[darkdevil]

Hi,

The typical 1,2-diol synthesis required the use of potassium permanganate in alkaline aqueous solutions. Here is the problem, I have a water insoluble alkene that I want to transform it into a 1,2-diol for further reactions. I cannot make it dissolve in water, nor making the permanganate dissolve in organic solutions. It is also recommended that the diol synthesis from alkene using this method should be kept at a cold temperature, so that heating may not be appropripitate. I just wonder how can I make my diol?
I am wondering if I should use an alternate method like epoxidation of alkene first and then do a hydrolysis to make the 1,2-diol
(stereochemistry is not a problem in my case)

[mike0194]

You could use an alcohol as the solvent? That should dissolve both the alkene and the NaOH.

[kriggy]

You might want to use Milas or Upjohn dihydroxilations with OsO₄
https://en.wikipedia.org/wiki/Milas_hydroxylation
https://en.wikipedia.org/wiki/Upjohn_dihydroxylation

Maybe there are other methods Sharpless hydroxilation maybe?

I never did any of those so Im not sure if they work in other solvents than water but if you find oxidant soluble in organic solvent then you should be good

[darkdevil]

You could use an alcohol as the solvent? That should dissolve both the alkene and the NaOH.

Thank you. I also found a paper that describes the dihydroxylation of alkene using a tertiary alcohol or acetone as solvent. Maybe I should try acetone first.

[darkdevil]

You might want to use Milas or Upjohn dihydroxilations with OsO₄
https://en.wikipedia.org/wiki/Milas_hydroxylation
https://en.wikipedia.org/wiki/Upjohn_dihydroxylation

Maybe there are other methods Sharpless hydroxilation maybe?

I never did any of those so Im not sure if they work in other solvents than water but if you find oxidant soluble in organic solvent then you should be good

Thank you.. but there are some difficulty to order Osmium Tetroxide in my place and I would like to try a simpler and safe method first.

[kriggy]

You could use potassium osmate as a source of OsO4 in situ. But I agree that its better to start with safe and easy methods first

[darkdevil]

It seems that there was something happening using Acetonitrile as solvent, and potassium permanganate solution. I can see another spot appeared in the TLC.

The new spot in TLC showed that it is soluble in chloroform, I then used chloroform and did a liquid-liquid extraction. I collected the chloroform solution, and removed chloroform usinf the rovap. I then obtained a power that is insoluble in everything! I did the TLC again and then spot disappeared.
Is the 1,2-diol so reactive that it formed polymers (polyethers) with chloroform? I think I will try to use ethyl acetate again next time.

[MOTOBALL]

Was this silica gel TLC ?

Did you run the plate in straight Chloroform or a mixed eluent ?

What are the Rf values of the alkene and the new spot ?

[clarkstill]

You could try the Prevost/Woodward reaction?

http://www.organic-chemistry.org/namedreactions/prevost-reaction.shtm

I've had reasonable success with the catalytic version, with periodate as the terminal oxidant (Org. Lett., 2005, 7, 5071).

[TheUnassuming]

Are you sure your assumed diol isn't in the polar/water layer of the extraction?

[darkdevil]

I just checked the NMR of the product, and I think the alkene is over oxidized and the product could possibly be a carboxylic acid (I submitted a sample for mass spectrometry analysis to confirm). The image below is the TLC of the starting material and right after the reaction for 30 minutes at room temperature.


If I lower the reaction temperature, my substrate may easily precipitate from the solvent since it is not very soluble in acetonitrile. Shall I change the solvent or I should employ another method now?

[darkdevil]

OH! I just read Wikipedia about some basic Organic Chemsitry I alkene oxidation with KMNO₄,

I performed my reaction in a neutral condition. I think I shall do one reaction in basic condition. I totally forgot how different the products would be under different pH for an alkene oxidation with permanganate.

[darkdevil]

There is another example I found on the internet about alkene oxidation.
The example is a vinyl compound (same case as mine) and here is the quoted text:

"In basic conditions, treatment of alkene with potassium permanganate forms a vicinal diol. Oxidative cleavage by permanganate in neutral or acidic conditions, however, leads to cleavage to form carbonyl compounds by means of the same cyclic manganate ester intermediate. Where ozonolysis, another method of oxidative cleavage of alkenes, produces an aldehyde or formaldehyde, cleavage with permanganate produces a carboxylic acid or carbon dioxide respectively. "


Reference is here: http://www.wikipremed.com/03_organicmechanisms.php?mch_code=030202_080

[TheUnassuming]

Looking at the TLC, I don't think you have converted the alkene to the diol or the acid.  The difference in polarity should be starkly different with either of those products from the starting material.

[Enthalpy]

For my information: would the alkene react with H₂O₂ to make the diol, or with N₂O to make the epoxy, as vapours, diluted in N₂ to avoid a flame?
Apologies for interrupting.