I get lesser yields when performing LiHMDS reaction. I have a doubt how I could judge when all nBuLi converted HMDS into LiHMDS.
I guess there is a method with diphenylacetic acid acting as an indicator (turns yellow)
Hi Vadivel,
NMR on 1H or 29Si is ultimate method. But reaction proceed with evolution of butane and heat that can be easy detected by bubblers (H2SO4) and digital thermometers with 1/10 -1/100 Grad scale. Effects are detectable for mmol quantities by use 1-2M BuLi and neat HMDS (or half-diluted with hexane). Reaction is fast (some seconds) at RT. After butane evolution is ceased, allow reaction mixture to cool at 0-4C Grad overnight to get large perfect crystals of LiN(SiMe3)2. Such crystalls can be handled in relative dry air without precaution. Excess of HN(SiMe3)2 is mandatory because presence of BuLi-traces make matherial pyrophoric.
J. Org. Chem. 1976, 41 (10), 1879-1880.
http://pubs.acs.org/doi/abs/10.1021/jo00872a047
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