Latsabb
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Purification of Benzalphenone (Chalcone) question.
Tomorrow I will be creating Benzalphenone from Benzaldehyde and Acetophenone, without a solvent. (hopefully) The plan is to finely grind NaOH with a
mortar and pestle, and then add equal molar amounts of Benzaldehyde and Acetophenone together, and mix well. This is a branch off of a distillation
and recrystallization method using ethanol as a solvent.
Now, my question is, if this actually works out, and I get crystallization (unknown at this point), I need a way of purifying the product. Both of the
reactants are fairly insoluble in water, but still somewhat soluble. (0.3-0.6 g/100mL range) From what I can find on the internet, the product is
insoluble in water. Now, with only three things in added, all of which at least somewhat soluble in water, would a water wash be reasonable for this
purification?
I am looking at adding 6-7 grams of each reactant, and assuming at least a 60% yield, that means that I am looking at around 2.5-3 grams of each left
over. (actual yield should be much higher, but I want to be safe) This means that I would need to flush it with a liter of water to be thorough, and I
am thinking of doing five 200mL washes.
Does this seem reasonable? Or am I overlooking something/over simplifying? Being that both the reactants and the product are soluble in ethanol, but
the product is only slightly so at lower temps, I could dissolve everything, and do a recrystalization, but then I am going to lose out on yield, and
I am going for as high as possible.
Any input would be greatly appreciated!
[Edited on 23-2-2015 by Latsabb]
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Crowfjord
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Mood: Ever so slowly crystallizing...
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Since the reactants are liquid above 20*C, perhaps you can wash with a couple hundred milliliters of warm water, and filter the crude solid product.
Then recrystallize. This is assuming that the chalcone is not soluble in benzaldehyde/acetophenone, though, which it could be. In such a case,
distillation or column chromatography would probably be best, but I don't know if either of those are options for you. If the above cannot be done,
then straight recrystallization of the whole reaction mix may be your best bet.
[Edited on 23-2-2015 by Crowfjord]
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Metacelsus
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We did a chalcone-forming reaction in my organic lab class, with m-chlorobenzaldehyde and p-methoxyacetophenone. I'll have to dig through my notes,
but I think we did a recrystallization, and I'm certain we didn't use distillation. The solubilities of these compounds are probably different from
yours, however.
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Latsabb
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The reason that I want to avoid the recrystalization is because the object is to try and produce the chalcone without the use of a solvent. Now, the
reaction will be done without a solvent, but then a solvent would be needed in order to do the crystallization. Using water as a solvent for washing
isnt an issue, though.
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Latsabb
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Well, things didnt go as planned, lol. It looked good at first, and made a thick yellow paste, which was promising, since the crystals that I was
after were of the same color. After some minutes, the paste turned very thick, like a glue, making it impossible to get off of the mortar and pestle.
I was forced to heat the mortar, and add ethanol to slowly dissolve it all. I figured that I would just recrystallize it then. I also added 11 mL of
water to try to flush out. The problem was that it never fully dissolved, even after I added 20 mL of ethanol. (Only 13.1 mL of reactants were added)
I ended up with two phases. The upper phase was a dark orange liquid, while the lower phase was a pasty mass, not unlike old mayonnaise. I vacuum
filtered it, and tried to recrystallize again, but to no avail.
So I went again, but this time did the mixing in a beaker after I ground the NaOH into a powder. Everything was an almost split pea soup kind of color
before turning into the thick paste again, with the yellow color. This time I did not add any water, and tried to dissolve it in just warm ethanol.
(while the beaker was in a 40 C water bath) Again, it would not dissolve. I added 25 mL of ethanol, and I was not greeted by two layers this time.
Just a gooey yellow mass with some extra liquid around. As I cooled it in an ice bath, the mass seemed to actually be absorbing/reacting with the
ethanol, as the liquid around the mass was cut down considerably. I decanted the remaining liquid, which was only 10mL. Substantially less than the
amount of solvent I added. The mass was similar to silly putty in consistency, and seemed to almost form strands when stirred...
The only reason offered by my professor was that it had possibly polymerized, although no one was sure as to why or how. Good times, lol.
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