Chlorination, Etherification And Oxidation Of Alcohols Via Lewis Acid

In recent years, the notion of green chemistry and combinatorial chemistry were well established in chemistry, from the viewpoint of the environmentally beginning, it is significant and necessary to develop a transition metal-free catalyst system that exhibits low metal usage and less toxic reagents coupled with simpler reaction conditions and easier work-up procedures.The thesis reviewed the research progress of transition metal-free catalytic oxidation of alcohols from four sections. These include the oxidation of alcohols catalyzed by TEMPO, the oxidation of alcohols catalyzed by bromide, the oxidation of alcohols catalyzed by iodide, and the other transition metal-free catalytic alcohol oxidation systems.The main application of these transition metal-free catalysts in much chemical processes was emphasized. As a kind of transition metal-free catalysts, their prospect and the problems they faced were also discussed in this part.Chlorination of alcohols has been accepted as one of the most important and commonly used transformations in organic synthesis and development of such a procedure is still desirable in academia as well as in industrial research. For these multicomponent or too reactive reaction systems, some limitations keeps them away from industrial scale production. For instance, difficult product separation, large amount of waste disposal, expensive material cost, and low atom efficiency. Halogenated aluminates AlCl₃, applied as efficient chlorination reagent for hydroxyl groups of substitution alcohols is described. Primary and secondary benzylic alcohols could be transformed into corresponding aromatic halides with almost complete conversion and unique selectivity. As chlorination reagent, AlCl₃ has an incomparable advantage over others, such as low material cost, commercial availability as well as convenient product isolation. The etherification of alcohols catalyzed by BF₃·Et₂O is reported. Benzhydrol and its derivatives could be transformed into corresponding compounds in high conversions and selectivities.On the basis of green principle, here a simple, substrate selective and transition metal-free oxidation of alcohols catalyzed by brominated aluminum has been developed with green oxidant using 1,4-dioxane as the only solvent. Bromo anion proved to be efficient for the selective oxidation of alcohols using air as terminal oxidant under hight temperature or solar light. Bromo radical was generated in the first step, and then a series of reactions were occurred. After completion of the reaction, the anticipated aldehyde or ketones were detected. Primary and secondary alcohols could be oxidized to corresponding carbonyl compounds under mild conditions in short time. Aliphatic alcohols have a low activity in this oxidation reaction. Alcohols could be oxidized under natural weathering conditions without using any special equipment. We anticipate that this green procedure will make the protocol appealing to synthetic chemists.Porous tubular Al₂O₃ was synthesized through impregnation method using aluminum chloride hexahydrate as aluminum source and cotton as template. Microcrystalline cellulose was prepared by acid hydrolysis of cotton with concentrated sulfuric acid. This microcrystalline cellulose was used as template to prepare another type of tubular Al₂O₃. Stair-like porous Al₂O₃-AlBr_x(x = 1～5) could be prepared using hydrobromic acid as chemical tailor. The morphology, surface area, pore volume, pore size and characteristic of the Al₂O₃-AlBr_x(x = 1～5) could be controlled by using different concentration of hydrobromic acid. The same morphology Al₂O₃-AlBr_x(x = 1～5) obtained by tailoring the prepared Al₂O₃ with different concentration of hydrobromic acid also had different catalytic properties. As can be seen, Al₂O₃-AlBr_x(x = 1～5) obtained with higher concentration of hydrobromic acid has higher activity than lower hydrobromic acid. However, with increase in the concentration of hydrobromic acid, the morphology and pore structure ofγ-Al₂O₃ was tailored more and more serious. Considering all of these prognostic factors, the optimum concentration of hydrochloric acid during the tailored period was 3 mol/L. In the optimum reaction condition nearly 100% selectivity and conversion could be obtained in the oxidation of alcohols.