A Green Synthesis of
Camphor
Introduction:
The objective of the experiment is to oxidize a secondary alcohol, isoborneol to ketone camphor
and to determine whether the purity is at least 95%. Secondary alcohols can be converted to ketones
using very strong oxidizing agents such as chromic acid. However, there exists chromium compounds
that are known to be corrosive and generally harmful and pose as a legal disposal issue due to their
harmful nature.
In this experiment camphor will be prepared by oxidizing a secondary alcohol, isoborneol. An
environmentally friendly way to oxidize a secondary alcohol is by using bleach which contains 5.25% of
sodium hypochlorite. Adding small amounts of acetic acid facilitates the reaction by converting sodium
hypochlorite to hypochlorous acid (HOCl). This is the active oxidizing agent.
Oxidation of isoborneol is an exothermic reaction, in order to avoid the creation of side product;
the temperature should be controlled below 40 degrees Celsius. Extreme heat can lead to creation of
camphoric acid, so heat should be controlled by using the ice-bath as needed.
Enough sodium hypochlorite should be added to ensure that reaction has reached its completion.
When hypochlorous acid (HOCl) is present in excess, a small portion can be transferred to starch and
potassium iodide indicator paper and tested. The indicator paper should turn dark blue. Starch and
potassium iodide will oxidize iodide ions to iodine. Excess HOCl that remains after can be destroyed by
sodium bisulfite (reducing agent).
Camphor is very compact and its molecular structure is symmetrical which gives it the property to
change directly from a solid to a vapour when heated. Therefore, camphor can easily be purified by
sublimation technique. Sublimation is a phase change in which a solid phase passes directly into the
vapor without going through an intermediate liquid phase. Solids which have vapour pressure below
melting points can be purified by 1) heating the solid to sublime it 2) condensing the vapor on a cold
surface 3) scraping off the condensed solid. Sublimation is not a very accurate method as recrystalization
or chromatography. The advantages of sublimation technique is that solvent is not required and not too
much transferring is involved, so losses in transfer can be kept low, (John W. Lehman, pg 653).
Sublimation is the only new technique used in this experiment, other simple techniques like
cooling, temperature monitoring, mixing, addition, weighing, vacuum filtration, drying solids, melting
point measurement are also used in this experiment.
Results:
Mechanism:
Calculations:
Discussion:
The first step in the lab is to set up an apparatus for addition under reflux. This apparatus is
comprised of a separatory-addition funnel, claisen adapter & West condenser. Once the apparatus is
safely clamped, 1.96g of isorborneol was measured and mixed with 1ml of acetic glacial acetic acid in a
125-ml Erlenmeyer flask. To reiterate, the acetic acid is added to help facilitate the reaction and convert
sodium hypochlorite to hypochlorous acid (HOCl). After the acetic acid is added, 5 ml of bleach (NaOCl) is
added to the mixture and then placed underneath the previously erected apparatus. 20ml of NaOCl is
then placed in the separatory-addition funnel and slowly added to the mixture. The addition is in small
portions and the temperature is monitored so as to not allow the temperature of the reaction mixture to
exceed 50 degrees Celsius, this is a preventative measure to ensure that there’s no formation of
unwanted products such as camphoric acid.
The next step would be to test the reaction for excess oxidant. The oxidizing agent in this
experiment is HOCl, using KI paper it’s possible to test the solutions’ acidity. Because the solution is
acidic the paper will test positive; the iodine on the paper will oxidize and the paper will turn blue. The
opposite of this would be the paper turning white indicating a negative result; this is when the solutions
is basic or neutral. If the test is negative then NaOCl must be added to maintain an excess of HOCl. The
reaction reaches completion after 30 minutes (a white precipitate is formed) and it is at this point where
the amount of NaOCl is in solution is 22.5 ml. The solution is then neutralized by adding 3 ml of sodium
bisulfate. This is done to ensure that HOCl will not be found in the product.
Before filtration, the solution is cooled to 5°C, once this is accomplished vacuum filtration can
begin. At the same time the product is washed with cold water in order to remove excess reactants. Once
the product is dry it will appear as a solid white compound and will be inserted into a sublimation
apparatus. Camphor is known to sublimate from solid to vapour at high temperature. While going under
sublimation, camphor is condensed and collected and appears as a white-flaky solid. Once collected the
product is weighed to be 0.101 g and the melting point is recorded as 134°C. The mass of isoborneol/ kg
of camphor is found to be 17%.
The calculated percent yield is 5.3%, therefore, the reaction never reached completion this may
be due to not enough kinetic energy being supplied to the solution, the rate at which reactants collide is
increased and failure to do so leaves the reactants stationary. A consequence of this is a very slow
reaction. Also, since the reaction is kept at low temperature there is less free energy available in order to
reach the transition state. Since the mixture did not reach completion, during sublimation, large amounts
of isoborneol is found in the final product. Therefore, there exists a 25.1% difference in melting points, it
significantly lower than it should be due to impurities in the final product. However, since some of the
product was formed, product consisted of 83% camphor.
To conclude, the major step in this experiment is ensuring that the reaction goes to completion,
if enough energy is not supplied to the reactants the reaction will not go completely forward. This will
leave traces of reactants in your final product (impurities) and consequently lower the yield.