xfusion44
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Mesityl oxide synthesis
Hi!
A few months ago I asked (in short questions thread), how to separate solvents in paint thinner (I wanted to obtain methanol). One of you recommended
adding NaOH to the solution, which would react with one of the solvents and make other solvents easier to separate. There was also a small amount of
acetone in that paint thinner, so NaOH also reacted with it to make diacetone alcohol which should readily dehydrate to form mesityl oxide. So, when I
tried this, I could really see a few drops of yellowish, oily substance floating on top of solution after the reflux has been done. I was assuming
that was the mesityl oxide.
Most of the time I've been dealing just with inorganic chemistry - that's what got me into chemistry, but when I saw that yellowish substance I
thought to myself I should try myself in organic chemistry.
So, I read the page on wiki, about mesityl oxide and it says it's made with aldol condensation of acetone to give diacetone alcohol which readily
dehydrates to give mesityl oxide. I was a bit unsure about the "dehydration" part of this text but since I already made that yellowish compound
before, I thought: ok, let's try this... Before I proceeded with practical part, I decided to check if there are some procedures available on
synthesis of mesityl oxide. I found this: https://archive.org/details/classbookoforgan030530mbp (download PDF and check page 14-15) also available here: http://www.prepchem.com/synthesis-of-mesityl-oxide/
So, I started wondering if this would really be as simple as I thought it would be. Wikipedia says something like: "mix naoh and acetone" - that's it.
And the procedure on those links above says to bubble HCl into the acetone and then let the thing sit for two days, separate layers, wash with conc.
NaOH, distill...
I know that aldol condensation can be catalyzed by both acid and base. It looks to me like that procedure uses acid (HCl gas) but why do you need to
wash the product with NaOH? Just to neutralize HCl?
It also says on wiki that isophorone may be formed under same conditions by a Michael addition but in that procedure it says phorone, not isophorone.
Is that because acid, instead of base was used?
However, I decided to go with base catalyzed aldol condensation.
I didn't know how much NaOH to use, but since it's used as a catalyst I thought that different quantities would only affect speed of reaction. So, I
made a solution of NaOH (10g of NaOH in 30ml of water). To this I added 100ml of acetone and tried to mix all together, but it didn't seem to be
working  High concentration of NaOH probably didn't want water to mix with
acetone, right? However, even though I couldn't mix the thing, I started refluxing (3h on 1.5kW hotplate). At the end, acetone was slightly yellow. I
decanted the bottom hydroxide layer and distilled the top layer. Almost 100ml of acetone were recovered and I was left with a few drops of dark brown
liquid with the smell of hmm, moldy wood or something burned?..
2nd try: 50ml's of acetone, mixed with 50ml's of water and maybe 3-5g of NaOH. This time I was able to mix it properly.
I also left those few drops of brown liquid in the flask.
Again, refluxing for 3h. I proceeded with distillation about 12h later. I got pretty much all of the acetone back and also a lot of water. Distillate
turned a bit yellowish at higher temperatures, but thermometer never got over 97°C. I think that was because the distillation slowed down
significantly after all of the acetone came over. Oh, and there was so much foaming going on in the boiling flask (probably because of NaOH?). And
again I was left with that brown liquid (a tiny bit more of it, this time). I wanted to distill that liquid but it looked like it would just form a
solid which would stick to the bottom of boiling flask, so I decided not to distill it. Does anyone know what could that solid be? It looks almost
black - like burned sugar...
I also have a question about dehydration of diacetone alcohol. Does it really "readily" dehydrate? Doesn't it need some conditions to do that? Where
does the water go when it dehydrates?
Oh well... I just wanted my mesityl oxide. Excuse me for not knowing much about organic chemistry.
BTW, I'm also a bit worried that all those procedures might produce some explosive compounds or is there nothing to worry about?
Thanks for your help
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Metacelsus
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Read this: http://www.orgsyn.org/demo.aspx?prep=CV1P0199
(this procedure uses barium hydroxide as a base, but I imagine sodium hydroxide would also work)
and this: http://www.orgsyn.org/demo.aspx?prep=CV1P0345
(for dehydration of diacetone alcohol)
Also, as to your concern about explosive compounds, I can't think of any that might form.
[Edited on 7-2-2016 by Metacelsus]
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Marvin
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Acid and base will catalyse self condensation of acetone, but sodium hydroxide tends to result in polymeric resin like products. The HCl would need
to be neutralised before distillation or it's just going to come over with the product and then continue catalysing.
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xfusion44
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@Metacelsus
Thanks! I haven't tried with barium hydroxide, but I did try with sodium hydroxide and it doesn't seem to work well. Maybe I'd need to reflux for a
few days, instead of 3 hours? But then the mixture would probably just get darker and darker. BTW, why mustn't barium hydroxide get into the lower
part of the flask? And also, why do you need to use steam or oil bath instead of hot plate directly?
@Marvin
Thanks! So, would barium hydroxide make any difference? Oh, so that's why NaOH was used in that procedure...
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Metacelsus
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Quote: Originally posted by xfusion44  | | BTW, why mustn't barium hydroxide get into the lower part of the flask? And also, why do you need to use steam or oil bath instead of hot plate
directly? |
From the Orgsyn procedure: "Acetone and diacetone alcohol are in equilibrium with each other. The speed of both reactions is greatly accelerated by
the presence of a base. The equilibrium mixture contains only a few per cent of diacetone alcohol, but the dissociation of diacetone alcohol to
acetone proceeds so slowly in the absence of barium hydroxide that it is possible to increase the concentration to 80 per cent by this procedure."
As for the heat source: Hot plates weren't around in 1921. The heat source probably doesn't matter much.
[Edited on 7-3-2016 by Metacelsus]
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Doctor Cat
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what about calcium hydroxide?
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NitratedKittens
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Could strontium hydroxide work as well?
Basket of kittens for you ........BOOM
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unionised
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One important criterion is that the Ba(OH)2 isn't soluble.
Another is that you can get it as fairly stable little lumps, rather than powder.
You can probably manage that with Ca or Sr hydroxides too.
NaOH probably won't work because enough will dissolve that it will end up in the lower flask.
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