[darkdevil]

Hi, I am performing the following reaction using NBS and water as the bromohydrin source. The starting material is allyl alcohol. And I expect my product to be a racemic mixture of a bromo diol.


However, the H NMR spectrum does not seem to give my desired product. I wonder what went wrong?
This spectrum is after extraction with ethylacetate and then using D2O as the solvent in NMR. The two sharp peaks at 2.7ppm and 4.7ppm shows a total of 5 protons. and I am not sure if the middle splittings are due to proton exchange with my diol and D2O


Later I found out that the product was insoluble in diethylether. I then precipitated it and collected the white powder. But surprisingly the H NMR result was different (see below). And the two sharp peaks at 2.7ppm and 4.7ppm now sum up to a total of 3 protons only.


What actually happened? Did I synthesized the diol or did I made something else??

[darkdevil]

Comparison of the two NMR spectra

[Dan]

The peak at 4.8 is H₂O
The peak at 2.7 is succinimide

You product is probably in the diethyl ether and it was the succinimide that precipitated.

[darkdevil]

The peak at 4.8 is H₂O
The peak at 2.7 is succinimide

You product is probably in the diethyl ether and it was the succinimide that precipitated.

Oh.. So the multiplets are signals of my diol?

[opsomath]

Isn't this product a liquid at RT?

[Dan]

So the multiplets are signals of my diol?

Yes, the peaks for your diol will be multiplets in that region.

Isn't this product a liquid at RT?

Yes it is

[darkdevil]

So the multiplets are signals of my diol?

Yes, the peaks for your diol will be multiplets in that region.

Isn't this product a liquid at RT?

Yes it is

Will I see the diols protons in NMR if I use D2O as solvent? Will there be protons exchange?

[discodermolide]

In D₂O the OH protons will exchange to give OD. So you will not be able to see them.

[orgopete]

Are you following a lit procedure? I might expect the product to have appreciable water solubility, so what is your material balance?

[darkdevil]

Are you following a lit procedure? I might expect the product to have appreciable water solubility, so what is your material balance?

Thank you for the replies
I followed a literature, and te used 1-methylcyclohexene as the starting material. It demonstrated the synthesis of a Markovnikov's bromohydrin using NBS
. But my product is actually a diol, and it is very soluble in water.
Today I tried using diethy ether to do an extraction from the crude product, and im now removing the solvent. Will keep this updated

[darkdevil]

I used diethylether to extract my "diol" and also the succinamide. Upon high vacuum, some white powder still formed and I suspect it is sucinamide. I filtered off the white solids, washed the solid and collected the filtrate for NMR analysis.
The HNMR of my cmpound is more or less the same except the multiplets are a higher. THe succinamide peak is still there
. I used D2O as solvent. And if the multiplets represnt the protons on the aliphatic chain, they are all gobbled up and I do not have any reference peak(s) to give out the integrals of the multiplets

[orgopete]

Since the product is a known compound and apparently commercially avaiable, why not just try a literature procedure?

[discodermolide]

Succinamide from NBS reactions is insoluble in CCl₄, Your diol may dissolve in that solvent, if so suspend the mixture in CCl4 cool to 0°C and filter off the succinamide. remove solvent and there should be your product!

[Babcock_Hall]

At least one isomer of the product is commercially available.  Is there some reason you don't wish to use it?