Green Chemistry

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Green Oxidation of Borneol to Camphor

This lab converted borneol to camphor using a green oxidation. Sodium hypochlorite was used instead of the less “green” Jones reagent. Borneol was mixed with glacial acetic acid and oxidized with sodium hypochlorite to make crude camphor. The crude camphor was purified by sublimation. The final product was characterized by obtaining a melting point and inferred spectroscopy. The experiment was carried out to see if bleach could oxidize borneol and if it is greener than using a Jones reagent. Sure enough camphor was made with a 4.03 g of unsublimed camphor and 0.08g of pure camphor with a 2 % yield (in moles). No melting point or IR peaks were obtained. However, the literature value of the melting point is 177.0 °C and an IR peak from 1680-1750 cm-1 with no alcohol peak. Introduction:

Oxidations are used in organic chemistry to perform certain tasks in a laboratory. Visualizing how an oxidation reaction works in organic chemistry is a bit more difficult to point out than in general chemistry. But the concept is still the same. The idea of an oxidation reaction is to decrease the electron density around a carbon. Essentially, it is the loss of an electron around a carbon. To identify if an oxidation has occurred in organic chemistry the following could happen: replace a less electronegative atom with a more electronegative atom; replace a bond to hydrogen with a bond to oxygen; or replacing a single bond with a double bond by the loss of hydrogen. Oxidations are very convenient when trying to synthesize an aldehyde or ketone for this reason. Since there is less electron density around a reactive carbon center, the oxidation n of the carbon will be more positive. Usually a more electronegative atom such as a halogen, nitrogen, or oxygen replaces hydrogen bonded to the carbon. The oxidation states of these atoms are -1(and =O is -2) and +1 for hydrogen. So to balance these negative atoms the carbon must change to a more positive oxidation state. As a result the oxidation number of the carbon will increase when a more electronegative atom added or if hydrogen is lost.

For an oxidation reaction to occur chromium based reagent can be used. There are two types of chromium based reagents that help achieve the oxidation, Jones and PCC. These are used to convert an alcohol to either an aldehyde or ketone.

The Jones reagent is H2CrO4. This reaction is wet, i.e. water is in the reaction vessel. The Jones reagent is generated by sodium dichromate, sulfuric acid (strong acid), and water. One mole of sodium dichromate makes two moles of Jones reagent. In an oxidation reaction the jones reagent is generated in situ. For example, in a Jones oxidation of a secondary alcohol the Jones reagent attached to the oxygen from the hydroxyl group to form a chromic ester intermediate which would look orange. The chromium’s oxidation number at this time would be +6. The chromium then attacks the hydrogen connected to the carbon. The final products are a ketone and Cr(IV) residue which would be a dark forest green. A Jones reagent will not undergo a reaction with a tertiary alcohol because no hydrogens are available for the Cr(+6) to attack. When a primary alcohol undergoes a Jones oxidation a carboxylic acid is form, not an aldehyde. Since it is a wet reaction, water in the reaction vessel will form the hydroxyl group to form a carboxylic acid.

Jones oxidations will over oxidize the final product so to avoid this situation another reagent must be used. PCC or the Collins’ reagent reacts in a dry vessel without the presence of water. PCC is generated by a strong acid (H+), ClCrO3-, and reacts in CH2Cl2 (not water). The outcome for secondary and tertiary alcohols reacting with PCC is the same as the Jones oxidation. The only difference is the product of a primary alcohol with PCC will be an aldehyde because no over oxidation will occur.

Once an oxidation has been achieved via Jones...
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