Environmental+Concern

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**3. 1 Environmental Concerns in Synthesis of Aldehydes and Ketones from Alcohols**
There is no doubt that greening the oxidation of alcohols to aldehydes and ketones is a very challenging problem concerning chemical synthesis today. Currently, oxidation of alcohols is usually involved with inorganic oxidants that are relatively inexpensive, but produce heavy-metal side products that are highly environmentally hazardous. There have been a number of attempts and effort to replace stoichiometric oxidants with catalytic processes in the oxidation of alcohols.

**3. 2 Traditional Oxidation of Alcohols**
Most widely used synthesis process of aldehydes and ketones from alcohols is the conventional stoichiometric oxidation process that uses inexpensive chromium-based reagents such as pyridinium chlrochromate (PPC), pyridinium dichromate (PDC), or Jones reagents to synthesize aldehydes and ketones. These processes take place in large batch reactors, requiring the use of harsh solvents and oxidants.



PCC, PDC and Jones reagent are used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. However, the use of chromium-based reagents are controversial, as they produce heavy-metal waste and contain highly toxic chromium (VI) ions, a known carcinogen. The widespread industrial use of the chromium catalyst is a concern because it is known to damage the skin and bones of humans. Unfortunately we can not minimize the use of chromium if we wish to continue with this same process. In order to acheive a reasonable yeild, chromium must be supplied in an absolute minimum of stoichiometric amounts. However it is common in practise to supply large excess in order to increase the yeild.

 New methods of in-flow catalysis hope to eliminate the need for toxic reagents such as these.