Sciencemadness Discussion Board

need help with oxidation conditions

spirocycle - 21-4-2011 at 08:27

I have some polystyrene that I am going to depolymerize today, but before I start working I like to write up my procedure.
After depolymerization, I am going to hydrate and then oxidize.

For hydration, a teacher recommended 10% sulfuric acid.
does 1.5 mL for every gram of styrene sound reasonable? and stir for 15 minutes?

I figure the carbocation intermediate is pretty stable so the reaction will probably progress quickly.

for the oxidation step, I really only have permanganate and 3% peroxide. How concentrated should I make the permanganate to allow the oxidation to the ketone, without cleaving the side chain?
what pH should it be at? heat? time?
I'm actually kind of lost on the specifics of this condition.

spirocycle - 24-4-2011 at 10:34

anyone gonna help out?
i know I can just experiment, but I dont really have a whole lot of sulfuric acid to play around with.

blogfast25 - 24-4-2011 at 12:44

Have you searched the organics part of the board? Your question maybe better posted there. Specify perhaps also how you plan to depolymerise.

Without experience with that specific hydration I think your styrene/H2SO4 ratio sounds about right... Probably needs refluxing though...

For the permanganate question, stoichiometry of the reaction and solubility of KMnO4 in water should give some clues. Using the stoichiometric amount of permanganate should be a reasonable starting point. Heat very moderately depending on how fast you see the purple permanganate react away. Acid conditions needed but precise pH not very important, at a guess. Say pH 3 - 4, with H2SO4. You should see the reaction proceeding and ending with all the MnO4- reacted away, so 'time' should reveal itself.

Hope this helps...

spirocycle - 24-4-2011 at 13:06

the depolymerization went very well with simple distillation of the polymer.
I didn't post in the organics, because i've been told that new topics there require references.
I don't have any specific references for this reaction, just the knowledge that hydration and oxidation generally occur in similar conditions.

The main issue I'm having with the hydration is: how do I know if heat favors the forward or reverse reaction?
Does the large excess of water (10% H2SO4) fully combat that issue?
I guess I could do a bromine test with a small sample every few minutes.

blogfast25 - 24-4-2011 at 13:28

That kind of hydration is often carried out using acetone or methanol as a solvent with quite a low concentration of the target reagent, then reflux at 70 - 85 C. See one example here: http://www.sciencemadness.org/talk/viewthread.php?tid=15171&...

(scroll up and down for info on ratios)

I’m not claiming this is going to work for your specific reaction but it is a hydration of a terpene (double bond).

Testing regularly with Br2 is a possibility for sure.

spirocycle - 24-4-2011 at 13:36

wouldn't you get some aldol products using acidified acetone?

ScienceSquirrel - 24-4-2011 at 17:07

Quote: Originally posted by spirocycle  
wouldn't you get some aldol products using acidified acetone?


A small amount of aldol products may be formed but they wil be in equilibrium with acetone and water under aqueous acid conditions.
Self condensation of acetone requires strong acid or base and forcing conditions

spirocycle - 26-4-2011 at 08:59

an old teacher recomended using household bleach as the oxidant
sound reasonable?

blogfast25 - 26-4-2011 at 12:32

For the oxidation of the sec. alcohol to methyl phenyl ketone? Bleach always contains free Cl2: could halogenate your double bond. K2Cr2O7 and KMnO4 really are the most recommended oxidants here... Neither are hard to get.

spirocycle - 26-4-2011 at 17:56

if the bond is hydrated, there is no double bond to halogenate.

blogfast25 - 27-4-2011 at 06:52

No, but it depends which reaction get's preference, doesn't it? Would you also consider oxidising in the presence of small amounts of Br2? :P

Commercial bleach (sodium hypochlorite in dilute solution) is a widely used strong oxidiser, especially by hobbyists, but I don’t feel it has a place here… Still, only experiment can tell.

Can you descibe the conditions of depolymerisation a bit more?

spirocycle - 27-4-2011 at 08:13

I would do the hydration first, and then add bleach.
If the excess styrene were to be halogenated, it wouldnt affect my yield because the alkene wouldnt be oxidized either way.

I dissolve a few foam cups and bowls in minimal acetone, and leave it out to dry for a bit in the sun.
then I put the mostly dry chunks in a 500 ml flask.
It is distilled over a bunsen burner with an air-cooled condenser.
some acetone comes over, but then a hydrocarbon layer comes over.
Hopefully this week I can get an IR spectrum of the product.

blogfast25 - 27-4-2011 at 12:09

Yes, my bad: you carry out the hydration first and separately.

To check if bleach (hypochlorite) has the potential to oxidise the sec. OH group to C=O, compare the reduction potentials of KMnO4, K2Cr2O7 and ClO-.

Did your styrene come over at about 145 C? There’s always the chance of getting dimers and trimers…

Of course you can just test your hypothesis on on oxidising alcohols with hypochlorite: reflux some IPA with bleach and see what happens; you should get acetone if you're correct (personally I doubt it)...

[Edited on 28-4-2011 by blogfast25]

spirocycle - 28-4-2011 at 13:21

turns out that my "styrene" was mostly acetone. . .
So I'm going to reattempt and only collect the portion that is immiscible with water.
I'll get an IR spectrum to see what I have.
I'm fairly competent at IR analysis, but honestly, I am stumped at how I could tell the dimer from the monomer.

usually alkene c=c stretch is 1680-1640, and aromatic c-c stretch is 1600-1585 and 1500-1400.
But i'm not sure if a peak 50 wavenumbers away will be that distinct

blogfast25 - 29-4-2011 at 07:36

I did think you were a bit cavalier about the depolymerisation of polystyrene, which is a decidedly stable polymer (no conjugated double bonds for instance).

Perhaps try this: make a fairly concentrated solution of styrofoam in acetome in a clear bottle (UV transparent material!) and allow it as much sunshine as you can muster for about a week or so. Then distill.

Telling the monomer from the dimer (trimer etc.) may be hard with IR but of course the BP of the oligomers will be that much higher that they should be separable quite easily from the lower boiling styrene. Perhaps distill the obtained styrene one more time, collecting only the 145 C fraction?

spirocycle - 29-4-2011 at 07:45

I'll do that.
But while i'm waiting for the UV depolymerization, I'll try another pyrolysis, with more prolonged heating.
If I'm lucky, i'll get to use the rotovap.

blogfast25 - 29-4-2011 at 09:29

I wonder if a bit of peroxide, either H2O2 or slower acting organic peroxides (caution! Dangerous stuff although many are quite tame...) might help cleave the backbone. In polymers like polyolefins, radicals are the enemy of the methylene (-CH2-) backbone. A form of accelerated ageing or weathering if you prefer...

kmno4 - 29-4-2011 at 14:25

Quote: Originally posted by spirocycle  
the depolymerization went very well with simple distillation of the polymer.

It is very probable that you obtained mixture, with low styrene content. The rest is benzene and toluene.

blogfast25 - 1-5-2011 at 05:58

Hmm... possibly the but the main cleavage point will be the methylene backbone, at a guess. There are some patents out there that speak of high styrene yields for the depol. of polystyrene, as always for what they're worth of course.

spirocycle - 3-5-2011 at 11:12

Well I reran it, this time heating more and for longer.


Rather than collecting in a regular flask, I collected in a sep funnel charged with a few ml tap water.
This way, the phases will separate.
After about an hour of distilling, I obtained two distinct phases, the top, organic phase was a pale yellow, and the bottom, aqueous phase was murky white.

The organic phase was collected, and washed with 20 mL of water. The phase was then dried with 1.01g MgSO4
This product passed the bromine test.
I'll get around to writing it up more formally, but my notebook got wet and its drying now

blogfast25 - 3-5-2011 at 13:13

Oh, the 'wet notebook defense', eh? :)

Sounds promising though... Details will be appreciated.

spirocycle - 3-5-2011 at 14:10

32.87 g PS (CD cases) was dissolved in acetone and dried to a final weight of 40.37 g.
This was distilled for 65 minutes. The plastic became frothy and discharged a thick white smoke that condensed to form the distillate. The distillate was collected in a separatory funnel charged with around 5 mL tap water to form two distinct layer. The aqeous layer (bottom) was cloudy, and the organic layer was pale yellow. The Aqueous layer was drained, and the organic layer was washed with 20 mL fresh DI water. Separation yielded 18.31g of product, presumably styrene among other things, which is 55.7% yield.
It should be noted that the boiling flask was left with a mass of thick black, tarry substance that has proven marginally soluble in kerosene.
An IR spectrum will be taken tomorrow.

blogfast25 - 4-5-2011 at 04:46

So no UV or peroxide in this case. Still, 18 g of (we assume) hydrocarbon distillate is very respectable. Any idea of the temperature at which the distillate came over?

As kmno4 suggested, when taking the IR, look out for signatures of benzene, toluene, ethylbenzene… apart from styrene itself of course.

What’s your bromination procedure? Modified slightly it could be used quantitatively…

Cleaning up your distillation flask may be a job and a half: boling up with very strong alkali should dissolve the carbon.

spirocycle - 4-5-2011 at 07:49

I have no thermometer attachment for my 19/22 set so I really have no idea on the boiling point.
My bromination procedure is pretty simple,
dilute about 1 mL liquid bromine with about 10 mL DI water.
Add a couple drops to a test tube.
Add a couple drops of the hydrocarbon to the tube, and shake
the color disappeared quite quickly
I dont really have a way of accurately measuring small volumes, so quantitative analysis may be tricky
ethyl benzene and toluene will be easy to discriminate against (methyl rock and methylene scissor), but benzene may be a bit trickier. I'll upload it later this afternoon once I get it.

blogfast25 - 4-5-2011 at 12:15

No thermometer is a drawback: it would make a redistillation of the styrene suspected liquid also fairly meaningless.

A semi-quantative procedure with bromine could be as follows. Either use a styrene standard or another compound of well known unsaturation content (and fairly reactive too - any low MW alkene would do). Add the same (small) amounts of both liquids to two identical test tubes.

Now add bromine solution to each tube, drop by drop, allowing plenty time between additions (the reaction will be slow when full bromination is near). Comparing the number of drops needed to brominate the standard and the sample would give you a pretty good idea of how the two compare in terms of unsaturation content. A ‘comparative titration in a test tube’, if you will…

spirocycle - 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]

blogfast25 - 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]

spirocycle - 5-5-2011 at 12:37

theres the scan, sorry about that

spirocycle - 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

blogfast25 - 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]

spirocycle - 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.

spirocycle - 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"

blogfast25 - 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.

spirocycle - 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.

blogfast25 - 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…

spirocycle - 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!

blogfast25 - 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]

spirocycle - 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.

blogfast25 - 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]

spirocycle - 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.

blogfast25 - 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.

spirocycle - 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!

blogfast25 - 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.

blogfast25 - 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.

blogfast25 - 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&...

spirocycle - 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.

blogfast25 - 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!'

spirocycle - 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.

entropy51 - 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

blogfast25 - 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…

spirocycle - 10-5-2011 at 12:33

Third and fourth trials were similar failures.
I added 10ml acid, 4ml styrene each time, and tried to gradually add the stoich amount of KMnO4, and despite stirring, cooling, and gradual addition, I'm just left with a thick sludge.

Nicodem - 10-5-2011 at 13:10

If I understand you correctly, you want to prepare acetophenone from styrene, no matter how?

If that is the case, then abbandon futile attempts at the hydration of styrene. It is not going to be in no way simple. Have you checked the literature on the conditions and yields?

Why don't you try a chloroalkoxylation followed by elimination? It is much more simple and should give good yields if the methodology is properly developed.
I would first chloromethoxylate styrene with trichloroisocyanuric acid in methanol. This is a high yielding reaction (see DOI: 10.1055/s-2003-36250, the article was already posted in some other thread). Then you just need to find the proper conditions for the elimination step. I would suggest heating the 2-phenyl-2-methoxyethyl chloride in a KOH/glycol solution at 100-120 °C. Use 1.1 equivalents of KOH or NaOH and ethylene or propylene glycol as solvent (or any other suitable solvent you can get). After TLC shows full conversion of the starting material, cool the mixture, add 2 equivalents of conc. HCl and stir at 50 °C for one hour. This should be enough to hydrolyze the alpha-methoxystyrene to acetophenone in a one-pot procedure. After extraction, you will need to fractionate the crude to isolate acetophenone.
I have some experience with a related conversion of a beta-chloroether to the corresponding ketone, though I used ethyl cellosolve as a solvent for the elimination. The yields were relatively good. I don't remember much details and it would not help you if I dig up my lab notes, as that was not done on plain styrene.

spirocycle - 10-5-2011 at 14:12

I dont have many of those chemicals (glycol or TCiCA).
Do you think that a hydrobromination, followed by an Sn1 (with AgNO3) in water would give better results?

if the hydrobromination is anywhere near as fast as the bromination, it should be simple enough. I just havent been able to find any resources mentioning it.

blogfast25 - 11-5-2011 at 05:24

Quote: Originally posted by Nicodem  
If that is the case, then abbandon futile attempts at the hydration of styrene. It is not going to be in no way simple. Have you checked the literature on the conditions and yields?



We found a reference (a google book) to acid catalysed styrene hydration which stated the rate constant (first order reaction in both alkene and hydronium) for styrene was about 200 times higher than for 1-hexene, due to electron pushing by the π ring. No recipe or methodology was provided though.

So what precisely makes simple hydration of styrene so problematic in your view? Tendency to polymerise? Something else?

Trichloroisocyanuric acid is quite OTC, right? I seem to recall someone on SM based an excellent chlorine generator on it…


[Edited on 11-5-2011 by blogfast25]

Nicodem - 11-5-2011 at 06:39

Quote: Originally posted by blogfast25  
So what precisely makes simple hydration of styrene so problematic in your view? Tendency to polymerise? Something else?

Cationic polymerization can be reduced by performing the reaction in homogeneous media. So it is just a matter of choosing the right cosolvent and ratio with water. Dioxane is probably the best solvent for such things. Diethyl ether is miscible with aqueous H2SO4, so it should be useful as well (depend on how diluted though). Radical polymerization can also be inhibited by using inert atmosphere and radical traps like hydroquinone or 2,6-di-t-butyl-4-methylphenol (less than 1 mol% is usually added). The major obstacle is the reversibility of the reaction, which makes it difficult to develop a preparative reaction and avoiding side reactions. The more acid used, the further left is the equilibrium point. Too little acid and the reaction rate is impractical. Generally this means that you need to screen the conditions (particularly the amount of acid) and follow the reaction at short intervals. It is simply to much work just to obtain a mediocre yield at the end.
The alternative is to do a literature search, as chances are somebody already developed the methodology for a preparative reaction.
Another alternative is to use HgSO4 catalyzed hydration. Hg(II) is a soft acid and thus efficiently catalyzes the addition of water on the double bonds, but the elimination requires a hard acid which can be kept on the minimum required for the Hg(II) catalytic cycle.
Quote:
Trichloroisocyanuric acid is quite OTC, right? I seem to recall someone on SM based an excellent chlorine generator on it…

Yes, trichloroisocyanuric acid can be bought anywhere. Where I live they sell it in any larger supermarket with stuff for house use. Ethylene or propylene glycol can be bought at any gas station (at least in my country). I don't know where spirocycle lives, so that he can not buy such ubiquitous stuff.

spirocycle - 11-5-2011 at 08:35

It's not that I can't find it, its that I can't afford it.
I am actually pretty sick right now, so I can't really do any more experiments, but when I recover I will try to hydrobrominate the styrene, and from there, hydroxylating should be easy enough with AgNO3 around, right?

blogfast25 - 11-5-2011 at 10:20

Thanks Nicodem, very interesting...

Nicodem - 13-5-2011 at 09:22

Quote: Originally posted by spirocycle  
but when I recover I will try to hydrobrominate the styrene, and from there, hydroxylating should be easy enough with AgNO3 around, right?

I don't know about the hydrobromination of styrene, but I'm almost sure I saw a post at Hyperlab where the hydrochlorination of styrene is described. Try searching for "styrene" at the forum search engine. Also, I guess you can find examples of hydrobromination in the literature, if you only try. It's nothing exotic, so there should be some preparative reaction described in the journals.
As for the reaction with AgNO3, I can't know. Have you done a literature search already? It might just give styrene back.

spirocycle - 13-5-2011 at 09:59

I'll do a literature search to confirm, but it doesn't seem likely to give styrene back.

Assuming the hydrobomination worked, and I mix rapidly with silver nitrate, the benzyllic carbocation will likely form, and water should act at the nucleophile. the only way for styrene to reform would be if there was a hydride source.

Nicodem - 14-5-2011 at 13:54

Quote: Originally posted by spirocycle  
the benzyllic carbocation will likely form, and water should act at the nucleophile. the only way for styrene to reform would be if there was a hydride source.

That does not make much sense to me. If the carbocation forms it can react with water, but in two different ways, as water can act as nucleophile or as a base. Therefore, given the ease of proton elimination from 1-phenylethyl carbocation, you can easily get styrene back. I don't know what you get, because I have not done a literature search (not interested enough).

Hydration of styrene via Co(II) catalysed oxidation-reduction:
Bull. Chem. Soc. Jpn., 63 (1990) 179-186.
Inorganica Chimica Acta, 157 (1989) 171-174.
J. Am. Chem. Soc., 107 (1985) 3534-3540.

Photochemical hydration of styrene:
J. Org. Chem., 48 (1983) 869-876.

I have not read the whole thread, so I do not know what's the purpose of all this. But obviously it is not about obtaining acetophenone, as this is as cheap as it can get. In any case, I do hope you are aware that the Wacker oxidation of styrene gives acetophenone in a single step?

spirocycle - 14-5-2011 at 19:38

I am aware, and I see how the purpose may seem obscure but this is the deal. I'm pretty inexperienced in the lab and don't really have a whole lot of cash to spend. I want to make acetophenone (just a couple grams) cheaply. Yields don't need to be great because styrene is cheap. I can't afford the catalyst for the wacker oxidation, and the only (kind of) polar aprotic solvent I have at hand is acetone.
Since the hydration seems kind of tricky based on what you said and my several attempts, I'll try the hydrobromin(chorin)ation and then try the silver nitrate thing.
I see how I could end up with some styrene again, but I feel that given the reactivity of the double bond in styrene (at least in hydration), it would likely give mostly the alcohol.

blogfast25 - 15-5-2011 at 04:43

Quote: Originally posted by Nicodem  
That does not make much sense to me. If the carbocation forms it can react with water, but in two different ways, as water can act as nucleophile or as a base. Therefore, given the ease of proton elimination from 1-phenylethyl carbocation, you can easily get styrene back. I don't know what you get, because I have not done a literature search (not interested enough).



I don’t quite understand how that squares with the high rates of styrene hydration compared to the textbook example of 1-hexene, the former being reported having a rate constant about 200 times higher than the latter. That points to a very stable carbocation, no? Although I can see how that can lead to polymerisation…

kmno4 - 15-5-2011 at 13:09

Direct H+ catalysed hydration of styrene to 1-phenylethanol seems to be simple to do. However I could not find any preparative procedure for this .....
The books I have say that "hydration of alkenes has no larger preparative meaning".
In case of simple alkenes, reaction with H2SO4 (40-80%) gives alkyl mono- and di- sulfates as main primary produsts. In the next step these sulfates are converted (more or less easily) to alcohol.
For styrene it is not so simple because it is prone to self condensations giving various "dimers" or just oligomers. It is also valid for benzyl alcohols - they are not stable in strong acidic media, especially H2SO4.
Example article (via DOI) : 10.1021/ja01167a019