Identification of Unknown Ketones

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Purpose:

The purpose of this experiment was to identify one ketone with Thin Layer Chromatography and one using NMR spectrometry. We will do this by making 2, 4 a DNPH derivative and checking the melting points.

Theory:

By Using specific methods of compounds detection, we can match an unknown compound with a known compound because similar compounds will display similar characteristics. In this experiment, identifications of the unknown ketone was accomplished using thin layer chromatography, melting point, and NMR spectrometry. Thin layer chromatography is very quick but sensitive way of determining the components of a mixture or a specific compound from a list of knowns. This method is the one which was utilized in the following experiment. When comparing a sample of known compounds with an unknown’s Rf values and appearance on the thin layer chromatograph these characteristics can be used to easily determine which known the unknown is. The Rf values are important in determining the more polar molecules from each other, while the color and appearance can be used to separate compounds with similar polarities. The color added by the reaction with 2,4-dinitrophneylhydrazine eliminates the need to compare colors of the different knowns with the unknown. The other method used to help determine which ketone the unknown was, was nuclear magnetic resonance spectrometry or NMR. NMR utilizes radio frequency waves to determine the number of carbons present and what they are connected to. With this information and the type of hydrogen present from the NMR, an accurate estimate of the unknown ketone can be made.

Ketone| Mol Wt| BP(deg C)| D (g/mL)| Derivative MP|
2-propanone| 58.1| 56| .791| 126|
2-butanone| 72.1| 80| .805| 117|
2-hexanone| 100.2| 128| .811| 106|
2-heptanone| 114.2| 151| .811| 89|
2-octanone| 128.2| 173| .819| 58|

Reaction/Calculations:

There were no reactions in this lab.

Known ketones:

2-propanone2-butanone2-hexanone

2-heptanone2-octanone

Mass of unknown: .17g
Melting Point of Unknown: 87 deg C

TLC Slides:

Rf Values:

Unknown K = 3cm/6cm = .5

2-Propanone: 2.6cm/5.5cm = .47

2-Hexanone: 2.9cm/5.4cm = .53

2-Heptanone: 3.2cm/6.2cm = .51

2-Butanone: 2.3cm/6.4cm = .35

Methods/Safety

The experiment was followed verbatim pages 122-123 in Lehman with the following exceptions. As time was an issue, students worked in groups to prepare known ketones with 2,4-dinitrophenylhydrazine instead of each student preparing every known individually. Also, NMR printouts of already tested ketones were provided instead of doing the spectrometry during lab.

When performing this experiment, we were to remember the following safety precautions. Ketones are flammable and may be harmful if inhaled or absorbed through skin. Avoid contact, breathing in vapors, and putting near flames. 2,4-dinitrophenylhydrazine is harmful if absorbed and will dye hands yellow. Ethyl Acetate, Toluene, and Petroleum are also flammable and may be harmful. Finally, Neuterochloroform is toxic and may be carcinogenic. We should avoid contact and inhalation with it.

Data/Observations/Results

It was observed that when 2,4-dinitrophenylhydrazine was added, a yellow substance was formed. The results for the thin layer chromatography were pretty decisive. The slides as well as the Rf values of 2-heptanone and my unknown were very similar. I looked at height and size of the spots on the slides to determine this. Rf value of the unknown (K) was .5. This value was closest to my Heptane Rf value of .51. Also, the melting point of my unknown (87 deg C) was very close to the melting point of 2-heptanone derivative (89 deg C) found in the table in the Theory section of this report. Therefore, I found that 2-heptanone was my unknown (K).

The results for the NMR were found rather easily. By observing...
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