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Study On The Clean Oxidation Process In Ionic Liquids

Posted on:2011-01-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H ZhaoFull Text:PDF
GTID:1101360305998725Subject:Inorganic Chemistry
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The oxidation reactions, through which about 60% of chemical products are synthesized, are very important in chemical industry. However, they are conventionally carried out with stoichiometric amounts of inorganic high value metal salts such as potassium permanganate as oxidants in the volatile organic solvent. The use of such reagents leads to environmental and economic problems associated with recycle or disposal of the reduction co-products etc. From both economic and environmental point of view, the effective oxidation processes that use clean and inexpensive oxidants, such as molecular oxygen in the clean solvent is the most gratifying technique route. In recent years, some progress has been made for replacing the traditional oxidants with molecular oxygen and peroxide hydrogen. Unfortunately, the poor activity and the low selectivity were often found when using oxygen or peroxide hydrogen as the ultimate stoichiometric oxidant, which limited the application of them. The higher selective oxidation is one of the major challenges in the synthesis of fine chemicals and intermediates.The main contents in this dissertation are as follows:1. A novel aqueous solution-ionic liquid biphasic catalytic system was established for the oxidative degradation of chitosan under mild conditions. In this process, the environmentally acceptable and inexpensive molecular oxygen was first used as oxidant, the metal phthalocyanine was immobilized in ionic liquid as catalyst and the water as medium carriying the reactants and the products. Under vigorous stirring and heating, the reactants fully contacted the catalysts in the emulsion and chitosan efficiently degraded into the water-soluble materials. At the end of reaction, the catalytic system could be easily separated by simple decantation and could also be reused in subsequent runs without apparent change in activity. These characters are in favor of the elimination of pollution and the reduction of the economic cost in the large-scale production of the water-soluble chitosan derivatives in chemical industry.2. A novel homogeneous and recyclable catalytic system was applied in the oxidation of nitrotoluenes to nitrobenzoic acids. In this method, molecular oxygen was used as oxidant, the metal phthalocyanine immobilized in ionic liquid omimBF4 (water-immiscible at roomtemperature but water-miscible at >80℃) as catalyst and the alkaline aqueous solution as medium to carry the products. At the end of reaction, the catalytic system could be easily separated from the aqueous phase by simple decantation and could be reused in subsequent runs without apparent change in activity. The route was economical, environmentally friendly, compared to the conventional methods and could be readily applicable to large-scale oxidation of nitrotoluenes to nitrobenzoic acids in chemical industry.3. A new three-component catalytic system, water/ionic liquid/metal phthalocyanine complex, was studied for the oxidition of cysteine to prepare cystine. It was found that the water/ 1-n-hexyl-3-methylimidazolium tetrafluoroborate (hmimBF4)/iron (Ⅱ) phthalocyanine (FeⅡPc) system exhibited an excellent catalytic activity in the oxidition of cysteine. Cystine was obtained with 98% isolated yield for 12 hours at the temperature of 80℃. Further more, the catalytic system can be easily recovered and recycled in the following run without apparent reduction in catalytic activity.4. The indirect electrochemistry oxidation of benzyl alcohol could be carried out in the protonic ionic liquid methylimidazolium hydrogen sulfate with high selectivity and current efficiency. The indirect electrochemistry oxidation of methanol and other short chain aliphatic alcohols to their corresponding carbonyl compounds with protonic ionic liquid ethyl ammonium hydrogen sulfate as the reaction media can be efficiently performed under mild conditions. In this process, an initial electro-oxidation of hydrogen sulfate ion at the anode generated the active oxidative species of persulfate ion. Upon the oxidation of alcohols with persulfate ion, hydrogen sulfate ion was recovered and the substrates were selectively oxidized to their corresponding carbonyl compounds which could not be further oxidized to the carboxylic acids in the non-aqueous solution. In other words, the reaction only consumed alcohols and produced the corresponding aldehydes or ketones with the co-product of hydrogen gas in the electrochemistry oxidation of alcohols. Further more, the corresponding carbonyl products could be separated from the electrolyte solution by the refluxing method, and the electrolyte solution could be recycled without apparent decrease in activity. Thus, this approach avoids the problematic by-products and separation difficulty in the preparation of the short chain aliphatic aldehydes and ketones.5. Tunable bromination of naphthalene catalyzed by the ionic liquid of 1-n-butyl-3-methyl imidazolium bromide (bmimBr) are introduced to synthesize 1-bromonaphthalene (1-BN) and 1,4-dibromonaphthalene (1,4-DBN). Naphthalene conversion of 100% was achieved and the selectivity of 1-BN and 1,4-DBN was as high as about 100% respectively. Thus, naphthalene bromination can be tuned to produce 1-BN and 1,4-DBN in the same catalytic system just by changing the reaction conditions. Moreover, bromine atoms were able to totally transferred into products. As water was the only byproduct of this process, it was a completely 'clean' method for the selective bromination of naphthalene.
Keywords/Search Tags:green oxidation, ionic liquid, chitosan, degradation, nitrobenzene, cysteine, aliphatic alcohols, electrochemistry, naphthalene, bromination
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