In this work, fluorescein was incorporated with an equal molar of 1-chloro-4-nitrobenzene and double potassium carbonate (molar ratio), the solvent of this reaction is dimethylacetamide (50 ml for 5 g of fluorescein).

The solution was stirred in at 110 °C for 24 h, after that cooled to the room temperature and precipitated in cold water, but a solid, similar to potassium carbonate, remains at the bottom of the reaction vessel, and the efficiency is very low (25%). I don't know the cause of this problem.

This is the structure that I expected for first stage:

enter image description here

In the next step the solid that was obtained from the previous stage, incorporated with 10% Pd/C and methanol. 30 eq hydrazine monohydrate was added dropwise and the solution refluxed at 50 °C for 12 h. After that the solution was filtered to separated catalyst and the crystals of diamine was obtained, but the efficiency of this stage is very low too.

  • $\begingroup$ What did the tlc of the first reaction mixture look like? Did you lose the chloronitrobenzene?. $\endgroup$ – Waylander Jun 18 '19 at 16:05
  • 1
    $\begingroup$ @Waylander, Unfortunately, I did not use TLC to control the end of the reaction. $\endgroup$ – sara Jun 18 '19 at 16:23
  • $\begingroup$ Then you'll know better next time you run this. Can you post the structure of your required product $\endgroup$ – Waylander Jun 18 '19 at 16:34
  • 1
    $\begingroup$ @Waylander, thank you so much. I added the structure of the first stage's product. $\endgroup$ – sara Jun 18 '19 at 18:09
  • $\begingroup$ How effective was the stirring? Did you get evolution of CO2 during the early stages of the reaction? $\endgroup$ – Waylander Jun 18 '19 at 19:03

What I think is happening is that you are not getting enough mixing between your reagents, the solid remaning is unreacted potassium carbonate. I think you can reduce the amount of potassium carbonate you are using - you only need 1 eq as it is dibasic, and use finely powdered if you have access to it. Run the reaction more dilute with a more powerful stirrer (have you an overhead stirrer?) so that material does not stick to the side and follow it by TLC. If this does not improve the outcome I would consider using a strong organic base such as DIPEA or DBU in place of the potassium carbonate so that everything is in solution.

  • $\begingroup$ Could it be necessary to use a stronger solvent like DMSO? $\endgroup$ – sara Jun 21 '19 at 7:38
  • $\begingroup$ It might help. DMSO or DMF but I think the problem is not enough solvent and ineffective mixing $\endgroup$ – Waylander Jun 21 '19 at 8:37
  • $\begingroup$ If the amount of hydrazine monohydrate used to synthesize diamine is too high, what problems might it occur? $\endgroup$ – sara Jun 29 '19 at 10:46
  • $\begingroup$ Given that the procedure uses 30eq of hydrazine, I don't think using more will be any problem. It is decomposed by the Pd/C catalyst. If the reduction is going poorly, I would look firstly at the quality of the catalyst and secondly investigate alternative reduction conditions e.g. Ammonium formate, Pd/C in reluxing EtOH or iPrOH $\endgroup$ – Waylander Jun 29 '19 at 11:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.