derivatization of 1,2 diols

[chemcad]

Dear all,

I am not using chromatography, but think that the derivatization methods used by you guys could solve my problem:

I am trying to get rid of Glycerol and Propylene Glycol in a mixture containing Diethylene Glycol. Glycerol and Propylene Glycol have adjacent OH groups (1,2 diols), whereas the OH groups lie far apart for DEG. I read that cyclic boronates or siliconides can be used to protect adjacent OH groups. Would those work or also react with Diethylene Glycol?
I have also thought about Periodic Acid and lead Tetraacetate, which cleave Glycerol and Propylene Glycol, but not DEG. However, they produce side products that interfere with my subsequent enzymatic assay.So something that "clips on to" the adjacent OH group may work better (?).

Does anyone know what the best way is to protect/get rid of OH adjacent OH groups (Glycerol, Propylene Glycol) but leave OH groups that are far apart (Diethylene Glycol) intact? The fewer side products are formed the better it would be.

It would be great if you had some advice. Thanks so much in advance and best wishes!

[Consumer Products Guy]

Are you trying to physically separate these or assay them???? If assaying, use GC: dissolve in DMF, add trimethylsilyl derivatizing agent, shake, and inject on nonpolar capillary, easy, plenty of papers on glycerin & propylene glycol assay done this way. We do this routinely in my lab for EG, DEG, PG, DPG and glycerin.

[chemcad]

Thanks for your answer. Wouldn't Sylylation also attack the OH groups in DEG and hence react with everything? I am not using chromatography. We are basically just trying to get rid of Propylene Glycol and Glycerine in the lab, so that only the DEG OH groups are left. We then assay the left over DEG with a reaction on the bench. Chromatography wouldn't be useful for our approach. But we cant use it for our purposes. So we want to react everything away (all 1,2 diols) EXCEPT of DEG OH groups. Any suggestions?

[Consumer Products Guy]

Thanks for your answer. Wouldn't Sylylation also attack the OH groups in DEG and hence react with everything? ?

Yes, trimethylsilylation will also combine with the DEG, so this may not help with your enzymatic assay now that I re-read your post (this is a chromatography forum, remember). Don't most of those use colorimetric reactions to monitor reactions with a known substrate?

[WK]

Hi CPG,
I remember a similar reply to a question I put to you a while back. I resolved that with direct injection to a wax column. It was determination of DEG in glycerin. Being out of the lab I can't remember my LOD but I think its 0.1%w/w. Trying to determine DEG in glycerin might be difficult using silyl derivatization at this level? Do you get enough signal with a split injection to a 5 type column? Can you suggest another suitable solvent for this reaction? Unfortunately some of my other samples are in ethanol - how would this work wrt derivatization?
Regards
WK

[Consumer Products Guy]

Hi CPG,
Trying to determine DEG in glycerin might be difficult using silyl derivatization at this level? Do you get enough signal with a split injection to a 5 type column? Can you suggest another suitable solvent for this reaction? Unfortunately some of my other samples are in ethanol - how would this work wrt derivatization?
Regards
WK

We assay trace ethylene glycol and diethylene glycol in glycerin and other PEG-type materials on DB-5 type capillary after dissolution in DMF or pyridine then trimethylsilylation, works fine. One must start at maybe 80 to 110C oven temperature to separate EG from solvent and derivatizing chemical, then ramp up. I'm sure a DB-1 would do as well. We can measure readily under 0.1% EG or DEG. If your solvent was ethanol, methanol, etc., your derivatizing chemical will react with that too, so not usable for this.

We've also used the USP "624" type capillary for this assay in glycerin, works OK, but not good for other PEG-type materials as they don't come off the column. I think USP recently changed its solvent to methanol instead of water. USP glycerin monograph details changing the split liner from the glass-wool type used in Identification B to a specialty split liner for Related Compounds test. Why? Because it's USP !!!