Sciencemadness Discussion Board

working with bromine

andre178 - 7-5-2010 at 10:14

I am trying to prepare triphenyl methane using chromoform, chlorobenzane and magnesium by doing a Grignard. It's really messy, expensive and seems non productive, is there a more clean way of doing it?

rrkss - 7-5-2010 at 10:48

You don't have an activated electrophillic carbon in that mix to run the grignard. Probably the easiest way I see for you to do this is run a grignard with a benzoic acid ester and bromobenzene. That will give you triphenylmethanol. Then you can run a HI/Red phosphorous reduction to remove the alcohol group giving you the desired product or use some other way to remove the alcohol group.

Remember to add an excess of bromobenzene as 2 equivalents will be added to the benzoic acid ester and some will be consumed attacking the alcohol produced by the grignard attacking the carbonyl in the ester.

[Edited on 7-5-2010 by rrkss]

UnintentionalChaos - 7-5-2010 at 22:16

Quote: Originally posted by rrkss  

Remember to add an excess of bromobenzene as 2 equivalents will be added to the benzoic acid ester and some will be consumed attacking the alcohol produced by the grignard attacking the carbonyl in the ester.

[Edited on 7-5-2010 by rrkss]


That's lost as a magnesium alkoxide, not an alcohol.

http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...

rrkss - 8-5-2010 at 04:28

Quote: Originally posted by UnintentionalChaos  

That's lost as a magnesium alkoxide, not an alcohol.

http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...


Yes you are right, I was thinking of the product produced after the workup to the intermediate.

Nicodem - 8-5-2010 at 06:14

Quote: Originally posted by andre178  
I am trying to prepare triphenyl methane using chromoform, chlorobenzane and magnesium by doing a Grignard. It's really messy, expensive and seems non productive, is there a more clean way of doing it?

I'm assuming "chromoform"=chloroform, "chlorobenzane"=chlorobenzene and that thus your preparation involves the reaction of phenylmagnesium chloride with chloroform?
I found it bizarre that triphenylmethane would be formed this way in a preparatively useful way. Sure, it looks possible for the the dichlorocarbene, formed from the reaction of PhMgCl with CHCl3, to react with another PhMgCl to form a carboanion which would reform a carbene by chloride elimination, and this reacting further till triphenylmethyl carboanion. But chances that this would happen so smoothly for this being a preparative reaction were in my opinion the domain of wild imagination. So I found it an interesting enough topic to search the literature about it, but could only find one paper (Tetrahedron, 29 (1973) 349-352, attached) mentioning such a reaction gives a relatively fantastic 76% yield (the paper itself is otherwise focused on the reaction of the so formed carbenes with cyclohexene). However it cites a book as the reference (by Kharasch and Reinmuth: Grignard Reactions of Nonmetallic Substances) which I don't have access to to (and this book is most likely not the primary source anyway).
So I ask you to do now what you should have done in the first place already - to please share the reference as I would truly like to read more about this type of reactions.

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andre178 - 10-5-2010 at 09:53

Quote: Originally posted by Nicodem  
Quote: Originally posted by andre178  

So I ask you to do now what you should have done in the first place already - to please share the reference as I would truly like to read more about this type of reactions.


Oh gosh, you mentioned earlier it was to up to the imagination, actually that's where that reaction came from. I am using the theoretical bookstuff I learned in years of OCHEM. At this point I am like a toddler sticking cubes in the square shape cutoff, and cannot get the balls in the triangle shaped one.

Eclectic - 10-5-2010 at 12:35

http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0839