This lab's purpose is to re-emphisize the importance of keeping a good and thourough lab notebook so the experiment can be replicated by other scientists. It will also allow more practice for purification techniques that've been learned over the semester. This lab works to stress main ideas that are important in lab work and prove to be useful in various experiments.

1.  From general chemistry you know that in an oxidation reaction, electrons are lost and in a reduction reaction, electrons are gained.  Please find and write a description of an organic oxidation reaction (remember that your Wade text is a good resource). This needs to be a written response.  Drawing the chemical equation of an oxidation reaction will not suffice as an answer.

An oxidation reaction of an organic compound increases the carbon to hetero-atom bonds while decreasing the number of carbon to hydrogen bonds. This reaction involves the transfer of electrons two an oxidizing atom and a redutcion atom. The oxidizing atom will see a gain in charge while the reducing with see a decrease in charge. The electrons lost and gained must be equal between the products and reactants. These reactions are essential for biological processes and other reactions where the transfer of electrosn are necessary.

2. Your sample needs to be absorbed onto silica gel.  How should this be done? Your answer needs to include information about what rotatory evaporation is.  You can refer back to your techniques book for information.

Rotatory evaporation is when the volume of a solvent decreases by distributing it as a very thin film in a vessel with lower pressure and higher temperature. The solution, which will have been dissolved by a slightly more polar solvent than the elutent running through the solution, will be pipetted onto the silica gel being careful not to disturb the slurry. This will create a thin band which will be used in effective column chromtaography.

• Set up a steam bath and place it onto a hot plate to let it boil.

• Measured 2.00 grams of benzoin and 7 mL of concentrated nitric acid.

• The benzoin and nitric acid were combined into an Erlynmyer flask.

• Once the steam bath was brought to a vigorous boil, the flask was placed on top of the bath and left to boil for 11 minutes.

• The solution turned orange and brown/orange gas started to come out of the flask.

• The solution was removed and 37.5 mL of DI water was added and the solution was cooled to room temperature then placed in an ice bath for about 20 minutes.

• Once the solution was removed from the ice bath, the crystals were vacuum filtrated out(yellow crystals were present).

• The pre-weighed flask was weighed to be 102.22 grams

• The flask with the product was weighed to be 104.57 grams.

• 2.35 grams of crude product was collected.

• The product was divided into two flasks weighing 1.16 grams and 1.19 grams.

TEST FOR PRESENCE OF BENZOIN

• 0.5 mg of crude product was added to 95% ethanol.

• 1 drop of 3 M sodium hydroxide was added.

• The solution did not turn purple(if benzoin was present, the solution would turn purple).

RECRYSTALLIZATION

• The flask with 1.16 grams of crude product was used and transferred to a beaker.

• 7 drops of ethanol were put into the beaker with the product.

• Measured 10 mL of ethanol into a flask and placed it on the hot plate to boil.

• Once it started to boil, it was added to the beaker with the solid and ethanol which was also placed upon heat, until the solid was completely dissolved.

• Once completely dissolved, it was removed from the hot plate.

• DI water was added dropwise (about 15 drops)until the cloudy point was reached then the solution was left to cool(the solution turned opaque and whiter).

• The mass after recrystallization was weighed to be 1.11 grams.

• Conducted analysis via TLC with a standard and melting point analysis.

COLUMN CHROMATOGRAPHY

• Prepared to pack the column by placing fiberglass and a small layer of sand at the bottom of the column.

• Packed the column with a slurry composed of silica gel and a 4:1 hexane/ethyl acetate mixture.

• Placed another small layer of sand on top of the slurry.

• Put 1.19 grams of crude benzil into the column

• Put another layer of sand on top of the product and fill the column with a 4:1 hexane/ethyl acetate mixture.

• A light yellow band was observed running through the column.

• 24 samples of 3 mL were collected and every 3 was tested by TLC to determine when benzil was being collected by comparing to a standard.

• All the samples containing benzil were collected in an Erlynmeyer flask and placed upon a hot plate for vacuum evaporation.

• The crystals present were burnt orange/red.

• The crystals were scrapped and weighed to be 0.72 grams.

• Conducted analysis via TLC.

Yeild of Crude Product

Mass before experiemnt: 2.00 grams

Mass after experiment: 2.35grams

% yeild = (2.35/2.00) * 100% = 118%

Recrystallization

Mass before recrystallization: 1.16 grams

Mass after recrystallization: 1.11 grams

% yeild = (1.11/1.16) * 100% = 95.7%

Column Chromatography

Mass before column chromatography: 1.19 grams

Mass after column chromatography: 0.72 grams

% yeild = (0.72/1.19) * 100% = 60.5%

Melting Point Analysis

Melting point of pure benzil: 94.8°C

Melting point of recrystallized benzil: 92-95°C

Looking at the various forms of analysis, I'm confident pure benzil was isolated. First, the reaction to get the crude product was over 100% which means it was heavily product favored as the reaction of benzoin with nitric acid is. The crude product was then tested with ethanol and sodium hydroxide to see if benzoin was still present through color change and it was indicated that it wasn't. Next, the product was purified by recrystallization. Looking at the TLC plate, it is obvious that benzil was present as the spot is almost identical to the standard with corresponding Rf values. The re-crystallized product was also analyzed by melting point analysis. The melting point analysis showed that the product melted between 92-95 degrees celsius which is within the range of pure benzil's melting point providing further evidence pure benzil was isolated.

Column chromatography was also used as another purification technique. This technique was also successful in isolating pure benzil as shown on the TLC plate. The spots are almost identical along with their Rf values and they're both solid signifying the presence of one compound in solution. The column chromatography, however, wasn't as successful in recovering as much mass as recrystallization. Both techniques were very successful in isolating and purifying benzil but it was much easier to have a higher yield in recrystallization than in column chromatography.

Overall, this experiment went very well as the compound was successfully isolated and the practice of various isolation and analysis techniques were utilized and compared. I learned about the use of column chromatography for substances that don't have as distinct color bands as those in the previous column chromatography lab. It was interesting taking samples and using TLC analysis to determine when the compound of interest was fully isolated and no longer remained within the column.

I practiced the use of recrystallization again after not utilizing that purification technique for so long. Utilizing qualitative skills within the recrystallization such as determining when it's boiling, its cloudy point, etc. was useful in helping to purify and isolate the compound of interest.

If I were to repeat this experiment again, I would TLC more samples from the column chromatography to further check and verify benzil is present and I would collect more samples which would hopefully lead to a higher mass recovery of the compound.

1.  What experimental detail was missing from the lab report you were given?

In the experimental section of our lab report, we were missing how to conduct the test for benzion vs. benzil and its color change within sodium hydroxide and ethanol.

2.  Why is it important to record all that you do in the laboratory?

It's important to record all procedures done within the lab to ensure the experiemnt can be succesfully replicated by other scinetists to re-analyize the lab results and further verify the chemistry behind the lab.

3.  After today’s lab, what changes will you make in your own recordings keeping in mind that someone next year might be asked to follow your instructions?

After today's lab, I will be sure to write more detailed and thoughrough procedures as I do them. This will help create better lab reports to be easily replicated and more accurate as I report them while doing it in the lab.