3 ‫ מתוך‬1 ‫עמוד‬
11 '‫ניסוי מס‬
Reduction-Oxidation Reactions (Redox).
1. 2-Methylcyclohexanone
OH
O
20g sodium dichromate dihydrate are dissolved in 60ml water. 27.2g concentrated
sulfuric acid are slowly added to the well stirred, ice cooled dichromate solution. The
solution is then diluted with water to a total volume of 100ml. The solution is chilled
in an ice bath for at least 15 min.
50ml diethyl ether and 11.42g 2-methylcyclohexanol are placed in a 500ml 3-necked
flask. The flask is fitted with a reflux condenser and a dropping funnel. The flask is
cooled in an ice bath for 15 min. 50ml of the cold dichromate solution is added
dropwise through the dropping funnel over a period of 5 minutes (calculate what the
rate must be) while the contents of the flask are efficiently stirred and cooled with an
ice bath. The rest of the dichromate solution (which was kept on the ice bath) is also
added dropwise at the same rate as the previous 50ml. When the addition is complete
the mixture is vigorously stirred for 20 min. A saturated bicarbonate solution is added
slowly (copious foaming may occur) until the aqueous layer is neutralized. The
organic layer is separated in a separatory funnel, and the aqueous layer is extracted
with two 30ml portions of diethyl ether. The organic phases are combined and
washed once with 5% aqueous sodium carbonate and then with water. The ether
solution is checked for presence of peroxides with potassium iodide paper, dried with
magnesium sulfate for 5 minutes and one third of the solution filtered into a small
distillation flask. The ether is quickly distilled (you may use the rotavap for this part
if you wish), another third of the solution is filtered to the flask and the ether
evaporated. Finally the last third is filtered, the ether evaporated and the residue is
then carefully distilled under vacuum to yield pure 2-methylcyclohexanone (b.p.
1650C at atmospheric pressure).
Notes: Be extremely careful when handling concentrated acids, especially sulfuric.
Hydration of sulfuric acid is extremely exothermic, use caution during the dilution
step. In case of spills on any part of the body wash immediately with copious
amounts of water, then with a saturated sodium bicarbonate solution then with water
again.
2. 2,6-Dimethylcyclohexanol (mixture of isomers)
O
NaBH4
OH
Dissolve 1g 2,6-dimethylcyclohexanone in 20ml ethanol. Add 0.2g sodium
borohydride and stir the solution for 10 min. Dilute the solution with 20ml water and
extract the reaction mixture with two 20ml portions of hexanes. Dry the combined
organic phases with magnesium sulfate, filter and evaporate the solvent. Take a small
amount ~10mg and send it to analyze by NMR. Prepare a silica gel column and try to
11 ‫ניסוי מספר‬
3 ‫ מתוך‬2 ‫עמוד‬
separate the isomers. Use TLC to help you choose which solvent mixture to use for
the column, you may use a mixture of ethyl acetate with petrol ether. The R f of the
highest running compound should not exceed 0.4. You may need to use iodine to
develop the TLC to see your compounds clearly after the reduction step. Compare the
NMR sample of the original mixture with your final products after purification by
column chromatography. Think about which isomers you are (at least) theoretically
able to separate and which not.
3. Heptanal
H
N
• CrO3Cl
O
OH
Reference: Experimental Organic Chemistry Principles and Practice; L. Hardwood
and C. Moody. Pages 520-522.
Notes: You will receive the necessary amount of PCC so you only need to do the
oxidation step.
When you filter the solution through the Florisil (or silica gel) pad make sure to use a
büchner funnel and work as quickly as possible. If the heptanal remains in the silica
gel for a long time it might react (think about which reactions may happen).
Use the coil heating mantle to heat the liquid quickly and distill your compound
under vacuum to minimize decomposition of the product.
4. 3-Aminoacetophenone
O
NO2
O
NH2
Reference: Experimental Organic Chemistry Principles and Practice; L. Hardwood
and C. Moody. Pages 492-494.
Notes: You may do experiment No. 5 if you have enough time. It is also a reduction
reaction of 3-nitroacetophenone, but it gives a different product (chemoselective
reaction).
5. 1-(3-Nitrophenyl)ethanol
OH
O
NO2
NO2
11 ‫ניסוי מספר‬
3 ‫ מתוך‬3 ‫עמוד‬
Reference: Experimental Organic Chemistry Principles and Practice; L. Hardwood
and C. Moody. Pages 492-494.
Notes: You may do experiment No. 4 if you have enough time. It is also a reduction
reaction of 3-nitroacetophenone, but it gives a different product (chemoselective
reaction).
11 ‫ניסוי מספר‬