I do an esterification reaction between a hydroxyl-containing material (lowest Pka is 4 ) and a carboxylic one (has long alkyl chain) using DCC and DMAP, knowing that the product would be amphiphilic in nature.
Acetic acid or bicarbonate washed reaction mixture were compared to the reaction mixture using TLC (figure attached). DMAP spot has brownish-purple color upon pigmentation by Iodide. DCC spot has Rf value of 1.
what is the explantion of TLC results; is there a product, why the red spot disappeared after more reaction time, could the blue spot be the product ?
Better experimental conditions: carboxylic acid 2ekv, DCC 2.1ekv and DMAP 2ekv in DCM or acetonitrile, time TLC after 1h then 24h and 48h.
The included TLC looks somehow strange to me (OH component more polar than COOH ?); it seems that without the exact structures of the starting material(s) and reaction conditions the discussion and possible recommendations will have very little value ...
If Steglich's esterification fails, larger amounts of reagents must be applied, so my recommendation remains. Of course, it would be good to know the exact structure of the starting material and whether the reaction was carried out with minimal amounts of reagents (DCC and acid; 1.1 eq) and DMAP only as a catalyst (10-20 mol%). A carboxylic acid with a long chain goes above OH that's right.
Explanation of TLC results: Acetic acid or bicarbonate washed reaction mixture (after 90hrs) shows that you have water soluble possible product (blue spot) so avoid extraction and evaporated reaction with silica then purified with column. Unfortunately, large spots from acid and DCC may mean that the reaction did not proceed as expected.... therefore, if the blue spot is not a product, better experimental conditions must be applied.
Goran Benedeković thanks for your helpful response
you are right regarding COOH has long alky chain, further it has succinate moiety with free carboxy end, while the OH reactant has a primary OH, secondary OH, and two enolic hydroxyls
the equivalance was employed in this reaction is 1COOH:1OH:2DCC:10%DMAP
i am planing to do column chromatography
Regarding the equivalence, i performed the same reaction with higher equ. of reagents (1:1:4DCC:2DMAP), two spots only appeared on tlc, lower spot that pigments purple as DMAP and a solvent frontline spot; cospotting of OH with DMAP shows the same LOWer spot, so i thought that high DMAP eq.# could interact with the acidic OH reactant and prevents the reaction.
Article Synthesis, antiproliferative activity and SAR analysis of (−...
The Steglich method of esterification is not good for polyhydroxy compounds because of the possible migration and decomposition of the intermediately obtained primary ester. Steglich also failed in my cases on trihydroxy substrates. See my paper for compound 11. It's good that you said you have a polyhydroxy compound so now your problem is clearer.
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