Advice about preparing xanthates

[chem_tr]

Hello, I'm planning to synthesize a xanthate derivative from an alcohol and carbon disulfide. I will probably need to use sodium hydride to facilitate addition to the double bond, and I need advice about using NaH, and if possible, some experimental details about the reaction. I will look for Organic Syntheses Website for additional information, but your comments are also important for me.

Thank you

my 200^thmessage

 

[movies]

NaH is a really nice reagent to use, although it is sometimes a little unpredictable (not in a dangerous way). Typically you get it as a 60% dispersion in mineral oil. That means that when you weigh it out only 60% of the weight is actually NaH, so adjust your calculations accordingly. Make sure that the NaH is a greyish color. If it's white it's probably no good. One other caveat to the mineral oil dispersion, depending on your solvent, you may need to wash the oil away with some hexanes. I've never had to do this myself though. If you're running your reaction in THF, then that is usually good enough to use without washing the NaH.

A typical procedure for using NaH would be something like this:

A mixture of NaH (88.0 mg, 2.2 mmol) was stirred in THF (3 mL) for 30 mins and then cooled to 0 degrees C. To the resulting slurry was added a solution of [amide] (2.0 mmol) in THF (1 mL). The resulting mixture was stirred at 0 degrees for 15 mins, then warmed to r.t. and stirred an additional 45 mins, and finally quenched with an appropriate electrophile.

You might not need to stir for that long since alcohols are more acidic than amides.

You should look up the Chugaev reaction, as that is what I assume you are doing. Check out this link: http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/onr74.htm

 

[chem_tr]

What about an acyl chloride?

Hello, I've been thinking of an acyl chloride now, as it is available, unlike the alkyl chloride of the reagent I'm planning. Movies, I'm waiting for your comments especially about the feasibility of the reaction, but other members are very welcome for any contributions. Please view www.students.itu.edu.tr/~akkurtb/misc/ksantat_acil_klorur.zip[/URL]

 

[movies]

That reaction would probably happen as you have it drawn. The product would be very unstable though, since it is essentially an anhydride. There is a very real possiblity that you wouldn't be able to isolate that product.

 

[chem_tr]

You are right, Movies, it seems that I will have to find the alkyl halide derivative instead of synthesizing the acyl halide. The xanthate ester (with alkyl halide) is said to be stable up to several hundred degrees. It is better for me to pursue it in this way. Thank you for your kind suggestion.

 

[movies]

If you can make that acid chloride (or ester or acid) then you should be able to reduce it to the alcohol and then exchange the alcohol for a halide with SOCl₂ or PBr₃.

 

[chem_tr]

With $NaBH_4$ or $LiAlH_4$ and so on, right? Exchange with $SOCl_2$ is an easy one, I've done this several times before. Actually, I have the acid on hand. Do acids give alcohols easily with these reagents? For example, may I use aqueous $NaBH_4$?

 

[movies]

NaBH₄ isn't strong enough to reduce acids, usually. LiAlH₄ can though. You might also try NaBH₄ + I₂, that can reduce acids but no one knows why it is so much more powerful than NaBH₄ alone.

Here is a reference for the activated NaBH₄: J. Org. Chem. 1993, 58, 3568-3571.

 

[chem_tr]

It possibly involves radicalic mechanism. Thank you for the reference, I'll read it. I didn't want to use $LiAlH_4$, since it is a "violent" reactant. But I can use it too.