[ScottJohnson]

Hi everyone, i'm just wondering if anyone has an idea about my little problem:

I'm studying the dehydration of ethanol with an acid catalyst (H2SO4) to form diethyl ether and water at school. Its an electrophilic SN2 reaction.

The reaction says that catalysts are H2SO4 as well as heat. My question is: what is the purpose of the heat (which is about 160 degrees Celcius) and will the reaction go ahead if it is done at room temperature. Also, does anyone have any ideas about the % yield of the ether?

thanks everyone.
-Scott

[AWK]

Synthesis of sulfuric ether is an equlibrium reaction, hence yield strongly depends on ratio of reagents used and removing at least one of reaction products (but better both). Optimal temperature is about 130 C. This temperature allows fast reaction between C2H5OSO3OH and C2H5OH and remowing products (ether and water) from reaction mixture but not sulfuric acid (b.p. 296 C) as well as an unreacted ethanol  (it also strongly depends on the amount of concentrated sulfuric acid used. At higher temperatures a dehydration of ethanol to ethene goes and start predominate at about 180 C.

[ScottJohnson]

hi there, thanks for the reply! i didn't even know that it was an equilibrium type reaction.

but i just want to clarify on a couple of things: Firstly, will the reaction go ahead at room temperature?

and also, is the product 'Sulphuric Ether' or 'Diethyl Ether' ?

Oh one more thing, is there anyway to separate the ether from the water and reactants apart from distillation? I don't know... something like freezing?

thanks again for your help.

[AWK]

Its an electrophilic SN2 reaction.
i didn't even know that it was an equilibrium type reaction.
Each substitution reaction is an equilibrium reaction, by the way SN2 means Nuclephilic (not electrophilic) Substitution of the second order.

Firstly, will the reaction go ahead at room temperature?
Only the first part of reaction proceeds at room temperature, namely
C2H5OH + H2SO4 = C2H5OSO3H

'Sulphuric Ether' or 'Diethyl Ether'
These are synonyms

is there anyway to separate the ether from the water and reactants apart from distillation? I don't know... something like freezing?
Ether is poorly soluble in water but with ethanol if forms homogenous mixture three-component mixture. You should take into account separation all three components - the easiest way is distillation.

[ScottJohnson]

aren't SN2 reactions one step only? If so, why would there be a sulphuric ether synthesis.

perhaps i'm confused majorly  

but thanks for the added information

[AWK]

This is two step reaction - esterification (ethyl hydrogen sulfate is formed) and substitution (the former reacts with ethanol - which is a rate determining step)

[limpet chicken]

I had a little ether in a coke bottle last night, I might as well put the question here as it not worth making a new thread over, but it turned a bright pink color on shaking to fill the bottle with ether vapor, the ether was purified from starting fluid of a brand known to be a clean one previously.

Any ideas of what could be the mysterious contaminant? of course, it may just have been traces of vanilla coke but if there are any known contaminants that turn pink I would like to know.

[jdurg]

'Sulphuric Ether' or 'Diethyl Ether'
These are synonyms

I have to STRONGLY disagree with you on this one AWK.  Diethyl ether denotes two ethyl groups combined in an ether formation; H3CH2C-O-CH2CH3.  There is NO sulfur atom whatsoever in diethyl ether.  If there was, then sulfuric acid would not possibly be a catalyst in the dehydration reaction because it would be consumed.  A catalyst cannot be consumed in a reaction without being regenerated.  

[AWK]

I have to STRONGLY disagree with you on this one AWK
Sulfuric ether as symonym of diethyl ether is commonly used in chemical technology, pharmacy
and so on
http://www.websters-online-dictionary.org/definition/sulfuric+ether

If there was, then sulfuric acid would not possibly be a catalyst in the dehydration reaction because it would be consumed
Catalyst can be consumed in one step of multistep rraction, then restored before the end of reaction as in the ether synthesis.
C2H5OH + H2SO4 = C2H5OSO3H
C2H5OSO3H +C2H5OH = H2SO4(l) + C2H5OC2H5(g) + H2O(g)

[jdurg]

I have to STRONGLY disagree with you on this one AWK
Sulfuric ether as symonym of diethyl ether is commonly used in chemical technology, pharmacy
and so on
http://www.websters-online-dictionary.org/definition/sulfuric+ether

If there was, then sulfuric acid would not possibly be a catalyst in the dehydration reaction because it would be consumed
Catalyst can be consumed in one step of multistep rraction, then restored before the end of reaction as in the ether synthesis.
C2H5OH + H2SO4 = C2H5OSO3H
C2H5OSO3H +C2H5OH = H2SO4(l) + C2H5OC2H5(g) + H2O(g)

Yes, but that's when the ether contains the sulfur atom.  In the case of diethyl ether, there is absolutely no sulfur atom in it.  In the intermediate, yes, it does exist, but not in the final product and that is what the original poster was asking about.  I think there's just some confusion on what is being asked.    The intermediate in the reaction is a sulfuric ether, but not the final product.  (I also mentioned in my previous post that  "A catalyst cannot be consumed in a reaction without being regenerated."  In this case, the sulfuric acid is regenerated so it is indeed a catalyst in the production of diethyl ether).  


EDIT:  Okay, I do have to admit that I was incorrect.  Apparently sulfuric ether is a commonly used synonym for diethyl ether.  Either way, I think it is a horribly incorrect way to describe diethyl ether since the name would denote the presence of a sulfur atom which diethyl ether does not contain.  It's an appropriate term to describe how the ether was synthesized, and I think that it can cause confusion especially if a different ether is also generated by sulfuric acid.

[limpet chicken]

Sulfuric ether is a pretty archaic term, it was in use at least by 1890, as it is in some old medical books discussing home synthesis of the anaesthetics in use at the time, the term comes I believe, from the use of oil of vitriol in producing the ether (couldn't resist throwing in another oldy there )

[ScottJohnson]

thanks guys very much

does anyone know about ratios of reactant to catalyst? Also, how can i possibly heat up the reaction without the lab exploding? i think the flash point of ether is 35 degrees celcius or something.

[Mitch]

boiling chips prevent flash explosions.  

[migueldario]

hi everyone,

I will synthesize diethyl ether from ethanol and I  have a question about how to calculate "yield"

in general terms the procedure is as follows

Ethanol is mixed with sulfuric acid and heated to 140 º C in a simple distillation system

then adding more alcohol will drop by drop

The distillate is put in a fractional distillation system and collected the fractions distilled at 35 º C and 75 ° C

practice procedure indicates that I collect the fraction distilling at 35 ° C and distilled to 75 º C

I think the product is collected at 75 º C must be the alcohol unchanged

I think I must subtract the volume of the collected fraction of the total aggregate volume of alcohol

and from this difference calculate theoretical moless

I think this is because in this case the reaction takes place in a simple distillation system in which part of the distilled alcohol without having a chance to react

%Y = (moles/theoretical moles)x 100

I'm right?

excuse my poor english