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Author: Subject: ethyl ether preparation problem
blazter
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sad.gif posted on 9-6-2003 at 19:05
ethyl ether preparation problem


With a few days left in my independant chem class i decided to do what seemed to be a fairly easy synthesis of ethyl ether from sulferic acid and ethanol. Using the procedure by eleusis from rhodium's site 1 mol of what seemed to be concentrated H2SO4 (166ml) was mixed with 1 mol of 85% ethanol (36ml) in a RB flask. According to the msds on the alcohol it is about 5% methanol, 9% isopropyl, and a bit less than 1% methyl isobutyl ketone. The RB flask was fitted with a 2 hole stopper, one for a buret which was used as an addition funnel, and the other hole led to a condensor. The temperature was taken from the oil bath which consisted of olive oil. It seemed to have no problem heating to the required 135C for the reaction. A teflon coated magnetic spin bar was also dropped into the flask.

Now, everything was fine up to this point, the temperature of the oil bath climbed slowly probably over about an hour, but the funny thing was that when the temp reached about 135C the contents of the flask turned VERY black. Like old motor oil black and about as viscus too. Dissapointed that nothing was distilling over, another mol of alcohol was added (~36ml) at about 2 drops a second. After all that nothing distilled over, not even a drop.

About the only reasons i can think of failure is something to do with the other components of the ethyl alcohol posioning the reaction somehow. Or that the acid was not 100% concentrated. It was of a thick syrupy consistancy, whith a very slight yellow tinge to it. According to my teacher it should be about 18 molar concentration.

Anyone care to speculate why this reaction failed? Anyone else ever have success producing any ethyl ether via this method? I am very interested in replies before the week is out.
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blazter
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[*] posted on 10-6-2003 at 12:44


Well, come to think of it, there was a bit of a strange odor from the flask afterwards. I'm not exactly sure what ether smells like but I'm fairly sure that what i smelled wasn't the alcohol that was in there to begin with. It had a smell similar to the alcohol but it seemed to be a bit sweeter. Hard to describe really, but it was different. I am also curious about what might have caused the deep black coloration. It seems that the alcohol forms an intermediary with the sulferic, is it possible that it is what causing the color change?

Thanks for the reply, I think i might try reconcentrating the sulferic by boiling it and trying one last time with paint thinner instead as the alcohol source.
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madscientist
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[*] posted on 10-6-2003 at 13:56


Quote:
1 mol of what seemed to be concentrated H2SO4 (166ml) was mixed with 1 mol of 85% ethanol (36ml) in a RB flask


There's your problem. The volume of one mole of concentrated sulfuric acid is about 54mL, and the volume of one mole of ethanol is about 56.5mL. Too much sulfuric acid and not enough ethanol (that is what you used) will result in nothing but ethene gas.




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[*] posted on 11-6-2003 at 01:10
Anicdotal but still..


This may seem somewha off topic(in regard to you'r question)but I thought it worth mentioning.The reaction is MUCH smoother with only ethanol and water to deal with.A double vodka would be easier to work with since it's only water and ethanol.Though there is the cost and this way is'nt that bad...
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[*] posted on 24-7-2003 at 07:09


Black could be simple, dumb, elemental carbon, as H2SO4 is notorious for it's dehydrating (and oxidizing) ability.
Fine C particles could also make the liquid viscous.:o
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