Sciencemadness Discussion Board

It is possible to have H2SO4 this cold?

Asphyxiated - 4-3-2012 at 20:47

Hello guys,

I am new to this forum and I just thought of a question that I can not seem to answer. Without going into much detail the synthesis I am looking at requires concentrated sulfuric acid (not a problem) but it must be kept at -16C for the duration of the reaction, is this possible?

I mean H2SO4 has a melting point of 10C so how would it be possible to add a solid (which the other substance is in this case) to sulfuric acid kept at -16C? It would be a solid at this point wouldn't it? Might they have meant 16C instead of -16C?

Thanks guys!

[Edited on 5-3-2012 by Asphyxiated]

[Edited on 5-3-2012 by Asphyxiated]

weiming1998 - 4-3-2012 at 20:51

Sulfuric acid is H2SO4, and there are a lot of things that can lower the melting point of it (water, for example, can lower the melting point from 10 to -40C!) If you don't mind, can you please inform me what the reaction is?

Edit: I suppose a solid soluble in H2SO4 (or the products are soluble/produces water) can lower the freezing point. Your experiment could also mean doing the reaction at reduced pressure, thus having a lower melting point.

[Edited on 5-3-2012 by weiming1998]

Asphyxiated - 4-3-2012 at 21:32

Well my family is in the perfume industry and we use a chemical called 2-phenylpronalal (also called 2-Phenylpropionaldehyde) and I just found out that mixing that with H2SO4 yields phenyl-2-propanone (yes p2p the chemical with all the stigma attached to it because of idiots making meth). PLEASE UNDERSTAND I DO NOT PLAN TO DO THIS. I was just curious as to how the H2SO4 could be at such a low temperature here, but the melting point of 10C is for absolutely pure H2SO4 is what you are saying? My "concentrated" sulfuric acid is only 98% with the rest being water, so it would have a much lower melting point?

I am not a complete idiot when it comes to chemistry but anything non-perfume related is when it is time to open a book or ask someone.

I hope the mere fact that I am asking about p2p doesn't just end this discussion, I truly am not making meth and probably wont even do this experiment, I just happen to have a lot of 2-phenylpropanal around and came across this synthesis and said "huh".

Seriously :D

[Edited on 5-3-2012 by Asphyxiated]

[Edited on 5-3-2012 by Asphyxiated]

Bot0nist - 4-3-2012 at 21:37

What the fuck? S2OH4?
Quote: Originally posted by Asphyxiated  


I am not a complete idiot when it comes to chemistry


I don't believe you.
Quote: Originally posted by Asphyxiated  


I hope the mere fact that I am asking about p2p doesn't just end this discussion.



Based on its surrounding content (or lack there of), I'd say it will...

[Edited on 5-3-2012 by Bot0nist]

Asphyxiated - 4-3-2012 at 21:44

Sorry? As I said I am not a chemist, I normally call Sulfuric Acid, "Sulfuric Acid", the chemical structure is not burnt into my mind. This is really about the melting point of sulfuric acid. I am not asking for help on anything because I DO NOT plan to carry it out. As you can tell from writings this would probably be unwise but cant I ask questions man?

Why is it such a terrible thing to talk about a hypothetical synthesis in theory when the by product is only a precursor requiring many more reagents. Its not like 2-phenylpronalal + H2SO4 = meth or anything. What happened to the free exchange of information and ideas? I thought this board, of all places, would be willing discuss this with me.

Sorry if I offended anyone here.....

[Edited on 5-3-2012 by Asphyxiated]

weiming1998 - 4-3-2012 at 21:52

Looking at the structures of these two substances, http://en.wikipedia.org/wiki/Phenylacetone
http://www.sigmaaldrich.com/catalog/ProductDetail.do?D7=0&am...
it might be possible to make one from the other. However, the addition of H2SO4 will not add another branch of H3C to the molecule, as H2SO4 does not contain carbon. Also, one is a ketone, the other is an aldehyde. I do not think aldehydes can be converted to ketones in one step.

[Edited on 5-3-2012 by weiming1998]

Bot0nist - 4-3-2012 at 21:54

Quote: Originally posted by Asphyxiated  
Sorry? As I said I am not a chemist, I normally call Sulfuric Acid, "Sulfuric Acid", the chemical structure is not burnt into my mind. This is really about the melting point of sulfuric acid. I am not asking for help on anything because I DO NOT plan to carry it out. As you can tell from writings this would probably be unwise but cant I ask questions man?

Why is it such a terrible thing to talk about a hypothetical synthesis in theory when the by product is only a precursor requiring many more reagents. Its not like 2-phenylpronalal + H2SO4 = meth or anything. What happened to the free exchange of information and ideas? I thought this board, of all places, would be willing discuss this with me.

Sorry if I offended anyone here.....

[Edited on 5-3-2012 by Asphyxiated]


I am not offended at all. Your first post, mentioning P2P, had glaring, basic chemistry errors in it and seemed lazy to me. I personally don't care if you churn out liters of p2p or not. Please provide a link to the reference to the reaction you are referring to, and we could be of more help. Sorry for being mean.

Welcome to SciMad Asphyxiated. :)

[Edited on 5-3-2012 by Bot0nist]

Asphyxiated - 4-3-2012 at 22:01

I don't know if it is online, probably is but here is what the paper I am reading states:

9 g of 2-phenylpropanal is slowly added with good stirring during 35 minutes to 40ml concentrated sulfuric acid, while the temperature of the reaction mixture is kept at -16°C. After all the 2-phenylpropanal has been added, the mixture is allowed to stand at the same temperature for another 15 minutes, and then the mixture is poured onto crushed ice (100-150g is probably a suitable amount). When the ice has melted, the organics are extracted from the water phase by 3x50ml diethyl ether, the pooled organic phases dried over MgSO4, the ether distilled off and finally the residue is vacuum distilled (bp 91-96°C at 11 mmHg) to give 5.6g (62%) of phenyl-2-propanone.

It also states:

It is not possible to effectively separate 2-phenylpropanal (bp 222°C/760mmHg) from phenyl-2-propanone (bp 214°C/760mmHg) through simple distillation and certainly not via vacuum distillation as the boiling points are too close. Fractional distillation could theoretically be used to separate them, but the size of the column that would have to be used makes that option impractical. A good idea for separating a mixture of the two is to oxidize the mixture with a mild oxidant which won't affect the P2P, but which will oxidize the aldehyde to 2-phenylpropionic acid. The acid can then be separated from the ketone by dissolving the mixture in a non-polar solvent and washing the solution with dilute sodium hydroxide. The P2P stays in the organic layer, which is then dried over MgSO4, the solvent removed under vacuum and the residue vacuum distilled to give pure P2P.

This can also be accomplished with Mercuric Chloride:

30g of 2-phenylpropanal is heated together with a mixture of 60g mercuric chloride (HgCl2, 1 eq.) and 450ml 75% ethanol in a pressure-safe sealed glass container for 4.5h at 100°C in a boiling water bath, during which time a precipitate forms. Water is added, and the solution is steam-distilled (during which operation the precipitate redissolves). The distillate is extracted with ether, dried, and the solvent is evaporated. The oily residue is then vacuum distilled with a fractionating column to collect the phenyl-2-propanone in a yield of 80% or more, bp 92-101°C at 14mmHg.

When 0.1 equivalents of HgCl2 was used, only 10% phenyl-2-propanone was formed, the rest consisted of unchanged aldehyde.

Asphyxiated - 4-3-2012 at 22:04

I am assuming that the concentrated sulfuric acid acts as the oxidizer from the second paragraph as well as "re-arranging the 2-phenylpropanal", not sure how this is accomplished though.

Asphyxiated - 4-3-2012 at 22:08

Note: I also have plenty of mercuric chloride as well, so either way is doable, I just liked the sulfuric acid one better because it is carried out cold rather than hot. But I don't plan to do it so lets discuss which is actually better or if they work at all.

Asphyxiated - 4-3-2012 at 22:56

hmm no responses since I posted it, does this just not work? The paper seems to indicate that this is not just theory, at least for the reaction with mercuric chloride, since they have the addendum of "when 0.1 equivilents of HgCL2 was used, only 10% of phenyl-2-propanone was formed, the rest consisted of unchanged aldehyde".

Anyone have any thoughts on this at all?

Asphyxiated - 4-3-2012 at 23:12

Quote: Originally posted by weiming1998  
Looking at the structures of these two substances, http://en.wikipedia.org/wiki/Phenylacetone
http://www.sigmaaldrich.com/catalog/ProductDetail.do?D7=0&am...
it might be possible to make one from the other. However, the addition of H2SO4 will not add another branch of H3C to the molecule, as H2SO4 does not contain carbon. Also, one is a ketone, the other is an aldehyde. I do not think aldehydes can be converted to ketones in one step.

[Edited on 5-3-2012 by weiming1998]


The H2SO4 is not adding CH3 it is removing it. You are looking at the molecules backwards it is 2-phenylpropanal that has a CH3 (methyl?) group, not phenyl-2-proponone.

2-phenylpropanal linear fomula = CH3CH(C6H5)CHO

phenyl-2-proponone linear formula = C9H10O

Im not exactly sure how this occurs but the molecule of p2p is much simpler than 2-phenylpropanal

UKnowNotWatUDo - 4-3-2012 at 23:15

This reaction appears to me to be a rearrangement, or actually a series of rearrangements. Here's my best guess for the reaction mechanism:

I would imagine the mercury ion act as a lewis acid and is attacked by a lone pair on the carbonyl oxygen and breaking the pi bond, creating a carbocation. This then allows for a methyl shift leaving a secondary benzylic carbocation which is fairly stable (as far as carbocations go). To get from this stage to phenylacetone would require a hydride shift and the release of the mercury ion, recreating the carbonyl pi bond.

Like I said, this is only a guess as I am not familiar with this particular reaction. Could be exactly what's happening, could be so wrong it's not even funny.

Also in the future I would recommend using the edit feature instead of posting three times in a row. It also generally takes longer than a couple hours to get responses to your posts, if you get any at all. So making a post about there still being no posts about your post is a little crazy. Other than that, welcome to the forum.

Asphyxiated - 4-3-2012 at 23:25

Quote: Originally posted by UKnowNotWatUDo  
This reaction appears to me to be a rearrangement, or actually a series of rearrangements. Here's my best guess for the reaction mechanism:

I would imagine the mercury ion act as a lewis acid and is attacked by a lone pair on the carbonyl oxygen and breaking the pi bond, creating a carbocation. This then allows for a methyl shift leaving a secondary benzylic carbocation which is fairly stable (as far as carbocations go). To get from this stage to phenylacetone would require a hydride shift and the release of the mercury ion, recreating the carbonyl pi bond.

Like I said, this is only a guess as I am not familiar with this particular reaction. Could be exactly what's happening, could be so wrong it's not even funny.

Also in the future I would recommend using the edit feature instead of posting three times in a row. It also generally takes longer than a couple hours to get responses to your posts, if you get any at all. So making a post about there still being no posts about your post is a little crazy. Other than that, welcome to the forum.


ha, didn't think about just editing them. Sorry about that.

I was concerned about no responses cause i got about 5 immediately and then nothing. But thanks for your response. It helps a lot. This is a "rearrangement" reaction as you stated.

Does this in theory also work for the H2SO4 reaction? I assume it does as the authors claim that the H2SO4 reaction is much 'nicer' than the mercuric chloride one.

Sorry for pushing for answers.

Thanks again!

turd - 5-3-2012 at 01:09

Quote: Originally posted by Asphyxiated  
I don't know if it is online, probably is but here is what the paper I am reading states:

9 g of 2-phenylpropanal is slowly added with good stirring during 35 minutes to 40ml concentrated sulfuric acid, while the temperature of the reaction mixture is kept at -16°C. [...]

You are not only lying but also doing it pretty clumsily. Plucking the first sentence of your "paper" into google gives the online source:
http://www.erowid.org/archive/rhodium/chemistry/phenylaceton...

It also gives the original source:
Chem. Ber. 60, 1050 (1927)

An article written in German.

Asphyxiated - 5-3-2012 at 02:32

Why is it that my original topic which had nothing to do with this got turned into some hate fest? Is there not chemistry at play here? can we all not get along? i SERIOUSLY have no plans to do this. i SERIOUSLY have 2-phenylpropanal for not this reason.

UKnowNotWatUDo - 5-3-2012 at 03:15

In the spirit of answering the original question, here is a link to graphs and tables of various properties of the acid with change in water concentration for all who are interested.

http://www.resistoflex.com/sulfuric_graphs.htm

watson.fawkes - 5-3-2012 at 07:35

Quote: Originally posted by Asphyxiated  
Why is it that my original topic which had nothing to do with this got turned into some hate fest?
Now that's an easy question. First you said
Quote: Originally posted by Asphyxiated  
I don't know if it is online, probably is
Then in turns out that it is online, the original is in German, so it's almost certain that you got it online.

Which means my highest-likelihood scenario is that you've been lying.

You have been mostly-indistinguishable from acting the lazy cook, which isn't taken to kindly around here. So I'm not surprised you're getting a bad reaction.

Also re: SERIOUSLY. "Methinks the lady doth protest too much."

turd - 5-3-2012 at 11:20

Quote: Originally posted by Asphyxiated  
Why is it that my original topic which had nothing to do with this got turned into some hate fest?

It is curious that you consider stating an obvious fact "hating". It's even more curious that you feel the need to camouflage your source and then do it in such an unintelligent way.
Quote:
i SERIOUSLY have no plans to do this. i SERIOUSLY have 2-phenylpropanal for not this reason.

Then this thread is for the birds. We have more than enough boring wouldbe-couldbe-chemistry threads already.

unionised - 5-3-2012 at 11:43

Just for the record, I happen to agree that it's interesting (and also amusingly ironic) that
http://en.wikipedia.org/wiki/Phenylacetone
which is fairly tightly controlled is an isomer of
http://www.wolframalpha.com/entities/chemicals/2-phenylpropi...
which is relatively common.

and
http://www.thegoodscentscompany.com/data/rw1010241.html
which is not only fairly readily obtained, but has the right carbon skeleton.

Add to that the fact that I'm fairly sure that the conversion to the ketone is thermodynamically favoured and this might be interesting.
If it's true then what are the Feds going to do about it?

ScienceSquirrel - 5-3-2012 at 13:48

The reaction does work, I think it may be a semipinacol type rearrangement. Yields are generally low so it has not become a preferred route to phenylacetone and phenylacetaldehyde is used as a perfumery chemical.
I have done reactions in cold sulphuric acid and in my experience it supercools. It becomes a lot more oily as it gets colder but it does not set.

Asphyxiated - 5-3-2012 at 15:40

Well the feds are going to do nothing cause that synth has been around for a long long time. It's easy to access, I use no special licenses or pay special hazmat fees to have it shipped to me, again not for making p2p.

Thanks to all that went the extra step of confirming that this synth is possible, but once again that was not my concern. When i first posted this thread I had no intention of mentioning p2p because all i cared about was the physical properties of H2SO4, specifically concentrated.

For full disclosure I am certainly interested in how these manufacturing processes work but I am not looking to head to prison for several years of my life. So yes I ran across this when looking up p2p synths and this caught my eye cause I got the jar of 2-phenylpropanal outside on the shelf. Also my gen chem sequence was over 3 years ago. I'm training for physics not O-Chem.

I do see that my posts give the appearance of "the lazy cook" but i assure you it is more of a "lazy theoretician" more than anything.

:D

2-phenylpropionaldehyde semipinacol rearrangement question

Asphyxiated - 20-3-2012 at 21:04

Hey all,

I posted about this before and was hoping I could get some other aspects of the reaction explained a little bit more. The reaction I am referring to is:
Quote:

9 g of 2-phenylpropanal is slowly added with good stirring during 35 minutes to 40ml concentrated sulfuric acid, while the temperature of the reaction mixture is kept at -16°C. After all the 2-phenylpropanal has been added, the mixture is allowed to stand at the same temperature for another 15 minutes, and then the mixture is poured onto crushed ice (100-150g is probably a suitable amount). When the ice has melted, the organics are extracted from the water phase by 3x50ml diethyl ether, the pooled organic phases dried over MgSO4, the ether distilled off and finally the residue is vacuum distilled (bp 91-96°C at 11 mmHg) to give 5.6g (62%) of phenyl-2-propanone.


Yes this reaction does create p2p, however I am still only interested in the mechanisms at work here rather than actually carrying it out. I have been told to be up front about this, so my question is in regards to this statement:
Quote:

It is not possible to effectively separate 2-phenylpropanal (bp 222°C/760mmHg) from phenyl-2-propanone (bp 214°C/760mmHg) through simple distillation and certainly not via vacuum distillation as the boiling points are too close. Fractional distillation could theoretically be used to separate them, but the size of the column that would have to be used makes that option impractical. A good idea for separating a mixture of the two is to oxidize the mixture with a mild oxidant which won't affect the P2P, but which will oxidize the aldehyde to 2-phenylpropionic acid. The acid can then be separated from the ketone by dissolving the mixture in a non-polar solvent and washing the solution with dilute sodium hydroxide. The P2P stays in the organic layer, which is then dried over MgSO4, the solvent removed under vacuum and the residue vacuum distilled to give pure P2P.


The way that I understand the reaction is that the H2SO4 causes the rearrangement as well as oxidizing the remaining 2-phenylpropionaldehyde to 2-phenylpropionic acid? I am wondering exactly how anything is rearranged before it is simply converted to the acid. Is this the reason for keeping the tempurature at -16C during the initial addition and then the conversion to acid happens as it raises in temperature (in the aqueous phase)?

I am just really curious as to how this works because I know that conc. sulfuric acid is also an oxidizer, which must be what they refer to in the second quoted paragraph, so when does the rearrangement take place?

Anyhow, if I get any replies, thank you for helping me in my understanding of chemistry (however basic it is).