low reactivity of benzylhydrazine

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

jaffa19812003@yahoo.co.uk - 13 May 2005 08:18 GMT

Some help needed with my masters project please. I've managed to
C-acylate dimedone with Boc-homoleucine followed by condensation in
EtOH with benzylhydrazine.2HCl. The cyclic product of the 2nd step was
low yielding and took 100h (much longer than cited in literature),
probably due to the diisopropylethylamine used not sufficiently
neutralsing the HCl in the Bz salt. However, I'm sure there are some
other contributing factors for the low yield that I haven't pinpointed.
Can anyone offer some suggestions?

Many thanks

Reply to this Message

muha - 17 May 2005 12:19 GMT

incresing the reaction temperature (one can use closed pressure tube
with teflon cap and O-ring, for up tu 30C over the solvent boiling
point), adding more hydrazine reagent, adding more base, etc. Also you
want to be sure that your ethanol is not denaturated with methyl
isobutyl ketone, which would react with benzylhydrazine also.

If things do not work well, you can try a differeent solvent,
trifluoroethanol for example.

Reply to this Message

Gabriel Tojo - 17 May 2005 12:22 GMT

What matters in the second step, as well as in the first one, is the
pH.

I would try the reaction in EtOH or MeOH with a buffer at different
pH?s around neutral.

Reproducibility of reactions, even those published in the best
journals, must never be given for granted.

Best regards.

Gabriel Tojo

Reply to this Message

Natural Science Forum / Chemistry / Organic Synthesis / May 2005

low reactivity of benzylhydrazine