Mohamed Adnan April 8 2014Professor Mollica Lab Tuesday 2:15-6:05 PM

Identification of Unknown 1 (#211)I. Introduction:

The identity of an unknown solid was determined through qualitative tests. The chemical principles of melting point, solubility, functional group testing, and derivative testing were used. The melting points were compared to literature values given in the course lab manual. Solubility test results showed the acidic, basic, or neutral properties of the substance. Functional group tests determined the class of the compound. The possible functional groups were limited to aldehydes, ketones, phenols, or alcohols. Derivative tests were used to convert the unknown compound to a known class of compound through a predicted chemical reaction. The identity of the resulting product was confirmed through a melting point test, which distinguished the original unknown from similar compounds. 1H-NMR spectroscopy confirmed the identity of the unknown.

II. Objective: The goal of this experiment was to determine the identity of Unknown #211 using the

tests provided.

III. Procedure:A. Melting Point and Solubility

Upon obtainment of the unknown, basic general physical observations were made. The melting point was then determinedin seven trials to yield a single temperature. Following this, the solubility of the unknown compound in five solvents was tested. To do this, five test tubes were set up and in each test tube, 2 mL of one of the following solvents were added: water, 5% NaOH, 5% HCl, 5%NaHCO3, and concentrated H2SO4. Using a mortar and pestle, the unknown was ground, and a few crystals were added to each test tube using a spatula. The contents of the test tubes were stirred. The test tubes were gently heated and left on the side for later observation.

B. Carbonyl Classification TestsAround 10 mg of unknown were dissolved in di(ethylene glycol) diethyl ether in a small

test tube. One mL of 2,4-dinitrophenylhydrazine was added and the contents of the test tube were then shaken vigorously. The resulting product was set to the side and observed for precipitate.

Around 10 mg of an unknown were dissolved in reagent-grade acetone in a test tube. Several drops of the chromic acid reagent were also added, drop wise, while shaking the mixture. The test tube was then observed for precipitate.

For the Tollens test, 1 mL of Tollens solution A was mixed with 1 mL of Tollens solution B in a test tube, yielding a gray precipitate. Ten percent ammonia solution was added drop wise to the mixture to dissolve the precipitate just by a little bit. In a separate test tube, 10 mg of the unknown were dissolved in the minimum amount of di(ethylene glycol) diethyl ether. The unknown solution was added a little at a time to the solution of Tollens A and Tollens B and the ammonia. The contents of the test tube were then shaken vigorously. The solution was then heated gently in a warm water bath and then set aside to observe for a silver mirror.

4 Drops of the unknown liquid were added to 2 mL of water in a large test tube. 2 mL of 3 M sodium hydroxide was added and then 3 mL of the iodine solution was slowly added to the

mixture. Stopper The test tube was covered and shaken vigorously. The solution was then observed for the formation of yellow precipitate.

For the Ferrous Hydroxide Test/ Nitro test, 10mg of unknown solid was added to 1.5 mL of 5% aqueous ferrous ammonium sulfate. Then 1 drop of 2M sulfuric acid, followed by 1mL of 2M potassium hydroxide in methanol was added to the solution, which was shaken vigorously.

C. DerivativesTo prepare the semicarbazone derivative, 0.5 mL of a 2M stock solution of semicarbazide

hydrochloride was added to a test tube, followed by 0.15 g of the unknown. Ten drops of pyridine were then added and the mixture was heated in a hot water bath set at 60°C for 10-15 minutes. The test tube was then removed from the bath and set aside to cool. The contents of the test tube were collected through vacuum filtration. The product was air dried over a week’s period and the melting point was then measured in three separate trials.

To prepare the 2,4-dinitrophenylhydrazone derivative, 10 mL of the 2,4-dinitrophenylhydrazine solution was added to a test tube. In another test tube, 0.15 g of the unknown was dissolved in a small amount of 95% ethanol. This solution was then added to the measured amount of 2,4-dinitrophenylhydrazine solution. The solution was warmed gently in a hot water bath at 90°C. The test tube was then set aside to cool, and the resulting crystals were vacuum filtered out. The product was air dried over a week’s period and the melting point was then measured in three separate trials.

D. Nuclear Magnetic Resonance A few crystals of the unknown were weighed and crushed in a mortar and pestle and 10

mgs of the unknown were added to a test tube with 1 mL of chloroform-D. The unknown was dissolved. The resulting solution was transferred to an NMR tube and then processed in the NMR machine.

IV. ResultsInitial observations of unknown:White, solid, slightly sparkly crystals looked like table salt. No recognizable odor.

Melting Point:Trial 1 Trial 259-60°C 59.5-60.5°C

Solubility Tests: Water 5% NaOH 5% HCl 5% NaHCO3 Conc. H2SO4

Insoluble Insoluble Insoluble Insoluble soluble

2,4-DNPH Test:Initial observation: No precipitate formed as the solution was clear red-orange, but after setting it out for approximately 15 minutes, a precipitate did form. The test was repeated two times and the solution was clear red-orange and an orange-red solid precipitate formed.

Chromic acid test: solution became cloudy after dropping the chromic acid into the unknown 1 mixture after 45 seconds.

Tollens test: Addition of Tollens A to Tollens B formed a gritty gray precipitate. Addition of 20 drops of ammonia solution partially dissolved the precipitate. Addition of this solution to the unknown produced a silver mirror coating on the inside surface of the solution test tube.

Iodoform test: a red solution formed, with precipitate.

Nitro test: The solution formed a dark color after adding 2M Potassium Hydroxide and did not form a brown-red precipitate.

DNPH Derivative: mixture of unknown and DNPH solution made the solution red orange. After gentle heating, a red-orange precipitate was produced. Precipitate was isolated through vacuum filtration.

Semicarbazone Derivative: after recrystallization, product was white and powdery.

Functional Group Test Observations Result

Aldehyde & Ketone

DNPH An orange/yellow precipitate formed. Positive

Aldehyde Tollen's Test Silver-mirror deposited around test tube walls.

Unclear/Positive

Aldehyde/alcohol Chromic Acid Red/orange liquid and yellow cloudy precipitate appeared after 45 seconds.

Negative

Methyl Ketone Iodoform A precipitate formed but in a red liquid Unclear/Negative

Nitro Group Ferrous Hydroxide Test

A dark purple solution formed, red-brown precipitate did not form.

Negative

Melting Points of Derivatives:

Trial 1 DNPH Trial 2 DNPH140-143°C 148-160°CTrial 1 SemiCarbazone: Trial 2 SemiCarbazone146-148°C 151-162°C

NMR Spectroscopy: Results Attached

V. Analysis and DiscussionThe unknown compound was completely insoluble in water, 5% NaOH, 5% HCl,

5%NaHCO3, but was soluble in H2SO4, but most compounds are soluble in H2SO4. Based on its lack of solubility, it was likely that the unknown was an inert compound, making it either an alkane or an aromatic compound. However, because solubility tests alone are not reliable enough to make such judgments, further tests were necessary.

After fifteen minutes of waiting, the 2,4-dinitrophenylhydrazine carbonyl classification test yielded a deep orange/yellow sparkly precipitate. This is a positive result for this test indicating that there is an aldehyde or ketone present that was able to react with the 2,4-DNPH, forming the 2,4-dinitrophenylhydrazone precipitate. The fact that the precipitate was such a deep orange/yellow also indicates that the compound is most likely a conjugated ketone. Despite this, sometimes, allylic and benzylic alcohols can yield a positive result so further analysis was necessary.

At the same time though, addition of Chromic acid reagent to the unknown produced a red/orange and cloudy solution, which is a negative result. A positive result would have been indicated by a green precipitate and a loss of the orange color in the solution, but neither of these changes took place. This negative result indicates that there is no aldehyde present in the compound. Because the 2,4-dinitrophenylhydrazine test indicates the presence of a carbonyl but the chromic acid test rules out aldehydes, the unknown likely has a ketone in it.

After adding the Tollens mixture to the unknown, the solution became a silver mirror precipitate on the inner walls of the tube, indicating a positive result for the Tollens test. The positive Tollens test indicates that it may be an Aldehyde, which contradicts the results of the negative Chromicacid test. The reason for a positive Tollens test may have been due to impurities that could have interfered with the unknown solution. Consequently, another compound that was an aldehyde may have been present in the test tube, which would explain the positive silver mirror formation.

The Iodoform test aimed to depict a yellow precipitate if it was a methyl ketone, but only a red solution with some precipitate formed. Since the precipitate was unclear and not yellow, the unknown may not be a methyl ketone. Further tests, melting point, and NMR will provide insight as to if Unknown #211 is either an aldehyde or ketone.

After adding 2M Potassium Hydroxide for the Nitro test, the solution became a dark purple color and there was no red-brown precipitate. This meant that the unknown does not have a nitro group attached to the compound.

For the NMR, there were several peaks near the 7-8 ppm region, indicating the presence of several hydrogen’s on two aromatic rings. There is a small singlet peak at 5.0-5.5 ppm, which is possibly the hydrogen allylic to the ketone and attached to two phenyl groups. There was also another singlet peak at 2-2.5 ppm, which indicates the presence of the hydrogen’s on the methyl group that is attached to the ketone. There were no other significant peaks aside from a small peak at around 1-2 ppm, which mayhave just been a result of the machine itself or an impurity in the solution. This means that there probably were no other hydrogen’s on the compound aside from those on the aromatic rings and hydrogen’s next to the ketone. This limited the choice down to only one compound, 1,1-diphenyl acetone.1,1-diphenyl acetone is consistent with this NMR result because there were peaks only in the aromatic region of the NMR and nowhere else. Other test results indicated the presence of a ketone so it is likely that the two benzene rings were joined by a ketone. This is also consistent with the melting point of the unknown.

The compound was recrystallized to get a pure product, which was then tested for the melting point for a highly accurate reading. The melting point was found to be 59.5-60.5°C, which corresponded to the compound Desoxybenzoin (Melting point: 60°C). Based on the melting points of the derivatives, and the NMR spectra the 1,1 diphenylacetone (Melting point: 61°C) is a more likely candidate for unknown #211 since the melting point is only 0.5°C above the recorded range. According to compounds sold by Sigma Aldrich, the recorded melting point of desoxybenzoin is 52-56°C, which is out of the range of the observed melting point. In the same company’s catalogue, the 1,1-diphenylacetone had a literature melting point of 59-63°C, which falls within the range of the observed melting point.

The semicarbarzone derivative melting point was slightly lower in the experiment (151-162°C) than the recorded value for 1,1-diphenyl acetone (170°C), which was a reason for worry. However, derivatives tend to be far less accurate than the actual melting point, so with this in mind, dismissing the results yielded from the derivatives was acceptable.

The NMR spectrum is a more accurate depiction of the unknown than the Iodoform test, which can have false results. The Iodoform test should have been a positive test for the 1,1-diphenylacetone by forming a yellow precipitate, but the NMR spectra depicts 1,1-diphenylacetone rather than desoxybenzoin.

VI. ConclusionBased on the melting point of the unknown, the positive DNPH test, the negative chromic acid, the nitro test, and the results of the NMR, Unknown #211 is 1,1-diphenyl acetone.

Figure 1: 1,1-diphenylacetonehttp://www.chemicalbook.com/SpectrumEN_781-35-1_1HNMR.htm