From: Soren R. Jensen (srj$##$kemi.dtu.dk)
Date: Tue May 21 2002 - 10:00:04 EDT
Dear Kees,
I can agree to most of what Jacob wrote. But I will expand a little on point 6:
In my experience the best thing is to find a solvent in which the compound
is not too soluble - e.g. 1g in 25-50 ml at r.t. (it will probably be much
more soluble at higher temperatures and less at 0 C).
You also need another solvent with the following 2 properties: 1) the
compound must be very soluble in it, and 2) the boiling point must be lower
than that of the first.
Place 1g of your compound in a flask and add 10 ml of solvent 1. Add also
1-10 ml of solvent 2 and see to it that all the compound goes into solution
by swirling or stirring. Now leave the solution without a stopper
(overnight? - some laboratory dust is probably good) until you can see some
precipitation of the compound. If you get crystals - fine. If it is oily -
you failed, and you can try again. You can also use other solvents and
change proportions.
This does not always work. I still have an oily substance which I started
to work on in 1985. It is a sugar-benzoate, and I feel certain that it
should be crystalline. I look to it almost every year when I remember and
re-dissolve it in a little EtOH, and leave it to evaporate.
Good luck - Soren
<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>-<>
Soren Rosendal Jensen
Department of Chemistry
Kemitorvet, Build. 201
Techn. University of Denmark
DK-2800 Lyngby, Denmark
tel: +45 4525 2103; fax: +45 4593 3968
http://organisk.kemi.dtu.dk/staff/vip/srj/srjpage.htm
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