[smieci2k]

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.

[HP]

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

[Albert]

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).

[smieci2k]

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.

[HP]

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  

[Will]

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 SOCl_2(l) (similar to SO₂Cl₂ i guess, except you get SO_2(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!

[HP]

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  
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

[Will]

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!

[HP]

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!!

[Will]

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!

[HP]

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 !

[Will]

:laughing: Well noticed!

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

[HP]

The book pages i see are some yellow hope your letter come on time to the old lady  
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

[Will]

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.

[HP]

I was joking about your letter friend. I have some knowledges about why the paper yellowish with thev years   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...