In this experiment, your goal is to separate and identify two solid organic compounds - an alcohol and a ketone.When you come to lab, you will be given a vial which contains a 1:1 mix of a solid alcohol and a solid ketone. Column chromatography is the method that you will use to separate them. Before you can do the column, you need to determine which solvent system will give optimal column separation; this solvent system is determined by running a series of TLCs in different solvent systems. Once separated, each compound is identified by matching its melting point, IR, and NMR with that of known compounds.
This experiment hones your techniques in column and thin-layer chromatography: if you do not do these procedures properly, the compounds will not be separated. Once you have separated the compounds, identifying them is a puzzle for you to solve. The melting point, IR, NMR, and even appearance of each compound are clues about their identity. We provide you with a list of possible unknown compounds. (This situation reflects some real-world organic laboratory synthetic situations, since often a chemist is working in a scheme and has a pretty good idea of the identity of an isolated compound.) When you believe that you have properly identified each unknown compound, you will write supporting arguments for your compound assignments in a 1-2 page paper. Write the paper as if you are "convincing" someone else that the compounds are indeed the ones you state that they are.
Two lab periods are scheduled for this experiment. During the first lab period, run TLCs of the mixture to determine the ideal solvent for separation. During the second lab period, separate the compounds by microscale flash chromatography (this procedure is illustrated below; also review the section on column chromatography). If time allows during the second lab period, take melting points and run IRs of the separated compounds; if not, you can finish gathering the data during spare time in subsequent labs. Note: The unknowns are solid compounds, so you need to use the thin-solid film method of sample preparation for IR.
For each separated unknown:
FT-IR Analysis
Prepare the sample as a thin-solid film. Briefly: dissolve a few crystals in a few drops of acetone, pipet the solution onto a single IR plate, allow the solvent to evaporate, and then place this single IR plate in the spectrometer and run the spectrum. Please see this spectroscopy page for a detailed procedure.
Print a copy of your spectrum. Then, click on the "search" button and the computer will search the database for potential matches for your compound. Print the information from the search.
Using all or some of this data, determine the identity of each of your unknown compounds, and argue your assignments in a 1-2 page paper.
