The apparatus for the first portion was designed to measure temperature, add reagent dropwise, and prevent evaporation by keeping part of the flask cool. Our assembly of three-necked round-bottomed flask, thermometer (right), addition funnel (left), and West condenser (center) is shown below:
The flask was set in a heating mantle mounted atop a stirring motor.
The objective was to add approximately 150 mL bleach to the reaction flask of cyclohexanol and acetic acid over a period of 30 minutes...while maintaining a temperature between 40 and 45 degrees Celsius. Our biggest struggle during this reaction was staying within those boundaries. Fortunately, we picked up a few tips along the way that will help when we repeat this reaction with our own compounds.
We found that setting the heating mantle to level 20 (out of 100 - slightly ambiguous) and lowering the heat to level 5 once reaching the desired temperature range was the best method for regulating temperature. Increasing the addition rate of bleach is helpful in reaching this temperature range more quickly. Additionally, when the liquid mixture temperature exceeded 45 degrees, moving the flask to an ice water bath for no longer than ten seconds was sufficient to return to the temperature range without significantly dropping in temperature. (A temperature lower than 40 degrees could slow the reaction rate and lower percent yield of the final product.) After the 30-minute addition period, the mixture is left to stir for 20 minutes at maintained heat, during which time the solution forms a foamy, yellow-colored ring at the surface.
Another small set-back occurred when we realized that we didn't have the necessary saturated sodium bisulfite solution to neutralize the excess bleach. The solubility of sodium bisulfite crystal is 42 g / 100 mL, and we decided to prepare a 50-mL sample in a small flask by swirling. For the next run-through, we plan to prepare this solution during the 20-minute stirring period.
Adding thymol blue indicator turned the entire solution a golden yellow. About 17 mL concentrated sodium hydroxide were required to reach pH 9, at which time the solution had become royal blue in color.
For the second portion, a simple distillation apparatus was assembled, this time incorporating a Claisen adapter, a distillation head, and a small round-bottomed receiving flask:
The objective was to separate the organic cyclohexanone product by steam distillation. Interestingly, because so much water is produced during this reaction, an azeotrope of cyclohexanone and water forms with a boiling point of 95 degrees Celsius. This is primarily due to hydrogen bonding between the two compounds. Once this azeotrope is distilled into the receiving flask, solid sodium chloride is added to attract the water away from the cyclohexanone and form a more distinctive aqueous layer for separation.
Though this process should have been simple and straightforward, we encountered trouble during the drying process. Some salt remained in solution, so while the drying agent was effective in removing the water, the organic solution was not pure. We solved this issue by pipetting the liquid into a glass pipet stuffed at the bottom with cotton - the cotton allowed the pure liquid to seep through but captured the salt. After the liquid was transferred into a sample vial, we added more drying agent and left the product to sit overnight. We will characterize our product in the morning.
Overall, I am optimistic about tomorrow's results and have enjoyed the process thus far. I will be interested to see how the reaction proceeds when I test my own compound.
No comments:
Post a Comment