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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: lukas.stib on July 04, 2020, 07:04:20 AM

Title: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 04, 2020, 07:04:20 AM: Hello chemists,

I synthesized pentan-2-one from ethyl acetoacetate and sodium hydroxide. I did everything according to the instructions, where they used 10 g NaOH, 100 ml H2O and 15 g ethyl acetoacetate. For more product, I used three times everything, so 30 g NaOH, 300 ml H2O and 45 g ethyl acetoacetate. I refluxed for 2 hours. It is written in the instructions that 2 layers are to be formed after 2 hours refluxing, the oily layer is pentan-2-one. Unfortunately, nothing was created; I cooled the flask in cold water, and now, after 45 minutes, nothing still formed. Can you advise me what to do?

Thank you, Lukáš S.
Title: Re: Problem in the synthesis of pentan-2-one
Post by: sjb on July 04, 2020, 07:40:01 AM: How did you know that the reaction was complete after 2 hrs? Aside from the scaling issue, you don't have the same source of chemicals or set-up as the original paper. I would tend to use the times in papers as a guide rather than the absolute truth.
Title: Re: Problem in the synthesis of pentan-2-one
Post by: lukas.stib on July 04, 2020, 08:22:18 AM: I always perform syntheses as they say in the instructions. So you think I should have refluxed longer?
Title: Re: Problem in the synthesis of pentan-2-one
Post by: Babcock_Hall on July 04, 2020, 11:00:12 AM: Can you monitor the reaction by TLC?
Title: Re: Problem in the synthesis of pentan-2-one
Post by: lukas.stib on July 04, 2020, 11:35:59 AM: What´s TLC?
Title: Re: Problem in the synthesis of pentan-2-one
Post by: Babcock_Hall on July 04, 2020, 01:08:44 PM: Thin-layer chromatography. You will need at least one solvent system and a means of detection.
Title: Re: Problem in the synthesis of pentan-2-one
Post by: rolnor on July 04, 2020, 01:47:46 PM: The boilingpoint of the startingmaterial is 180°C so TLC is not optimal, the product is volatile also.
Maybe run the reaction in the same scale as in the reference to start with?
Title: Re: Problem in the synthesis of pentan-2-one
Post by: Babcock_Hall on July 04, 2020, 03:27:06 PM: Particularly the product (on the basis of its volatility) would be difficult to detect, now that you mention it.
Title: Re: Problem in the synthesis of pentan-2-one
Post by: lukas.stib on July 04, 2020, 04:07:23 PM: Thank you very much.
Title: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 06:06:10 AM: Hello chemists,

I'm re-synthesizing pentan-2-one, which I started yesterday. Now I did not use 3 times the raw materials, but I used the amount in the instructions, so 10 g NaOH, 100 ml H2O and 15 g ethyl acetoacetate. Now I perform reflux for more than 2 hours, as they write in the instructions. Reflux is more than 3 hours, and still 2 layers have not formed. I let the flask cool to normal temperature, and there are still no 2 layers.

I don't know what I did wrong; on your recommendation, I left the reflux for more than 2 hours, and it still doesn't bleed the product. Do you know what I'm doing wrong?

Thank you, Lukáš S.
Title: Re: Repeated synthesis of pentan-2-one
Post by: rolnor on July 05, 2020, 08:45:32 AM: Its a bit of a mystery but now you know where to look for problem, is your startingmateriel OK? Does the product somehow evaporate?
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 09:39:42 AM: So, I cooled it down, but still no 2 layers. So I started distilling. Due to the fact that pentan-2-one has a high boiling point, distillation has already started around 60°C, and I do not know what it was. The smell was like acetone, so I guess it was pentan-2-one, but it had a different scent. I distilled to 98°C, then stopped. I think I can also smell ethyl alcohol, but I'm not sure. But the main smell of the distillate resembles acetone. I poured CaCl2 to dry, I'll let it dry until the next time.

And also my thermometer, which is from China, is probably not accurate, so the exact temperature of the start of distillation may have been different.
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 05, 2020, 11:20:32 AM: Did you used ethyl ester of 2-ethylacetoacetate?
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 01:05:06 PM: I used ethyl acetoacetate or ethyl-3-oxobutanoate (IUPAC).
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 05, 2020, 01:20:34 PM
Title: Re: Repeated synthesis of pentan-2-one
Post by: Babcock_Hall on July 05, 2020, 01:45:11 PM: How would distillation separate water from 2-pentanone? Can you cite the reference to the procedure that you are following?
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 01:53:39 PM: In the instructions, they wrote that the oily layer was dried over CaCl 2 and then distilled. I distilled immediately after reflux (not 2 layers), and I dried the distillate with CaCl2. I poured a lot of CaCl2. An aqueous layer of CaCl 2 and water was formed below, which is very large, so that the water distillate contained very much. I have molecular sieves 3A, which I haven't used yet, but I have little CaCl2, so I'll probably add the sieves later.

And i used this ester:
https://en.wikipedia.org/wiki/Ethyl_acetoacetate
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 05, 2020, 01:58:31 PM: This ester gives acetone.
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 02:01:54 PM: It's weird, they say in my tutorial that pentan-2-one should be formed :o
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 02:05:46 PM: I ´m adding a file.
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 05, 2020, 02:09:43 PM: Ethylacetoacetic ester and ethyl acetoacetate - different compounds.
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 02:31:14 PM: It's weird, the internet search always finds me ethyl acetoacetate :o
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 05, 2020, 02:40:47 PM: Search correctly
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 02:53:35 PM: OK, thank you very much for your help for me.

So therefore explains why the boiling point in my distillation began at 61°C, and was felt after acetone; it was acetone !!!

OK, for pentan-2-one I must have ethyl-2-ethyl-3-oxobutanoate, or by oxidation of 2-pentanol by dichromate.
Title: Re: Repeated synthesis of pentan-2-one
Post by: rolnor on July 05, 2020, 04:27:10 PM: So, the startingmaterial was not OK, nice that you got that cleared up. Why do you want to make this ketone, you can buy it?
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 05, 2020, 04:45:32 PM: I'm very embarrassed that I was wrong. Unfortunately, I live in the Czech Republic, and my internet browser has always found ethyl acetoacetate, which is bad for this synthesis. Simply, these 2 names of these esters merged into one.

I can buy pentan-2-on, but I do it for fun, and when I buy it, I don't like it anymore...
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 06, 2020, 12:25:41 AM: Ethyl 2-ethylacetoacetate is about 50 times more expensive than ethyl acetoacetate.
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 06, 2020, 02:36:21 AM: I know, I've found it in several stores, and the price is crazy! :o
Title: Re: Repeated synthesis of pentan-2-one
Post by: AWK on July 06, 2020, 02:56:02 AM: The need for this reagent is negligible and the synthesis on a larger scale is quite dangerous. That is why reagent companies use synthesis on demand and hence the high price. But the synthesis itself is quite simple, although requiring anhydrous conditions.
Title: Re: Repeated synthesis of pentan-2-one
Post by: lukas.stib on July 06, 2020, 04:34:20 AM: OK. So, thank you very much, you help me very much.

Lukáš S.
Title: Re: Repeated synthesis of pentan-2-one
Post by: billnotgatez on July 06, 2020, 02:40:49 PM: FYI @lukas.stib I merged both of your threads on this topic for easier usage.
Title: Re: Repeated synthesis of pentan-2-one
Post by: Babcock_Hall on July 06, 2020, 05:03:52 PM: In the body the decarboxylation of one of the ketone bodies, acetoacetate, produces another one, acetone.