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Author: Subject: need help with oxidation conditions
spirocycle
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[*] posted on 4-5-2011 at 13:03


Any commonly available alkenes that would be suitable?
Here is the scan (sorry for the bad quality):



just an explanation: The red is 4 scans, and the black is 16 scans
if its too hard to see, the carbonyl stretch (along with c-c stretch and a peak around 1250 ) is apparant in the 4 scan, but drops drastically with the 16 scan indicating acetone which evaporated as the scan progressed.
However, the there also appears to be some normal alkane stretch with both scans, and even some weird peaks slightly to the right of the alkane stretch that I can't identify

[Edited on 5-5-2011 by spirocycle]
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blogfast25
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[*] posted on 5-5-2011 at 04:28


Styrene itself would be the ideal standard, of course. Other than that alfa-alkenes (alkan-1-enes) would be good. Octan-1-ene is a C8 (like styrene) and would have a strongly comparable unsaturation molar content. But hex-1-ene and hept-1-ene may be more available. As ‘lab reagents’ they may be a little pricy (I haven’t looked) but your educational institute may stock some, you only need a few ml.

One substance that’s very OTC and cheap and that contains double bonds is the terpene limonene (‘orange oil’). Not sure how reactive the hexene double bond is though… much less so than the terminal ethenyl group I would imagine.

I can’t see the IR spectrum unfortunately (see FAQ to display images: http://www.sciencemadness.org/talk/faq.php?page=messages#7)

Have you tried one of the several excellent IR spectra internet databases that allow you to retrieve the digitalised spectrum of many known substances for comparison?


[Edited on 5-5-2011 by blogfast25]
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spirocycle
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[*] posted on 5-5-2011 at 12:37


theres the scan, sorry about that
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spirocycle
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[*] posted on 5-5-2011 at 12:39


also an update, i added the hydrocarbon to about 150% its own weight of 10% sulfuric acid in a sep funnel. its been shaken continously for over 30 mins now, and it still passes the bromine test. any other suggestions? im stilll shaking
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blogfast25
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[*] posted on 5-5-2011 at 13:22


The hydration reaction is very slow, even more so at RT. From what little I've seen and heard about them it can take several hours at BP. Brominations are more or less instantaneous by contrast...

Reflux the acid/HC mixture for at least 1 - 2 hours, possibly longer, then compare Br2 tests between 'treated styrene' and 'non-treated styrene'.

Still can't see any spectra: you have to resize, I can briefly see it at reload but it's far too large. See e.g. (Resized Image)See the FAQ for the syntax of an image with forced size...

Oh wait: I can now see it at the top of the page: the huge size has forced it there... I'm priting this off for comparison tomorrow: it has brilliant resolution at this size! :D

[Edited on 5-5-2011 by blogfast25]

[Edited on 5-5-2011 by blogfast25]

[Edited on 5-5-2011 by blogfast25]
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spirocycle
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[*] posted on 5-5-2011 at 13:40


since entropy is lowered in this reaction wouldnt heat favor the reverse reaction?

I shook it for about two hours already and gave up for the day.
I'll finish it tomorrow.
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spirocycle
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[*] posted on 6-5-2011 at 05:40


according to: http://www.practicalchemistry.org/experiments/the-hydration-...
hexene can be hydrated with 75% sulfuric and shows a funky mechanism involving a sulfate ester.
Every other source I found shows a direct hydration with hydronium and sulfate is known to be a terrible nucleophile so I dont really trust that mechanism.
Either way, its such a short reaction I'll try it with a mL or so of the "styrene"
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[*] posted on 6-5-2011 at 06:22


I printed of the spectrum of the hydrocarbon phase and compared (manually) it to the printed spectra of styrene, methylbenzene, ethylbenzene, benzene and acetone (obtained from various sources). I have to say I’m not an expert on IR interpretation and this kind of stuff belongs firmly in my (halcyon) uni days.

But the resemblance between the spectrum and styrene’s spectrum is quite striking, especially that ArH cluster at about 3000 and what I believe to be a C=C peak at about 1500. But there are some similarities with the spectra of methyl and ethyl benzene resp. too.

At about 1700 is a strong peak that doesn’t belong in the spectra of either styrene, methyl or ethyl benzene but matches perfectly with the 1715 C=O peak of acetone.

Combined with the positive test with Br2, I’d tentatively conclude that the sample contains styrene, some acetone and possibly other simple aromatics

On the side of the hydration, the hex-1-ene to hexan-1-ol method sounds very convincing. No real reason (that I can think of) to believe this won’t work with the electron rich phenyl group in the styrene.

Why are you so sure entropy is lowered in the reaction? If true that still doesn’t mean temperature would reverse it. It’s the change in Gibbs Free Energy ΔG = ΔH - TΔS that decides whether the reaction can proceed (for ΔG < 0) or not. ΔH (reaction enthalpy) is likely to be considerable (that is << 0) for this reaction, thus making entropic effects quite insignificant.
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spirocycle
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[*] posted on 6-5-2011 at 07:55


I'm sure entropy is lowered because 2 mols liquid form 1 mol liquid.
But if it is exothermic enough, like you said, it would have negligible effects.
after I run some errands, I'll try the method I posted.
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[*] posted on 6-5-2011 at 08:55


Good point about the 2 liquids. And it's hexan-2-ol that's obtained in your link, my bad.

Your hydration reaction product should be 1-phenylethanol (1-hydroxyethyl benzene, CAS: 98-85-1). MP = 20 C, BP = 203 - 205 C. You might be able to freeze it out…

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[*] posted on 6-5-2011 at 10:29


dissapointing news. . .
I added the sulfuric acid as mentioned, and found it easier to shake in a sep funnel.
After little to nothing happened, it heated up rapidly, shot the stopper out of the top and charred the entire organic layer!
The reaction was cooled in an ice bath, doused with water, and the organic phase captured.
This last process turned the organic phase from a black color to a pale grey/brown (think cappucino)
At this point, it is clear that something unintended happened, as after all this it STILL passed the bromine test!
Whatever, frustrated, I decided to pour in the bleach to see if I could get any hint of that nice pistacio smell.
Nothing but a goopy mess!
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[*] posted on 6-5-2011 at 12:14


Okay, so you’ve had a runaway reaction (you haven’t lived if you haven’t seen one of those :)). The high heat of reaction causes the mix to heat up, causing the reaction to accelerate, causing even more heat to evolve even faster, etc, in a catastrophic chain of events. The good news is that you got reaction.

Now have the guts to start again, this time cooling the alkene properly as the method prescribed and adding the acid much more gradually. It’s possible the styrene is much more reactive to this nucleophylic attack than hex-1-ene, perhaps because of the electron rich π ring. I wouldn’t worry too much about the bromine test at this point, just get the reaction right and contained. The runaway could have created all kinds of stuff so it doesn’t really count…

Edit: this interesting web reference seems to indicate that the rate of styrene hydration with aqueous H2SO4 is about 100 times faster than for hex-1-ene, assumed in same conditions (scroll down to p. 484, Table 5.1):

http://books.google.co.uk/books?id=g5dYyJMBhCoC&pg=PA483...

Maybe you should cut back a bit on the H2SO4!



[Edited on 6-5-2011 by blogfast25]
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spirocycle
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[*] posted on 7-5-2011 at 07:28


Yea, I think I'm gonna have to break down and buy the styrene to work with.
I can't afford the time to keep distilling polymer.
Thanks for the advice. This is my first real chem project, and you've been a great help.
so here is what I will try next:
Styrene will be chilled in an ice bath, and I'll add 1.5 molar ratio of 75% sulfuric acid dropwise probably over about a half hour or so depending on heat evolution, with lots of shaking in between. Then I'll quench it with an equal volume of cold water and collect the organic layer upon separation.

The styrene I will buy is 5% parrafin, but I assume that this alkane will not pose any issues in this reaction.
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[*] posted on 7-5-2011 at 07:43


Well, it’s been a learning curve on my side too and I’m the ‘eternal student’ type, so it’s all good.

Yes to your proposed hydration method. I came up with the same procedure thinking about it myself last night. Just monitor heat development closely: no heat = no reaction, too much = runaway.

I’m very tempted to try this myself now. Where are you getting the styrene from (the paraffin won’t interfere, for sure)? I’d actually like to measure the standard enthalpy of reaction of this hydration and I’ve got a decent electrical compensation calorimeter.

The article that was referred to as the source of Table 5.2 (above), is below, unfortunately behind a paywall. The abstract shows that this would be of great value for this and similar projects.

W.K. Chwang, V.J. Nowlan and T.T. Tidwell, J. Am. Chem. Soc., 99, 7233 (1977)

I’ll see if SM’s paper retrieval system could get hold of the paid version.




[Edited on 7-5-2011 by blogfast25]
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spirocycle
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[*] posted on 7-5-2011 at 07:50


http://www.tapplastics.com/shop/product.php?pid=41&http:...
but, im having second thoughts based on the price. (its only $4/lb in store) I just need to find a local store.
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[*] posted on 7-5-2011 at 08:22


Yes, $13 for 8 oz is internet robbery. Should be able to find this quite easily in Europe too.
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[*] posted on 7-5-2011 at 08:50


If it were only $13 dollars, I would sacrifice for it. but theres another $15 or so in shipping!
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[*] posted on 7-5-2011 at 11:43


Well, yeah that’s (part of) the Tinkerwebs for ya.

I would try offline shops and businesses in the area of ‘polyesters resins’, ‘surf or skateboard repair’ and such like. Even RC model shops may stock small quantities of ‘polyester resin thinner’ (styrene). I’ll be looking in my local RC model shop this WE.
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[*] posted on 8-5-2011 at 09:09


I've received access to two highly relevant papers of the hydration of various alkenes with H2SO4. If you'd like a copy, please U2U me with your email address.
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[*] posted on 9-5-2011 at 03:23


These are the links to both papers (pdf)

http://www.sciencemadness.org/talk/files.php?pid=209214&...

http://www.sciencemadness.org/talk/files.php?pid=209214&...

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[*] posted on 9-5-2011 at 15:38


Thanks for those papers!
I tracked down some local styrene ($7 for a pint) that claims >=100% purity (duh), and doesn't list any impurities. Should be plenty pure for this reaction.
I'll start some experiments tomorrow afternoon.
I'll start small scale, and it looks like in high enough acid concentration, heat isn't needed for styrene.
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[*] posted on 10-5-2011 at 04:48


Yeah, it ain't cheap: buy it by the tonne for polystyrene production and they practically give it away, put 500 ml in a bottle and the mark-up is at least a 1000 %, 'Thanks very much!'
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[*] posted on 10-5-2011 at 10:22


so two trials so far. First time, 5 mL 70% sulfuric, 2 mL styrene cooled in an ice bath while mixing. The aqueous layer was all cloudy, and a weird orange precipitate was sparsely noticeable.
It was heated in a warm water bath around 45C (the paper used 50C), when a polymerization reaction occured. garbage.

the second time, I added the acid a bit slower with more mixing and cooling, and after about 10 minutes of continuous stirring, the smell of styrene faded a bit and an odd sweet smell was noticeable. It was quenched with an equal volume of water, and the organic layer tested with bromine to indicate the presence of an alkene still. Thats no issue though, because it should only be about 90% yield max, which means there will always be an alkene present.
I have no more hypochlorite, so the oxidation was attempted with potassium permangante, but I got a little impatient and accidently lit it on fire.
It appears that the hydration is mostly successful, but I will probably need some pool bleach to get the oxidation down.
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[*] posted on 10-5-2011 at 12:01


Quote: Originally posted by spirocycle  
when a polymerization reaction occured. garbage.
Should you perhaps have some inhibitor, like maybe hydroquinone, in there?

Quote: Originally posted by spirocycle  
but I got a little impatient and accidently lit it on fire.
I hate when that happens!:o
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[*] posted on 10-5-2011 at 12:24


So you’re going with bleach for the oxidation, eh?

Have you considered isolating the assumed 1-phenylethanol? Other ‘garbage’ = potential for further strange stuff happening…
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