Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: kriggy on April 23, 2015, 11:20:34 AM
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Hi there,
I did an reaction (N-acylation of isatine with acetanhydride with no base) that is from organic syntheses (Organic Syntheses, Coll. Vol. 3, p.456 (1955); Vol. 28, p.70 (1948).) so it should work without any troubles.
Anyway I already perfomed this reaction in the past and everything was ok however today I run into a problem: I did an TLC which clearly showed that there is no starting material present and only product is in the reaction and did the workup (cool to RT, filter and wash with ether). The color of product was right (dark green, starting material was red) however the HPLC shows that there is basicaly only starting material and not my product. I have no idea what is going on since other analysis that are performed on that HPLC mashine are fine.
Any ideas?
btw heard that TLC is more sensitive that UV/VIS detectors in hplc systems, is that right?
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What was the eluent (mobile phase) in TLC and what in HPLC?
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TLC was hexane:Ethyl acetate 1:1 and in HPLC its acetonitrile water gradient starting from 80:20 water:ACN to 20:80 water:ACN. The separation in TLC was real good (product about 0,9, starting material about 0,5)
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What about hydrolysis in the column?
Although amide hydrolysis is difficult, isatine is relatively sensible to hydrolysis (please, take a look to the literature). Remember that you have high pressure, may be buffers or remaining trace of buffers and C18 silanes (static phase) or similar that sometimes behave as surfactants.
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Could be its just weird that it didnt happen before. Thanks for advice, I think I will run NMR to be sure