difficult to select a derivatization reagent

[s2008]

Hello all,

If a chemical has both carboxyl (-COOH) and hydroxyl (-OH) groups, how could you select derivitization reagents? silylation (like BSTFA) will react with both group and complicate the final products. Alkylation using BF3-methanol will lead low recovery of the final derivitizated products. Any super idea or suggestion?

Thanks

[zokitano]

What about using diazomethane, CH2N2?
It definitely reacts very rapidly (at room temperature) with carboxylic acids and gives methyl esters in very high yelds. The reaction with OH groups isn't favored.

One drawback is that you'll have to be very careful when using CH2N2 in laboratory, because it is explosive agent even at room temperature.

Just a thought,

Regards

[s2008]

Thanks, However, as you mentioned. Diazomethane is a dangerous chemical: explosive and cancergeneric and currently peaople try to avoid it.

[zokitano]

Forgot to mention earlier:

What kind of molecule you're dealing with?

In other words:
What do you want to achieve with derivatization:to enhance volatility, to gain decent chromatographic separation of analogues, to extract your analyte from the matrix more efficiently...?

silylation (like BSTFA) will react with both group and complicate the final products. Alkylation using BF3-methanol will lead low recovery of the final derivitizated products.

Do you assume or have you tried to derivatize your compound with these derivatization agents and that has failed?

What kind of detector are you using on your GC?

Regards

[HW Mueller]

Chemists have learned to handle diazomethane. You have to be extraordinarily gifted to cause problems if the prep instructions are followed. (For instance, those of Aldrich)

[Rosie]

I think your alkylation (esterification) of the carboxyl could work better with EtOH rather than MeOH. Ethyl esters are more resistant to hydrolysis than methyl esters.

[fsistere]

You can see "Bulletin 909A of SUPELCO".- "Guide to derivatization reagents for GC"

[Paladin]

I checked out the Supelco bulletin, thanks.

Anybody try derivatizing w/ Trimethylsilyldiazomethane and then running on GC?

Stupid Question: Why do carboxylic acids not chromatograph well?


Thanks

[Consumer Products Guy]

Stupid Question: Why do carboxylic acids not chromatograph well?

Too polar. I'd use BSTFA and derivatize both in this case. We use BSTFA a lot.

[Bruce Hamilton]

I checked out the Supelco bulletin, thanks.

Anybody try derivatizing w/ Trimethylsilyldiazomethane and then running on GC?


Thanks

There has been a recent laboratory fatality ( in Canada ? ) from using Trimethylsilyldiazomethane, not sure of details, but a Google search will find some discussion, associated with the t-BuLi death this month in UCLA chemistry labs.

Many of these derivatisation compounds are insidious - by the time they irritate you, you have inhaled enough to cause irreversible fatal damage. But for GC sample prepartion, the scale can be very small, and of low risk if hazards are compensated for.

I prefer derivatising free acids with fresh diazomethane ( fewer spurious peaks ) , however the precusor reagents are increasingly difficult to obtain, eg ( Aldrich's Diazald is no longer available here. I also prefer using pyridine/acetic anhydride for acetylation of lipids, cheap, leave overnight and inject.

Please keep having fun,

Bruce Hamilton

[Paladin]

Thanks for the help, gents.