Rhodium (Chief Bee)
02-28-02 23:39
No 274959
       Li-CH2-CN?  Bookmark   



See the middle figure in the nitrile prep section. Sounds really interesting, right? Would that reaction work with 2,5-dimethoxybromobenzene, lithium and acetonitrile?

If one does not want to use commercial BuLi to prepare LiCH2CN, can it not be made in situ from any alkyl halide and lithium (from batteries) in pet ether, followed by acetonitrile? Any refs for this? Today's chemists are so lazy, they always buy expensive, pre-formed reagents instead of doing the art of synthesis themselves.

RX + 2 Li => RLi + LiX
RLi + CH3CN => LiCH2CN + RH + LiX 		 
 
 
 
    kapen
(Stranger)
03-01-02 04:25
No 275106
       Re: Li-CH2-CN?  Bookmark   

to swik half the fun is being able to find things yourself and involve as few people as possible.
Just say know. 		 
 
 
 
    slappy
(Hive Bee)
03-01-02 09:23
No 275206
       Re: Li-CH2-CN?  Bookmark   

You need a non-nucleophilic (sterically hindered) base to prepare LiCH2CN, like Lithium Diisopropylamide or the Lithium amide of 2,2,6,6-Tetramethylpiperidine. With Butyl Lithium you will see some addition to the nitrile I think.

You cannot just do an aromatic nulceophilic substitution like that. You would need either a very electron deficiant ring, or some kind of lewis acid. These kind of additions are commonly done using Chromium Tricarbonyl Arene complexes (Cr(CO)3Ar).

I don't think that buying pre-made solutions makes you a lazy chemist. Not having to make things like this up, gives you more time to concentrate on your work. The only thing that I don't agree with is the prices that chemical suppliers charge for them. But if you're not footing the bill, what does it matter? 		 
 
 
 
    hest
(Hive Bee)
03-01-02 10:03
No 275218
       Re: Li-CH2-CN?  Bookmark   

Buli and MeCN will doo the job (beilstein) but when they substitute an aromatic molecule they alwayes use Cr(CO)3Ar as a catalyst (wonder why laugh) But the ide is fun. Once I get the time I'll try it on bromobenzene (whthout the catalyst) 		 
 
 
 
    slappy
(Hive Bee)
03-01-02 17:26
No 275339
       Re: Li-CH2-CN?  Bookmark   

Cr(CO)3Ar is not a catalyst, i.e. you need it in stoichiometric amounts. It is a 6 Half sandwich complex. You have to take your substituted benzne, and react it with Cromium Hexacarbonyl (Cr(CO)6), which is extremely toxic and also explosive.

After you have your Cromium Tricarbonyl complex, you have 6 donation into the metal, which decreses the electron density  at the ring, and makes it suseptible to nucleophilic attack.