Question

I am making LiNMe2 using n-Buli (5.5 equiv.) and dimethylamine (5.0 equiv), -15 ºC, dry THF and under nitrogen atmosphere.

I have been doing the reaction and I can observe conversion of starting material (nitrile compound) by HPLC analysis. However there are multiple peaks observed.

The article I am following reports using NaHCO3:Na2CO3 1:1 buffer for the work up. The reaction mixture was added to the buffer with stirring under 5ºC and precipitation was observed. Been attempting to do that, but no precipitation is observed. Instead it is forming an oil that floats on top. Anyone who has worked on something similar or who can advise?

Answer 1

The student's synthesis of LiNMe2 with n-BuLi and dimethylamine is yielding multiple products, and the workup procedure is not resulting in the expected precipitation. Reactions conditions and purification methods might need optimization to achieve a cleaner product.

Step-by-step explanation:

The student is trying to synthesize LiNMe2 by reacting a nitrile compound with n-BuLi and dimethylamine in dry THF under a nitrogen atmosphere, followed by a workup using a NaHCO3:Na2CO3 buffer. The issue at hand is the appearance of multiple peaks in the HPLC analysis of the reaction mixture, indicating the presence of byproducts or unreacted starting materials.

Furthermore, instead of the expected precipitation during workup, the student is observing the formation of an oil that floats on top of the buffer solution.

It's possible that the conditions of the reaction or workup are not being met precisely, or if the reaction scale differs from that described in the literature, this can also affect the outcome. The student might need to further optimize the reaction conditions, such as the temperature, equivalents of reactants, or concentration.

Additionally, obtaining a clean product may require more thorough purification techniques, such as column chromatography or recrystallization, depending on the solubility and stability of the compounds involved.