Bromine

Bromine from NaBr

10 NaBr + 2 KMnO4 + 8 H2SO4 –> 5 Br2 + 2 MnSO4 + 8 H2O + 5 Na2SO4 + K2SO4

Materials:

  1. NaBr (102.894g/mol, Sol H2O 90.5g/100ml @ 20C, 121.0g/100ml @ 100C)
  2. Conc. H2SO4 Sulfuric Acid (98% or Kleen-out  is 93-99%) (98.079 g/mol, 98% 1.84g/ml pKa -3)
  3. KMnO4 (158.034g/mol, mp 240C, H2O sol 63.8 g/L (20 °C), 250g/L (65 °C))

Reaction Solvent: H20

Wash: Conc H2SO4

Purification: Distill over H2SO4

Output: Br2 (159.81g/mol, 3.1 g/ml, bp 58.8C/137.8F)

Procedure

Set-up: 2L RB with simple distillation, add funnel, heating mantle and mag stir

  1. Dissolve 500g NaBr (4.86mol) in 600ml water, heating if needed to dissolve
  2. Add 158.0g KMnO4 (1.0mol, 0.21x NaBr)
  3. Add 408.0g 98% H2SO4 (4.24mol, 225ml)  slowly to maintain red color in still head as Br2 distills
  4. Warm solution near end to complete conversion
  5. Wash with 60ml conc H2SO4 (layers need ~ 1 hour to settle)(Br2 is on bottom)
  6. Distill over H2SO4 to remove residual impurities

Theo yield 388.3g

Trial 1

Materials: 99% NaBr from Menards, 99% KMnO4 from a hydroponics supply house, Sulfuric acid Menards “Kleen-out”

2L RB with add funnel, mag stir, heating mantle and simple distillation set-up:

500g NaBr added to 600ml H2O in portions, allowing each to dissolve (to avoid overwhelming the stir bar).

159.0g KMnO4 added over ~ 1 minute (mostly a steady pour)

KMnO4 added

408.5g H2SO4 added dropwise from the add funnel, starting at 1 drop/s. Temp slowly climbs. At ~1hr, set mantle to 80 C, but after 15 minutes (mantle temp sensor said 88C), significant fumes puff out the take off vacuum connection with each drop of H2SO4, so turned mantle off again

15min 1hr, mantle to 80C Mantle off

Don’t see a rush to try to distill any formed bromine, so stay at a slow rate until all H2SO4 added (5.5 hrs). Then put mantle at 80C and distilled until drop rate fell below 1drop/2s, then raised in successive 10C-15C increments up to 130C. Took ~3.5hrs of distillation after last H2SO4 added (longer would have been better, but was out of time).

End of H2SO4 addition End Distill, Mantle 130C 500ml Receiver

Washed with 100ml H2SO4.

332.4g, 86% yield

Product was stored in amber glass bottles with PTFE cap liner

One of the caps failed within 4 weeks and material was transferred to a new one