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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: hblondie26 on May 07, 2013, 08:42:02 AM

Title: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 07, 2013, 08:42:02 AM
Compound 5 (I have attached it in the attachments) can be prepared either by reacting an organometallic reagent with an aromatic nitrile, or by reacting a different organometallic reagent with an aromatic carboxylic acid (assume appropriate work up.)


(a) Which aromatic compound and organometallic reagent would you use in each of the preparations described above?

I have whittled it down to the following 2 possibilities -

C6H5CN + C5H10MgBr

C6H5COOH + C5H10Li

Please can you advise if I am on the right track or do I need to split the carbon and hydrogens to show the structure ie:
 
(CH33)22CCHCH22MgBr 


Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: Dan on May 07, 2013, 10:36:30 AM
The molecule in your attached document is this:

C1CCCCC1C(=C)CC=C(C)C

I assume what you meant was this?

C1=CC=CC=C1C(=O)CC=C(C)C
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 07, 2013, 11:42:04 AM
Yes I did mean the molecule you put up I thought that that is what I uploaded. Sorry.

On that basis are my workings out correct?
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: opsomath on May 07, 2013, 11:56:44 AM
That lithium reagent will simply react with the acid.
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 07, 2013, 12:18:31 PM
How about this

(CH3)2CCHCH2Li and C6H5COOH
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: discodermolide on May 07, 2013, 12:33:07 PM
All that will happen there is you will get the lithium salt of the acid and the corresponding alkane from the organometallic bit.
Perhaps it may be worth considering an acid derivative?
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 07, 2013, 01:01:24 PM
Do you mean something like LiAlH4? Lithium aluminium hydride.

So (CH3)2CCHCH2LiAlH4 us the aromatic carboxylic acid?
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: discodermolide on May 07, 2013, 01:12:24 PM
No I mean an acid derivative which will react with an organometallic reagent to give a ketone.
Not an aluminium hydride.
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 07, 2013, 01:46:20 PM
Sorry, I am confused my question says an aromatic carboxylic acid , so do you mean I should choose a different type of carboxylic acid - not use the C6H5COOH ? 
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: discodermolide on May 07, 2013, 01:53:03 PM
No you make a derivative of benzoic acid which will react with an organometallic reagent to give a ketone.
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: opsomath on May 07, 2013, 02:43:16 PM
I was actually confused by the question as I don't think there's a common reagent which goes directly from carboxylic acid -> ketone, although actually Grignards will do this with the carboxylate (a little known fact). So I guess they want you to prepare the ester as Disco suggested? The way the question was worded, it sounded like you had to use the acid.
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 07, 2013, 07:50:51 PM
I think that that is where I am confused as well as I think my tutor wants me to use the carboxylic acid directly - I will clarify with her and then let to know my answer. Thank you for th help so far - back to the drawing board for me this morning !
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: orgopete on May 08, 2013, 02:01:05 PM
Use the nitrile. It resists adding a second lithium reagent. Hydrolysis of the imine intermediate gives a ketone. This is just one method that could work, assuming this reaction was covered in your class.
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: opsomath on May 08, 2013, 02:06:25 PM
I thought the original question part II required a carboxylic acid (nitrile was the part I).
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 08, 2013, 03:19:18 PM
The question is actually in 2 parts - first one is asking for the aromatic nitrile plus OM reagent and then the 2nd part is asking for an aromatic carboxylic acid plus OMreagent to be used - both ending up with the same molecule.

I don't know what acid derivative to use unless you do something like

C6H5CH3COOH

WIth the nitrile I have used MgBr
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: opsomath on May 08, 2013, 03:33:49 PM
Well, I stand by my original answer; you can directly react an organometallic (including organolithiums) with a carboxylate, making a ketone after workup.

http://www.orgsyn.org/orgsyn/orgsyn/prepcontent.asp?prep=cv5p0775

Alternatively, you could make a Weinreb amide using an amine coupling procedure, then react it with an organolithium or similar.

http://en.wikipedia.org/wiki/Weinreb_ketone_synthesis#Preparation
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: orgopete on May 08, 2013, 09:50:42 PM
Quote from: opsomath on May 08, 2013, 03:33:49 PM
Well, I stand by my original answer; you can directly react an organometallic (including organolithiums) with a carboxylate, making a ketone after workup.

http://www.orgsyn.org/orgsyn/orgsyn/prepcontent.asp?prep=cv5p0775

Alternatively, you could make a Weinreb amide using an amine coupling procedure, then react it with an organolithium or similar.

http://en.wikipedia.org/wiki/Weinreb_ketone_synthesis#Preparation

I agree, those are possibilities. Would you think those reactions were part of the class the poster was taking?
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: opsomath on May 08, 2013, 09:59:25 PM
Haha heck no, maybe the carboxylate but certainly not the Weinreb. That's why I was confused. I think OP may have accidentally left something out.
Title: Re: Oragnaometallic reagent with aromatic nitrile and aromatic carboxylic acid
Post by: hblondie26 on May 12, 2013, 04:00:52 AM
 Hi, I didn't leave anything out of the original posting - we are studying 2nd year chemistry and as such have not covered Weinreb. We have done carboxylate though.

I have copied and pasted the exact question and compound below.

Thank you for all the previous help.

Compound 5 can be prepared either by reacting an organometallic reagent with an aromatic nitrile, or by reacting a different organometallic reagent with an aromatic carboxylic acid (assume appropriate work up).
 (a) Which aromatic compound and organometallic reagent would you use in each of the preparations described above?