue washed with
degassed, SO2 containing water, then ethanol and ether and finally
dried on high vacuum. Yield: 80% (from CuSO4.5H2O)

Adapted from Jander, G.; Blasius, E. "Lehrbuch der analytischen und präparativen Chemie", p. 486, 13. Edition