November 5, 2005
Today was an attempt at making methyl bromide. I followed a procedure from the Journal of the American Chemical Society, Vol. 51 pg 2535. So I of course needed an elaborate apparatus (see above) lots of fun glass bending (yes, all the tubes are glass). So, in order, a 1 L 2 neck FB flask is on the hotplate stoppered with a thermometer in one neck and attached to a Vigurex column from which a tube runs to a bubbler in a 1 L 2 neck RB flask filled with a sodium hydroxide solution to scrub HBr produced and other acid gasses. The gas from here goes through CaCl2 in order to remove some water and finally into a gas bubbler in a cooler surrounded by a dry ice/kerosene mixture to condense the methyl bromide. I thought it looked pretty cool.
The reaction flask contained 107 g methanol, 133 grams of sodium bromide, 345 grams of sulfuric acid and 115 ml of water. Problem is that it took me so long to make the apparatus that I was in a hurry to get things started so I poured in the sodium bromide, water, and methanol then added the sulfuric acid, but it heated up too quickly and I had to add in portions but I got more impatient and poured the rest in and put the column back on the apparatus. The mixture heated greatly beyond the cooling ability of the column and menthol made it over into the hydroxide wash. It precipitated out, maybe too much NaOH for the methanol to just dissolve. So it eventually cooled down and I got bubbles coming over at a good pace with no external heating, just stirring. I let the reaction go for some time then realized the methanol in the hydroxide solution might be a problem, actually, in retrospect, what was going on, there was some insoluble layer that came over and it was at the bottom of the flask, distinctly organic and insoluble in water. If it were methanol for some reason and rendered insoluble it should have been at the top... hummm. Anyway, my worry at the time was that methanol + base equilibrates with methoxide and methoxide + alkyl halide goes to ether and I didn't want methyl ether to be product because it would condense in the dry ice however because it was aqueous I wasn't expecting much from that.
Anyway, I dumped out the base wash and cleaned it out good and replaced it and started heating for the first time. But it was too much for the column to cool and some more methanol started to threaten to come over. I lowered the heating and kept going, more bubbles coming over at a decent rate. So a couple hours later I was wondering why I wasn't getting anything in the area where the methyl bromide should have condensed, there was just a kind of sulfur smell that was very faint. Re-reading through the paper I decided to hook up a Liebig condenser instead of the Vigurex column (DuH!!!) and ran some water through it turning up the heat. This was the method that I read in a different text, reflux the methanol and keep it low in the condenser and the methyl bromide will escape through the top. But some time later still nothing. Puzzled I checked my connections and discovered that the stopper I had in the reaction flask with the thermometer was eroded by the mixture, the rubber part was loosed and gasses were escaping there! I could hear them and feel them so I removed that stopper and replaced it with a different one to keep in the gassses. But I could only run it a short time like this, the light outside was fading so I took another container and upended the gas scrubbing bottle where the CH3Br was condensing into the other container receiving maybe 2 ml of methyl bromide... terrible! So now I have my new modifications, involving the Liebig like I should have used, maybe put a trap in there, also a better stopper will help. Also I need to re-check if I am using the right amount of NaBr mine is somewhat hydrated.
Next time I also need to mix the water and H2SO4 first and allow to cool amply, then add the NaBr and then the methanol. So, assuming I get methyl bromide next time. Weigh it, dissolve in ether, add magnesium turnings to make my Grignard, cool and add acetone dissolved in ether then heat for a bit and add water to quench the reaction mixture, finally distilling off the ether and getting my desired t-butanol! Huzzah! (Easier said then done, but I did do a Grignard once at school)
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