Overview

=**2. Catalysts, and their uses in the oxidation of alcohols to ketones and aldehydes** =

  toc

2.1 Properties of catalysts
A catalyst is a substance that allows kinetic barriers in reactions to be bypassed. This in turn allows the reaction to occur even at a lower temperature that would not have been possible before. Though the activation energy is lowered, the extent of reaction does not change, and there is no effect on the chemical equilibrium of a reaction because the rate of the reaction increases in both directions.



However, a substance can still be called a catalyst even if the substance is deactivated in a step, and regenerated in later step. The most important aspect of a catalyst is to have no net consumption. The general catalytic cycle can be described through a loop process as shown below.



Though a catalytic reaction can increase the rate of a reaction, it still is dependent on kinetic properties. Therefore, the effectiveness of a catalyst is determined by the frequency of the catalyst contacting the reactants. In addition, though catalysts are not consumed in the immediate reactions, side reactions are possible, and thus a great amount of research and care must be taken into account for the selection of a catalyst.

**2.3 Flow Chemistry**
Due to the exothermic nature of certain oxidation processes, flow chemistry is used to combat those issues and allow previously uncontrollable processes to be completed.

<span style="font-family: Georgia,serif;">A general use for flow chemistry can be seen below :

<span style="font-family: Georgia,serif;">media type="youtube" key="A7Gb7sF4sjk" height="480" width="853" align="center"

<span style="display: block; font-family: Georgia,serif; font-size: 150%; text-align: justify;">2.4 Oxidation of alcohols
<span style="display: block; font-family: Georgia,serif; text-align: justify;">The oxidation of alcohols to aldehydes and ketones have traditionally been done through the use of inorganic oxidants such as Cr(VI) reagents. However, due to their inefficiency and difficult waste management (requiring difficult separation of products), research in catalytic oxidation processes has been done recently to combat these issues.

<span style="display: block; font-family: Georgia,serif; font-size: 150%; text-align: justify;">** 2.5 The reason for oxidation of alcohols to aldehydes and ketones **
<span style="display: block; font-family: Georgia,serif; text-align: justify;">The uses of aldehydes and ketones are extremely important in the creation of many different chemical compounds. Aldehydes are fundamental in the production of resins, plasticizer’s, detergents, perfumes and flavors, while ketones are useful in industry for their uses as solvents, polymer precursors, and pharmaceuticals.

<span style="display: block; font-family: Georgia,serif; font-size: 150%; text-align: justify;">2.6 General Production
<span style="display: block; font-family: Georgia,serif; text-align: justify;">The selective oxidation of alcohols to ketones and aldehydes is one of the most prominent reactions in organic chemistry, yet the production has traditionally been done using stoichiometric ratios of inorganic oxidants such as Cr(VI). The issue with using this method is that there is low atom efficiency and the product that is created requires an extra separation process that is difficult due to the nature of the product. The production of ketones and aldehydes is very complicated, but also extremely important so they are produced in large scale for all their many purposes. The production of formaldehyde alone is around 6 million tons per year, while butyraldyde has a production around 2.5 million tons per year. At the scale of which these chemicals are produced, it is very important to find ways to provide environmentally friendly methods of productions in order to minimize the waste and byproducts of these reactions.

<span style="display: block; font-family: Georgia,serif; font-size: 150%; text-align: justify;">2.71 Catalysts
<span style="display: block; font-family: Georgia,serif; text-align: justify;">The ninth principle of green chemistry is to use catalysts instead of stoichiometric reagents, and this is a prime example of its effects both in creating more environmentally friendly processes, increasing atom efficiency and making economic sense in application. By using a catalyzed oxidation process, environmental damage can be minimized due to the possible inert, non-toxic, non-volatile, insoluble and often-recyclable properties through using catalysts. These properties allow the product of these reactions to be easily separated and for the waste products to be safely disposed of. In addition, the oxidizing processes are based on the use of O­ 2, air, super-critical CO 2 and H 2 O2 which are generally green and rather inexpensive substances to obtain.

<span style="display: block; font-family: Georgia,serif; font-size: 150%; text-align: justify;">2.72 Flow Chemistry
<span style="display: block; font-family: Georgia,serif; text-align: justify;">Some of the benefits by combining the oxidization of alcohols to aldehydes and ketones through a flow process includes a lower thermal mass of the fluid used in comparison to the thermal mass of the system. This allows for more control over the temperature of the media faster and easier so that the exothermic reaction can occur safely in large scale production. Another benefit of using a flow reactor is the ability to control and introduce pressure into the system. With a pressurized system, any gasses introduced will be forced into higher concentration levels and thus allow for greater extent of reaction. Higher concentrations of gases also allow the catalyst to work more efficiently as there is higher chance for the reactant gas to be exposed to the catalyst being used. Finally, with a flow reactor, the product stream produces a much smaller amount than through a batch process that helps with the exothermic nature of the reaction, as well as any possible toxic and flammable properties of the product.