[darkdevil]

Hi there,

I know there are numerous ways to make a vicinal diol from alkene. I tried to oxidize the alkene with cold alkaline KMnO4.. but it was a mess. I couldnt isolate my desired product. And I read papers about the  KMnO4 oxidation method, and it says it is not a good to way to make diols since it may over oxidize the alkene and the actual yield is quite low indeed.

Since oxidation of alkene to diols with cold alkaline KMnO4 is widely seen in many organic chem textbooks, but many documentations described it is not a facile way to do so. I havnt tried other methods like 1) osmium tetraoxide 2) alkene --> epoxide (with mCPBA) --> diol (with NaOH) , because I have no experience in these.

Has anyone have any experience to make a vicinal diol from alkene? What are the usual employed methods?  What are the tricks for the alkaline KMnO4 method??
Everything seems easy and straightforward in textbooks but it is completely different when come in hands. :O
THankssss!

[opsomath]

One of the first reactions I ever did as an undergrad with no experience was oxidation of an alkene with mCPBA. It was a pretty easy, clean reaction. (I was trying to make the epoxide, not the diol, but it shouldn't be that different.) KMnO4 is well known to be a giant mess; I've never used it for alkenes but even doing Ar-CH3 to Ar-COOH was a huge pain. Brown MnO2 everywhere.

So I'd recommend the peracid reactions, either mCPBA, peracetic acid, or the like. Here are some Org. Syn. examples of how to do it:

http://orgsyn.org/orgsyn/pdfs/CV3P0217.pdf

http://orgsyn.org/orgsyn/pdfs/CV5P0414.pdf

Please be aware (in addition to warnings in the preps linked up there) that these are dangerous compounds if not handled properly.

[Dan]

I've used the Upjohn method on several occasions and good to excellent results.

http://www.organic-chemistry.org/namedreactions/upjohn-dihydroxylation.shtm

I used cat. (1 mol%) K₂OsO₄ (which is oxidised to OsO₄ in situ) with 1.5 equiv NMO.

[darkdevil]

Thank you for the replies!

I think I will try the peracid method first.
In case it doesnt work, I will buy from K2OsO4 and try the UPjohn method. Will keep this updated! Thanks

[magician4]

pls. note that almost all osmium based chemicals are both VERY costly and VERY dangerous (i.e. toxic)

  this is definitively nothing for beginners to handle

also note, that if you're interested in stereochemistry, there would be a difference between those peroxid-routes mentioned , and the KMnO₄ approach: the peroxides will result in trans-diols, whereas from the permanganate route you will gain cis-diols

regards

Ingo

[Archer]

I am in full agreement with magician4, Osmium tetroxide causes permanent blindness, mild toxic effects are just dammage to your sight I have seen referred to as a "halo effect" not sure what this means but sounds bad!

adding sodium bisulfite solution to MnO₂ (post oxidation) removes this sludge from permangante oxidation reactions.

One of my first reactions I did in industry was to oxidise a fatty acid with OsO₄ as a catalyst. Even so it was so expensive that we found it better to use KMnO₄ and centrifugation to remove the sludge. I later discovered that bisulfite converts MnO₂ to MnO which is soluble in acidic solutions.

[Archer]

I read papers about the  KMnO4 oxidation method, and it says it is not a good to way to make diols since it may over oxidize the alkene and the actual yield is quite low indeed.

I have never found KMnO₄ to give particularly low yields, provided that the reaction is not heated (which causes cleavage of the diol), indeed it should be kept cool if anything. If your stoiciometry is correct you shouldn't over oxidise the reaction.

Try it on a cheap substrate first.

[opsomath]

I definitely agree about the workup with bisulfite to remove manganese oxide from the reaction mixture, if you try the KMnO4 route again. (I thought it reduced it to Mn(II)? ) Anyway, it makes it go away. Very handy.

[Archer]

I definitely agree about the workup with bisulfite to remove manganese oxide from the reaction mixture, if you try the KMnO4 route again. (I thought it reduced it to Mn(II)? ) Anyway, it makes it go away. Very handy.

I meant manganese (II) oxide by MnO, not manganese with zero charge. Lol, my sister and I had a very confusing email conversation regarding mercury metal Hg0 and what I thought she meant mercuric oxide HgO.