Functional Group Interconversion (FGI) Oxidation Of a Secondary Alcohol to a Ketone

Written by Brian

Description:

In this lab we tested the premise that if an organic reaction involving functional group interconversion (FGI) works on one molecule, chemists anticipate that the reaction will work to do FGI on other related molecules. Individually for this lab I was assigned 2-heptanol as my alcohol. To oxidize this secondary alcohol to attempt to make a ketone we first obtained a 3-neck round-bottom flask. This was then fitted with a thermometer so that we could read the temperature of the contents. Next we added a reflux condenser and a magnetic mixer were also used. Next we added the proper amount of glacial acetic acid (26.25 mL, 0.87 mol), and 15.3 mL of 0.105 mol 2-heptanol. After we added a separatory funnel to the third hole of the flask and added a 10% molar excess of NaOCl to the funnel. We placed the flask in an ice bath and then added bleach from the funnel at a temperature-controlling rate. This took roughly 25 minutes, after the bleach was added we moved the mixture to an ice bath to cool for another 20 minutes.

I tested my sample at this point with starch-KI paper and the paper turned a shade of purple so after adding more NaOCl the sample then turned the indicator blue. Next we added Na2SO3 until the solution turned colorless. From here we cooled the reaction mixture and added 26.25 mL concentrated sodium hydroxide solution. Finally we performed a steam distillation and after collecting roughly 50 mL we retained the top of the two layers and dried our collected sample in a vial with anhydrous sodium hypochlorite. This vial was then saved in our drawer until day 2 of the lab. On day two we further distilled our sample and collected the product in an appropriate short boiling range for our ketone. Finally we collected GC, IR and NMR data for our sample.

 

Data:

Temperature at which boiling occurred: Thermometer read 110 C

Boiling point of desired/expected ketone: 151 C

Weight of Small vial/flask when empty: 16.78g

Weight of Vial w/collected sample: 18.39g

(All data charts/graphs attached)

 

Discussion:

From our sample we distilled we collected GC, IR and NMR data. From this data if we successfully oxidized our secondary alcohol (2-heptanol) we would expect the ketone (2-heptanone) to have formed. The GC (Gas Chromatography) we performed yielded a slightly less than desirable chart/graph. Based on our GC results we recorded roughly 45% purity indicating a relatively impure compound/mixture was analyzed. What was desired was 100% impurity but that was not the case. In comparison to the NMR spectrum data we obtained during the library assignment our data was actually relatively similar with some of the expected chemical shifts. The chemical formula for 2-heptanone is C7H140 from this we would expect chemical shifts at roughly 2.5ppm and 1ppm. Many of the CH2’s would have a1ppm shift with two having 3 lines and 2 having 5 lines due to varying amounts of hydrogen’s on adjacent carbons.

Based on our IR data for 2-heptanone we would expect C double bonded to O peak at about 1800-1700 1/cm. We know this because ketones have a characteristic C double bonded to O (Carbonyl) absorption at about 1750-1700 1/cm we would also expect a peak at about 3000-2850 for general C single bonded to H. Based on our IR peaks and NMR exam I would say that my oxidization was slightly successful but nowhere near perfect. With a 45% purity rate, some peaks that do not agree with what would have been expected and boiling that occurred at a much lower recorded temperature our results were not exactly as desired. The temperature however on the thermometer has recorded for me seemingly wrong before meaning that it would fluctuate and record a much lower temperature than the known temperature. Whether this is due to the thermometer, the laminar flow hood, or what I am not certain.

The vial we collected our sample in weighed 16.78g when empty and 18.39 when filled therefore we collected roughly 1.61g of what was supposed to be ketone sample. Because the thermometer was seemingly incorrect I had to make a general guess as to what temperature to collect the ketone sample based off the known boiling point for 2-heptanone. I collected my sample roughly in the middle after about half of the sample we were distilling had been collected in the Erlenmeyer flask. What was not expected to be ketone sample was discarded and the small 1.61g was analyzed and based off the results the Oxidation as successful and the ketone 2-heptanone was formed but likely it did not form perfectly or with a high percentage yield and the sample was also likely collected at the wrong temperature/time due to problems with accurate readings on the thermometer.