identification of unknown compound by extraction

Topics: Solvent, Carboxylic acid, Ethanol Pages: 6 (1248 words) Published: January 31, 2014
Extraction, Purification and Identification of an Unknown Mixture

The purpose of this experiment was 1) to separately extract any amines, phenols, carboxylic acids, salts/sugars and/or neutrals, present in a supplied mixture. 2) to purify two of the components by recrystallisation 3) to identify the two purified compounds by melting point, and mixed melting point tests. The unknown amine was identified as benzocaine, and the unknown carboxylic acid was identified as benzoic acid. References

Merck Index 12th Edition (on cd-rom)
Chemfinder (
Organic Chemistry Laboratory Manual:
Separatory funnel (3.1.3)
Drying a liquid (
Weighing (3.4.3)
Melting point (2.4.3, 4.1.1-
Recrystallising (3.5-3.5.1)
Suction filtration (3.2.3)
Experimental procedures outlined in experiments (5.2.1, 5.3.2, 5.5.1) “Separation of a mixture by extraction” hand-out

Procedure / Observations

Note to TA: Since the procedures were changed significantly from those detailed in the references and since this is written as a combined report for the three laboratories, the changes will be noted during the recount of the procedure. Observations have been included with the procedures to give a better “flow” to this report. This reporting style isn’t anything new, it is similar to that found in chemical abstracts. I hope this agrees with you.

Laboratory 1: Separation by solvent extraction
2.996g of sample 7A was weighed out into a 125ml flask. 50ml of dichloromethane was added.

All of the mixture dissolved, indicating that the mixture did not contain any salts or sugars.

2x20ml HCl washes using a 250ml separatory funnel were done on the mother liquid. The aqueous washes (top layer) were combined and the mother liquid saved. The pH was raised with 3M NaOH(aq). Crystals formed, and would dissolve again, until the pH was raised high enough to turn red litmus paper indicator blue. The white crystals stayed in solution and settled to the bottom. They were suction filtered off. Some amine crystals were lost due to a faulty vacuum source. The crystals were allowed to air dry. After drying, 0.821g of unknown amine crystals were recovered.

3x20ml saturated NaHCO3(aq) washes were done on the mother liquid. The aqueous washes (top layer) were combined and the mother liquid saved. The pH was lowered with 3M HCl(aq) in an ice bath. Upon addition of HCl(aq) the solution effervesced. The solution was acidified until the solution stopped effervescing and congo red indicator turned blue. White fluffy crystals formed, and were suction filtered off from the aqueous solution. After drying, 1.654g of unknown carboxylic acid crystals was recovered.

2x20ml 1.5M NaOH(aq) washes were done on the mother liquid. The aqueous washes (top layer) were combined and the mother liquid saved. The pH was lowered with 3M HCl(aq) in an ice bath until congo red indicator turned blue. No crystals were formed. No phenol compound was present.

The mother liquid was dried with sodium sulfate, and decanted from it into a flask. A boiling stick was added and the sample was evaporated to dryness on a steam bath. 0.170g of neutrals were recovered and discarded.

Impure carboxylic acid and amine samples were placed into separate labeled vials and stored until laboratory 2.

Yieldamine = (massamine) / (mass7A sample)
= (0.821g/2.996g) (100%)
= 27.4%

Yieldcarboxylic acid = 55.2%

Yieldneutral = 5.74%

Yieldtotal = (massamine + masscarboxylic acid + massneutral) / (mass7A sample) = 88.2%

Laboratory 2: Purification through recrystallisation
A small sample of each compound was tested in a small quantity (1-2ml) of water, methanol, ethanol, acetone, and hexane to choose one suitable for recrystallisation.

Carboxylic Acid

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