Author Topic: Epoxide to Ketone Rearrangement with LiI  (Read 2412 times)

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PrimoPyro

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Epoxide to Ketone Rearrangement with LiI
« on: October 08, 2001, 05:23:00 PM »
Hello. I have been reviewing the data on the catalyzed rearrangement of our favorite epoxides to our favorite ketones. The subject at this time: Rearrangement with Lithium Iodide, (LiI). In several papers, The general procedure for the reaction is to take the epoxide of safrole or isosafrole, allylbenzene or propenylbenzene (explanation in a second) and react it with Lithium Iodide, causing it to rearrange itself to the corresponding ketone: MD-P2P, or P2P, respectively. Now I have a few questions on these procedures that I dont understand:

All of the following information was gleaned from Rhodium's site.

First off, according to the procedure in the last entry of

https://www.thevespiary.org/rhodium/Rhodium/chemistry/phenylacetone.html

, entitled Phenyl-2-Propanone (very last entry), and I quote: "12g of 1-Phenyl-1,2-epoxypropane (propenylbenzene epoxide) was dissolved in 18 ml of tetraglyme and treated with anhydrous LiI..." For this reference, it specifically cites the usage of the 1,2-epoxypropane, corresponding to the epoxide of the propenylbenzene.

However, another reference,

https://www.thevespiary.org/rhodium/Rhodium/chemistry/peroxotungstate.html

, on the pertungstate epoxidation, explicitly shows the epoxide in the 2,3 configuration, corresponding to the allylbenzene. Both references state that upon addition of anhydrous LiI, these isomeric epoxides both rearrange to the same ketone (2-Propanone).

My question is very specific here: Does it matter which epoxide is used, the propenyl or allyl, for the rearrangement with LiI to the 2-Propanone?

Next question: Both of the aforementioned references state that the epoxides were dissolved in tetraglyme. Chemfinder states: Tetraglyme = Synonyms: 2,5,8,11,14-Pentaoxapentadecane; Tetraglyme; Bis[2-(2-methoxyethoxy)ethyl] ether; Dimethoxy tetraglycol. Well, its B.P. is very nicely high and all, but its hygroscopic and sensitive to air, too. Not too great. The LiI is anhydrous. Not good to couple that with a hygroscopic solvent. I dont know how to make it, nor do I want to buy it.

The third reference I looked at for this reaction,

https://www.thevespiary.org/rhodium/Rhodium/chemistry/uspat4731482.html

, see example one: MD-P2P, the procedure makes no mention of tetraglyme. This gives me hope.

Is tetraglyme necessary for the reaction to occur? Could something like a nonpolar, or ether, or an alcohol, be substituted for it? If you know which and which not, please be specific.

Also, in case anyone still thinks tetraglyme is a good solvent, note that chemfinder states its flashpoint at 116°C, but the reaction is carried out at 130°C for 5 hours.

Next question: Can NaI be substituted for LiI? If not o well, but its worth a shot at asking. I can always toss battery powder on some iodine.... :P  (no Im not that stupid)

Well, thank you for any information you decide to tell me. I really think this is a neat alternative to the glycolysis with nasty H2SO4, but hasnt really gotten too much interest. Id like to find all this out, so maybe my future dreams will include its synthesis and a writeup. Thank you.

                                         PrimoPyro

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terbium

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #1 on: October 08, 2001, 11:30:00 PM »
Next question: Both of the aforementioned references state that the epoxides were dissolved in tetraglyme. ... Well, its B.P. is very nicely high and all, but its hygroscopic and sensitive to air, too. Not too great. The LiI is anhydrous. Not good to couple that with a hygroscopic solvent. I dont know how to make it, nor do I want to buy it.
The tetraglyme was no doubt chosen as being a good solvent for the LiI. I imaging that other ethers such as THF or dioxane would also dissolve LiI well enough to work but they aren't going to be any easier to get than tetraglyme. I have no idea what chemfinder may mean about it being "sensitive to air", it is no more sensitive to air than dioxane or THF.


Also, in case anyone still thinks tetraglyme is a good solvent, note that chemfinder states its flashpoint at 116°C, but the reaction is carried out at 130°C for 5 hours.
You have to remember what flashpoint means. The flashpoint is just the temperature at which the vapour pressure of the substance is enough to support a flame. You are perhaps confusing flashpoint and ignition temperature, they are very different. For example, the gasoline in the tank of my automobile has a flashpoint below room temperature but I do not worry about the gasoline bursting into flame when some is spilt on the ground on a hot day because while the flashpoint temperature has been exceeeded the ignition temperature has not.

The one thing that you have to be careful of with the polyglymes is that at a high enough temperature they will rearrange into lower molecular weight substances with a concomitant rapid rise in vapour pressure. I have ruptured stainless steel cylnders rated for 2000 psi when this happened but I was heating the tetraglyme to a temperature of around 250°C. I have been told that the same sort of rapid decomposition can occur when heating crown ethers. Speaking of crown ethers they would also be good for solubilizing the LiI in some other solvent.

Stonium

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #2 on: October 09, 2001, 12:26:00 AM »
You still want this moved, Primo?

Tell/Me,
Stoni

IudexK2

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #3 on: October 09, 2001, 01:07:00 AM »
SWIM can confirm this works with LiI.3H2O, can't remember what solvent was, but it definately wasn't tetraglyme, think it may have been MeCN...?

Sweet dreams,
IudexK

PrimoPyro

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #4 on: October 09, 2001, 01:17:00 AM »
Which epoxide was used? 1,2- or 2,3-? Basically, was safrole, or isosafrole used to make the epoxide?

                                          PrimoPyro

I collect synthetic drug precursers. Aren't you jealous? Member: C_F and pyrotek FanClubs  8)

Osmium

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #5 on: October 09, 2001, 03:09:00 AM »
Ethyl acetate works well. Other esters should work too.

IudexK2

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #6 on: October 09, 2001, 05:50:00 AM »
Epoxide was formed from safrole by electrolysis... solvent was EtOAc.

PrimoPyro

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #7 on: October 09, 2001, 02:52:00 PM »
terbium: Thanx, I didnt know about the dangers of polyglymes. And yea, I was confusing flash point with auto-ignition temp. Thanx.

Osmium: Thank you. Ethyl acetate is very easy to come by. Easy and fairly cheap to buy, even easier to make with alcohol + acid + KHSO4.

ludexK2: Thank you as well. I needed to know which isomer os safrole to form the epoxide on. Using regular safrole eliminates the isomerization step with KOH, thus making it even more attractive.

Could you describe your procedure for the electrolytic epoxide formation on safrole? Forgive me if this has been covered a lot, I havent seen or heard of this at all yet. Thank you, everyone.

Ive heard that the LiI rearrangement "doesnt work" "hasnt been proven" "isnt efficient" etc., but Ive heard all that about methods I KNOW to work also, such as the wacker. I really want to dream of this.

So all that really remains is: Does anyone know or can anyone speculate, if NaI can be substituted for LiI? (equimolar of course) Does anyone know the mechanism for this reaction? The responsible party = cation or anion? Which? Both?

                                               PrimoPyro

I collect synthetic drug precursers. Aren't you jealous? Member: C_F and pyrotek FanClubs  8)

Rhodium

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #8 on: October 09, 2001, 03:06:00 PM »
NaI would probably not work, it is the cation (Li+) that is the active agent. According to JACS 93, 1693 (1971) either LiClO4/benzene or LiBr/HMPA/benzene works too. The HMPA is used to solvate the LiBr in benzene. JOC 63, 8212-8216 (1998) uses InCl3 for the transformation, and

https://www.thevespiary.org/rhodium/Rhodium/chemistry/bismuthepoxide.pdf

uses BiOClO4. All three papers give detailed explanations of the reaction mechanisms.

Depending on the substrate, either the halohydrin is the intermediate, or a free carbocation. This may mean that you could make safrole bromohydrin by mixing Br2/H2O/safrole, and then rearrange it to the ketone with a lithium salt. 

Note that LiI is very hygroscopic too. LiBr is not, but it is difficult to dissolve in many organic solvents.

PrimoPyro

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #9 on: October 09, 2001, 03:32:00 PM »
WOW.

I hadnt yet looked at those documents. Ok, so LiX it is. I dont like all those exotic inorganics, either. (gosh, arent I just a picky little bitch? :P ) I think the safrole + peracetic method __> 2,3-epoxide is the best so far. I wonder about oxidizing safrole/isosafrole with a solution of KMnO4 in MeOH. Just a thought.

Thanx Rhodium, that was exacoty what I was asking for.

                                              PrimoPyro

I collect synthetic drug precursers. Aren't you jealous? Member: C_F and pyrotek FanClubs  8)

Rhodium

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #10 on: October 09, 2001, 03:37:00 PM »
You must buffer the peracetic with sodium carbonate for it to surely form the epoxide (or use the oxone method), or else even the acetic acid may cause the epoxide to open to a diol ester (which does not rearrange with LiI). Reference for buffered peracetic: J Chem Ed 73, 555 (1996)

Search for a relative recent post by Ritter where he tells about KMnO4 oxidation of isosafrole to the diol.

terbium

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #11 on: October 09, 2001, 08:25:00 PM »
You must buffer the peracetic with sodium carbonate for it to surely form the epoxide (or use the oxone method), or else even the acetic acid may cause the epoxide to open to a diol ester (which does not rearrange with LiI).
So, if you are planning on using peracetic acid it would seem better not to try to attempt to make expoxide and use LiI but to use conditions that will create the diol (ester)and then use H2SO4 to rearrange this.

PrimoPyro

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #12 on: October 09, 2001, 08:33:00 PM »
Ah terb, but the idea is to avoid H2SO4 altogether. And to for sure use LiI. If this means I have to test completely uncharted waters, so be it. I just didnt want to use weird exotic inorganics like the pertungstic acid or the (BiOClO3???) was it? Something like that. I ASSumed peracid would work fine, and because acetic is easier to come by than performic, I figured, hey, peracetic it is.

Well, peracetic it isnt anymore I guess. Something else... Oxone maybe? Im enchanted with LiI, thats all. I have to use it. Its the road less traveled, and that makes it more appealing. ;)

                                               PrimoPyro

I collect synthetic drug precursers. Aren't you jealous? Member: C_F and pyrotek FanClubs  8)

jim

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #13 on: October 09, 2001, 09:16:00 PM »
IF you look around you will find that many over the counter oxygen detergents use sadium percarbonate as the active ingredient.  Sodium percarbonate is really just sodium carbonate bonded with H2O2, that is in a concentrated solid form, waited to be released upon dissolution in water.  This might be what you are looking for with a buffered peracetic acid reaction.

By the way is that article in text form some where Rhodium... ?

Rhodium

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #14 on: October 09, 2001, 11:12:00 PM »
Which one, that one from J Chem Ed?

PrimoPyro

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #15 on: October 09, 2001, 11:40:00 PM »
jim: sodium carbonate bonded to hydrogen peroxide? DOnt metal ions cause the degradation of peroxide to water and oxygen? "Hydrogen peroxide readily decomposes in light or in the presence of metal ions to give water and oxygen"

Oxford's Dictionary of Chemistry, 3rd ed. H2O2 entry, page 253.

Rhodium: HAHA ;D  That title is GREAT! Did you do that, or someone else as a joke? LMAO ;D

                                                   PrimoPyro

I collect synthetic drug precursers. Aren't you jealous? Member: C_F and pyrotek FanClubs  8)

Rhodium

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Re: Epoxide to Ketone Rearrangement with LiI
« Reply #16 on: October 10, 2001, 02:31:00 AM »
Primo: Sodium percarbonate is a 2:3 ratio Na2CO3*H2O2 complex which is pretty stable at ambient conditions when dry.

Damn Unobtainium, I want my Chief Bee title!

IudexK2

  • Guest
Re: Epoxide to Ketone Rearrangement with LiI
« Reply #17 on: October 10, 2001, 06:46:00 AM »
Electrolytic epoxidation and isomerisation of the epoxide to the phenylacetone:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/guest.phenylacetone.txt



Sweet dreamz,
IudexK