I performed an Ulmann type reaction bewteen 2-pyridone and bromobenzene, with these reaction conditions in a schlenk tube:
- 0.3 eq CuI
- 2 eq of K2CO3
- 1 eq of pyridone
- 1.1 eq of bromobenzene
- DMF dry as solvent
- 130° C
During the extraction (DCM/NaHCO3 saturated solution) I observed a great amount of an unsoluble brown solid (both in water and organic phase), which promotes the emulsion formation during extraction. May somebody know what is this brown solid?
Hi, the Potential Sources of the Insoluble Brown Solid could be:
1. Copper(I) Oxide (Cu2O) or Copper(II) Oxide (CuO) Formation: The use of CuI as a catalyst under elevated temperatures can lead to the partial oxidation of copper(I) to copper(I) oxide or further to copper(II) oxide, especially in the presence of air or oxygen impurities in the solvent. These copper oxides are insoluble in both water and organic solvents and could contribute to the observed brown residue.
2. Polymerization or Decomposition Products: The high reaction temperature (130°C) and the presence of DMF (N,N-Dimethylformamide) can lead to side reactions, including the thermal decomposition of DMF or the starting materials, leading to the formation of complex polymeric or decomposed materials that are insoluble in the reaction medium.
3. By-products from Halide Impurities: Bromobenzene and even CuI may contain halide impurities that could react under the given conditions, forming insoluble materials. For instance, bromine-derived side products could potentially contribute to the formation of the observed residue.
4. Reaction of DMF with K2CO3: Under certain conditions, DMF can react with strong bases like K2CO3, leading to the formation of insoluble products. This interaction is less likely but can occur under specific conditions of temperature and concentration.
Thank you Phil Käding ! I performed yesterday the reaction in an extremely dried system and the quantity of the brown impurities was less than the first time.
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