It is a material 73% pure and I want to achieve more than 98% purity. I put 20g in an elution column (60cm X 4 cm paked wih KIESELGUR), elute with CH2CL2:ACETONE (2:8) SOLVENT WAS EVAPORATED BUT CRYSTALS did not form.
Hello Antonio,
You may find the attached to be useful.
Also, crystallization, while widely used in chemistry, is an art. Did you get a solid, non-crystalline precipitate? If so, I would dissolve it in a hot, pure solvent (maybe hexane with a minimal amount of acetone). Then let it slowly cool.
If there was no precipitate at all, then your compound probably is still on the column or has hydrolyzed to an even more water soluble compound.
Joe
Thank You Joe. I had run a GC/MS to TECHNICAL METHAMIDOPHOS it contains 5 main impurities with similar structures: 1. O,O-dimethyl phosphoramidothioate, 2. N- methyl homolgue of (1), 3. methamidophos N-methyl homologues, 4. O,O,O-trimethyl phosphorothioate, 5. O,O,S-trimethyl phosphorothioate. I did what you recommended me I get only 5% of a solid with a composition simmilar to technical material but with the compounds 1,3, augmented x 2. This is the first time I got solidified (christallized)material,then I am happy for your help.
Antonio,
You are working with a difficult mixture, not only are there a variety of homologs and isomers but you even have optical isomers present. Crystallization can be useful but sometimes it is impossible to remove all impurities that way. (See Radioisotope detectors for investigations on phenolic biosynthesis, JA Saunders, JD Olechno (1988). in “Progress in HPLC: Flow-Through Radioactivity Detection in HPLC”, Vol. 3. Ed. H Parvez, A Reich, S Lucas Reich, S Parvez, pp. 167-189. VSP Press, Utrecht, The Netherlands.)
Is your technical grade material in a carrier? Does it have any solvents or surfactants to help solubilize it for application? If so, these can often cause problems with chromatographic separations. I would eliminate them first. I would try the crystallization method to get rid of the excipients and see if you can get your mixture of semipurified compounds. That solid material can then be run on a chromatographic column. Did you use isocratic or gradient elution on your earlier attempts?
The other possibility is to load your technical material onto the column and then was with hexane or other solvents in which methamidophos is not soluble in order to get rid of the excipients (although many surfactants will not be eluted by alkanes).
Then start a gradient where you slowly increase the amount of acetone in the eluent. This might give you better separations.
You mention that by GC, there are 5 major contaminants in the methamidophos. How much methamidophos is present? Is the concentration of methamidophos much greater than the amount of any of the impurities in the mixture?
Best regards and Feliz Navidad.
Hello Antonio: Can you send me your e-mail address? Best regards, Dusan Berek
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