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Author: Subject: Styrene to Acetophenone
Orenousername
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[*] posted on 23-5-2016 at 01:12
Styrene to Acetophenone


I dug up an interesting article on the selective oxidation styrene monomer to acetophenone under very mild conditions which I will attach.

This seems to be a very convenient route to acetophenone; the only other procedures I have found for preparation of acetophenone require high temperatures or strong chlorinating agents.

However, I don't really understand the mechanics in the reaction and have a few questions which I'm hoping you guys can clear up for me:

1. What is the purpose of iodine in the reaction? I'm assuming it strips the double bond from the oxidized carbon and helps the oxygen selectively choose the soon-to-be carbonyl carbon, but wouldn't the iodine simply replace one of the hydrogens?

2. What role does the "photoirridiation" play in this?

3. Why is the reaction performed in ethyl acetate and why is acetone added to perform deiodination?

Also, as a side note, do you think n2o would be a viable alternative to o2 as the atmosphere? I will try this reaction with n2o as soon as I obtain some iodine.

Oops, forgot attachment.

[Edited on 5-23-2016 by Orenousername]

Attachment: 8538.pdf (669kB)
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Eddygp
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[*] posted on 23-5-2016 at 07:53


What is the problem with H2SO4/H2O to the (Markovnikov) 1-phenylethan-1-ol and then oxidising with CrO3/H+? (genuine question)

(I understand that CrO3 might not be the nicest thing to have in an amateur lab, but other oxidising agents can be found for this)

The paper explicitly says that its aim was the metal-free oxidation, that is why it seems so complex - it has to follow a mechanism that overcomes the difficulties in not having metals to oxidise it.

[Edited on 23-5-2016 by Eddygp]




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Orenousername
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[*] posted on 23-5-2016 at 15:01


Do you have any literature ref. for that path? I'm pretty new to this so :P. But yeah CrO3 is pretty nasty, could KMnO4 be a suitable substitute?

Anyways, iodine and fluorescent lamps are pretty easy to obtain and I would just like to understand the (possible) mechanisms a bit more.




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[*] posted on 23-5-2016 at 15:09


Quote: Originally posted by Orenousername  
Do you have any literature ref. for that path? I'm pretty new to this so :P. But yeah CrO3 is pretty nasty, could KMnO4 be a suitable substitute?

Anyways, iodine and fluorescent lamps are pretty easy to obtain and I would just like to understand the (possible) mechanisms a bit more.


I think you have to be careful with the KMnO4 to make sure it doesn't give you benzoic acid.




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[*] posted on 23-5-2016 at 16:00


Hm, I see. I think I will try to reproduce results from the paper. I tried reacting styrene with H2SO4 and water in a 1:1:1 molar ratio, but nothing really happened except the water/h2so4 layer got cloudy and the styrene polymerized. I didn't want to reflux it because cleaning polystyrene out of my condenser would be a pain, but I had it on vigorous stirring for about 30 minutes.



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Dr.Bob
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[*] posted on 23-5-2016 at 17:30


1. What is the purpose of iodine in the reaction? It is adding to the double bond to form the iodo alkane compound, the other H comes from the water.

2. What role does the "photoirridiation" play in this? - It generates the iodine radical which adds to the double bond. Most halogenations require deep UV light, they are using a fluorescent bulb instead, the iodine may absorb better in the weak UV range, closer to blue, which fluorescents emit some amount of.

3. Why is the reaction performed in ethyl acetate? I don't know, look at the previous paper for that info. It does not absorb UV light, does not react with iodine, and dissolves the substrates well.

and why is acetone added to perform deiodination - read the paper, they explain several reasons and explainations right it in.

Also, as a side note, do you think n2o would be a viable alternative to o2 as the atmosphere? No, they are not likely interchangable in this reaction. Even air will work, just 5 times slower (air is about 1/5 O2).

Given that acetophenone is not that hard to make, I don't seen much utility for this, it uses a large amount of iodine, and that is often harder to get than acetyl chloride or acetic anhydride. Plus, styrene will polymerize quickly in the presence of air, and pretty much anything, so you might just end up with some goo that resembles a melted coffee cup.

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[*] posted on 24-5-2016 at 00:24


Thanks for clarifying Dr.Bob. I'm still a bit hazy on the purpose of the acetone though, in the article they only say that it is the only effective solvent for deiodination and later compare it to 2-heptanone and describe the formation of iodoheptanones from this reaction. Would it be safe for me to assume that iodine is removed from the iodoketone by forming iodoacetone(s?) with the acetone?

I don't know about the other users on here but acetyl chloride and acetic anhydride not exactly trivial to obtain for me, but iodine is a simple oxidation away. I am worried about polymerization though, but I think styrene will be more reactive towards iodine than itself(hopefully).

I also saw some articles online about PdCl2/CuCl2 catalyzed oxidation of styrenes to acetophenones but they want $40 to read one of them :o. Do you guys know anything about this process? I saw that some of these reactions were performed in supercritical CO2 though.. I don't know if I have a facilities to replicate that.

And one last thing, do you guys think that bromine or even chlorine could replace iodine for this reaction? Bromine wouldn't be too useful but if chlorine could be used instead that would be nice.




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[*] posted on 24-5-2016 at 18:43


> they want $40 to read

Try http://sci-hub.cc/ or http://sci-hub.bz/
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[*] posted on 24-5-2016 at 18:54


Yeah, that's the Wacker oxidation:

http://en.wikipedia.org/wiki/Wacker_oxidation

This one is actually very well-documented for free online because it's an important reaction in the synthesis of a certain illegal drug, which means there are a lot of guides for carrying it out with improvised equipment:

https://www.erowid.org/archive/rhodium/chemistry/wacker.krv....

https://www.erowid.org/archive/rhodium/chemistry/wacker.benz...

https://www.erowid.org/archive/rhodium/chemistry/wacker.nitr...

The good news is that it will translate to styrene (as long as it's soluble in methanol, which IIRC it is), though you'd use 7 mL of styrene for 10 of safrole. Benzoquinone is the preferred method; the KRV method is somewhat dangerous (shaking a pressurized bottle of methanol :X) although it can be safer if you use a device to shake it instead of your hands.
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[*] posted on 27-5-2016 at 05:20


:o thanks paddy.

Thanks atara, these preparations look a bit more economically practical (granted that you have a source of palladium). The KRV method seems fairly easy to adapt to a stronger reaction vessel; I'm thinking PVC piping with a valve, as it can usually withstand some pretty high pressures. I have some modified steel hobby tanks for oxygen/propane as well but Wikipedia states that PdCl2 is very reactive towards even stainless steel.. I think that the PVC vessel would be much safer though. I will probably give this a try as well when I obtain some palladium.

I am currently replicating the process outlined in the paper I attached at a 10mmol scale (because my scale isn't accurate enough for smaller). The mixture has been stirring for about 4 hours now and I will post results when I am finished.




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[*] posted on 27-5-2016 at 23:45


You can order coins or bullion. It's expensive, but there are no shipping requirements or anything and bullion is sold to private individuals all the time. Converting to PdCl2 entails dissolution in aqua regia IIRC, although there are probably other methods, including perhaps HCl + H2O2...
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[*] posted on 28-5-2016 at 03:00


Racemisation is all about creating a planar sp2 hybridised carbon in a reversible way. Keto-enol tautomerism can be important in racemisation and, in fact, molecules like 3-methylhexane-2,4-dione, when enantiomerically pure, will easily undergo racemisation in the presence of any acid or base.

[Edited on 28-5-2016 by Eddygp]




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[*] posted on 28-5-2016 at 20:35


I'm gonna try extracting it from a catalytic converter, although it might be difficult to separate it from the platinum. The iodine process ended in a blob that resembled a PURPLE melted coffee cup :( I didn't really feel like extracting 1mL from a 50mL purple blob.. It also stank of styrene dimers and trimers, so I'm going to call that reaction a failure.



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[*] posted on 29-5-2016 at 03:06


first of all,thanks for finding such a good paper,I don't understand the reason for this hate debate
Quote: Originally posted by Orenousername  

And one last thing, do you guys think that bromine or even chlorine could replace iodine for this reaction? Bromine wouldn't be too useful but if chlorine could be used instead that would be nice.

I don't think Cl2 or Br2 could be used here,here's why

1. Cl2 and Br2 would be too reactive and would just add across the double bond

2.I2 has this amazing property of reversibly reacting with alkanes(that's why you can't make iodoalkane by just reacting alkane and I2,like how you do for Cl2 and Br2 because the iodoalkane formed would again react with HI to give back the starting compounds.You have to use an oxidising agent like HNO3 to convert the HI formed to I2 so that there is no HI left)

3.also,but maybe not relevant here,I2,do to presence of D orbitals can show heptavalency.This is not possible in Cl2 and although Br2 can theoretically show more valencies,those are too unstable to be of any use
Quote: Originally posted by Orenousername  
The iodine process ended in a blob that resembled a PURPLE melted coffee cup :(. It also stank of styrene dimers and trimers, so I'm going to call that reaction a failure.

I don't understand,Organic letters is a reputed journal.Surely they wont print phony reactions :mad:

[Edited on 29-5-2016 by CuReUS]
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[*] posted on 29-5-2016 at 06:00


CuReUS, I think the main problem was my styrene. I do not have the facilities to perform vacuum distillation so my styrene was likely already contaminated with dimers and shorter chain polymers. I performed simple distillation after pyrolysis of polystyrene with a small amount of hydroquinone added, but I'm not sure if this was sufficient. Based on smell alone I could only detect the monomer however, and it was visually clear. The rest of the reagents however, were pretty pure. I'm sure acetophenone was present, but without a vacuum source it would be very annoying to isolate.

Also, thanks for clearing that up. I thought that chlorine would bind too strongly but bromine seemed reasonable, although I would rather work with iodine anyways.

[Edited on 5-29-2016 by Orenousername]




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