This paper reports the synthesis of hexamethylenebisacetamide (HMBA) without organic solvent or gas protection via amide exchange reaction of hexamethylenediamine (HDA) with CH3CN and H2O catalysed by CuO. The authors report the method to be more efficient than previous methods as “Herein, a simple and efficient copper catalyst was used to replace noble metal catalysts in the reaction of HDA, CH3CN and H2O without organic solvent or gas protection, with an isolated yield of 96%”. The selectivity for the synthesised products recyclability of the CuO catalyst was also investigated by the authors.
The Reaction of Interest:
- The authors have divided the whole study into parts. The first part was the selection of the catalyst for HDA to HMBA conversion. As indicated in Table 1, the selectivity was the predominant factor for choosing the catalyst as most of the copper based ones showed activity that was easily replicated. The activity of Cu(NO3)2 was also tested along with the reported catalysts. It performed much better than most of the ones tested by the authors with conversion of 96% and selectivity 90% but was still below that of CuO.
- The second aspect considered, was the recyclability of the catalyst. Herein, the effectiveness of CuO was found to be significantly higher than others. Cu(NO3)2 was not found to be as suitable since it could not be recovered.
- The third parameter evaluated by the authors was the feasibility of similar reactions to produce different diacetamides from different diamines, including aliphatic diamines (linear chain and cyclic diamines) and aromatic diamines. The results listed in Table 2 were replicated with all the amines and confirmed the findings of the authors. The results with OPDA were certainly negative with respect to the desired product as the benzimidazole formation was found to be almost 98%.
- The fourth criteria investigated by the authors was followed and results were found to be in favour of HDA, CH3CN, and H2O in molar ratio 1:3:6 for effective catalysis.
- The overall selection of procedure and catalyst was very good and there is not much scope for further modifications since the product yield, selectivity and recyclability of the catalyst is very good. The only area which can be modified slightly is by using Cu(NO3)2 as catalyst which will make the reaction proceed at room temperature and in about 120 minutes. The downside of that is the non-recoverability of catalyst, but this modification can be used in some specific need.