OChem Lab #6- Chromatology

Jesse Hofseth Rick Politician July 11, 2005 O. Chem 231 Lab #6 Write Up - Chromatography Results: The solvent used in this part in methylene chloride, a slightly polar solvent. Since likes move with the likes, the least polar solute would have moved farthest up the TLC plate. Thus, flourene is least polar, fluorenone has the intermediate polarity and fluorenol is the most polar. Our unknown's Rf is identical to that of fluorene. There are no other Rfs within .21 of fluorene, so we can identify the unknown with good certainty (assuming our experiment was run correctly). Methylene Chloride worked most successfully as it produced two dots in the mixture column, and that both of these dots corresponded to dots at similar levels in the benzil and benzoin columns. This supports the fact that the mixture contains both benzil and benzoin. The data suggests that fluorene and fluorenol are slightly polar like methylene chloride. Methanol and water are too polar to be a successful solvents. Hexane is too non-polar. Acetone has a good polarity, but both benzil and benzoin react too similarly to the stationary and mobile phases to differentiate which is which in the mixture. We did not use our hands efficiently enough to gather a 0 sec reading as the initial sodium borohydride was poured into the methanol solution. This data indicates that the fluorenone significantly reacted with the sodium borohydride to produce fluorenol between 15-30 seconds after the sodium borohydride was added. Conclusions: Chromatography is an extremely useful tool for chemists. By utilizing that fact that most compounds will react uniquely to the stationary and mobile phases, one can identify compounds present in a solution. Chemists also need to be aware of the importance of choosing the correct solvent for TLC. Solvents too polar or ones near the neutral end of the spectrum may not attract the unknown compounds into the mobile phase. Even this though, could give us a clue as to the polarity of the unknowns. TLC can also be used to analyze how certain environmental conditions affect a reaction. Conducive conditions will speed up a reaction and can be seen be early samples taken from the solution matching up with the isolated products spot after being run on a TLC plate. In contrast, inhibiting conditions will slow down a reaction. The early samples taken from the solution will produce spots near the same level as isolated reactants spot. Questions: 1) a. 2-Phenylethanol and acetophenone ? Use Methylene Chloride b. Bromobenzene and p-xylene ? Use Hexane c. Benzoic acid, 2,4-dinitrobenzoic acid and 2,4,6-trinitrobenzoic acid use ? acetone 3) a. Use a less polar solvent that will separate the two components and allow them to be less activated in the mobile state, such as hexane. b. Use a more polar solvent that will separate the two components and allow them to be more activated by the mobile state, such as acetone. c. One option would be to watch the TLC plate while it's being developed. When the solvent front reaches 1cm from the top of the plate, remove the plate. Another option would be to remove the filter paper that is saturated with the solvent, to slow the rate of movement of the solvent front.