Preparation Of Chitosan Supported Metal Ions And Its Application In Catalytic Study

Chitosan is a natural biopolymer with abundant amino and hydroxy groups which play an important role in coordination between chitosan and metal ions; in addition, the amino of chitosan molecules was of great help in the reduction and stabilization of transition metal ions. As an excellent heterogeneous catalyst supporter, the poor solubility of chitosan in most solvents (include water or common organic solvents) guarantees the stability of the chitosan-metal complex in the reaction, the recycled catalyst could be used and the loss of precious metals could be avoidable.First of all, the comments of chitosan, MCRs, propargylamines and the reduction of 4-NP were all reviewed in this paper. By reviewing previous references, chitosan-metal complexes had been reported as heterogeneous catalysts in some research work. However, to the best of our knowledge, there are no reports about chitosan-supported Zn for the synthesis of propargylamines and chitosan-Au nanoparticles complex for the reduction of 4-NP.With the excellent capacity of coordinating with transition metal ions, Chitosan-Zn complex was obtained as a heterogeneous catalyst for synthesizing propargylamines. In an effort to develop an optimal catalytic system, various reaction conditions were studied . The one-pot reaction of benzaldehyde (1 mmol), piperidine (1.2 mmol), phenylacetylene (1.3 mmol) and toluene (3 mL) was selected as the model to synthesize propargylamines. Without any co-catalysts, the reaction was carried out under mild conditions and the catalyst was tolerant to EDG, EWG, sterically hindered substituents of aldehydes, and acyclic amines. Via a C-H activation, Chitosan-Zn behaves as an efficient heterogeneous catalyst in the three-component reaction of aldehydes, terminal alkynes, and amines to afford the corresponding products in good to excellent yields (60%-90%).Also, the chitosan-Au complex was prepared for investigating the reduction of 4-NP. Since chitosan could reduce Au(III) to Au(0) under mild condition by itself, no environmental toxicity or biological hazards (for example, NaBH4) was needed to introduce to the reaction. Through control experiments, we had come to a conclusion that the chitosan-Au complex had higher catalytic activity on which the Au nanoparticles were reduced moderately by chitosan itself. In contrast to previous reports about the reduction of 4-NP by Au or Ag catalysts, our chitosan-Au complex had a higher TOF(Turnover Frequency).In summary, chitosan-Zn complex and chitosan Au nanoparticles were good heterogeneous catalyst which were easily prepared, recycled with high catalytic activity, and high TOF.