Organic Chemistry

Rick Politician August 1, 2005 Identifying Unknown 29E Purpose: This lab aimed to introduce us to the "real" world of science, where not everything has a straightforward answer. We were encouraged to think on our own and come up with solutions to the problems that we encountered. By utilizing the skills we have learned in our previous chemistry and organic chemistry labs, we were to pinpoint our compound from a list of a couple hundred possibilities. Process of Discovery and Results: The first experiments I did involved using my innate senses of sight and smell. My compound seemed to contain leaf like crystals of a white compound. The scent of the compound was semi-strong, but I do not have a developed sense of smell and could not match the scent to a group of compounds I had previously smelled in lab. The second experiment I ran was to determine a melting point for my unknown. The melting point is an excellent tool for narrowing down the list possible compounds that my unknown could be for two reasons. First, each compound has a specific melting point that is different in a statistically significant way from most of the other compounds. That is, even including an error of plus or minus 10 degrees Celsius still allows one to eliminate around 90% of the possible unknown identities with a strong degree of confidence. The melting I took was 53.5 - 56.3 degrees Celsius. Adding the plus or minus 10 degrees Celsius, my range of melting points became 43.5 - 76.3 degrees Celsius. Appendix 1 of our lab book contains the tables of possible unknowns and shows each compound's melting point. The next experiment I conducted was a solubility test. This test has the potential to significantly narrow down the list of possible unknown compounds to certain functional groups. First, I added water to a small sample of my unknown in a test tube. The unknown crystals spread out and seemed to float on top of the water. Similar results were achieved in the solvent NaOH, HCl and H2SO4. My compound did not dissolve in the water, which told me that my substance was not polar and probably not intermediately polar either. NaOH is strong base and would indicate that the unknown is an acid if the unknown dissolved in the NaOH. If my unknown had dissolved in the hydrochloric acid, that would have indicated a base, especially an amine group. Even if my unknown group is insoluble in HCl, the unknown still could contain an amine that is substituted with two or three benzene rings. Sulfuric acid is last solvent that I used on my unknown. Sulfuric acid dissolves neutral compounds, but not does affect inert compounds. My unknown was slightly soluble in sulfuric acid. It took approximately 5mL of sulfuric acid to dissolve 0.5grams of my solution over a 2 minute time. This meant my compound had inert components, as well as reactive components that reacted with the H2SO4. The Beistein Test was the next experiment ran on my unknown. This experiment tested for both halides and aromatics. A halide was indicated by a green flame when the compound was burnt while an aromatic was indicated by sparks and soot. This experiment was less conclusive since the results were more difficult to evaluate. For instance, copper wire used to suspend ones unknown over the flame also burned green after being oxidized. Also, the experiment took place in the lab hood and any soot produced would quickly be sucked up through the hood. Because of this ambiguity, I ran this experiment 6 times. I found no green flame, but did find sparks and soot in 5 of the 6 experiments. Therefore, with some certainty, I determined that my compound contained aromatics At this point, I looked at my experimental results and synthesized a list of possible compounds. The Beistein and solubility tests indicated an aromatic ring. The solubility test also indicated that there was some sort reactive functional group in the molecule. I had the option at this time to run experiments that tested for specific functional groups until I found which ones were parts of my unknown, or use the IR to identify the functional groups. Running an IR is less expensive, faster and can indicate many functional groups with the one test. Using the IR I can identify a few compounds that my unknown probably contains. At that juncture, I could specifically test for individual functional groups indicated by the IR to gain more conclusive data. My IR spectra contained a double peak near 1500 to 1600, and a single peak around 3000. This peak indicate an aromatic ring and reinforce my previous experimental results. There was also a peak around 3400. This peak indicated either an OH or NH2 group. I compared this data with my melting point data. According to Appendix 1, there were no aromatic alcohols, aromatic carboxylic acids or phenols with melting points in my range of 43.5 - 76.3 degrees Celsius. Therefore, I determined my unknown must be aromatic amine. In Appendix 1, there were six potential primary amines and two potential secondary amines that fit into my melting point range. I also knew from my solubility test with HCl that my compound was not a primary amine since a primary amine with one benzene ring would have been soluble. Therefore, my compound had been narrowed down to the secondary amines diphenylamine and N-phenyl-1-napthylamine. I looked both of these compounds in The Handbook of Chemistry and Physics to see if I could gain any new valuable information about the two complexes. Diphenylamine was described as looking like leaves (which my unknown did). The handbook's statement regarding diphenylamine also matched that of my unknown. When I looked up N-phenyl-1-napthylamine in the handbook, it stated that this compound was slightly soluble in water. From my solubility experiments, I found my unknown to be insoluble in water. This information led me to ruling out the N-phenyl-1-napthylamine. From the experiments and research I have conducted, I would conclude that my unknown is likely to be diphenylamine. To reinforce this prediction, a NMR or mass spectrometer experiment could be employed. An NMR would provide me with information regarding the functional groups present in my unknown and their relation with one another. Using a mass spectrometer would indicate the mass of the unknown and, thus, how many aromatic rings it has. I could also look up the mass spectras of diphenylamine and N-phenyl-1-napthylamine online. If either of their fragmentation patterns (fingerprints) matched that of the mass spectra I got from testing the unknown, that information would allow me to discern which compound was my unknown.