I'm trying to react a aromatic aldehyde with the blue toluidine dye wich has a NH2 group atached on the aromatic ring. I performed it in methanol with molecular sieves adding 5 drops of acetic acid. After more than 12 hours I have no observed spectral alteration on UV-VIs althouhg the TCL show a weak new spot. How can I proceed to obtain my imine?
Did you try reflux? Although you have NH2 group, its next to methyl group and its attached directly to aromatic ring, so its not gonna be as nucleophilic as a true primary amine.
https://pubs.acs.org/doi/suppl/10.1021/jo4002504/suppl_file/jo4002504_si_001.pdf
Check out this supporting information. They have an aniline with a methyl group right next to it like yours in TABLE S2 and they attack an aromatic aldehyde but only under basic conditions and reflux.
Lucas, How about adding a Lewis acid catalyst? Should you consider activating the aldehyde with a common Lewis acid?
Water is also an issue in your reaction. Try to see if the conditions used in the following article help.
S. Morales, F. G. Guijarro, J. L. G. Ruano, M. B. Cid, J. Am. Chem. Soc., 2014, 136, 1082-1089; http://dx.doi.or/10.1021/ja4111418
Gentlemen, from my experience with Schiff bases, the solvent must be dry and no acids can be added since they hinder the reaction and do not help it. Heating is a must to help drive off water from the intermediate and form the imine double bond. One more thing, aromatic amines are easily oxidized, so you should purify your amine first. You can work under inert atmosphere if necessary.
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