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
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    $\begingroup$ @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
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    $\begingroup$ @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.

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  • $\begingroup$ 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

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