Author Topic: PhMgBr synthesis use of na  (Read 2203 times)

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acx01b

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PhMgBr synthesis use of na
« on: May 18, 2004, 01:58:00 AM »
Bromobenzene, Et2O, Iodine, Magnesium turnings, Sodium

Ether is dried with MgSO4 (MgSO4 powdered and microwaved)to get cloudy dried ether, then distillation gives clean ether.

Bromobenzene has not been dried, but Na doesnt reacts in it, so it must be already dry.

Iodine has been made with Iodine teinture (I2 in ethanol): I2 and ethanol (and maybe other things?) has been let to evaporate for 24h, and solid mess has been heated slowly, the purple vapours catched directly on a very cold glass (no distillation).

Magnesium (2Grams) is heated dried with a few iodine crystals (0.1 --> 1 mg of iodine), enough to see the dark purple-pink vapours, then Bromobenze (0.5ml) and Ether (10ml) added.
something is boiling: we can see the reaction.
but 2-5min later: it stops! (heating doesnt make it strating again)
Na(50mg) is added, and crushed in the ether.
rest of Bromobenze is added, and some ether(10ml).

2hours later, the purple-brown clean solution begins to be couldy.
1hour later: the solution is totally brown and is not clean anymore. the test tube is hot, but boiling is not seen.

4hour after the beginning, it's not hot anymore, and when water is added violent reaction happens.

without Na, the reaction starts after 5hours or more instead of 2, and sometimes doesnt start at all!!!

magnesium "activated" by I2 is covered in surface with some MgIO3 and MgI2.

in ether: PhBr + 2 Na --> PhNa + NaBr
          PhNa + PhBr --> Ph-Ph + NaBr
but in probably very low yields we could have too:
          PhNa + MgI2  --> PhMgI + NaI
that would make the Magnesium very activated because we have Mg metal in surface.

maybe use of CH2Br-CH2Br would make the reaction start immediatly ?