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A Possible Resolution to Conventional Oxidation Methodology Problems

** 4.1 Use of Molecular Oxygen as a Reagent **
One of the methodologies that resolve heavy-metal waste problems is aerobic oxidation where O2 is a terminal oxidant. Our planet’s atmosphere is filled with air containing approximately 20% of molecular oxygen in its system. Also, the only bi-product of the oxidation of alcohols is H2O. This means the use of O2 is very economically prudent but also highly environmentally friendly.



4.1.1 Use of Catalyst
The use of molecular oxygen or the atmospheric oxygen is very appealing. However, the oxidation capability of oxygen is not strong enough to use alone in the system. With this type of oxidation, catalysts are combined to accelerate the reaction.

4.1.2 Choice of Catalyst
Recently transition metals such as ruthenium, palladium, copper, cobalt, and vanadium have been exploited and researched for the catalysts in oxidation of alcohols, however, these catalysts require large amount of transition metal and/or co-catalysts in its reaction. According to Mizuno et al., Ru/Al2O3 was chosen as a catalyst in this system for its reasonable cost, and commercially availableness. This catalyst is reusable for more than seven cycles. Catalytic cycle of Ru-catalysed oxidation of alcohols is presented below. Dr. Mizuno first presents this catalyst in 2003 **.





4.2 Batch Process vs. Continuous Flow Process
 Aerobic oxidation reaction is virtually never used in large-scale industry because they use a multi-use stirred batch process reactor that is unsuitable and hazardous to perform highly explosive catalyzed aerobic oxidation.

 However, this concern is now resolved by using the continuous flow process, also known as flow chemistry. Also continuous flow reactors enable reactions to be performed with an unprecedented level of control. Some examples are the control of pressure of reagents. Because the flow reactor enables to work O 2 in a higher pressure (5 to 25 bar) then batch reactor (0.2-3 atm), the reaction rate was significantly enhanced to give comparable results to batch processes in much lower reaction time as seen in figure 4.4, figure 4.5, and figure 4.6.





4. 3 Industrial Use of this Methodology
This methodology can be used in pharmaceutical industries that require safe, delicate synthesis of aldehydes and ketones.

4. 4 Future Discussion and Improvement
<span style="display: block; font-family: Georgia,serif; font-size: 13px; text-align: justify;">There are several improvements and exploitation that can be made, such as: <span style="display: block; font-family: Georgia,serif; font-size: 13px; text-align: justify;"> -molecular oxygen without additives in water -reaction without use of solvent <span style="display: block; font-family: Georgia,serif; font-size: 13px; text-align: justify;"> These methodologies are environmentally and technologically the most desirable methods however, efficient widely usable catalysts are unknown at this moment.