We are trying to convert partial functional groups of polyamidoamine (PAMAM) dendrimer from NH2 to COOH followed by the usage of succinic anhydride. Couple literatures mentioned that they removed methanol (storage solvent) and proceeded synthesis, however some other literatures did not mention about this. I'm curious if removal of methanol is preferred for further synthesis. I have tried both scenario, however could not find a huge differences and I would like know if removal solvent affects on synthesis.
Also, I would like to hear if anyone had experience on seeing color changes (become cloudy from transparent) during synthesis of dendrimer for converting NH2 to COOH using succinic anhydride. I dissolved dendrimer and succinic anhydride in DMSO separately and combined two solutions. Once two solutions combined, I had seen that mixture got cloudy from transparent and some day, it stayed as transparent though we mixed two solutions (dendrimer and succinic anhydride in DMSO). We assume that intermediates ,which are not likely to dissolve in DMSO, possibly formed. I appreciate any sharing experiences on seeing cloudy colored solution during synthesis or any suggestions/thoughts on this experiment.
Dear Suji Lee, the alcohol is removed because it may reacts with both NH2 and COOH groups, mainly at high temperature. The cloudy state, yes it may be attributed to partial initial insolubility due to inhomogeneity between the different compounds. My Regards
Abdelkader BOUAZIZ Thank you so much for suggestion. I have follow up questions, do this cloudy state possibly indicate the synthesis is incomplete?
I set two sets of the synthesis under same conditions (temperature, equivalence of materials), however one vial turns into cloudy state within 1 min and the other vial stayed as transparent. Could this phenomenon result from stirring condition (thought its minor)? Thanks
No thanks. One think you should check under the conditions you are dealing with is the possible oxidation of DMSO by Swern, Kornblum oxidations or any other possible reactions. My Regards
I think that the cloudy state is a salt of partially reacted PAMAM with itself. During reaction of anhydride with PAMAM intermediates occur which contains amino groups and acid groups, The salt formation leads to a physical crosslinking and for this reason precipitation. A possibility to avoid this salt formation is to add the PAMAM slowly to the solution of the anhydride so that there are nearly no free amino groups. Perhaps the DMSO can be replaced by a more innocent solvent like THF, dioxane, acetonitrile or DMF. Methanol can react also with the succinic anhydride resulting in MeOOC-CH2-CH2-COOH but the amino group is much faster in reaction with the anhydride so that the alcohol content is not very important.
Burkhard Koehler Thank you for the suggestions! I reset the experiments by adding the PAMAM slowly. It looks like, at some point (or at some ratio between dendrimer and anhydride solution), clear color converts to cloudy state. I will try to change solvent after seeing the result from experiment. I will keep posted.
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