Synthesis of Methyl p-Bromobenzoate

Postlab: Now comes the real purpose of the experiment! You may have been the victim of sabotage! Someone (perhaps the instructor or a fellow classmate) has secretly been working to ensure that your experiment was not successful by intentionally sabotaging part of the procedure. Thus, you will now attempt to determine two things:

1. The identity of the person who is the saboteur. The results of everyone's experiments will be compiled and presented to you for analysis. If you can find someone who had a successful experiment, they could be the guilty party. If not, then the instructor is the guilty party.
2. What exactly was done to cause the experiment to fail? This will help you to think critically about the process of the experiment and give you some issues to address when discussing your observations and drawing conclusions.

Although this seems like a daunting task, there are several simple methods for determining the problem that exists with your experiment. It would be a good idea to focus on the starting materials to be sure that they are correct.

1. Sulfuric acid catalyst: Was this changed? Another acid (such as hydrochloric or nitric) would not affect the procedure but if the catalyst was not an acid then no reaction, or a different side reaction, could occur. A test with litmus paper would be a simple test to determine if the catalyst is an acid.
2. Methanol: Again, can you be sure that this was your alcohol or that you had an alcohol at all? This could also lead to no product or an entirely different product altogether. Use the IR spectrum, NMR spectrum, and/or mass spectrum that you will receive to analyze the alcohol.
3. p-Bromobenzoic acid: There is also room for error here. Is it really a carboxylic acid? Does it contain bromine? Is it para substituted? Again, changes in the identity could lead to no reaction or a different product. The spectrum (NMR, IR and/or MS) that you receive/obtain will again be helpful.

In the postlab discussion, you should indicate what was done to the experiment that caused it to be unsuccessful. You should also discuss how this change affected both the overall procedure and the final results (i.e. was the product a solid and if so, what was the melting point?) Upon receiving the experimental data for the entire class, you should also be able to identify the saboteur. Any person (including you!) who reported the correct melting point could then be the guilty party since their experiment was not sabotaged. If no one has obtained the expected results, then the instructor is the most logical culprit.

Background: This is an odd place to receive this information but here is the justification for this experiment. Although it was doomed to failure in most cases, the goal of this experiment was to demonstrate that much useful information could be obtained even from an unsuccessful experiment. Even a failed experiment does not have to be a complete waste of time and can provide a chemist with valuable information about what occurs during the reaction.

It is likely that in this experiment you faced a situation that most chemists encounter from time to time; the results of the experiment are not what you would have expected or predicted. Sometimes this results from a side reaction that was not anticipated. Other times, simple human errors can be the culprit. Bottles can be mislabeled or misread, leading to the addition of incorrect reagents. Impurities introduced by the experimenter or present in the starting materials may inhibit the reaction or cause a different reaction pathway to occur.

Regardless of the cause, analysis of the experimental results, whether they were expected or not, is vital to a full understanding of an experiment. If there was success, it is certainly important to have a complete understanding of the procedure so that the experiment can be replicated. If the experiment failed, it is important to discover why this happened so that history will not repeat itself costing time and money. This is an important skill to learn and it may be helpful to you in writing meaningful discussion sections in future reports as you consider the potential sources for error in other experiments.