LAB #3: SEPARATION OF BENZOIC ACID, 2-NAPHTHOL, AND 1,4-DIMETHOXYBENZENE

Prelab.

*Read: Zubrick, Chapter 15 and 16. These chapters provide background information, explanation of techniques, and procedures eall compounds used in this experiment.

*Draw the structures of benzoic acid, 2-naphthol, and 1,4-dimethoxybenzene. Provide the balanced acid-base reactions.

*Draw a flow chart of the extraction procedure.

*Make a table of physical constants and safety considerations. Include only relevant data for this experiment.

Grading.

Completion 5 pts

(includes lab and a report turned in on time)

Prelab 3 pts

Procedure 2 pts

Results 5 pts

Conclusion 5 pts

In lab.

You will separate a mixture of equal parts of benzoic acid, 2-naphthol, and 1,4-dimethoxybenzene using extraction. You will identify each substance by IR and melting point and determine the percent recovery of each from the original mixture.

Dissolve 0.18 g of the mixture in 2 mL of tert-butyl methyl ether (TBME)in a test tube (Tube 1). Remember, when weighing out materials, you do not need to get exactly 0.1800 g. Instead, slowly add the material to the weighing paper on the balance and record the ACTUAL weight. DO NOT put any compounds back into the original bottle!!

Add 1 mL of saturated aqueous sodium bicarbonate to this solution. Mix the contents of the tube thoroughly by pulling the two layers into a pipette and expelling them back into the test tube. Do this several times. Allow the layers to separate and then draw the aqueous layer into another test tube (Tube 2). Repeat this step two more times using 0.5 mL of the sodium bicarbonate mixture each time. Add 0.2 mL of TBME to the combined aqueous layers. Mix thoroughly, remove the ether layer and discard it. This is called backwashing and serves to remove any organic material contaminating the water layer.

Add 1 mL of 3 M aqueous sodium hydroxide to the original ether solution (Tube 1). Mix the two layers and remove the aqueous layer and add to another test tube (Tube 3). Repeat this step two times with 0.5 mL of 3 M sodium hydroxide solution. Backwash the combined aqueous layers with 0.2 mL of TBME.

Backwash the original ether solution (Tube 1) with 0.5 mL of a saturated NaCl solution. Here, the backwash serves to remove any aqueous material that might contaminate the organic layer. Transfer the organic layer to a dry test tube and add anhydrous sodium sulfate until the drying agent no longer clumps together (see Chapter 10 of Zubrick)

At this point, you have your three compounds separated into three different tubes! Make sure you know which compounds are in which tubes. Now the trick is to get the solid products. The following steps can be done simultaneously. Think carefully about how to be efficient and not waste time.

Tube 1 is an ether solution with drying agent. Filter the drying agent off. Then, remove the solvent by gently warming the test tube in a water bath while directing a stream of nitrogen onto the surface of the ether. Once you have a solid product, it will need to be recrystallized with methanol as the solvent. Collect the crystals on the Hirsch funnel.

Tube 2 and Tube 3 are both soluble in an aqueous layer because they are deprotonated. The resulting anion is soluble in water. However, we want the protonated form of the products. Use concentrated HCl to acidify the aqueous solutions. As soon as your products have been protonated, they will begin to precipitate out of solution. Add HCl dropwise until no more precipitate forms. Recrystallize both of these compounds from boiling water. When you are warming the solutions in a water bath, clamp the test tubes up so that they are not resting on the hotplate! Collect each set of the crystals on the Hirsch funnel.

Postlab.

Find the melting points of the recovered benzoic acid, 2-naphthol, and 1,4-dimethoxybenzene. Leave the crystals uncapped in your drawer to dry before determining your melting points. Calculate the percent recovery of each of the products. Obtain an infrared spectrum of each product. Include an IR data table in the results section of your report. Analyze them, commenting on the signals of major importance in each spectrum. Compare the IR spectrum of your products with IR spectra of authentic compounds (Aldrich Library of IR Spectra). Comment on the purity of each fraction and discuss possible experimental problems which may have resulted in low yield or impurities.

DISPOSAL PROCEDURES

The filtrate of tube 2 and 3 should be neutralized and sewered.

Benzoic acid, 2-naphthol, and 1,4-Dimethoxybenzene will be collected in a labeled waste container in the

vented cabinet.

Sodium chloride solution and sodium sulfate can be sewered.

t-butyl methyl ether is collected in a labeled waste container.