HgDinis25
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Transesterification
I've been thinking about a way to purify Denaturated Alcohol. I know this topic has been covered a number of times here, but I haven't found this type
of aproach yet - Transesterification.
So I wondered, can the following reaction happen?
EtONO + MeOH --> EtOH + MeONO
MeNO2 is way more volatile than EtNO2 and would leave the reaction vessel as a gas. So, one could add a small quantity of Nitrous Acid to Denaturated
alcohol and expect the following two reactions:
HNO2 + MeOH --> H2O + MeONO
HNO2 + EtOH --> H2O + EtONO
However, any EtNO2 formed would quickly react with MeOH:
EtONO + MeOH --> MeONO + EtOH
EtONO has a b.p. of 17ºC while MeONO has a b.p. of -12ºC. The reaction should be done in near freezning temperatures.
Does this process seems plausible to you? Because it seems to be an esay aproach to get rid of the Methanol in denaturated alcohol.
PS1: One should use a minimum amount of HNO2, just enough to drive all the methanol away.
PS2: I'm not taking into account the seperation of the water formed. That has already been covered in other topics.
[Edited on 4-5-2014 by HgDinis25]
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Nicodem
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There is no reason for it not to happen, but without an acid or base catalyst it might take too long to be of any practical significance. Obviously,
you will need to check the literature for an actual procedure.
Also, mind that the "-NO2" group in organic chemistry is the nitro group. So "EtNO2" would be nitroethane rather than the ethyl nitrite
which you seem to talk about. The rational formula with shorthand usage for ethyl nitrite is "EtONO" (rational formulas are called this way because
they represent the compound in a rational way- rather than empirical - which means that they need to reflect the structural features in a
non-ambiguous way).
| Quote: | MeNO2 is way more volatile than EtNO2 and would leave the reaction vessel as a gas. So, one could add a small quantity of Nitrous Acid to Denaturated
alcohol and expect the following two reactions:
HNO2 + MeOH --> H2O + MeNO2
HNO2 + EtOH --> H2O + EtNO2
However, any EtNO2 formed would quickly react with MeOH:
EtNO2 + MeOH --> MeNO2 + EtOH
EtNO2 has a b.p. of 17ºC while MeNO2 has a b.p. of -12ºC. The reaction should be done in near freezning temperatures. |
If you were to nitrosate a mixture of methanol and ethanol, you would likely get a mixture of methyl and ethyl nitrite. Since there is nearly no
thermodynamic difference between the two reactions (for the formation or transesterification), the proportion would mostly depend on the initial
methanol/ethanol ratio.
If you would want to do a reactive distillation with a fractionation column (I'm not sure if this is what you imply, but it is the only logical sequel
to what you wrote), you would need to assure the presence of a transesterification catalyst to assure rapid enough kinetics and an extremely efficient
column (not to mention the technical difficulties in cooling to well bellow -12 °C).
| Quote: | | Does this process seems plausible to you? Because it seems to be an esay aproach to get rid of the Methanol in denaturated alcohol.
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Plausible and reasonable ("easy") are two very different concepts. Obviously, what you propose is totally unreasonable as a way of removing methanol,
because it would achieve absolutely nothing competitive in addition to polluting the ethanol. You forget that you still need a fractionation column!
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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HgDinis25
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I was talking about the Nitrite all the time. Yes, you're correct about the rational formulas, however I based mine on page 118 of the following book:
http://books.google.pt/books?id=VqosZeMjNjEC&pg=PA119&am...
| Quote: |
If you were to nitrosate a mixture of methanol and ethanol, you would likely get a mixture of methyl and ethyl nitrite. |
Are you saying no Transesterification would happen?
EtONO + MeOH --> MeONO + EtOH
| Quote: |
You forget that you still need a fractionation column! |
A fraction column for what? Seperate Ethanol from a compound with a b.p. of -12ºC? 
Edit: I edited my first post, to correct the rational formulas. However, I think it's pretty obvious the reactions were meant for the Nitrite Esters.
[Edited on 4-5-2014 by HgDinis25]
[Edited on 4-5-2014 by HgDinis25]
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Nicodem
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Quote: Originally posted by HgDinis25  | | I was talking about the Nitrite all the time. Yes, you're correct about the rational formulas, however I based mine on page 118 of the following book:
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As far as I know, Len is not an organic chemist and his book was probably not reviewed independently before publishing. Also, he named the compounds
correctly in the text and only made errors in the reaction equations. Errors only become critical when they can cause wrong interpretations (like in
your post where you do not define what reaction you talk about and give no reference - even though you obviously had it all along!).
| Quote: | Are you saying no Transesterification would happen?
EtONO + MeOH --> MeONO + EtOH |
I said that even at the conditions where the transesterification kinetics are rapid, they would not significantly affect the ratio of ethyl nitrite
vs. methyl nitrite. Equilibriums obey equilibrium laws, so you would need to do a reactive distillation to affect the ratio. This makes your proposal
of applying this reaction to remove methanol from ethanol utterly obsolete (ethanol and methanol form no azeotrope).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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HgDinis25
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| Quote: |
(ethanol and methanol form no azeotrope) |
I fail to see on how does that relate to the topic. Perhaps you misunderstood?
What I'm trying to say is that, when reacting Nitrous Acid (perhaps with a SUlfuric Acid catalys) you would get the following reactions:
HNO2 + MeOH --> H2O + MeONO
HNO2 + EtOH --> H2O + EtONO
However, the following equilibrium would also be stablished
EtONO + MeOH <--> MeONO + EtOH
MeONO has a b.p. of -12ºC so would leave the reaction mixture immediately driving the equilibrium to the rigth. So, by using a small amount of
Nitrous Acid, one should be able to drive away all the methanol.
I fail to see why a reactive distillation would be needed. At 0ºC such reactive distillation (if we can call it a reactive distillation) is already
happening.
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hissingnoise
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| Quote: | | Perhaps you misunderstood? |
Hilarious!?!
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HgDinis25
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I'm sorry, I'm unable to see how any of the words mentioned, or the sentences formed by such words, form something resembling a hilarious situation.
Please do point me on the right, hilarious, interpreation of the following words:
"Perhaps you misunderstood?"
Now, on topic: I'm trying to give a crazy sugestion here. If you don't think it's going to work, you could point out why. If you're going to quote
Nicodem response on the eqiulibrium laws, I already covered that in my previous post.
I strongly suggest that you read the Forum Guidelines:
http://www.sciencemadness.org/talk/viewthread.php?tid=19143
| Quote: |
Avoid posting obsolete replies: Obsolete or off-topic replies are such that their content does not warrant their presence in the discussion thread.
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Any Inteligent thinking entity should agree that a comment containing "Hilarious!?!" is off topic. Actualy someone trying to defend it has
being on topic would be hilarious.
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hissingnoise
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| Quote: | | If you don't think it's going to work, you could point out why. |
Look? Nicodem has already pointed out to you clearly and concisely some reasons why your daft scheme won't work and you still don't seem to
get it . . . ?
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blogfast25
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| Quote: Originally posted by HgDinis25 | | Quote: |
(ethanol and methanol form no azeotrope) |
I fail to see on how does that relate to the topic. Perhaps you misunderstood?
|
Since as there is no azeotrope and there's almost 15 C difference in BP between MeOH and EtOH, fractionating would probably be considerably easier
than your scheme. That's why it's relevant.
You may disagree with that but the onus would be on you to proves us wrong, experimentally.
[Edited on 4-5-2014 by blogfast25]
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Nicodem
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| Quote: Originally posted by HgDinis25 | | Quote: |
(ethanol and methanol form no azeotrope) |
I fail to see on how does that relate to the topic. Perhaps you misunderstood? |
I doubt I misundestood you. It appears to me that this is exactly the crucial point of the topic. I reminded you about the non-existence of this
azeotrope, because from your replies one could deduce you believe about its existence.
| Quote: | | MeONO has a b.p. of -12ºC so would leave the reaction mixture immediately driving the equilibrium to the rigth. So, by using a small amount of
Nitrous Acid, one should be able to drive away all the methanol. |
You are making the typical beginner flaw: you expect that things occur because you wish them to occur. Let me explain where you fail by asking you
some questions:
Why would methyl nitrite leave the reaction mixture immediately upon formation?
Is methyl nitrite insoluble or soluble in ethanol? (How much?)
If the conditions are such that methyl nitrite can escape with the vapour phase, what prevents the ethyl nitrite to leave in proportion to its partial
pressure?
If methanol is the minor component and ethanol the major one, what would the ratio of their nitrite esters in the vapour phase be?
| Quote: | | I fail to see why a reactive distillation would be needed. At 0ºC such reactive distillation (if we can call it a reactive distillation) is already
happening. |
Why would a specific temperature (0 °C) make a difference?
You need a very efficient column to separate a minor product from another component that only boils 29 K apart.
I suggest you to read about the physics connected with phase changes, liquid-vapour equilibriums and Raoult's law.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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HgDinis25
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| Quote: |
Why would methyl nitrite leave the reaction mixture immediately upon formation? |
Methyl Nitrite is a GAS at room temperature (it boils at -12ºC, MINUS 12 degrees celcius).
| Quote: |
Is methyl nitrite insoluble or soluble in ethanol? (How much?) |
Completrly irrelevant. If it doesn't leave the reaction because of it being a GAS (yes, that physical state that tend to leave reaction vessels),
simple ddistilation would suffice.
| Quote: |
If the conditions are such that methyl nitrite can escape with the vapour phase, what prevents the ethyl nitrite to leave in proportion to its partial
pressure? |
Are you serious? Have you ever heard of refluxing? If a substance has a boiling point of 17ºC, it will condense in a condenser that has cold water
runing.
| Quote: |
Why would a specific temperature (0 °C) make a difference? |
OºC was an example. The temperature should be above -(MINUS) 12ºC and below 17ºC.
blogfast25, let me point out to my original post:
| Quote: |
I know this topic has been covered a number of times here, but I haven't found this type of aproach yet - Transesterification. |
I then said that it could be easy because I was refering to the people who don't own a fractional column.
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Tsjerk
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The solubility of methyl-nitrite in ethanol is completely relevant. Do you see ammonium gas running out of water? Even oxygen, which has a boiling
point more than 200 K below body temperature does dissolve in your lungs, you only get it out efficiently by boiling.
Did you ever tried to distil a compound with a boiling point of 17 degrees Celcius?
[Edited on 5-5-2014 by Tsjerk]
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HgDinis25
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| Quote: Originally posted by Tsjerk | The solubility of methyl-nitrite in ethanol is completely relevant. Do you see ammonium gas running out of water? Even oxygen, which has a boiling
point more than 200 K below body temperature does dissolve in your lungs, you only get it out efficiently by boiling.
Did you ever tried to distil a compound with a boiling point of 17 degrees Celcius?
[Edited on 5-5-2014 by Tsjerk] |
Like I said:
| Quote: |
Completrly irrelevant. If it doesn't leave the reaction because of it being a GAS (yes, that physical state that tend to leave reaction vessels),
simple ddistilation would suffice |
If Methyl Nitrite is soluble (still trying to find info on the topic), heating should drive most of it away. If not, simple distillation of the
Ethanol should be used.
| Quote: |
Did you ever tried to distil a compound with a boiling point of 17 degrees Celcius? |
I never mentioned distillation of Ethyl Nitrite (b.p. of 17º C). Please, if you disagree, do point out where I mentioned it.
If, however you're talking about the following quote:
| Quote: |
Are you serious? Have you ever heard of refluxing? If a substance has a boiling point of 17ºC, it will condense in a condenser that has cold water
runing. |
Be aware that refluxing and distillation are different. And one could have a reflux setup at room temperature, where the Ethyl Nitrite would condense
with very cold water running in the condenser. Actually, if the reaction is cooled enough, most of the Ethyl Nitrite won't even go to the vapor phase.
I should remember you that I am ONLY presenting an hypothesis, I'm not saying it is a definite method nor that I'm positive that it's going to work.
I'm looking for possible problems or reasons (well explained) that may cause it to fail. Until now, this has been a good brainstorming.
However, what's the need for that:
| Quote: |
Did you ever tried to distil a compound with a boiling point of 17 degrees Celcius? |
If you wanted to say that it's hard to condense a substance with a b.p of 17º C you could have said it right away.
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