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Ethanol + Sulfuric Acid... Question!


recursive
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I read on the magical Wikipedia that ethylene can be produced by distilling ethanol and sulfuric acid. So I set up my flasks, and mixed ethanol (denat. w/ methanol) with sulphuric acid from a photography chemical set. But then something unexpected happened: in the flask, small white crystals very quickly formed like sand, replacing about 2/3 of the liquid!

 

What is this, and why did this happen?

 

Thanks in advance!

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Ester formation

 

Under acid-catalyzed conditions' date=' ethanol reacts with carboxylic acids to produce ethyl esters and water:

 

RCOOH + HOCH2CH3 → RCOOCH2CH3 + H2O

 

[b']For this reaction to produce useful yields it is necessary to remove water from the reaction mixture as it is formed.[/b]

 

Probably a side reaction with water?

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Weird.

Those two liquids should be miscible in all proportions. There are possible by-products (ether, etc) gut in the presence of a lot of water you shouldn't get them. In any event, most of the possibilities are liquids.

 

My best guess is that one of the starting materrials isn't what you think it is.

Could the so called "sulphuric acid" be sodium bisulphate?

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Weird.

Those two liquids should be miscible in all proportions. There are possible by-products (ether, etc) gut in the presence of a lot of water you shouldn't get them. In any event, most of the possibilities are liquids.

 

My best guess is that one of the starting materrials isn't what you think it is.

Could the so called "sulphuric acid" be sodium bisulphate?

 

I'm pretty sure it's sulfuric acid. That's what it says on the label, and I've never heard of sodium bisulfate being used in photography.

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I think that the sulphuric acid might have aluminum sulfate in it, although I'm not sure what that would do...

 

Plus, even wikipedia is unclear as to what happens under normal conditions. In one place it says you get diethyl ether (a desirable result...), but then it says that this exact same process is used to produce ethylene, without mention of other chemicals coming out of this.

 

Can another acid be used in place of sulphuric acid?

 

If you know a better way of making diethyl ether, please tell me!

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Dehydration of alcohol to either alkyl-hydrogen sulfate or ether or alkene all come sdown to the reaction temperature as well as the amount of sulfuric acid.

 

Provided you use conc. H2SO4, then the reaction is controlled by temperature. Below 80ish oC you would only get equlibrium mix. of alkyl hydrogen sulfate.

 

When you increase the T to ca. 120ish oC, you will start distill of some ether

 

and to actually get alkene, you need to go to as high as 180ish oC.

 

Check my temperature again, too lazy to cross check them with the lit. =)

 

Oh, also, it is better to add alcohol slowly throughout the process to sulfuric acid, esp. if you aim for ether and alkene.

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"I think that the sulphuric acid might have aluminum sulfate in it, although I'm not sure what that would do..."

Among the things it would do is dissolve in sulphuric acid, but not in alcohol.

 

Ah-hah! Well that also means I purified the sulphuric acid, sort of.

 

Well, what are other dehydrating agents for ethanol? All the sources I've seen say that there are others, but they won't tell me which. Any searches I do for that sort of thing returns all sorts of funky patents, but nothing useful!

 

Dehydration of alcohol to either alkyl-hydrogen sulfate or ether or alkene all come sdown to the reaction temperature as well as the amount of sulfuric acid.

 

Provided you use conc. H2SO4, then the reaction is controlled by temperature. Below 80ish oC you would only get equlibrium mix. of alkyl hydrogen sulfate.

 

When you increase the T to ca. 120ish oC, you will start distill of some ether

 

and to actually get alkene, you need to go to as high as 180ish oC.

 

Check my temperature again, too lazy to cross check them with the lit. =)

 

Oh, also, it is better to add alcohol slowly throughout the process to sulfuric acid, esp. if you aim for ether and alkene.

 

If you are heating it over 120C, what keeps the ether from exploding?

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That's why you should never work with open fire for this operation, have a very efficienct condenser to cool down the products and transfer them away from the main reactor (where you heat up H2SO4) or use it directly (e.g. for the case of alkene).

 

At any rate, ether is cheap and easy to get, why bother doing this cumbersome method?

 

Ah-hah! Well that also means I purified the sulphuric acid, sort of.

 

Well, what are other dehydrating agents for ethanol? All the sources I've seen say that there are others, but they won't tell me which. Any searches I do for that sort of thing returns all sorts of funky patents, but nothing useful!

 

 

 

If you are heating it over 120C, what keeps the ether from exploding?

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Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate, prepared by reacting ethanol with sulfuric and phosphoric acid respectively, are both useful ethylating agents in organic synthesis. Ethyl nitrite, prepared from the reaction of ethanol with sodium nitrite and sulfuric acid, was formerly a widely-used diuretic.

 

http://en.wikipedia.org/wiki/Diethyl_sulfate ---watch out for this POISON!!!

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  • 7 years later...

...bump.

In case anyone ever looks at this old thing again. I would have to check because I don't know the boiling point of ether off the top of my head, but since I think a water cooled distillation column might not be cold enough to cause ether condensation, I might run iPrOH or extra EtOH over some dry ice (far easier to get ahold of than liquid nitrogen) and run that through the column.

 

Also, be careful. I have a bad habit of injuring myself with explosions. Haven't yet had an injury from an explosion without powerful oxidizers present though, so you might be okay with standard safety gear (ex: goggles and gloves.)

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