Melgar
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Ozonolysis
I'm interested in ozonolysis as a means of breaking up large organic molecules with limited use, into small organic molecules with more versatility in
various reactions. Now, initially the requirements for this sort of reaction were daunting. From what I've read, it's supposed to be carried out in
chloroform at really low temperatures, like -20 C. However, I recently learned how to make chloroform from acetone and chlorine bleach, so that's no
longer a major impediment. Plus, calcium chloride can lower the temperature of an ice water bath down to about -30 C, so it looks like dry ice isn't
necessary either.
This leaves two concerns: the source of ozone and the workup. Now, I recently purchased an ozone generator which is attached to a long tube with an
aerator on the end. It's used for making ozone from air, and has been extremely useful for getting rid of nasty smells. For instance, a leaky roof
caused water to drip through a light fixture into my roommate's room and on his carpet. A few days later, after we cleaned up the water, the room
reeked, but after about five minutes with the ozone generator on, you couldn't smell anything. (We also took more steps to dry the carpet) So
anyway, would this work? The manual claims it generates 600 mg/hour, so this may proceed slowly, but would it still work, or would I need a source of
purer oxygen?
As far as the workup, I read that an oxidative workup yields carboxylic acids while a reductive one gives aldehydes. This is useful since it allows
me to produce a greater range of chemicals, but for a reductive mix, I was thinking of using the powder from inside those hand warmers. Supposedly
it's mostly reduced iron powder with some relatively inert stuff like carbon and silica. What I read recommends zinc powder and water. So any
thoughts?
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bbartlog
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What are you trying to oxidize that you feel like you need this approach specifically? I mean, there are a great many other, seemingly simpler, ways
to oxidize stuff (hydrogen peroxide, sodium hypochlorite, atmospheric oxygen, Fenton's reagent, piranha solution ... just off the top of my head). So
barring some great selectivity I'm not sure I understand what you're trying to accomplish. If you're looking for formic acid (for example) there are
surely easier ways than ozonolysis of large organic molecules...
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Melgar
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Ozonolysis performs a very specific reaction, in that it reacts with a C=C bond, cleaving it and creating a carbonyl group on each side. Because it
acts so specifically, it's often used as a test to see what smaller components make up a large organic molecule. Hence, I'm not just interested in
oxidizing molecules, I'm interested in performing a specific type of oxidation reaction on them. Ozonolysis of styrene gives benzaldehyde, for
instance, but that's just one potential reaction. Basically, I'm trying to see how useful it would be to add "ozonolysis" to the list of reactions I
have the ability to perform.
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aonomus
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Isn't ozonolysis the one thats liable to explode at -78degC? My organic chem professor mentioned that during his post doc, he walked about 3 feet past
someone elses fume hood when their ozonolysis experiment flew across to the other side of the lab...
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entropy51
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Ozonides are extremely explosive if
accidentally allowed to warm up, and are somewhat unpredictable even when cold. I think -30 C is typically the temperature used. A shatter-proof
protective shield is a must IMO.
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starman
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Quote: Originally posted by Melgar  | | Ozonolysis performs a very specific reaction, in that it reacts with a C=C bond, cleaving it and creating a carbonyl group on each side.
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Mmm,interesting.Could this be used to cleave a long alkyl chain at the double bond specifically,said chain being on a phenol for instance?
Chemistry- The journey from the end of physics to the beginning of life.(starman)
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aonomus
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| Quote: Originally posted by entropy51 | | Ozonides are extremely explosive if
accidentally allowed to warm up, and are somewhat unpredictable even when cold. I think -30 C is typically the temperature used. A shatter-proof
protective shield is a must IMO. |
They go through a cyclic intermediate that has a peroxide functional group in it. Concentrated ozone and peroxide seems like a wonderful way to
rapidly oxidize your solvent into CO2, yes?
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medchem
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| Quote: Originally posted by Melgar |
As far as the workup, I read that an oxidative workup yields carboxylic acids while a reductive one gives aldehydes. |
Ozonide are very dangerous and have high liability of explosion.
Reductive work-up conditions are far more commonly used than oxidative conditions. In my case, I am using Dimethyl sulfide to quench the reaction.
Dimethyl sulfide produces aldehydes or ketones while the use of sodium borohydride produces alcohols (reductive) while oxidative workup like hydrogen
peroxide will give carboxylic acid.
ice + NaCl will reduce temperature upto -20
ice + hydrous calcium chloride gives around -30.
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Melgar
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| Quote: Originally posted by starman | | Quote: Originally posted by Melgar | | Ozonolysis performs a very specific reaction, in that it reacts with a C=C bond, cleaving it and creating a carbonyl group on each side.
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Mmm,interesting.Could this be used to cleave a long alkyl chain at the double bond specifically,said chain being on a phenol for instance?
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Presumably, yes. That's what I'm trying to find out anyway. If so, it would indeed be a very useful ability...
As for all the concerns about explosions, I heard that adding a small amount of methanol will prevent the accumulation of explosive reactants by
reacting with them before they reach high concentrations.
| Quote: | | They go through a cyclic intermediate that has a peroxide functional group in it. Concentrated ozone and peroxide seems like a wonderful way to
rapidly oxidize your solvent into CO2, yes? |
Like I said, that's why you have to use chloroform, although I think dichloromethane can also be used.
So, does anyone know how pure the ozone has to be? Can I just use my $70 room-deodorizer ozone generator?
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Melgar
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| Quote: Originally posted by medchem | | Quote: Originally posted by Melgar |
As far as the workup, I read that an oxidative workup yields carboxylic acids while a reductive one gives aldehydes. |
Ozonide are very dangerous and have high liability of explosion.
Reductive work-up conditions are far more commonly used than oxidative conditions. In my case, I am using Dimethyl sulfide to quench the reaction.
Dimethyl sulfide produces aldehydes or ketones while the use of sodium borohydride produces alcohols (reductive) while oxidative workup like hydrogen
peroxide will give carboxylic acid.
ice + NaCl will reduce temperature upto -20
ice + hydrous calcium chloride gives around -30.
|
I try and stay away from dimethyl sulfide. Isn't that an odorless chemical with deadly vapors? Err, actually I think that's dimethyl sulfate I'm
thinking of. In any case, zinc powder can presumably be used, and that'd be easier for me to get than dimethyl sulfide, unless it's the main
component of some product I don't know about. Still, reduced iron powder is even easier for me to get, so I'd like to know if I can use that instead.
Any idea?
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entropy51
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| Quote: Originally posted by Melgar | | Like I said, that's why you have to use chloroform, although I think dichloromethane can also be used. |
Several other solvents work just as well as CHCl3. CH3OH, EtOAc, AcOH...
| Quote: Originally posted by Melgar | | Still, reduced iron powder is even easier for me to get, so I'd like to know if I can use that instead. Any idea? |
My idea is that you should restrain your death wish and learn a little about this reaction before resorting to trial and error.
Ozonides are somewhat unforgiving. Why not try a reaction that has been characterized in the literature before striking out on a quest to see just
how unstable ozonides can be?
[Edited on 5-3-2010 by entropy51]
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mnick12
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Ehh not exactly as far as I am concerned Dimethyl Sulfide STINKS, as for dimethyl sulfate I have heard it has a garlicky onion smell ( like many
sulfur compounds) though I sure would not want to be the person to characterize it's smell. Also you are correct dimethyl sulfate has very high acute
toxicity, but perhaps even more awful than that is it's tendency to give you cancer after a small amount of exposure.
As for Ozonolysis do you have a specific reaction in mind? Its kinda hard to suggest easier alternatives without knowing what it is you are trying to
accomplish.
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Melgar
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| Quote: Originally posted by entropy51 | | Quote: Originally posted by Melgar | | Like I said, that's why you have to use chloroform, although I think dichloromethane can also be used. |
Several other solvents work just as well as CHCl3. CH3OH, EtOAc, AcOH...
| Quote: Originally posted by Melgar | | Still, reduced iron powder is even easier for me to get, so I'd like to know if I can use that instead. Any idea? |
My idea is that you should restrain your death wish and learn a little about this reaction before resorting to trial and error.
Ozonides are somewhat unforgiving. Why not try a reaction that has been characterized in the literature before striking out on a quest to see just
how unstable ozonides can be? |
Or even better, check out this paper:
http://pubs.acs.org/doi/abs/10.1021/jo800323x
If you can't get the whole thing, it basically says that you can do ozonolysis in a solvent of acetone with 5% water, and this will prevent the
buildup of ozonides.
| Quote: Originally posted by mnick12 | Ehh not exactly as far as I am concerned Dimethyl Sulfide STINKS, as for dimethyl sulfate I have heard it has a garlicky onion smell ( like many
sulfur compounds) though I sure would not want to be the person to characterize it's smell. Also you are correct dimethyl sulfate has very high acute
toxicity, but perhaps even more awful than that is it's tendency to give you cancer after a small amount of exposure.
As for Ozonolysis do you have a specific reaction in mind? Its kinda hard to suggest easier alternatives without knowing what it is you are trying to
accomplish. |
Not really, I'm just trying to add techniques to my repertoire, since I have limited time and money. Therefore, I'm trying to learn the techniques
with the broadest applications. Ozonolysis seems to be very useful in that respect, since it can be used to synthesize a large number of ketones,
aldehydes, and carboxylic acids that would otherwise need to be purchased individually online. If that version I just posted works well enough, I may
just be able to avoid the dangerous part of this reaction. By reading what it doesn't say, there appears to be a chance it only gives decent yields
for a subset of alkenes though.
Anyway, would pure oxygen need to be used in the ozone generator, or could it be one that works with air?
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DJF90
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Ozonolysis consists (mechanistically) of three steps:
1) 1,3-dipolar cycloaddition of ozone and the alkene to form the primary ozonide (a.k.a. malozonide),
2) retro-1,3-dipolar cycloaddition to form a carbonyl compound and a carbonyl oxide,
and 3) recombination of these two species in yet another 1,3-dipolar addition, forming the ozonide.
Workup is typically performed with one of three reagents:
=> Dimethyl sulfide is typical for the reductive workup, where carbonyl compounds are your goal. Triphenyl phosphine can also be used for this with
several advantages/disadvantages.
=> Hydrogen peroxide is typical for the oxidative workup, where carboxylic acids and ketones are your goal.
=> Sodium borohydride is typical for the reductive workup, where alcohols are your intended product.
Another reagent that reacts with alkenes to give the same products as O3/H2O2 is acidified permanganate. This may be a nice alternative for
you. Ozonolysis is an incrediably versatile reaction, and I've attached an extract from a book I have to prove this.
[Edited on 5-3-2010 by DJF90]
Attachment: Ozone as a versatile oxidising agent.pdf (431kB)
This file has been downloaded 1392 times
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hissingnoise
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| Quote: | | Anyway, would pure oxygen need to be used in the ozone generator, or could it be one that works with air? |
-Melgar, better concentrations of ozone are produced using oxygen as feed-gas but air is satisfactory if it is dry.
Moist air produces ozone contaminated by NOx. . .
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Melgar
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DJF90 - Thanks for the literature! I read in a text that zinc powder can also be used for the workup, and I think I'll use that because it's easier
to source and can be mixed with NH4NO3 and NaCl to give a powder that catches fire when it gets wet. Also, I read that the danger of explosion mainly
comes from having a flammable solvent saturated with oxygen, which certainly makes sense. The ozonides may initiate the explosion, but they don't
appear to fuel it.
hissingnoise - yeah, that sounds right. I can't remember what the air intake looks like on my ozone generator, but I'm hoping I can get it to pull it
through a jar of CaCl2.
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franklyn
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Reading is fundamental
Ozone resources _
http://www.valdosta.edu/~tmanning/research/ozone
To view this whole window here _ click the window to activate the right side scroll bar
http://educate-yourself.org/ozone/ozonereactionswithcommonch...
Practical _
http://www.bigclive.com/ozone.htm
http://www.bigclive.com/oz.htm
Ozone collected papers 23 MB zip => http://www.megaupload.com/?d=CS8QF5DV
.
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turd
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If you're after benzaldehydes, you might want to perform a literature search on oxidation with KMnO4. Yes, it's very tedious, only suitable for small
(say 10g) quantities and needs large solvent volumes, but still sounds more home-chemistry friendly.
Edit: Note: with oxidation I mean oxidative double bond cleavage.
[Edited on 7-3-2010 by turd]
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Melgar
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Oh btw, by "acidified" permanganate, do you just mean potassium permanganate mixed with HCl? Like permanganic acid or something? Because I can do
that too. I'm still interested in ozonolysis though because from what I've read, using a nonflammable solvent makes it a lot safer, and making
chloroform is pretty easy. I don't think KMnO4 is as selective as ozonolysis on double bonds though.
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