Identifying a Constituent of Panacetin

Rachel Kaufman

Friday PM

Experiment #3: Identifying a Constituent of Panacetin:

09/22/2016

Data and Results:

Mass of Unknown Before Purifcation: 1.868 g

Mass of Unknown After Purification: 1.040 g

Mass of Water Used: 22.3 mL

The purified unknown constituent was white and crystallized in appearance. It looked physically similar to the structure of crystallized sugar. The constituent was sticky when wet—it stuck to the filter paper after recrystallization. However, when it was dry it was coarse and flaky.

Melting Point Range: 115˚C-132˚C

Phenacetin Melting Point: 135˚C

Acetanilide Melting Point: 114˚C

Discussion and Conclusions:

The objective of this experiment was to determine the unknown component of Panacetin from experiment 2.  In this experiment I was not able to accomplish the objective because my unknown sample was not pure—it most likely contained some excess aspririn.

[pic 1]

Based on the extremely low amount of water used and the initial temperature at which my unknown began to melt—I was under the impression that the unknown was acetanilide. However, the correct identity of the unknown was phenacetin. The volume of water needed to dissolve the unknown should have been higher, which was the first giveaway. The second giveaway was the extremely wide range in melting points. The range in melting point typically should only be a few degrees while mine was greater than 15 degrees. Moreover, since the unknown was phenacetin the melting point should have been around 135˚C. When an impurity is found in a compound it typically lowers its boiling point. Hence, there was an impurity in my unknown and it makes sense that it was aspirin.

There is one particular source of error that could have caused my unknown to be impure. In experiment 2 when I separated the dichloromethane from the sodium bicarbonate, it is possible that some of the top layer leaked into the bottom layer meaning that when I later filtered the solution using vacuum filtration, my precipitate contained trace amounts of aspirin. This would also explain why my percent yield in experiment 2 was greater than 100%.

References:

Lehman. John W., Multi-scale Operational Organic Chemistry: A Problem-Solving Approach to the Laboratory Course. Second Edition, New Jersey: Pearson Education Inc., 2009.

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