QUALITATIVE ORGANIC UNKNOWN

EXAMPLE

REPORT FORM FOR UNKNOWNS

UNKNOWN LETTER AND NUMBER D5

PHYSICAL CHARACTERISTICS Unknown is a clear, pale yellow liquid. Since it contains two compounds, I may have two liquids or maybe a solid dissolved in a liquid. It doesn’t smell like anything familiar.

Melting point, if solid: No solid after separation (see separation scheme, below)

Boiling point, if liquid: After separation, the acid component boiled at 179-185°C. From the chart, this could be chloroacetic or pentanoic acid, or possibly even 2-chlorophenol or 2-methylphenol. The neutral component boiled at 124-128°C.

GENERAL SCHEME OF SEPARATION (IF A MIXTURE)

Dissolved the unknown in dichloromethane and extracted twice with 5% NaOH (Extract was basic after two extractions, so a third was not done).

Basic extract was acidified with 6M HCl, producing a liquid organic layer. Organic layer was extracted into dichloromethane, dried over anhydrous Na₂SO₄, and distilled to remove solvent. Distillation was continued to determine the boiling point of the unknown.

Dichloromethane extract from the original procedure was dried over anhydrous Na₂SO₄, distilled to remove solvent, leaving a liquid in the distilling flask. This liquid was cooled and remained a liquid, so was distilled to determine its boiling point.

SOLUBILITY

Results: Mixture was not H₂O or HCl soluble. It looked like some of the unknown was soluble in NaOH, but it was hard to tell, since it has two components. I thought I saw some bubbles when I tried to dissolve the unknown in NaHCO₃. It was definitely soluble in H₂SO₂.

After separation, the acidic component was soluble in NaHCO₃.

Inference: Since it was not soluble in H₂O, neither unknown is a low molecular weight compound. Since it was not HCl soluble, neither compound is an amine. This leaves an acid and a neutral compound as the possibilities. Since I thought I saw bubbles when I tried to dissolve the unknown in NaHCO₃, the acid is probably a strong acid.

After separation, the acid component was determined to be a strong acid, probably eliminating the phenols as possibilities. The next steps will be to perform the test for aromaticity and try to form an amide.

FUNCTIONAL GROUP TESTS

Results:

1. Test on acidic component for aromaticity was negative.

2. 2,4-D test on neutral component was positive.

3. Chromic acid test on neutral was negative.

Inference:

1. The acidic component is a carboxylic acid, not a phenol. This reduces the possibilities to chloroacetic acid and pentanoic acid.

2. The neutral component is either an aldehyde or a ketone.

3. The neutral compound is a ketone. From the chart of possible unknowns, it could be 2-hexanone or possibly cyclopentanone. A 2,4-D derivative should be the next step.

DERIVATIVE

Results:

1. Acidic component formed an amide whose melting point was 104-106°C.

2. Neutral component formed a 2,4-D whose melting point was 104-106°C.

Inference:

1. The acidic component is a carboxylic acid. Pentanoic acid is consistent with all of the data.

2. The data point to 2-hexanone as the neutral component.

NMR (submit a copy of the spectrum)

Inference:

1. For the acidic component, comment on the chemical shift of the acidic hydrogen and assign peaks to the rest of the spectrum.

2. Assign peaks to the spectrum.

IR (submit a copy of the spectrum)

Inference:

1. For the acidic component, comment on the -OH and -C=O absorptions, and the presence or absence of any other definitive peaks (in this case the absence of peaks indicative of an aromatic ring, which would have been present in a phenol).

2. For the neutral component, comment on the -C=O absorption and any other definitive peaks.

GC-MS (submit a copy of the printout)

Inference: Find the molecular weight from the M+ peak if it is present and comment on any fragment peaks you can.

MY UNKNOWN #D5 IS:

2-hexanone and

pentanoic (valeric) acid

NOTE: You may not need to perform all of the tests listed to unequivocally identify your unknown. We have simplified the process by limiting the possibilities to a very small list of compounds containing each functional group. However, even if you do not need to use them all, you should still understand the chemistry involved. To unequivocally identify your unknown, you must use chemical and/or spectral data to confirm its identity, not the process of elimination based on the potential unknowns from your list. For example, it is not sufficient to determine that your unknown is an amine whose boiling point is 43-47⁰ C. and conclude that it must be propylamine. You must do at least one more test (make a derivative, take an NMR or IR or GC-MS) to conclusively identify it as propylamine.