[Jamie1916]

Hi,

The first thing is a question that has came up a few times in past papers but I don't seem to have any material on it, the question is:

a) Write the mechanism for the formation of ethylacetoacetate (CH3COCH2COOC2H5) from ethyl ethanoate.

b) Starting with ethylacetoacetate how would you prepare hexan-2-one.

c) Starting with diethylmalonate how would you prepare propanoic acid.

This is just one of a few that I'm stuck with, the only stuff I know I'm confident with, with regards to the exam is stuff like Wittig Reactions, Grignard, Organolithium/Zinc


Thanks.

[opsomath]

I have to admit, starting the question with a complaint about your instructor and then not showing any getting-started work on these questions is rather off-putting. The usual etiquette for submitting questions for a class is to show the work you've done so far. I don't blame your instructor for not responding if this is what you gave him!

Anyway, why don't you show us what progress you've made so far? Some initial stuff you might want to look at:

http://en.wikipedia.org/wiki/Claisen_condensation

http://en.wikipedia.org/wiki/Malonic_ester_synthesis

Good luck!

[Jamie1916]

I think you've misunderstood what I mean. This question is straight out of a past paper, not one that he has specifically asked me to do or anything, just one that I have found on the University past paper section. I've emailed him asking what area we covered it in and what not as I can't seem to find it (might have missed the class or something, I'm not sure) but he hasn't responded at all. I'm not asking for the question to be done for me, more so just for guidance on what to look at in order to try and work it out myself, so I'll have a read at those links you have sent then give it a go and let you know how I get on!

[Honclbrif]

Look up the chapter on reactions of the carbonyl alpha-carbon (enolates). This should cover acetoacetate and malonate as starting materials in pretty good detail.

[opsomath]

Hi Jamie, I got that it was a past test, I just wanted to point out that you always get more attention on here if you show work that you've done in addition to asking your questions. Anyway, the questions you had are pretty straightforward applications of Claisen condensation and the malonic ester synthesis, so take a look and holler if you still have any questions.

[Jamie1916]

Okay for part a) I have got this :- (attached a picture, easier than try to type it all out)

[Jamie1916]

questions worded differently, but i think its just the same? Found an old example, so is this basically the correct mechanism?

[opsomath]

Looks good!

[Jamie1916]

I've re-written it out because obviously the two questions aren't identical, so what I have written out for the original question is:

CH3COOCH3 ---> CH2COOCH2CH2CH3 + CH3COOCH3 ---> CH2COOC2H5 ---> CH2COOC2H5
                                                                                |                        |
                                                                          H3C-COOC2H5       H3C-C=O

Confused myself if that would be right now or if the above example was correct the first time haha

[Doc Oc]

Minor correction: You have the arrow going from the alpha proton to the NaOH and it should be the other way around.  Some professors are particular about that.

[Jamie1916]

No problem. See in my orignial post for part a) it doesnt specify that NaOH is in the reaction so would i just leave that blank or does it always go in?

[Jamie1916]

I've done this for part c) .. bit confused though and i dont think it looks right!

[Doc Oc]

Although NaOH is not specified, the Claisen reaction does require some type of base.  My main point was that when you're pushing arrows, you always point the arrows from the electrons/nucleophile to the protons/electrophile.  So in your case, the arrow should be pointing from NaOH to the alpha proton, not vice versa.  Like I said, it's a minor point, but I've known some professors who are very picky about that.

For C, you've started with the wrong starting material, you need to use diethyl malonate.  C₂H₄ is also not an electrophile.  You have the right general idea, but it needs a little cleaning up.