Chitosan-based catalysts

Preparation of the chitosan based catalysts for several hydrogenation reaction in the liquid phase... 

The goal of this work was the investigation of alternative methods of Pd/chitosan based catalyst preparation for several reactions of hydrogenation in the liquid phase. The work focused on the following directions ... 

In general, activities of chitosan based catalysts prepared by impregnation method in hydrogenation of unsaturated organic compounds were comparable with those of traditional heterogeneous catalyst (as calculated per 1 mole of metal). It should be noted that the chitosan pretreatment influenced very much the catalyst activity. For instance, immediate Pd deposition from alcohol solution on dry chitosan fibers or micro beads led to almost completely inactive catalytic systems, regardless of the metal content. On the other hand, metal deposition on chitosan micro beads or fibers preliminary swollen in water dramatically improved the catalytic activity. 

Preparation of chitosan based catalysts for several reactions of liquid phase hydrogenation... 

Different chitosan-based catalysts are compared in Table 3. The reactions were performed at 70°C due to the thermal stability of the catalyst. The first ones focus on the influence of the drying procedure in comparison with an uncatalyzed reaction and a known heterogeneous catalyst (Table 3, entries 1-5). Lyophilized chitosan (Cl) does not display any activity when the aerogel is as efficient as the functionalised silica (C3). This result illustrates the accessibility to the amino groups of chitosan in its aerogel form. 

Table 3 a-Monoglyceride formation catalyzed by chitosan based catalysts... 

Table 4 Phthalocyanine chitosan-based catalysts characterization...

Novel chitosan based catalytic systems for hydrogenation of unsaturated compounds in the liquid phase were prepared. The catalytic performance of the obtained systems depended significantly on the chitosan forms (as the micro beads or chitosan deposited on the mineral supports), their preparation method and chemical modification of chitosan as well. The obtained chitosan based carriers and catalysts were examined by transmission and diffuse-reflectance FTIR spectroscopy. 

Two procedures for metal introduction in chitosan base were used impregnation and coprecipitation. According to the first procedure the metal deposition on chitosan micro beads was carried out from aqueous and alcohol solutions of NazPdCU, HzPdCU, RhCb, Rh2(CH3COO)4, ZnS04 and Pb(CH3COO)2. Pd and Pb/Zn in bimetallic catalysts was deposited by subsequent precipitation. Pd-Pb (Zn) atomic ratios were 1/1. Metal contents in the resulting samples were 0.5 - 4%. 

Selectivity of Pd/chitosan based systems in 1,4-butynediol hydrogenation. Catalyst... 

With the aim of avoiding the use of phosphorus-based ligands, we had previously developed catalysts based on silica supported bidentate iminopyridine ligand systems. These coordinate Pd well, and the catalysts are active and stable in both the Heck (20,22) and Suzuki (21,22) reactions. Since the catalysts are based on the functionalisation of an aminopropyl groups attached to the silica, these are ideal candidates to translate to a chitosan-based support, and indeed this was achieved in a straightforward manner (Figure 2). 

Formation of chitosan films containing either silica particles or carbon was also successful, and incorporation of ca. 10wt% of silica or carbon was possible without significantly altering the robustness of the film. This observation indicates that it should be possible to prepare films from existing silica-based and carbon-based catalysts by forming a composite film on either glass or aluminum (or indeed other surfaces). 

It has been shown by IR-spectroscopic investigations which evidence on the appearance of new absorption bands after chitosan introducing, elementary analyses data. (N, occurrence in the samples, which quantity depends on chitosan nature and isolation conditions) It leads to significant increase of sorption capacity and specific surface of sorbents, which contain chitosan from silk waren chrysalises. Where as these parameters decrease for sorbents with chitosan from crabs. Evidently it is connected to more dense structure of the last one. It has been shown, that yield of sorbent on the base of PES and chitosan obtained by sol-gel method has depended significantly on such factors as components ratio, temperature, catalyst quantity etc. 

Sodium borohydride reduces disulfides to thiols, which can then be used to reduce nitro groups. Based on the redox properties of 1,2-dithiolane, lipoamide (17) was used for the selective reduction of mono-substituted nitrobenzenes to the corresponding anilines. Lipoamide (17) can also be immobilized on hydrophilic polymers such as polyvinylamine, polyethyleneimine and chitosan. These polymeric reducing catalysts can be recycled and are easy to separate from the reaction mixture. The system has been used to reduce nitroarenes to anilines. ... 

The enzymatic treatment of chitosan in the presence of tyrosinase and phenol derivatives produced new materials based on chitosan.91 During the reaction, unstable o-quinones were formed, followed by the reaction with the amino group of chitosan to give the modified chitosan. The tyrosinase-catalyzed modification of chitosan with phenols dramatically altered rheological and surface properties of chitosan. The modification with chlorogenic acid onto chitosan conferred the water solubility of chitosan under basic conditions.92 A new water-resistant adhesive was developed by the tyrosinase-catalyzed reaction of 3,4-dihydroxyphenethylamine and chitosan.93 Poly(4-hydroxystyrene) was modified with aniline by using tyrosinase catalyst.94 The incorporated ratio of aniline into the polymer was very low (1.3%). 

With its high surface area and the accessibility to the amino groups, chitosan aerogel appeared as a good candidate to play the double role of support for metal complexes and organic base. Silica supported metallophthalocyanine are efficient catalysts for the oxidation of aromatic compounds [139]. The immobilization of hydrosoluble metallophthalocyanines (MPcS with M = Fe or Co) on chitosan aerogels afforded new heterogeneous catalysts for the aerobic oxidation of p-isophorone [140]. 

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