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Wednesday 16/1/2018

Purification of 1 (AS02) (attempt 2)

After allowing the solution to cool overnight, the product, as well as some impurities had crystallised out and were filtered off (fig:AS02vaccum). The crystalline precipitate was then washed with and hexane (fig:AS02product), resulting in an impure product (fig:AS02dry), that was confirmed with TLC.

Vacuum filtration setup Crystals of crude product, washed with MeOH and hexane Visual yield of crude crystalline product

The impure product was redissolved in minimal DCM and purified by column chromatography with silica gel 60 as the solid phase and DCM:MeOH (200:1) for the liquid phase (fig:AS02column). Since the product is clear in solution, UV light was used to make it fluoresce (fig:AS02glow). TLC was used on each fraction to identify if it contained 1. Three fractions were collected that contained 1 and for each, the DCM was removed by rotary evaporation. The resulting powder fluoresced blue-green (fig:AS02productfinal), indicative of there being 1 present.The dried product was then dissolved in minimal DCM, placed in a weighed vial and the solvent was allowed to evaporate off in a fume cupboard.

The column setup with (from the bottom up)cotton, sand, silica gel 60, the crude product, sand and the liquid phase Visualising the product under long wave UV light. The final rotary evaporated product glowing under long wave UV light

The dried product weighed in at 7.6 mg, with a calculated yield of 4.57%, indicating significant loss. Since column chromatography is my weakest wet skill, I suspect that it may have been the primary source of product loss. This was confirmed with NMR, indicating that while the product was there, the sample was very impure (fig:AS02NMR). The solution has been redissolved in minimal chloroform and is being allowed to recrystallise overnight.


NMR spectra of the eluted products from the column, with the proton peaks of 1 having been integrated

THF distillation

In a 1 L round bottom flask was added, \(\sim\) 500 mL of THF, some sodium shavings and a small quantity of benzophenone. The round bottom flask was placed in a heating mantle and above it was set up a solvent still-head, double coil condenser and a gas bubbler. Argon gas was pumped through the setup and the THF/benzophenone/sodium mixture was brought to a boil.

The still-head was set up to allow the solvent to pass back down into the round bottom flask to continue being dried.

After a few hours, the sodium was completely consumed, so more was added, along with more benzophenone.

The bottom of the THF still The top of the THF still Boiling THF - initial