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8th August 2016 @ 06:16

The Repeat Synthesis of 2-(4-chlorophenyl)-3-oxopentanenitrile (SGS 10-2) produced two separate compounds which were evident as two spots on the TLC when run in DCM. The crude material had initially been isolated as an oil, but it had crystallised over a period of a few days and so it was decided to attempt to obtain a pure samples of the solid component(s).The major compound appearing half way up the TLC (DCM) plate is currently assumed to be the target compound.  Pure samples of the two compounds were isolated as follows.

Firstly, the solid mixture was washed with 3x25 mL samples of DCM and filtered through fluted filter paper to yield a red-coloured solution and light lemon residue. TLC in ethanol of the residue indicated that it was a single material (See TLC in ethanol below).  Recrystalization of this material in ethanol yielded fine (like fairy floss) long, lemon coloured-crystals of SGS 10-2-1 which were sent to the University of Sydney for analysis.

Secondly, the filtrate was allowed to reduce its DCM content by natural evaporation, after which an equivalent amount of hexane was begun to be added.  The mixture surprisingly phase separated after the addition of a third of the hexane and a little more DCM was added to bring everything back to a single phase.  A silica column was then made up in a 2:1 mix of DCM:hexane and the concentrated, solvent-adjusted filtrate was eluted through the column - first with 2:1 DCM:hexane and then with 100% DCM.  TLC analysis of the eluted fractions indicated that the red-coloured target compound passed through the column with little retention. Stripping the column with ethanol to remove the residual red-coloured compounds revealed that all of the target material had been previously stripped by flushing with the DCM. The solvent in the solution of the target compound was allowed to evaporate, during which time a hexane fraction phase separated and was removed.  On standing for two days, the column chromatography purified red oil crystalised to provide a solid sample of SGS 10-2-2, some of which was sent to the University of Sydney for analysis.

Thirdly, it was apparent from TLC that SGS 10-2-2 was comprised of minor quantities of contaminants with a similar Rf to that of the main component and further purification was desirable to produce a purer sample for analysis  As the main component appeared to only slowly crystallise from the viscous crude oil, it was decided to attempt a low temperature recrystalization from DCM. A sample of solid SGS 10-2-2 was dissolved in a minimum quantity of DCM and placed in a freezer for two hours. No crystals had formed after this time, so a seed crystal was added to the solution and it was left undisturbed overnight.  Many small, orange, chunky crystals had formed by the following morning. Extraction of the crystals destroyed the nice appearance of the crystals, but eventually yielded almost free-flowing crystals of SGS 10-2-3, which were sent to the University of Sydney for analysis.  The supernatant from the recrystalisation from the analysis was evaporated to dryness (SGS 10-2-4) and also submitted to the University of Sydney for analysis.

Performed by: Milan Leonard, James Wood, Christopher Lai, Brandon Lee, Austin Zhang, Patrick Ngo, Dylan Siow-Lee, Charles Jameson, Malcolm Binns (Supervisor)

 


Purified fractions from SGS 10-2-crudeSample submitted to University of SydneyColumn Chromatography Purification of SGS 10-2-crude

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Re: Purification of SGS 10-2-crude by SGS
13th August 2016 @ 23:10
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