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Topic: Short organic synthesis  (Read 14554 times)

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smieci2k

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Short organic synthesis
« on: December 30, 2005, 06:29:49 AM »
Hello

First of all, please forigive me my poor English.

I have a problem with the organic synthesis as shown on the picture below. I was trying to guess the reagents A, B, C and D in the reversed order, but I am not sure whether I did it right. My guesses are in the rectangles.
I also cannot figure out what compound is A and what type of reaction is acetone+A -> B which is catalysed by sodium amide. Is it a reaction similar to mixed aldol condensation?

Thanks for your help in advance.

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Offline HP

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Re:Short organic synthesis
« Reply #1 on: December 30, 2005, 11:47:54 AM »
I think A is ethine  and this is Favorsky reaction catalyzed by NaNH2 or R-ONa
Second step H2/Pd i think theres some danger hydration and OH groups but may be this is selective only for the double bonds.
Third reaction R-OH + HCl--> R-Cl hm not very suitable for laboratory scale as you must work with dry HCl gas.
Fourth seems ok but very possible and Fridel-Crafts of two molecules Ph-Br  also your product with your product ;)
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Offline Albert

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Re:Short organic synthesis
« Reply #2 on: December 30, 2005, 01:24:29 PM »
Quote from: HP on December 30, 2005, 11:47:54 AM

Third reaction R-OH + HCl--> R-Cl hm not very suitable for laboratory scale as you must work with dry HCl gas.

Exactly what I was thinking: out of the fabulouse world of exercises, you'll never do this way. I think POCl3 to be the better reagent for doing it (I base this opinion on first-hand information: i.e. synthesis of isoniazid).
« Last Edit: December 30, 2005, 01:28:46 PM by Albert »
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smieci2k

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Re:Short organic synthesis
« Reply #3 on: December 30, 2005, 01:51:04 PM »
Thank you very much for helping me.

Favorskii reaction is definitely what I was searching for and A must be ethine.
According to the mechanism of Favorskii's reaction triple bond in ethine remains unaffected so reagent B should have triple bond instead of a double one which I have drawn in the picture above.
« Last Edit: December 30, 2005, 01:56:39 PM by smieci2k »
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Offline HP

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Re:Short organic synthesis
« Reply #4 on: December 30, 2005, 02:07:54 PM »
Aha Albert is right POCl3 is suitable areagent. Its possible also using PCl3 or PCl5 as chlorinating agents. SO2Cl2 very suitable too because the reaction products are gases + R-Cl product:
R-OH + SO2Cl2--> R-Cl + SO3gas + HCl gas
Of course R-Cl not gas if R enough long chain  :)
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Offline Will

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Re:Short organic synthesis
« Reply #5 on: December 30, 2005, 07:01:10 PM »
Hi!

Since the alcohol produced is tertiary, I think you could use concentrated HCl(aq), if this is too slow you can use ZnCl2 as a catalyst. Also, as well as the other chloronating agents mentioned you can also use SOCl2(l) (similar to SO2Cl2 i guess, except you get SO2(g)) and reflux with pyridine, as it assists the reaction by absorbing the HCl(g) as it is formed.

Apparently PCl3 isn't any good, don't know why! ???

Your english is very good, smieci2k, theres no way I could tell you weren't english!
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Offline HP

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Re:Short organic synthesis
« Reply #6 on: December 31, 2005, 04:13:26 AM »
Why not PCl3 with R-OH in the presence of Pyr or NEt3 it gives:
R-OH + PCl3--> R-Cl + H3PO3 + HCl
SOCl2 nice too then SO2 + HCl right  :P
In fact i think POCl3 + 3ROH may give PO(OR)3 - phosphate esters thats why when using PCl5 alcohol must be stoichimetric:
PCl5 + ROH --> R-Cl + POCl3 + HCl
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Offline Will

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Re:Short organic synthesis
« Reply #7 on: December 31, 2005, 07:42:56 AM »
Despite being told that PCl3 works fine for this reaction fine at A-Level, I am sure I have read in one of my organic chem books that this reaction doesn't give the desired product (even in the conditions HP mentioned I think). I had a guess at what you might get:

3 ROH + PCl3 --> 3 HCl + P(OR)3   (similar to POCl3?)

Maybe under extreme conditions you can get the reaction to happen as HP said.  I could be completely wrong though! ;D
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Offline HP

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Re:Short organic synthesis
« Reply #8 on: December 31, 2005, 08:50:27 AM »
Completely wrong, yes! Nucleophilic Substitution (SN1 or SN2) of alcohols with halogenating agent PCl3. I think mechanism this reaction has been ilustrated at this forum before..
Happy New year to all!!
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Offline Will

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Re:Short organic synthesis
« Reply #9 on: December 31, 2005, 09:15:09 AM »
LOL! :laughing:

OK HP! Thanks for correcting my anyway, I found where it says PCl3 cannot be used in my book (doesn't say why)- it says PBr3 and PI3 are fine for making alkyl bromides and iodides. I'll contact the author immediately!
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Offline HP

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Re:Short organic synthesis
« Reply #10 on: December 31, 2005, 09:29:48 AM »
Yes, contact him and tell him that I,HP have done this reaction with n-buthanol as 2nd year student and it works fine. Ethylchloride  BP 12.2 °C !
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Offline Will

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Re:Short organic synthesis
« Reply #11 on: December 31, 2005, 10:02:42 AM »
:laughing: Well noticed!

I've got the author's (Eileen Ramsden) address and I'll write her a letter now!
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Offline HP

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Re:Short organic synthesis
« Reply #12 on: December 31, 2005, 10:19:03 AM »
The book pages i see are some yellow hope your letter come on time to the old lady  ;D
You know the Exgzuperi phrase: " Only the thing we have tamed we could know" I can asure you that PCl3 works with n-buthanol as i have made this routine experiment when i was young alchemist, now alredy got my diploma... By theoretical consistents it should work with most of the simple alcohols but i doubt it's suitable for work with methanol and ethanol too ;)
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Offline Will

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Re:Short organic synthesis
« Reply #13 on: December 31, 2005, 10:58:43 AM »
The book pages are more yellow than it seems- I used the auto correct thing in Misrosoft Office Picture Manager to make it a lot whiter! She wrote the book 20 years ago but I still think shes alive!

I checked up PCl3 on Wikipedia and they say what I said happens with t-BuOH to EtOH and PhOH. You're probably right and the messed up reaction only happens with very simple alcohols and phenols.
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Offline HP

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Re:Short organic synthesis
« Reply #14 on: December 31, 2005, 11:15:39 AM »
I was joking about your letter friend. I have some knowledges about why the paper yellowish with thev years  :P but may be new topic that. Yes PCl3 not suitable for simple alcohol  but when i did my experiment with n-buthanol i didnt know that : my own ignorance has always lead me to progress  ;)
If i have some time i'll try the reaction ethanol PCl3 at my laboratory and will tell you the result...
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